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PaisleyPCdoctor
06-12-2017, 08:02 PM
Hi,
I recently purchased a China CNC 6040z (2.2kW, 4 axis, usb version with extras) for £1800.
I bought with FULL EXPECTATION AND ACCEPTANCE that it would require some upgrades and tweaks right off the bat. No problem.

I'm starting this thread to post about the problems and solutions s as I do them, in case it might help others in future (the forum spirit :-)

Here is the machine I purchased (attached).

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PaisleyPCdoctor
06-12-2017, 08:09 PM
My immediate attention was the water pump- threw it in the bin and got a much better and silent pump for £20 off eBay. Old pump binned. Never seen such a crap pump in my life!

PaisleyPCdoctor
06-12-2017, 08:21 PM
Second (and probably the biggest of the lot)- SHIELDING- or lack of it!

Absolutely nothing is shielded not even the VFD cable!

I started with external cables to Spindle and Stepper motors.

Supplied VFD cable looks nice flexible rubber 'pond flex' cable. It's plain unshielded 0.75mm2 3 core and earth. The earth wire IS connected to spindle (thank god), but no shielding.

I replaced the entire cable with shielded 1.5mm2 CY control cable. To be extra careful, I also added external copper braid shield. It's now double screened.

I didnt replace the stepper cable, I suply added a copper braid sleeving to the entire length. Obviously, the sleeve is connected to earth....

Actually, no. The aviation connector barrel on the chassis is making contact with paint, not metal. NO EARTH CONNECTION! I had to scrape off paint inside the case to sort that.

Next job is shielding the cables inside the control box, then probably moving VFD to its own enclosure.

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magicniner
07-12-2017, 01:57 AM
(X) Location, (Y) Location, (Z) Location!
The rest is just window dressing if the first 3 are not worth the cardboard it was shipped in :D

PaisleyPCdoctor
07-12-2017, 12:04 PM
(X) Location, (Y) Location, (Z) Location!
The rest is just window dressing if the first 3 are not worth the cardboard it was shipped in :D

Eh?

pd110961
07-12-2017, 12:31 PM
Hi Paisley.. where are you in the country mate?

m_c
07-12-2017, 12:44 PM
I suspect Nick was on the sauce last night ;-)

But his point was if the basic machine can't hold tight tolerances, then everything is else is superficial.

Shielding is not as big a problem as people often think it is. None of my Denford machines came with anything shielded other than two sensors on the Triac mill. Everything else, including the spindles (VFD on the Cyclone lathe, and DC spindle on the Triac) used unshielded wiring, but then they're not using TTL level logic for inputs.

PaisleyPCdoctor
07-12-2017, 03:53 PM
Hi Paisley.. where are you in the country mate?

I'm in Paisley. Scotland.

PaisleyPCdoctor
07-12-2017, 04:00 PM
I get that, however, as it's often repeated on this forum- not all China cnc are the same. Much of the reputation was for poor electronics was from early controller boards and VFD etc. I was very careful to get one with a newer controller (HC4-IV), decent steppers and a good spindle. There's nothing inherently wrong with the table and gantry design.

I know my way around electronics, so I wasn't bothered about doing some extra work to improve it. Even without the improvements, it hasn't glitches on me yet. It's done everything I've asked of it perfectly well.

At £1800 it's not the cheapest out there- I certainly wasn't going to spend £10k+

Plenty of people making really cool stuff with 6040's.

m_c
08-12-2017, 01:24 AM
There is plenty wrong with the basic machine design.
If you're only doing softer materials with light cuts, it's not a problem, but if you try pushing the spindle, you'll get resonance/poor cuts.

If you have a DTI, try setting it up against the spindle noseat a typical cutting height, then apply some pressure against the spindle and see how much deflection you get. Having three sets of unsupported rails between the bed and the spindle does not produce good rigidity.
Then try testing for backlash. The setup used for the ballscrew endfloat is a couple single row ball bearings (which are usually cheap rubbish), with preload controlled via a single nyloc nut. Then the stepper motor couplers will most likely be cheap aluminium bellow type, which will crack if driven hard.

Plus the general tolerances will be questionable.

And in case you're wondering why I know all this, is I bought a 3040z as the base for a digitizing machine, knowing full well it's shortcomings. It does it's job as digitiser, but I certainly wouldn't want to use it as a router and expect it to produce good quality cuts and not need continual fettling.

PaisleyPCdoctor
08-12-2017, 03:28 AM
I understand what you're saying and I agree to a point. Of course it's not going to be as good as a £10k+ machine, but I don't think it's as bad as you say. The newer models are build far better than the older (coupla years only) models. Either way, my only option is to try to improve in its weaknesses as much as I can and learn whilst doing it. It's fun anyway.

Take a look at this video (especially around 8minutes in). He's on my school of thought that the wiring is the main problem now, not the mechanics.

https://youtu.be/fdfJ_WZTxJY

Boyan Silyavski
08-12-2017, 09:53 AM
Is it supported or unsupported rails?

If its for a hobby and occasionally using it, there is nothing wrong. / Did i just say that??? :hysterical:/ . But if you are trying to make something and sell it... And not to speak of if you are accepting online orders. One needs a totally reliable machine for this. Or it will be pulling hair 24h

PaisleyPCdoctor
08-12-2017, 10:14 AM
The y axis rails are supported, the x axis is 2x20mm unsupported shafts (and ballscrew).
Z axis 2x13mm unsupported shafts with ballscrew.

