Hovering over "Buy"... care to sanity check my thinking?!

So I originally joined up and posted the following thread in the welcome forum pretty much 2 years ago :nightmare:...

http://www.mycncuk.com/threads/6914-...ick-hi-and-q-s

Since then I became overly cautious about diving in to CNC, and went for a 3D printer instead, and I must say I've really made (and continue to make) good use of it, making automotive brackets and so forth, and really feel like I've got my money's worth out of it. So my mind recently wandered back to my original plans for a home-made CNC so I started reading up again. And watching various YouTube videos, trying to find someone who had approached it how I'd like to approach it. Then I stumbled across this guy :-

https://www.youtube.com/user/featony

And *that* right there is exactly what I'd have envisaged as the perfect machine, and it also shows a build how I had figured it would have to be. And so it's confirmed for me that it's just too big a job to take on at the moment, I simply don't have that level of machinery around to make a decent enough job of it, and I see no point in doing it unless I'm going to do it properly.

Soooo... I'm thinking of a stop-gap learning exercise. Downgrade my expectations somewhat. And I'm finding it really hard to talk myself out of a cheap, crappy Chinese-made 6040 (I know, I hear the groans already). Thing is, even for their faults, I'm finding it hard to knock them in terms of outright value as a learning exercise. The 6040's have the 1605 ball screws, the high-speed (ish) motor for PCB work and by all accounts they'll do some soft aluminium as long as speed isn't a prime concern (it's not). I'll look to the VFD models with the better spindle, although won't fuss to much over the kw rating, they seem to vary anything from 0.8 to 2.2 on eBay.

Best I can make out, I can do some choice upgrades as time permits (or as they fail) :

• Replace wiring when it starts to fracture
• Fit a nice bed plate and level it myself
• Upgrade the electronics if/when they fail (sound like more "when")
• Swap the water pump pretty much straight away

Questions then...

1. Do they all come with limit switches now?
2. Various different representations of the control boxes on eBay; the 'newer' ones seem to be the black box design; is any of it really important or are they all equally as bad on the inside of that box?
3. Am I right in assuming the ballscrews are C7 grade so about the best that can be reasonably had at that size/price point?
4. I'm fairly au fair on the electronics/fabrication side of things, are there any cheap (open source/DIY) approaches to the motor drivers and control boards that I can look at to save money and get a higher quality solution? Would want something compatible with the main software, either LinuxCNC or EMC3/4.
5. Can't help but think while I'm at it move to EMC4 and USB
6. Any other choice upgrades/modifications I should consider? Thinking this is just a learning exercise for a few years, I'm happy to concede it won't deliver the quality level I originally intended in my welcome thread, but like I said, I'm just lowering my expectations and putting it down as experience.
7. Am I right in understanding the main limitation are these TBS drivers? Uprating them will allow the motors to be driven at higher V&A reliably? Are the TBS drivers just substandard/badly matched to the motors or something? It seems a common criticism... but then some get on fine with it "from the factory"?

I'm put off by the 3020 as I know they are cheaper but their use of trapezoidal screws concerns me for the accuracy/repeatability issues, particular with any PCB stuff I do, and also their slower, less powerful motor (again, my understand is the PCB milling will need some real high speed - I mean, ideally 60k+ but I can settle with 24k).

Am I being overly picky? Is the 3020 not significantly worse than the 6040 and I should just go super-cheap? Will the 3020 realistically do aluminium at *any* level, even if I accept the 6040 would only scratch at it :) ?

Then hopefully in a couple of years when I have more space and equipment (and knowledge!) I can contemplate doing something awesome like This Old Tony :)... but realistically, I just don't have the time right now :(

Thanks in advance for any thoughts/opinions. Happy to be shot down in flames ;)

edit: Thought - go 3020 and upgrade the ball screws to 1605-C7's? Worthwhile? Then uprate the spindle over time to a VFD?

Be afraid Very afraid.!!!. . . . . Nah but seriously now I wouldn't buy one unless it's purely for learning purposes and I wouldn't waste a penny trying to upgrade one. . . . Can't make Silk purse out of sows ear.!

