Lets eventualy start this CNC - MKI

Hi all,

'New' to the forum, although I have been browsing for over 4 years.

Eventually starting to CNC build process... MKI

I've done a LOT of reading, and calculations from several members (too many to mention)

Machine Aim:

• To mostly cut 6mm MDF, plywood etc.
• Also to cut 20-25mm woods (mixing from soft to hardish(oak))
• Aluminium cutting (3mm) - maybe somewhere down the line...

I want to have the ability to cut A2 size (i.e. 420mm x 594mm ) - So with cut size, clamps etc:
Cutting size: 480 mm x 640 mm

Hardware etc:
For hardware I was thinking:
Nema 23 (3.1Nm) - Drivers [ Was thinking some 50v Drivers from CNC4You - powered by 36v ? ]
SBS20 rails + Support blocks
RM1605 Ball Screws and nut (Above 2 items from Chai - I've made contact and he said he is still shipping to UK and ready to take my order)
Aluminium Profiles (40x80 heavy duty, Ix: 26.87cm4, Iy: 101.19cm4) - The Support Rails will be bolted on top of them, so extra stability...
Router/Spindle: Looking at the Makita RT0700CX for now.
The Z Axis has the ability to move 140mm, but will initially only us ~40-60 of that - unless I drop the table/raise the machine.

The entire machine will be bolted down on a bakelite(?) top (super flat strong surface) with steel support under the top.
(Will see if I need to weld a movable table one day...)

Software, I've played around with bCNC and got a Arduino with grbl running on two Nem17's with a CNC Shield (Drivers DRV8825 - Will not use these on final machine)

Below is my design so far: [Version 4 mind you, but at a stage where I feel confident to post to ask for further assistance and advice from experienced people ;) ]
(Some final adaptions from JoeHarris, but really, the credit goes to the entire MyCNCUK Forum member builds!)

Attachment 17354Attachment 17352Attachment 17353Attachment 17355

Your input and thoughts on the design would be most helpful!

HI Jacques Welcome to the forum. CNC4you do some very good 3.1Nm motors and are a good buy but you are limiting yourself with the drives AM882 or EM806 are much better and can be run them at a higher voltage 68V would be about OK. If you are mainly cutting MDF etc then 10mm screws for X and Y and 5mm on the Z.

Think about the router as the Chinese 1.5kw or 2.2kw water cooled with VFD are a much better bet.

Don't be temped to buy a kit of electronics as they are never matched as you will know if you have been reading the forum for the past 4 years.

Start a build log so all the questions etc will be in one place.. Good luck with the build

Thanks Clive.

Spindle: http://www.ebay.co.uk/itm/170745857956 ??

It has a ER11 Collet - are you limited to the cutters? (What Collet size do people recommend ?)
[ Any recommendations on spindles + water cooling systems anyone? ]

My thinking for the Makita RT0700CX was I could use it on the CNC & Other project. But in reality, a dedicated spindle is more realistic.

Thanks about the reminder about buying the Kit's... Originally I was thinking 4Nm Nema's. It is only a slight increase to got from 3.1Nm to 4Nm, but I'm not sure if the 3.1's are an overkill already...

About 10mm for XY & 5 for Z - I want to keep my options open to eventually cut small Aluminium parts (for toy cars etc - so 4mm) later down the line - but as stated, not essential.

Jacques

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Originally Posted by Jacques

Thanks Clive.

Spindle: http://www.ebay.co.uk/itm/170745857956 ??

It has a ER11 Collet - are you limited to the cutters? (What Collet size do people recommend ?)
[ Any recommendations on spindles + water cooling systems anyone? ]

My thinking for the Makita RT0700CX was I could use it on the CNC & Other project. But in reality, a dedicated spindle is more realistic.

Thanks about the reminder about buying the Kit's... Originally I was thinking 4Nm Nema's. It is only a slight increase to got from 3.1Nm to 4Nm, but I'm not sure if the 3.1's are an overkill already...

About 10mm for XY & 5 for Z - I want to keep my options open to eventually cut small Aluminium parts (for toy cars etc - so 4mm) later down the line - but as stated, not essential.

Jacques

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The 2.2Kw has a bigger collet but the 1.5Kw can be got with a bigger collet as well you will never really use a bigger end mill that 6mm on a machine like that. The water cooling is just a small fish tank pump about £3 and about 1 ltr Tupperware container.

The 3Nm motors are more than big enough if you can go with belt drive all the better as then you can use a 1:2 reduction if you need to.

I think you might have to beef the frame up as well.

Hi Jaques,

Clives suggestion to use 10mm screws is correct and it mostly do everything you want, even small stuff. But if you really want flexabilty then connect motors to screws using Timing belt and pulleys with 1:1 ratio then you have option to change up or down if required. Also and much better reason to use Timing belts considering the drives your thinking to use is to lessen resonance which affects motor performance/smoothness.

I'd also urge you to use Profiled linear rails rather than cheap Round rail Chai sells. While Round rail does work ok the slight extra cost of profiled rails makes huge difference to machine stiffness and reliabilty. It will also increase sellabilty and value much more than the extra cost difference.

Also with Motors you'll notice No Difference between 3.1Nm and 4Nm motors. The important thing to look for is inductance you want Lowest inductance possible. This will allow higher RPM and more torque for same voltage compared to High inductance motor.
Again Clives advice of AM/EM drives and 60-70Vdc is sound advice you'd do well to take up. Esp when using Slaved motors.!