Kev2960
09-12-2017, 10:15 AM
Hi, you seem to be fixing problems you may not have

PaisleyPCdoctor
09-12-2017, 07:20 PM
Prevention is better than cure.

Kev2960
09-12-2017, 11:42 PM
Yep Iíll go with that. Is this your first adventure into home cnc ?

PaisleyPCdoctor
10-12-2017, 01:39 AM
Yes. Never had a cnc before.
I work with electronics. Computers, circuit boards and garage equipment (brake testers etc). I'm forever having to knock together an enclosure, adapter, circuit board or prototypes for my own test jigs etc. The CNC is gonna make my life better!

Just today I was going to order some m16 washers with earth lugs. £36 for 50. I only need four. I'm gonna cut them myself from some 0.5mm copper sheet. That kinda thing.

I'm totally looking forward to using it for fun though- 3d reliefs, engravings etc.

Kev2960
10-12-2017, 08:33 AM
Morning, you sound like you have an interesting job. I also have a 6040 and had to iron out quite a few problems along the way. I've started a new blog to help newbies to home CNC to share the problems and solutions.
The CNC Blog (https://the-cnc.blogspot.co.uk/p/home.html)

PaisleyPCdoctor
10-12-2017, 10:44 AM
Cool. I like that dust attachment. I was planning to do something like that. I have some 1" hose I want to attach to spindle. Could you post a pic of how you attached yours?

Kev2960
10-12-2017, 12:48 PM
Hi there, the hose is a push fit (tightish) both onto the spindle and for the plastic hoover hose. I made it 0.1mm smaller than the dimensions on the drawing below. you can do this by reducing your cutter dia. Eg. cutter is dia 8.0 so tell the machine the cutter dia is 8.1
The material used is 12mm MDF

PaisleyPCdoctor
13-12-2017, 01:58 AM
Here is the inside of my controller box. Plenty of issues to deal with.

NOTHING is earthed or shielded.

The VFD should bt even be in this box and the VFD output wires are draped right over the unshielded inputs of the controller.

Many if the power cables are undersized. Labelled as 1.5mm, but looking at them, I don't even think they are 0.75mm2.

Plan... rewire the whole thing. Shield and ground everything. Move VFD to seperate shielded enclosure...23398

PaisleyPCdoctor
13-12-2017, 02:08 AM
That last post was from 2 days ago.
I've rewired and shielded everything.
Moved VFD to its own box.
Fixed a few electrical safety issues.
Pump switch removed. If the controllers on, cooling pump is on. Simple.

It's all technically sound, but I think I need to go back in later and make it a bit neater.

I also plan to replace the 24v fan with a 240v version.

I haven't decided whether to move VFD control panel to new VFD box or leave it there. I'll think some more about it.

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m_c
13-12-2017, 11:11 AM
Over the top springs to mind, especially since everything was working with no problems.

I'm sure you'll carry on with what you think is right, however I'm just posting for the benefit of anybody inexperienced who might read this and think that all this is necessary. It might reduce the chance of problems, but there are thousands of machines that run with unshielded wiring and VFDs inside control boxes, with no issues what so ever.

And if you really were doing everything correctly, your new choke/filter for the VFD should be mounted on a sub-plate, not directly to the case ;-)

Kev2960
13-12-2017, 01:15 PM
My machine has no shielding.
As far as the wire gauge goes the steppers on this type of machine only pull 3A max

PaisleyPCdoctor
14-12-2017, 09:36 AM
My machine has no shielding.
As far as the wire gauge goes the steppers on this type of machine only pull 3A max

The underrated wires were the 240v power lines, feeding the 2kW VFD and the 24V power supply. The low voltage wires to the steppers were actually a lot meatier.

PaisleyPCdoctor
14-12-2017, 09:39 AM
And if you really were doing everything correctly, your new choke/filter for the VFD should be mounted on a sub-plate, not directly to the case ;-)

It's just the photo, it's not mounted to the case, it's actually suspended in mid air. With the stiffness of the wiring looms, it's not going anywhere.

Kev2960
14-12-2017, 10:35 AM
I see, I thought you meant the drivers and stepper wires my mistake

m_c
14-12-2017, 10:41 AM
It's just the photo, it's not mounted to the case, it's actually suspended in mid air. With the stiffness of the wiring looms, it's not going anywhere.

I never realised the ferrite ring was still mounted in that bit of the photo. I was on about the silver box mounted to the side of the enclosure at the bottom of the photo. Technically any power components shouldn't be directly mounted to the case, they should be mounted on a sub-plate.

As there's a ferrite ring, I wouldn't bother shielding any of the power cabling in the case. Ferrites are very effective at stopping the noise that can potentially cause problems. I would however use good quality shielded and twisted pair wiring for the VFD speed control wiring, as noise on that can cause spindle speed instability. The control wiring less so. It will all be 12 or 24V, and it would take a lot of interference to cause any problems there.

PaisleyPCdoctor
14-12-2017, 02:27 PM
Good advice. Thanks. The control wires are all double shielded. The silver box you mentioned is an EMI filter for the mains inlet, but you are right, it should be on a sub board. Its earthed and so is the casing. I'm gonna leave it for now. Next time I rejig the innards, I'll move it.

Doddy
15-12-2017, 11:11 AM
From personal (and expensive) experience with unsupported rails from one of England's finest CNC manufacturers of fluffy-dice, look at the amount of deflection you get over the x-axis travel, particularly if you ever fancy trying isolation routing of PCB (sounds like you're in that sort of ballpark), and also spindle rigidity.