Q1: Not seen any of the Cheaper ones come with limit switches or Home switches.
Q2: Mostly junk and the better ones are still Cheap Analog drives best avoided.
Q3: Yes and C7 is more than good enough for router. C5 or higher screws will cost more than the machine.
Q4: Best advice is don't bother only ends with you buying proper drives. You can buy Lead shine Digital drives for less than £40 on ebay and nothing you'll find or build open source will come near in performance. No point trying to re-invent the wheel
Q5: Never heard of EMC4. Thou I think you may mean Mach4. In which case No stick with Mach3 for time being and Don't go with USB it's not stable enough. Ethernet is the way to go.
Q6: Upgrade what.? if 3020 or any of the Chinese machines then Nope don't waste a penny ugrading just use and sell when learnt and ready for better.
Q7: The TB based drives are Low voltage which if pushed have habit of letting out the Magic smoke. Again just avoid them they are bad news.

To learn with the Cheap chinese machines are great Entry into CNC but don't expect the world and Don't waste money trying to make better and you'll get value for money.

Ah yes, sorry, you're right, I meant Mach4. Ok, that's cool then, I'll stay with the parallel port. Glad I kept that old IBM Thinkpad now :D

On Q6, well, I didn't know - I was just after any thoughts/opinions. Sounds like it's just not worth it, so that's cool.

Digital drivers is a new one on me - guess some more reading to do - do they need different motors, presumably? No problem if it's a complex answer, I'll do some reading on the forum, just curious.

I guess any upgrades to the electronics can be considered an investment, assuming the drivers and motors remain matched..... maybe I can keep the motors and spindle, if nothing else, if/when I do make my own.

Am I right in thinking the main thing I need that's really lacking is the rigidity in the gantry, the quality of the runners, lack of support on the Y and just general strength/"trueness" in the aluminium extrusion approach...

Here's the crux question then - for the PCB work and aluminium work (slow, hobby, prototyping stuff, low volume, 0.1" through-hole and SMD designs) is the extra £400 on a 6040 worth it over the 3020? The only real differences I can make out are the crappier spindle, the crappier ball screws and the smaller working size. The latter I couldn't care about :)

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Originally Posted by brumster

Ah yes, sorry, you're right, I meant Mach4. Ok, that's cool then, I'll stay with the parallel port. Glad I kept that old IBM Thinkpad now :D

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No wouldn't use parallel port either. I was saying Go with Ethernet over USB but if choice is between USB and Parallel port then USB every time. Also Don't use Laptop with parallel port and Mach3 they are too unreliable.

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Originally Posted by brumster

Digital drivers is a new one on me - guess some more reading to do - do they need different motors, presumably? No problem if it's a complex answer, I'll do some reading on the forum, just curious.

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Digital drives are far superior in performance and reliabilty to Old Analog technology because of the advanced way they handle resonance and current/voltage etc. The difference is quite large and has to be experienced to appreciate the true difference.
They work just same regards motors you can use.

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Originally Posted by brumster

I guess any upgrades to the electronics can be considered an investment, assuming the drivers and motors remain matched..... maybe I can keep the motors and spindle, if nothing else, if/when I do make my own.

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Not really because any machine is only good as it's weakist link and there's too many weak links. Also if idea is to re-use on another machine then this needs careful consideration because how do you know what you'll need without having the machine design.?

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Originally Posted by brumster

Am I right in thinking the main thing I need that's really lacking is the rigidity in the gantry, the quality of the runners, lack of support on the Y and just general strength/"trueness" in the aluminium extrusion approach...

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It's multitude of things really which all bring it down. The actual strength isn't too bad it's the low quality of rails and bearings etc that let it down.

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Originally Posted by brumster

Here's the crux question then - for the PCB work and aluminium work (slow, hobby, prototyping stuff, low volume, 0.1" through-hole and SMD designs) is the extra £400 on a 6040 worth it over the 3020? The only real differences I can make out are the crappier spindle, the crappier ball screws and the smaller working size. The latter I couldn't care about :)

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Forget aluminium it will destroy the machine in no time. The rest it will do. Thou I would say stay away from the Cheap DC spindle and Lead screw versions. All have rubbish electronics so that's just a lottery.