Doddy
15-12-2017, 11:21 AM
Actually, no. The aviation connector barrel

I've heard these referred to as aviation connectors before now - as I understand it they are used for the headphones on radios. So, yes, they fly, but let's not oversell them. My main concern with them is these (and they are in common use for these machines) is that they aren't really rated for the currents that you might expect. For example

http://www.cliffuk.co.uk/products/cliffcon/zc.htm

You can see these are rated unto 1A. Probably not much of an issue for a small machine - your switching currents are going to be around 1.5-3A, but clearly out of spec for the connectors. My last iteration of <strike>upgrading</strike> updating my controller I replaced all with XLRs.

Neale
15-12-2017, 12:19 PM
Like Doddy, I use XLR connectors for my steppers. Ideally these should be hard-wired but I found that I was taking the control box in and out of the router frame quite a bit while building and testing and the XLRs work fine in practice. I also use those "aviation" connectors for signal wires (limit switches, VFD control connections, etc) and they are fine for that. I bought a bag of 5 or 10 from eBay or Aliexpress or somewhere like that fairly cheaply. I think they were described as "GX16", and come with various numbers of pins. Watch for the ones with a lot of pins - they aren't the easiest thing in the world to solder if you aren't a dab hand with a soldering iron!

PaisleyPCdoctor
16-12-2017, 12:28 AM
There are most definitely better connectors out there, but they are fine for the steppers. I still have one, actually 2 (male and female) at the VFD end of my spindle cable. Why 2?

The supplied VFD output connector was male. HUGELY DANGEROUS to have live connectors exposed like that! Live side of connectors must be female.
As I couldn't find a female panel mount socket, I opted to bring out the cable on a short lead with a female inline connector which mates with the male connector coming from spindle cable. I didn't want to wire it in directly cos I want to disconnect occasionally.

Anyway, after about an hour of constant (light) milling, the connector (inside) was no more than room temperature. I'm not worried.

PaisleyPCdoctor
16-12-2017, 12:37 AM
I think for now, I've went as far as I want to improve the wiring- mainly shielding, replacing cables and repositioning components.

My next area that I'm going to look at is the flexing of the unsupported x-axis 20mm linear bearing shafts. They can be flexed, tilting the spindle back and forth on the y axis direction. With decent pressure on top and bottom of spindle, I can deflect it by as much as 1.5mm (estimate) either way.

I knew about this design weakness BEFORE I purchased the mill, knowing that I may need to address it. No big deal- I'm having fun!

I have some ideas to mitigate the effect and later to help cure it.

PaisleyPCdoctor
16-12-2017, 12:50 AM
The first and easiest (and free) change is to the Z-axis assembly.
On this model, a 35mm spacer block has been added on top of the top bearing, increasing the Z axis length/travel by 35mm.

The way it's been built, I can very easily remove it and instead, mount it under the bottom bearing. The entire Z axis will be moved 35mm closer to the bed, but I can recover exactly that much by raising my spindle in the mount. I couldn't do that before as my tools wouldn't reach.

This will shorten the length of the "see-saw" motion, so in effect, the spindle tool will not move as far.

I'll measure deflection properly both before and after the modification.
Here a picture of the spindle and the 35mm spacer block.

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m_c
16-12-2017, 01:30 AM
If you're going to do what I think you are, it won't have any effect on the X-axis deflection. The pivot point (the rails), and the spindle/tool, will still be in the exact same positions relative to each other.

It will make a difference to the Z deflection, however I'm not convinced it will be that great. The Z-axis, although using unsupported rails, is quite a compact and stiff assembly. Although changing things around will reduce the pivot distance between tool and Z-rails, I wouldn't expect it to flex that much anyway. Certainly not much in relation to the flex of the X-axis.

PaisleyPCdoctor
16-12-2017, 01:56 AM
Thanks for the reply.

You are of course right, the pivot point and tool tip will be exactly the same distance so deflection will remain unchanged. However...

The mod will allow me to move the spindle (and tool tip) 35mm CLOSER to the pivot point (by raising the spindle motor 35mm in its mounts.

I'll work out the deflection angle and I'll be able to exactly predict (using distance to pivot point and angle) the deflection distance before and after.

I couldn't raise spindle any further without the mod because of tool reach.

PaisleyPCdoctor
16-12-2017, 02:06 AM
Although... on thinking about it, I'm really just lowering the spindle one way just to return it to the same position another way.

My head hurts. Lol.

I'll need to do some more thinking. Good catch! Appreciated!

Doddy
16-12-2017, 08:43 AM
My next area that I'm going to look at is the flexing of the unsupported x-axis 20mm linear bearing shafts.

Give us a pic.

PaisleyPCdoctor
16-12-2017, 08:03 PM
Here are pictures of the y axis assembly. Excessive flex in x axis direction.

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PaisleyPCdoctor
16-12-2017, 09:22 PM
Okay- some interesting results with dial gauge.

In middle of x axis (must be worst deflection zone), I can deflect the machine up or down a staggering 1.3mm! (worried).

I then thought- to prove the theory- deflection must be better or even minimal at either end of X-axis...

Its better, but still 1mm. So looks like its actually entire gantry flexing. Opens new possibilities.

Looking at Y-axis bearings, I previously closed the allen key sdjuster until it stopped, no further. I gave all 4 side screws a wee tweak tighter and deflection has been reduced to 0.4mm at ends and 1.1mm middle of Y axis.

I think theres another adjuster on top of bearing. I'll need to dismantle bed to get to it.

SIGH!

magicniner
16-12-2017, 09:51 PM
Go on mate, explain to me just how good they are, and how you'll fix yours :D

Still incomprehensible to you? :D

PaisleyPCdoctor
16-12-2017, 10:32 PM
Still incomprehensible to you? :D

Thanks for that constructive advice, I'll try that!

Now where's that middle finger emoji gone?

magicniner
16-12-2017, 11:49 PM
Thanks for that constructive advice, I'll try that!

Now where's that middle finger emoji gone?

Here you go -

You can polish it but then it will just be a shiny one ;-)

Kev2960
17-12-2017, 01:06 AM
Regardless of what some people say I think youíre doing a grand job.

PaisleyPCdoctor
17-12-2017, 03:11 AM
Regardless of what some people say I think you’re doing a grand job.

Thanks, mate. Appreciated.

I dismantled machine and nipped up all bolts. I tightened down all bearing adjustment screws (possibly to the point of uneccesary wear- who knows), but after that, the machine felt a whole lot more rigid! I didn't get a chance to measure anything as the wife forced me out into the real world to socialise. I'll measure tomorrow- but deffo better.

Kev2960
17-12-2017, 08:46 AM
Hi there, thatís interesting about the bearing adjuster screws. Can you tell me or send a photo. I might check mine, to be honest I didnít even know there were any
Kev

PaisleyPCdoctor
17-12-2017, 03:38 PM
Hi there, that’s interesting about the bearing adjuster screws. Can you tell me or send a photo. I might check mine, to be honest I didn’t even know there were any
Kev

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Zeeflyboy
17-12-2017, 06:33 PM
Aren't those just grub screws holding the bearing cartridge in place? I don't see how those would do any adjusting on the bearings other than distorting the casing or possibly forcing things out of alignment slightly.

My first (well actually second, but first was tiny) CNC machine was a similar design... was good enough to get started with and do light work, but unfortunately you will never be able to address the flex you get on those unsupported rails without just getting rid of them.

Whether that's an issue depends on what the goals are... cutting foam or other very light duty stuff will never show a problem, harder woods or light aluminium work can be done but you have to really work within the limits of the machine and accept that the tolerances and finish may not be what you hope.

Kev2960
17-12-2017, 06:45 PM
Theyíre probably just plain linear bearings and the screw just stops the bearing rotating or moving in itís housing.

magicniner
17-12-2017, 06:56 PM
Aren't those just grub screws holding the bearing cartridge in place? I don't see how those would do any adjusting on the bearings other than distorting the casing or possibly forcing things out of alignment slightly.

Tighten them enough and whatever is under them will eventually apply more pressure on one side of the rod, it isn't an engineering solution but if it works then the only remaining problems are wear and those floppy pesky unsupported rods ;-)

PaisleyPCdoctor
17-12-2017, 07:48 PM
The main gain was in Y-axis bearings.

They are adjusters. When they are tight, there is no noticeable flex/movement on the gantry. I tighten til they stop, then quarter turn to nip up. Gantry feels rock hard.

When I loosen the grub screws, the gantry flexes as if it's on rubber mounts. Difference is remarkable.

I'm just left with the flexing of the 20mm unsupported x-axis shafts. There's a youtube video where the guy replaces them with supported rails, but improvement was MINIMAL at best. Waste of time.

I have a better, cheaper and easier solution. Just sketching out the plan and I'll post it.

magicniner
17-12-2017, 08:20 PM
The main gain was in Y-axis bearings.

They are adjusters. When they are tight, there is no noticeable flex/movement on the gantry. I tighten til they stop, then quarter turn to nip up. Gantry feels rock hard.

Have you tried marking the rod with a marker pen to see if the contact is simply the screw against the rod? ;-)

Zeeflyboy
17-12-2017, 08:26 PM
The main gain was in Y-axis bearings.

They are adjusters. When they are tight, there is no noticeable flex/movement on the gantry. I tighten til they stop, then quarter turn to nip up. Gantry feels rock hard.

When I loosen the grub screws, the gantry flexes as if it's on rubber mounts. Difference is remarkable.

But that simply isn't how these bearings work, there is no pre-load adjustment... they are just a few rows of bearings inside a tube. You are achieving a reduction in slop most likely by forcing them out of alignment and thus introducing an increased load on one side. It achieves the goal but the problem is that the load isn't evenly distributed and wear will likely be accelerated.

Whatever works for you, but they are retainer screws not adjustment screws.


I'm just left with the flexing of the 20mm unsupported x-axis shafts. There's a youtube video where the guy replaces them with supported rails, but improvement was MINIMAL at best. Waste of time.

I have a better, cheaper and easier solution. Just sketching out the plan and I'll post it.

Supported rail doth not equal profile linear rail. My current machine is effectively a 6040 with proper 20mm profile rails and the difference is very obvious compared to the old machine... I don't need a guy on youtube, I've extensively experienced both. Of course even with proper rails you are still left with the general somewhat lightweight design but it's still a significant improvement over the previous model I had with unsupported rails like yours.

I'm not belittling you, you are obviously keen to get stuck in and learn - just be aware that despite what you may think at the moment, those unsupported rails (and to a lesser extent the supported rail on the bottom) are a limiting factor in this machine which you will need to learn to work around and will limit the level of tolerance and finish you can ultimately achieve in harder materials.

magicniner
17-12-2017, 08:26 PM
An engineer would understand that there is no way to adjust a linear bearing which has at least 4 bearing channels with a single grub screw.