All duly noted. Arrrgh, you're making me think maybe I should just build a scaled-down steel DIY jobbie instead :D !

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Originally Posted by brumster

All duly noted. Arrrgh, you're making me think maybe I should just build a scaled-down steel DIY jobbie instead :D !

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Welcome back to the forum. If you are careful you should be able to make a decent machine for about £1500 so have a look at some of the build logs on here and have a go with a new build thread and put some designs up. Good luck

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Originally Posted by brumster

All duly noted. Arrrgh, you're making me think maybe I should just build a scaled-down steel DIY jobbie instead :D !

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Good it was my intention to make you re-think and Encourage anyone to DIY build. You also don't need to build with steel if you haven't got the tools for it.
Aluminium profile and Aluminium plate still build a very strong and more than capable machine and can be used with minimal tools.
Use correct components along with good electronics and you'll have a machine that will knock all those Chinese machines and several other commercial offerings into tin hat.

I think my idea is to build it in steel just to test the theory and process of construction (I also have loads of 20 and 30mm box, 3mm wall, kicking about), although I fully appreciate it will be overkill at the size I'm looking. So idea is to build a small, desktop build but with the same concepts as the larger one I'd *like* to do one day (in another property, no doubt). But conscious I don't want to get too tied up with the construction/planning that I lose interest and it all dies a death. Having said that, I'm pretty determined in most things, so.... :-S

I'll do some more reading, mull over some ideas - and of course always value other opinions (no offence Jazz, I totally get what you're saying!)...

It would help if you decided on the physical size so that you can get some advise on the frame.

20 - 30mm box doesn't seem big enough unless you are going to build a 3D printer.

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Originally Posted by brumster

(no offence Jazz, I totally get what you're saying!)...

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No offense taken. It's common for people to dismiss Experienced advice and seek other opinions when they don't hear what they want to hear.!
Truth is they sooner or later realise the advise was good, unfortunatly it's usually cost them money to realise this. . . . Called the price of learning.!

Sad thing is it needn't have done if they'd only listen.

To be honest it's a double edge sword advising people because those that do listen never really fully realise the bullet they dodged by listening so you never really hear from them because things tend to go fine and without issues.
Those that don't are often embarresed so never really say anything publicly and just go with what was suggested first time. (Although do often get PM or email thanking me and asking again.!)

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Originally Posted by Clive S

It would help if you decided on the physical size so that you can get some advise on the frame.

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Line in the sand, let's say 600x400 working area, give or take 100mm. For this iteration.

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Originally Posted by JAZZCNC

No offense taken. It's common for people to dismiss Experienced advice and seek other opinions when they don't hear what they want to hear.!
Truth is they sooner or later realise the advise was good, unfortunatly it's usually cost them money to realise this. . . . Called the price of learning.!

Sad thing is it needn't have done if they'd only listen.

To be honest it's a double edge sword advising people because those that do listen never really fully realise the bullet they dodged by listening so you never really hear from them because things tend to go fine and without issues.
Those that don't are often embarresed so never really say anything publicly and just go with what was suggested first time. (Although do often get PM or email thanking me and asking again.!)

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Yeah, sure, I understand. And I am listening, don't worry. The choice for me is whether writing off £500-1000 on a crappy Chinese thing is a valuable learning experience versus investing the time and money into a £1500 DIY job first time - accepting that I might get things wrong, learn the hard expensive way.... I'm going to do some more stewing/thinking/reading.... mainly on the DIY side, get comfortable with the concept that I will have access to sub out any necessary work to those with the right tools.