I know you are hoping that you have found the Holy Grail that everyone else has missed but look at the way the system you are messing with actually works and you will understand that you are simply adding side load and wear in an attempt to resolve a problem with tolerance and clearance in the set of components you have unfortunately bought.

- Nick

magicniner
17-12-2017, 08:29 PM
But that simply isn't how these bearings work.

Don't waste your time!
There are things we understand, there are things we don't understand and there are things which we don't understand why we don't understand them, we are dealing with the third circumstance here :D

PaisleyPCdoctor
17-12-2017, 09:14 PM
If they are simply retaining screws, then fine- they weren't fastened when they built the machine and they are now in their proper location!

It's not like I've torqued them into the rod. Like I said, I screwed them in until they touched/reached resistance then gave them a QUARTER TURN.

The grub screws are obviously put there for a reason and being fully unscrewed (as they were) clearly serves no purpose whatsoever.

The bearings still run smoothly, no crunching or grinding.

The bearings were sloppy, now they are not. Moving on...

PaisleyPCdoctor
17-12-2017, 09:24 PM
I don't think replacing the x axis rails with supported rails will yield much benefit. It looks more work than its worth so I'm going to try a simpler approach.

I'll replace the back panel (3mm aluminium) with 10mm steel plate or possibly 25mm aluminium.

At the top and bottom of my Z axis assembly, I'm going to fit a runner wheel (or 2), adjusted to run tightly along the back plate (rolling along the x axis direction). For the spindle to rock back or forth, it will need to flex the back plate as well as the 2x20mm rails.

I currently cannot see any flexing left and right, just back and forth.

The mod should be cheap, but I will probably need to pay someone to mill some components for me.

PaisleyPCdoctor
17-12-2017, 09:29 PM
I also plan to mill the spindle mounting plate to allow a little tram adjustment left/right tilt. Back/forward tilt should be easy with shims.

But no point until I improve rigidity.

Zeeflyboy
17-12-2017, 09:31 PM
I wouldn't bother tbh... just get it up and running. If you want to revisit ideas later on after having actually put some use on it then do so.

The biggest flex for me on the unsupported rails came from the ability for it to twist (eg apply a force on the bottom of the cutter which is after all where the cutting forces come from) pushing it towards the back of the machine. The top rail will bend forwards and the bottom rail will bend backwards. The deflection is very measurable (and even visible) with quite moderate loads. Your solution of the rear panel doesn't do anything to change that, nor does a single wheel. Two wheels would go someway to solving half the equation (the rail being pushed towards the back) but not the other half (the rail being pulled away from the back). Even then I doubt you would see much benefit with the wheel slop/flex/wear.

In the nicest way possible, don't try to re-invent the wheel on this one. Get your machine up and running, get some use on it and if you find you need to improve on it then feel free, but in all honesty you'll probably come to the conclusion that you are better off building a new machine than trying to improve the 6040.

magicniner
17-12-2017, 09:34 PM
I don't think replacing the x axis rails with supported rails will yield much benefit.

Cool, let us know how ignoring horribly flexible machine components goes :D

PaisleyPCdoctor
17-12-2017, 10:35 PM
Zee flyboy,
I appreciate your input. Here my thinking.

If you push on spindle, the axis shafts flex. The pivot point is the ball screw, top rod flexes forward, bottom rod flexes back. Vice versa if you pull on spindle.

During this motion, the gantry stays stationary.
The backplate is attached to gantry.

Imagine the gantry didn't need to move left/right on x axis. If I placed a piece of metal from top of z axis to backplate and bottom of z axis to backplate- it would support the spindle and it wouldn't flex. Assuming of course back plate was rigid.

To allow x as is movement- Ill use wheels on the supports.

It'll work.

Zeeflyboy
17-12-2017, 10:46 PM
Yeah but in your example of the Z-axis bolted to the gantry, it can't pull away... a wheel isn't attached to the gantry it just rides on it. Sure it can't push into the gantry (well, beyond what degree flex of the wheel allows) but it can pull away from it. That's not even getting into the problem with swarf getting trapped under the wheels and wearing down the relatively soft aluminium surface.

What you need is something that can't push towards the gantry or pull away from it - ie a supported rail. Round supported rail however has the drawback that the shitty bearing becomes the weak point (even shittier than a fully round rail bearing is)... enter profile rail. Now you come full circle to what I was saying in the first place which is that the unsupported round rail is just inherently inferior to profile rail for milling anything substantial.

Honestly, what you are suggesting is a waste of time - imo the improvements will be minimal if noticeable at all. Combine that rear plate with proper linear rails and now you have a substantial improvement but are at the mercy of the next weak link. And onwards the chase continues.

Listen to me or don't, but I would sincerely suggest you just get cracking with your machine without any major effort/changes and take it from there. I would say after a few mods and chasing your tail you will come to the conclusion that it's better to just chalk it up to a good entry machine for learning/playing around and decide to build your own one rather than constantly trying to work around the inherent weaknesses of the design. Either that or you will decide that for whatever your intended purpose is, it's just fine.

Note that when I say the inherent weaknesses of the design, I'm not just talking about the unsupported rails... there are MANY issues with these machines and to address them all you would effectively end up building a new machine anyway - which is what I am now doing myself.

Just trying to save you some time and money in the process. Up to you if you want to heed that or not.