As per my intro thread, I'm not averse to some fabrication, some welding; I've built numerous cars over the years (I know that's not totally relevant but I'm just trying to convey that I know the right end of a spanner, that's all!)... but likewise it's that knowledge of what needs to be done that's making me double-think whether I can really do it DIY without any mills, lathes, etc... just a bench pillar drill and a hacksaw... :D

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Originally Posted by brumster

The choice for me is whether writing off £500-1000 on a crappy Chinese thing is a valuable learning experience versus investing the time and money into a £1500 DIY job first time - accepting that I might get things wrong, learn the hard expensive way

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The metal work is only a small portion of the expense. The real expense and BIG chance of wasting money is buying the wrong stuff. Cut corners here and you will without doubt waste money and cost more than buying decent gear in first place.! . . . It happens time and time again.!

Like wise you don't need massive tool collection either. Many great machines have been built with with just Drill press and hand tools. My first machine was built using just Drill press and hand held router. It wasn't pretty but was very accurate and cut nothing but Aluminium including this.
https://www.youtube.com/watch?v=wjDv...ature=youtu.be

Infact Joe on this forum is doing a very nice job with Minimal tools, he's also cutting alumnium with hand held router. http://www.mycncuk.com/threads/4513-...ghlight=router

Very nice :)

I have an offer from a forum member to go and take a look-see at his machines, and a general chat, so I'm going to take him up on his offer. Think I will feel much better once I've seen a DIY-constructed device, then make a decision.

Breaking out onto a separate topic a little.... on the electronics side of things... the stepper drivers and the motion controllers. Just want to check my understanding; is the following right?

Motor Drives

These are really nothing more than stepper driver ICs, of which obviously there are a plethora out there with various ratings in terms of voltage, current, stepping capability and safety features. Bolted on to that are the relevant amount of heatsinking, protection/filtering but ultimately they take a low-voltage signal from a microcontroller or parallel port - with appropriate optical isolation - and move the motors as requested. One tick = one unit of movement (in the appropriate direction, of course).

There are differences in terms of matching them to the motor (number of wires for unipolar, bipolar) and you can get analogue and digital ones, digital ones being better all-round but presumably more expensive. There are trade-offs with how you drive the motor in terms of microstepping, torque, heat generation and so forth. So you need to know your motors in conjunction with your drivers, and also what you're going to use them for (what's most important - torque or speed).

You can get ones with direct parallel port drive (so no motion control; driven straight from PC) but then the honus is on the PC as the controller, hence all the requirements in terms of it being able to keep up. Each pin on the parallel port controls a function, which limits you somewhat to the number of axes/functions you can make use of.

Other alternatively you can get drives controlled from a separate motion controller in between the drivers and the PC.

Motion Controllers
These do the interfacing between your PC (via parallel port, USB or ethernet port) and the motor drives, but instead take a proprietary protocol and convert that to the native signals for each axis drive (they don't take G-code). The benefit of these is they can layer on all sorts of fancy stuff like inertia concepts, but the big gain here is really offloading the requirements from the PC to keep up with the frequency of signals needed to instruct the drivers directly. The motion controller interprets the movement commands (move X from 0 to 100) to how many steps that needs on which axis, at what speed, and then takes on the job of reliably hitting the driver with the requisite clock signal and appropriate-timed control signal.

You potentially gain some speed/reliability on your machine and generally it's the way forward unless you just want to have a play at slow speeds direct via parallel.

When you guys refer to BOBs (Breakout Boards) you're generally talking about motion controllers, although you can get BOBs that combine both of the above.

It strikes me that keeping them separate gives more flexibility as the drivers need to match the motors; if you get a combo BOB you'd need to be sure that the drivers side of it matched your requirements and they weren't going to change.

Point, laugh, poke the shit out of the above where I've got it miles wrong :)

Motor drives say like the AM882 (Typical) are digital and have stall detection etc. are used after the BOB (and can be connected direct to the PP BUT not recommended) also they are used after the motion controller.

Motion controllers are generally fed from either USB or Ethernet port and they produces the pulses much better than the computer as they generate their own. Some motion controllers also have the BOB built in.