PaisleyPCdoctor
17-12-2017, 10:55 PM
I see what you mean about it moving away from wheels, but that would take a lot more force and I don't see how it would happen. The workpiece can only push from the very bottom.

The supported rail was my plan, but I seen the guy on YouTube done it and it didn't help at all. Maybe with the fat backplate though. The way the ballscrew is attached to the bearings just now make it look like a big job. I'll need to have a good think how to do it though.

BTW, I'm still using the machine in between mods. I did specifically buy it with intention of modding it and learning. I knew the weaknesses when I bought it, if anything it was a lot better than I'd expected. I didn't get disappointed. It's a hobby machine. I'm hobbying.

PaisleyPCdoctor
17-12-2017, 10:58 PM
I could possibly ADD a really fat supported rail on the other side of backplate, mounted to z axis assembly over and under the backplate.

hmm.

magicniner
17-12-2017, 11:00 PM
Just trying to save you some time and money in the process. Up to you if you want to heed that or not.

Save your breath, it's a brilliant machine with some little shortcomings which can be resolved with a hex key.

Or Not :-)

Zeeflyboy
17-12-2017, 11:03 PM
I see what you mean about it moving away from wheels, but that would take a lot more force and I don't see how it would happen. The workpiece can only push from the very bottom.

I think you underestimate how little it takes to produce chatter


The supported rail was my plan, but I seen the guy on YouTube done it and it didn't help at all. Maybe with the fat backplate though. The way the ballscrew is attached to the bearings just now make it look like a big job. I'll need to have a good think how to do it though.

Again, the supported rail that you are thinking of is not what I suggest. Supported rail is barely better than round rail... What I am suggesting is profile rail. Everything else you do without doing that is just really little more than pointless.


BTW, I'm still using the machine in between mods. I did specifically buy it with intention of modding it and learning. I knew the weaknesses when I bought it, if anything it was a lot better than I'd expected. I didn't get disappointed. It's a hobby machine. I'm hobbying.

Good, and I applaud garden shed engineering - it's quintessentially British. Even so, there is limited value in repeating the mistakes of others that have gone before you. One of the great things about our species is the ability to progress based on prior learnings of others rather than being doomed to constantly be stuck in a cycle of repeating the same failures... There is a reason why anything above the absolute most entry level machines use profile rail across hobby/industry and it's not because they weren't creative enough to come up with weird and wonderful solutions like wheels.

hanermo2
17-12-2017, 11:08 PM
Excellent thread !
I very much like the OPs grit-n-go attitude, esp. considering actual measurements re_ flex.

Very Well Done ! keep at it.

The major value to the OP is learning about rigidity, motion control components and actual needs of machine tools in cutting apps.

All others reading this may learn a lot about what is flexible and or sloppy (backlash, jitter, bend aka flex) in these machines, and by about how much, and what happens when you change one part at a time.

The vast majority of people do not ever measure stuff like the OP did re:flex.
The vast majority also give up, usually soon.

I am not giving advice here ... (tend to do too much of that..).

There is a big body of evidence that more or less all machines will do upto about 5x or 500% "better" with some tune-up, mods, and very carefully controlled cutting parameters- for a single specific tuned job when optimised for the machine and tools available.

This applies to the chinese 6040s, bridgeports, small lathes, big lathes.

Zeeflyboy
17-12-2017, 11:13 PM
]very carefully controlled cutting parameters

That part is the most significant by far imo... I've always said the most productive "mod" I ever did for the X2200L was learning to use Fusion360 and figuring out how to best use/tweak adaptive machining for my machine.

PaisleyPCdoctor
17-12-2017, 11:29 PM
Okay, I'll look at profile rails.
In your opinion, what are the Chinese profile rails like? Their prices look fine, but most of the branded ones I've seen are just far far too much for me.

magicniner
17-12-2017, 11:32 PM
Okay, I'll look at profile rails.
In your opinion, what are the Chinese profile rails like? Their prices look fine, but most of the branded ones I've seen are just far far too much for me.

You can't do that!
You have previously clearly stated that here's nothing wrong with what you have!
:D

Desertboy
17-12-2017, 11:35 PM
https://www.ebay.co.uk/itm/15-1500mm-2x-Linear-Guideway-Rail-4x-Square-Type-Bearing-Block-Machinery-Unique/173014800117?_trkparms=aid%3D222007%26algo%3DSIM.M BE%26ao%3D1%26asc%3D49568%26meid%3D5d1ba68f25bd482 a92681da6cb2aa14e%26pid%3D100011%26rk%3D2%26rkt%3D 12%26sd%3D182772661138&_trksid=p2047675.c100011.m1850

This is what I used on my gantry I'm very happy with it

You could buy a set of 1500mm with 4 carriages and a set of 300mm with 4 carriages for £200 and then cut the 1500mm down to get the usable lengths of rail to fit X&Y and swap the carriages across.

Zeeflyboy
17-12-2017, 11:41 PM
Okay, I'll look at profile rails.
In your opinion, what are the Chinese profile rails like? Their prices look fine, but most of the branded ones I've seen are just far far too much for me.

Seems people have got on fine with Noulei from what I've seen... it'll still be an order of magnitude better than round rail either way. Some good sellers on Aliexpress (I've bought HIWIN there before and been very happy) that will supply to your specs.