The Gcode is controlled from the machine controller ie Mach3 or Linuxcnc etc and fed to the PP or the motion controller

Does Mach3/LinuxCNC send actual gcode to a motion controller though? I thought not? It interprets the gcode on the PC, then some plugin relates that to wire signals that are specific to your motion controller (via a plugin on Mach3 for example) and then the motion controller converts that to the relevant pulses/etc...?

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Originally Posted by brumster

Does Mach3/LinuxCNC send actual gcode to a motion controller though? I thought not? It interprets the gcode on the PC, then some plugin relates that to wire signals that are specific to your motion controller (via a plugin on Mach3 for example) and then the motion controller converts that to the relevant pulses/etc...?

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No I was over simplifying it the Mach3 converts the gcode to pulses which then goes to the PP or motion controllor

Understood, thanks :eagerness:

Contemplating whether to make my own drivers and motion controller, but sounds like the latter is out! Too much coding effort anyway, I see there's an open source one out there and the code alone took 4 years of development... so no, I won't be going that route :)

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Originally Posted by brumster

Understood, thanks :eagerness:

Contemplating whether to make my own drivers and motion controller, but sounds like the latter is out! Too much coding effort anyway, I see there's an open source one out there and the code alone took 4 years of development... so no, I won't be going that route :)

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Good drivers are essential as they also take account of resonance, current control etc If you buy decent drive they can of course be used again if you decide on a bigger machine

Most I've seen seem to be configurable via jumpers or DIP switches so, presumably, as long as they can match the voltage and current ranges of the motors, presumably I can overspec on them now and re-use... makes sense. Ta

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Originally Posted by brumster

Most I've seen seem to be configurable via jumpers or DIP switches so, presumably, as long as they can match the voltage and current ranges of the motors, presumably I can overspec on them now and re-use... makes sense. Ta

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Motors are generally run at much higher voltages than the data sheets typical nema23 (low inductance) motors are run at about 68V with AM882 drives setting the current with the dip switches

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Originally Posted by brumster

These are really nothing more than stepper driver ICs, of which obviously there are a plethora out there with various ratings in terms of voltage, current, stepping capability and safety features. Bolted on to that are the relevant amount of heatsinking, protection/filtering but ultimately they take a low-voltage signal from a microcontroller or parallel port - with appropriate optical isolation - and move the motors as requested. One tick = one unit of movement (in the appropriate direction, of course).

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In simplistic terms yes but in reality then theres much more to good drives than this. How it handles resonance is very important and what makes the difference between poor and good working motors. Resonance cripples Steppers and the drive needs to be able to deal with this.
Making your own is an option but not one I'd recommend and I've seen many people take this route only to end up buying drives after much frustration.

Quote:

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Originally Posted by brumster

You can get ones with direct parallel port drive (so no motion control; driven straight from PC) but then the honus is on the PC as the controller, hence all the requirements in terms of it being able to keep up. Each pin on the parallel port controls a function, which limits you somewhat to the number of axes/functions you can make use of.

Other alternatively you can get drives controlled from a separate motion controller in between the drivers and the PC.

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Not exactly correct. You can get drives with built in Pulse engine so they don't need a PC Parallel port or External Motion controller. IE Stand alone
People often get the wrong idea about how Mach3 or Control software works. The control software doesn't create pulses it plots a trajectory data based from G-code and then hands this to Pulse engine which then does the Motion control side of creating pulses.
In standard trim Mach3 uses a Driver to do this function (paralllel port Driver) which then crunches some numbers and outputs the required pulses thru the parallel port to the drives directly (Usualy Via distribution board called a BOB).
If using an External Motion controller then it hands the trajectory data to The Plug-in for that Motion controller. The controller then does all the number crunching and send the pulses to the drives. The difference being External motion controllers can crunch numbers much faster and output much cleaner pulse stream which makes BIG difference to performance and reliablty.

Quote:

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Originally Posted by brumster

When you guys refer to BOBs (Breakout Boards) you're generally talking about motion controllers, although you can get BOBs that combine both of the above.

It strikes me that keeping them separate gives more flexibility as the drivers need to match the motors; if you get a combo BOB you'd need to be sure that the drivers side of it matched your requirements and they weren't going to change.

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No BOB is just a Distribution board for the I/O signals. Often Optoisolated for protection. Commonly you'll have Motion control board and connect to this 1 or more BOB's for Distribution of the signals.
Better Motion controllers Like those from Cslabs provide direct connection and remove the BOB from the picture.

BOB's, or should say Cheap BOB's are a common cause of many troubles with CNC machines and often under estimated to there importance.
They take all the Signals then distribute them to where needed so if the components used are slow or low spec then any signals going out will be degraded or slowed down.
Often you'll see people use External motion controllers with MHZ frequency capabilty and connect to BOB with 100Khz bottle neck components.
Like wise you'll see drives with Max frequency of 200Khz and people using Ex controller with much higher Frequency capabilty connected to 100khz strangling BOB so all that power is totaly wasted.

So what I'm saying is BOB is very important and while cheap works at the slower end it's pointless getting a External Motion controller for the speed and quality pulses and connecting to Cheap nasty BOB's.

A Good machine needs to have a balanced system with no weak link.

Thanks everyone; really good input. Got a good understanding now :) going to run some numbers tomorrow and come up with a "high level plan".... :D

Right then!

Dismissing the idea of a large, steel-constructed machine with serious aluminium milling capability. (1) I don't have the space to do it justice, (2) I strongly suspect a converted Bridgeport would be a far more sensible option.

So I've downgraded to a desktop-sized machine, and I'll focus on doing PCBs with that. When I move house and have more space, I'll contemplate the bigger build. So I'll use the desktop as a learning exercise. Which leaves 3 flavours to go for :
1) The aforementioned "bugger it and just get a Chinese 6040" for £900.
2) Build something completely on par with the 6040 myself, like-for-like.
3) Build an overspec 6040-like machine, mainly to learn on construction but also invested in the parts so they can be re-used on a bigger machine in the future.

I've been bouncing around CNC4YOU and eBay today, making a spreadsheet up to price these.

Option 1 we all know will do a minimal job, but I'll be replacing the electronics more than likely fairly soon. But it's a baseline, £900 for a rather average machine.
Option 2 I've worked out, CNC4YOU don't come out that well in this regard, and going eBay for the majority of it I've got a very high level ballpark price of £768... that's with the same spec ballscrews, supported rails, 1.2Nm NEMA23s, cheapo TB6560 drivers (the motor/drivers come in a 3-axis pack for £95). £175 on a spindle, 1605-C7 ballscrews for a 600x500mm working area. That price includes £130 on aluminium extrusion but there would undoubtedly be more cost on getting the relevant plates/etc for the Z-axis and so forth. So, to cut a long story short, I see no point in trying to build a 6040-like machine yourself for less money; I don't think it can be realistically done. They are great value for what they are.
Option 3, then, comes out at a £1262 plus the frame material, so if I bank on £1400-1500 I think that would cover it. This would be same size as a 6040, but like I said overspecced on the components - HGR15 linear rails, 4Nm NEMA23's, Leadshine DM556 digital drivers, the same old 2.2kw ER20 spindle and VFD, a 48v PSU, same 1605-C7 ballscrews (contemplating C5s, they're not much more), and then some guesswork on the Z-axis, cable, rails and so forth. Most of it UK sourced seems just as cheap, if not cheaper, than China. I guess the quality stuff is the same price wherever you source it from, and China has no interest flogging it!

Option 2 to me seems pointless. So it's a choice between option 1 and just get started playing with it, or option 3 and long-term investment.

I understand that £1500 buys a much larger machine but the reality is the costs are kind of irrespective of size; I know aspects of that don't make sense (do you really need 4Nm motors to mill PCBs?!) but I'm thinking re-use in the long term on the next project... and doing the construction with the components I'd use on a large build, so I can get savvy with them.

Because if I don't do that, then I really might as well just buy a 6040 and be done with it, given my size limits.