Have at least a rough plan though before ordering anything, and do bare in mind that you are addressing one of many mechanical weaknesses in the design... so if the plan is to continue to mod this particular machine, worth having a plan of what comes next and whether that will affect your mods here. For example, to change to profile rail you will likely have to make a new Z-plate and spindle mount. Is it worth changing that over to profile rail as well to avoid having to change it twice? Now your supported rails on the Y-axis are a weak point, then the ridiculous floppy bed, then the thin bendy gantry arms, then the piss poor use of retaining bearings for the ballscrews etc etc.

You see what I mean I hope... Just think it all out (almost like a new machine design) before committing to buying anything.

Then once you've done that and other mods, now you have semi respectable rigidity and realise your extrusions aren't straight enough... at best out come the shims, at worst another redesign. Then you decide you could have done a better job just designing from scratch. It doesn't end :)

PaisleyPCdoctor
17-12-2017, 11:46 PM
They certainly aren't expensive, thanks!

I'll look over the machine and see what the options for mounting are. A big fat back panel will certainly be needed.
Thanks again.

Desertboy
17-12-2017, 11:47 PM
I have original Hiwin's on my Y axis and the clone rail on my X axis they feel identical to me.

That clone rail I linked to is in Germany so no import tax and only took 3 days for delivery for me although will be slower at the moment of course.

Desertboy
17-12-2017, 11:56 PM
At some point it makes more sense just to use it as it for 6 months and then sell it as is and build your own from scratch using the lessons learned along the way.

I bet you'd have no problems selling it for what you paid for it as bad as it might seem it's still better than an xcarve or shapeoko so plenty of potential users out there.

PaisleyPCdoctor
18-12-2017, 03:09 AM
I'm looking at the hiwin hgr15, hgr20 and hgr25. Not a massive price difference for 500mm length.

I'm leaning toward the 20 but only because 15 seems small and 25 is possibly overkill.
I would have 2x rails on x-axis. I have never touched one of these so I'm guessing.

Not gonna jump in and buy straight away, just need to decide so I can mock up with correct dimensions.

Any recommendations would be warmly welcomed. Thanks.

Zeeflyboy
18-12-2017, 09:05 AM
HGR20 is the common choice - HG15 carriages can be very awkward to grease as there isn't a lot of space to get at the grease nipples.

HGR25 is overkill, but on my new machine I ended up using them on the Y-axis just because the dimensions suited my design.

Desertboy
18-12-2017, 10:24 AM
If you're going to fit Hiwin style rails the correct choice is the one that's easiest to retrofit to your existing plates if possible at all.

15mm Hiwin are a PITA to fit with 1605 ballscrew and BK12 fittings you need spacers, I fit my ballscrew sideways on, on my Y axis to solve this problem but still ended up with spacers on the X & Z.

15mm was a no brainer for me, even with the extra hassles but I traded time for my original Hiwin's in the end cost me 12 hours on a Sunday and 6 hours in the week for my 1.2m Hiwin's and 45cm ones on my Z. Was it a good deal? Like my friend tells me my time is worth nothing lol.

PaisleyPCdoctor
18-12-2017, 12:23 PM
So you went with 2x15mm hiwin on your x axis?

I was looking at my machine last night and weighing up the options. I think I can potentially leave my ballscrew and 20mm shafts on and ADD a 15mm hiwin, possibly 2 hiwin. Sounds crazy, but actually looks easier.

My main worry with the 15mm rails- spec says the attaching holes on the trucks are M3 threads. Is that right? Seems a lot of force for 4x M3 screws to handle.

Desertboy
18-12-2017, 03:37 PM
So you went with 2x15mm hiwin on your x axis?

I was looking at my machine last night and weighing up the options. I think I can potentially leave my ballscrew and 20mm shafts on and ADD a 15mm hiwin, possibly 2 hiwin. Sounds crazy, but actually looks easier.

My main worry with the 15mm rails- spec says the attaching holes on the trucks are M3 threads. Is that right? Seems a lot of force for 4x M3 screws to handle.

They're M4's at least my original Hiwin's and the clone rail I linked to are M4, the carriages are also M4.

My spindle mount actually bolts through the mounting plate and directly into the Hiwin's.

My X is 1.2m original Hiwin's, Y is the 1.5m clone rail I linked to (I only paid £99 but they are still a bargain at £120) & Z is 45cm Hiwin all 15mm

There's 90 T nuts holding the 1.2m and 1.5m to the extrusion with M4's you have no issues the extrusion will fail before the bolts lol.

Stainless steel bolts are not strong, high tensile are much much stronger next time I will use high tensile and they are cheaper to boot.

I've destroyed so many M4 A2 stainless bolts the caps round off so easy.

PaisleyPCdoctor
18-12-2017, 04:02 PM
I was going to ask how you drilled the holes to ensure proper allignment- I would struggle.the tbolt to extrusion will probably figure in my plans. Much simpler.
Thanks.

m_c
19-12-2017, 12:09 AM
The biggest problem is that you'd be bolting the rails to aluminium, not the bolts themselves.

There are various calculators online for bolt strength, and the first one I've just found puts an 8.8 grade M3 bolt at proof load of 2920N, and minimum ultimate load at 4020N. To put that in context, that means you could hang over 400Kg onto the bolt vertically, and it should not snap.
However I very much doubt an aluminium thread would support that 400kg.

I'd be looking at either helicoils, or bigger threaded inserts which I've currently forgotten the name off, to help spread the load on the aluminium.

PaisleyPCdoctor
19-12-2017, 01:41 AM
The thought did occur to me about load on threads, albeit not as precisely as you.

The way it's looking the rails will probably be mounted with trucks facing up and down (above and below the existing rods, so load will be perpendicular to the bolts, rather than trying to pull them out, if that makes sense.