Question - by my calculations a 5mm pitch ballscrew, 200 step motor and no microstepping would give me a 0.025mm per step movement, which is just under 1 thou... and with microstepping obviously could chop that in half a few more times if need be. There would be no reason for me to gear this down would there, given worst (toughest) case the most resolution I'd need on a PCB would be half a thou... (excluding backlash and rigidity issues, I know).

Am I right in thinking that to maximise accuracy, I need to keep the thing as rigid as possible, run it at appropriate speeds, but ultimately the ballscrews will define that resolution. So the quality of drive, the ballscrews, that's all just a case of how deep your pockets are - the bit that *I* can f**k up is not making the machine square/rigid.... anything else? I know accuracy is more than just resolution, it's about repeatability as well, but go easy on me, I'm learning... :D

Basically if I go NEMA23 4Nm, Leadshine digital drivers, a capable 48V 600W power supply, C5 (let's say that for now, given the price difference to C7's) 1605 ballscrews with anti-backlash nuts... the only other bits that are going to limit the accuracy/repeatability of the machine are my fudged-up design, or bad software/CAM....?

If I can accurately mill SMD boards (typically a pad spacing of 0.25mm between pads) then I'd be happy as larry.
If that's pie in the sky then you're really falling back to through-hold DIP stuff, which really could be 0.5mm or worse, and I then wonder whether it's worth all the bother, apart from as a learning exercise and investment for future upgrades. I guess it could probably do *some* aluminium work if I was careful/slow, but I'm kind of dropping the focus on that now.

Basically, £1500 on an over-specced DIY build the same size as a 6040 (but obviously better quality).... or spend £900 on a 6040, use it for a year or two, accept it's limitations, fix it as needed, then flog it on for £400 and consider it a learning exercise... or salvage it for the spindle if nothing else :)

I'm thinking the DIY route but happy for someone to tell me I'm mad for doing it/it makes no sense :)

P.S. Sorry for the clearly indecisive warblings... I do value your feedback though :)

Oh, and spindle run-out, I forgot that. Best I can make out from reading, the usual spindles have a mixed bag in terms of specs and it's probably just a case of cross my fingers and hope I don't get a Friday one...?

I've started designing anyway; when I get it to somewhere sensible I'll share for comment...

What are the merits for move the platform and fixing the gantry on the X, versus fixed platform and moving gantry? It strikes me the moving platform will be easier to design and construct but I'll have to accept a larger keep-clear space at the sides of the machine?

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Originally Posted by brumster

Basically, £1500 on an over-specced DIY build the same size as a 6040 (but obviously better quality).... or spend £900 on a 6040, use it for a year or two, accept it's limitations, fix it as needed, then flog it on for £400 and consider it a learning exercise... or salvage it for the spindle if nothing else :)

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Better Still spend £1500 use it for Two yrs hassle free and then sell it for £2000.!!. . . . .Make a Proper Job using correct components and that is perfectly feasible.

Aye, true :)

Not much replies to questions, which is fine we're all busy people, so I wonder whether this now needs moving to a new build thread? Would that make more sense? I'm not saying it's definitely going to happen yet but maybe that will get it better visibility....?

I made a start on the design anyway, made some assumptions....

https://lh3.googleusercontent.com/-s...42/CNC_001.jpg

80x40x4 steel box welded frame, X on the platform and a fixed gantry (Y and Z), single central C5 ballscrew, external size 600x500. BGR15 linear rail (why not), NEMA23 motor, big design question at the moment is direct drive or pulleys/belts? I know some of you seem to be fans of pulleys/belts; any reason to go that route? I don't need it for the gearing-down/accuracy as by my measure, even direct will give me the resolution I need (and microstepping, even better). Are there other good reasons to belt-drive?

Appreciate it needs bracing...

I need to get some ballscrew dimensions to understand how the motor/linkage needs to be spaced... when you spec a ballscrew are the "unscrewed" parts of the ends always a fixed dimension or will it vary from one manufacturer to another? I took a quick look at one datasheet I found but there were no dimensions on there (from Zapp Automation). CNC4YOU have some specs up for C7 ballscrews but would my C5's be any different?