If I end up leaving the 20mm rods in, it shouldnt be an issue. The load will be shared in some fashion between 4 bearings (or six if there's space to double up on the square rail trucks).

I've ordered a single 15mm hiwin clone from uk with 2 carriages. It'll be 100x easier to visualise a working plan with them in front of me.

Also- might have mentioned- to avoid the definite coking up of manually drilling all those mounting holes- I'm gonna use a bit of 2020 extrusion between rail and aluminium backplate. That seems less rigid but at least I can do it.

PaisleyPCdoctor
19-12-2017, 01:50 AM
I've destroyed so many M4 A2 stainless bolts the caps round off so easy.

Typical, I always have a bag of m4 a2 Allen key bolts in van. Use them to replace missing ones on machine access panels I work on. Thought I was being clever buying stainless, but I've decapitated 2 so far. I feel your pain. Lol

PaisleyPCdoctor
23-12-2017, 03:52 PM
I recieved my 500mm long, 15mm hiwin clone guide rail and carriages today. Sure singly quick.

Looks good, except these have M3 holed on the carriages (2x20mm spacing).
Suppose it will be all right as I'll end up with 2 of these rails in addition to my 2x20mm round rails. I'm sure the M3 threads will take the punishment.

23463

PaisleyPCdoctor
23-12-2017, 03:59 PM
I was thinking for ages last night about ways to increase the rigidity of the bed frame. Came up with all sorts of ways that would probably work, but I had a simple idea this morning.

I've got some 900x600x60mm concrete paving slabs laying around. I'm going to place the cnc on one of them and bracket the frame to that. It surely won't be able to twist and it will add a fair amount of mass to help prevent it bouncing around on fast movements.

Best of all, it's free.

PaisleyPCdoctor
23-12-2017, 06:01 PM
I've figured out how to add the 15mm square rails.

New backplate, 20-25mm thick aluminium, 100mm high. 2020 extrusion bolted to top and bottom edge. Square guides bolted to extrusions. Mounting plate coming out from under existing x axis bearing assembly for bottom rail.

Square block on top of top carriage to mount into handy t-slot in the spacer above existing bearings.

2 carriages top and 2 carriages bottom.

23464
23465

Desertboy
23-12-2017, 06:48 PM
Don't take the carriages off the rail EVER! Bearings can and do come out those carriages so the best thing you can do is put a bolt in either end for now so they're captive.

I think you have low profile rail which is why it's M3 not M4, it's still plenty strong and a superior solution to the round rail by a million times lol.

That's crazy quick delivery, how much did you pay? if it's not too rude a question.

PaisleyPCdoctor
23-12-2017, 07:36 PM
15mm x500mm square rails with 2x carriages was £37 off eBay. They were posted from uk but still surprisingly quick for Christmas time.

I ordered a second today, it'll arrive before I have time to build anything anyway.

I'm quite worried about getting the mounting holes correct. I think I'll mock it up in acrylic or something first. Once it's correct, I might pay someone to machine it in aluminium. Might be able to do it myself- we'll see. Lol.

I plan to buy two 20mm rails , 750mm long to replace the y axis bearings. Looks like a pretty easy job. That's gonna cost me £124 (china). After that, there's not much left and I'll just have to get on with actually milling stuff.

Desertboy
23-12-2017, 07:48 PM
15mm x500mm square rails with 2x carriages was £37 off eBay. They were posted from uk but still surprisingly quick for Christmas time.

I ordered a second today, it'll arrive before I have time to build anything anyway.

I'm quite worried about getting the mounting holes correct. I think I'll mock it up in acrylic or something first. Once it's correct, I might pay someone to machine it in aluminium. Might be able to do it myself- we'll see. Lol.

I plan to buy two 20mm rails , 750mm long to replace the y axis bearings. Looks like a pretty easy job. That's gonna cost me £124 (china). After that, there's not much left and I'll just have to get on with actually milling stuff.

I used 9045 Tslot extrusion with made it super easy to mount the rails but AFAIK they don't do M3 T nuts so would not be useful to you.

Although maybe not so useful to you KJN can can drill holes in extrusion at a reasonable price.

PaisleyPCdoctor
31-12-2017, 08:22 PM
Okay, Long term- I will probably rebuild the Z axis and most of the gantry. Problem is, I cant really mill aluminium at the moment. too much flex in x-axis. Heres what im thinking of doing to get it a bit more rigid.

Add two 15mm linear rails (4 carriages), to a 120x530x20mm aluminium flatbar backing plate (fixed to gantry). A 2020 extrusion top and bottom to aid fitting.

Here is the before and proposed after...

23522

I'm worried about the flex in the 2020 extrusion. Anyone got a better idea?

Thanks.

Desertboy
31-12-2017, 08:30 PM
Just an idea but you could replace the gantry completely with new aluminium plates and 9045 extrusion, if you take it real slow you'll be able to make them on your machine.

PaisleyPCdoctor
31-12-2017, 09:40 PM
I'll almost certainly end up doing something like that in future.
I want to try this first though. If it makes enough difference, I can mill my own parts out of aluminium to rebuild the way I want.

Just now i cant even trust drilling operations on the machine- far too much deflection on contact with material- even going really slow.

I have another coupla plans I'll post. I need the feedback.

PaisleyPCdoctor
31-12-2017, 09:54 PM
or this...

10mm plate attached to back of z axis assembly, linear rails on another 10-20mm plate attached to gantry.

23523