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Originally Posted by brumster

I know some of you seem to be fans of pulleys/belts; any reason to go that route? I don't need it for the gearing-down/accuracy as by my measure, even direct will give me the resolution I need (and microstepping, even better). Are there other good reasons to belt-drive?

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The main advantage of belts other than gearing is to reduce resonance and smoothen motor performance. This is why most use it.
Resonance cripples the performance of steppers so anything to help reduce it is welcome. Using Digital drives makes huge difference to stepper performance and smoothness.
Also regards Micro stepping don't think of it to increase resolution because while it does up to a point it's main purpose is to smooth motor performance. Noticed you also mentioned running Steppers at 200 steps (Full step) this would make them run awful so expect to use Micro stepping.

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Originally Posted by brumster

but would my C5's be any different?

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They are exactly the same regards end dimensions. But C5 screws require higher spec end fixings hence why they sell C5 end bearings other wise there's no point using C5 screws.

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Originally Posted by JAZZCNC

The main advantage of belts other than gearing is to reduce resonance and smoothen motor performance. This is why most use it.

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Right, that's what I needed to know! Ok, I'll go with belts, albeit on a 1:1....! Thanks.

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Resonance cripples the performance of steppers so anything to help reduce it is welcome. Using Digital drives makes huge difference to stepper performance and smoothness.

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I will be going digital, yes, there seems only a marginal increase in cost of the drivers and like I said, this is an investment/reuse later so no need to buy cheap first off. There's no point; if I just want to do cheap then I might as well buy a 6040 :)

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Also regards Micro stepping don't think of it to increase resolution because while it does up to a point it's main purpose is to smooth motor performance. Noticed you also mentioned running Steppers at 200 steps (Full step) this would make them run awful so expect to use Micro stepping.

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Yep, my point was that I didn't *need* microstepping for any resolution aspect; naturally I'd use it.

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They are exactly the same regards end dimensions. But C5 screws require higher spec end fixings hence why they sell C5 end bearings other wise there's no point using C5 screws.

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Yes, I'd noticed on the website, that's fine. Wasn't going to attempt to mix ;) but to know the end dimensions are the same is just what I needed to know. I'll model off C7 drawings/dimensions, but just spec everything at C5.

Perfect, thank you!

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Originally Posted by brumster

I made a start on the design anyway, made some assumptions....

https://lh3.googleusercontent.com/-s...42/CNC_001.jpg

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Fasten the 4 fixed bearings to the lower and the rails on the underside of the component above, your support is then always optimally positioned for the point being machined.

- Nick

Interesting; can you elaborate (or link to somewhere that explains) the advantages in laymans terms? I don't think I've ever seen it done that way... any construction challenges (alignment?)...? I guess it's only the same but inverted....

As an aside, I reworked the motor mount to be underslung for a pulley arrangement... using a generic eBay-sourced motor mount bracket

Attachment 17351

You want a design which keeps the alignment/support as close as possible to the cutting area, not one where the alignment/support moves away from the work area at either end of travel.
You can make the rails twice as long as the required travel and use multiple linear bearings to ensure support close to the cutting area.
Regards,
Nick

Right, I've made a decision! The design of a DIY machine can be parked because I'm going with this :-

http://www.mycncuk.com/threads/9412-Sieg-X3-and-Stand

...and I'll convert it over time. A home build came out at £1600 or so but my confidence that I'd build anything straight and true is low, probably more luck than anything. This X3 will let me do my aluminium parts without worry. Not sure how it'll be with accuracy on the PCBs but, pfft, we'll see. Nothing ventured, nothing gained - worst case I'll get an MF70 just for PCBs and convert that, using the X3 to make all the bracketry :)

If I had the space I've be doing a Bridgeport conversion but I don't have the space. If I was just doing large-area MDF and wood then likewise I'd be going with a home-made gantry system, but this approach just feels 'right' to me...

When I get round to starting it I'll post on here, might be a month or two yet, but I'll be honest at least :)

Thankyou all for your input; it has helped me make an informed decision and I've learnt a lot in the process, so that's been very useful and has helped me understand what I would be taking on.