For Components contact Fred Lee here and get a quote. He's good to deal with and his stuff tends to be slightly better quality than Chai's. Esp the End bearings for the screws.
http://www.aliexpress.com/store/314742

Thanks JazzCNC

It's not very clear on the design, but the intent is to use a belt with pulleys, 1:1 timing. (Very similar to JoeHaris' design) - as I've read, it helps with resonance and gives me the ability to do 1:2, or 2:1, or other rations if I allow a variable positioning of the Nema (which is the intent)

I looked at Profiled Linear rails - just seems to cost a tad more... although, would be easier to fit to the Aluminium profile... Will see what pennies I can get out the couch :)

Thanks for the 3.1Nm vs 4Nm motor advise - I think that's one tick I can put next to - "Buy Nema 23, 3.1Nm motors" :D

Once I have all the input and design tweaks, I'll know what length ball screws to get - So recommendation so far is RM1610 (with the end an extra 15mm for the pully) [This should give a resolution of 0.05mm (at full step) and 0.00625mm at 1/8 step - that actually pretty decent! ]

As for Slaved motors, should I go with 3 Nema's (One belt connecting both Y Axis to one Nema ?) - this will save on buying one driver and Nema, but worth it ?

Quote:

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Originally Posted by Jacques

I looked at Profiled Linear rails - just seems to cost a tad more... although, would be easier to fit to the Aluminium profile... Will see what pennies I can get out the couch :)

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Dig deep because worth every extra penny.

Quote:

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Originally Posted by Jacques

Thanks for the 3.1Nm vs 4Nm motor advise - I think that's one tick I can put next to - "Buy Nema 23, 3.1Nm motors" :D

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Remember Inductance not all motors are the same even if same Nm rating.

Quote:

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Originally Posted by Jacques

[This should give a resolution of 0.05mm (at full step) and 0.00625mm at 1/8 step - that actually pretty decent! ]

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Don't Full step action will be rough and Don't really think of Micro stepping to increase resolution and more to do with having smooth running motors. Buy Digital drives and you'll get lovely smooth motors with less Micro stepping.

Quote:

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Originally Posted by Jacques

As for Slaved motors, should I go with 3 Nema's (One belt connecting both Y Axis to one Nema ?) - this will save on buying one driver and Nema, but worth it ?

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Yes that's what I would do using 10mm pitch screw with 1.5:1 ratio which increases torque and still gives decent performance. I've used this setup on machines with heavier gantry than yours so know it works ok.

I am looking into the HIWIN Rails - and many people on the forum suggests 20mm because of grease, access to bearings etc. So I take it 20 is good,15mm bad ?

The motors I am looking at can be 3mH if you couple them in series, 12mH in Parallel configuration.

Those drivers are nice, £100 nice - will have to save up for them....

Busy re-designing for the Linear Rails... will post new design within the next week.

Quote:

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Originally Posted by Jacques

I am looking into the HIWIN Rails - and many people on the forum suggests 20mm because of grease, access to bearings etc. So I take it 20 is good,15mm bad ?

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No good or Bad about it really just 20mm are easier regards fitment etc but 15mm will still easily handle any forces.

Quote:

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Originally Posted by Jacques

The motors I am looking at can be 3mH if you couple them in series, 12mH in Parallel configuration.

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Think you may have got that wrong way round but if not then don't buy them.!! You want them wired in parallel and 12Mh is way too high.

Quote:

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Originally Posted by Jacques

Those drivers are nice, £100 nice - will have to save up for them....

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AM882 drives can be bought from Ali express for around £50-60. Also you can buy Hi-win rails from BST automation on Ali express much cheaper tyhan you'll find them in Uk.

Quote:

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Originally Posted by Jacques

I am looking into the HIWIN Rails - and many people on the forum suggests 20mm because of grease, access to bearings etc. So I take it 20 is good,15mm bad ?

The motors I am looking at can be 3mH if you couple them in series, 12mH in Parallel configuration.

Those drivers are nice, £100 nice - will have to save up for them....

Busy re-designing for the Linear Rails... will post new design within the next week.

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20mm is good because they are much easer to mount than the 15mm especially on the Z.

Zapp motor are a good buy http://www.zappautomation.co.uk/elec...tor-48577.html
or CNC4you as I suggested before https://www.cnc4you.co.uk/Stepper-Mo...s/Nema23-3.1Nm

Drive about £53 http://www.aliexpress.com/store/prod...570168083.html or similar

Ok - had some time and re-designed it with square rails :)

For the X, I'm thinking of using: 40x80 Heavy Duty Aluminium Extrusion (http://www.aluminium-profile.co.uk/a..._ITM02604.html)
8mm Slot Ix = 26,87cm4, Iy = 101,19cm4, Wx = 13,44cm3, Wy = 29,29cm3

The Y's, similar, but the 40x120 - Those will then get bolted down onto a lovely solid flat surface :) [Later to be upgraded to solid Steel table]

Question 1: For the X, the rails will be 80mm apart (bottom of rails), is this ok? Or should I rather go for the 120mm on the X - which means bigger side plates etc.

Question 2: I've gone for 10mm Aluminium all round (6mm to hold the motor on the Y, and attach the Ball nut housing) - thoughts ?
[ Most of the 'bend' will be in the lateral movement for the Y, and the square rails will 'support' the 10mm... so see no need to go more. ]

All Steppers 3.1Nm with pulleys, 1:1, and 1.5:1 for Y [Powered by 60V stepper drivers]

RM1605 for Z, and RM1610 for X & Y. (ends or F, extended from 15mm to 30mm)
BTS Automation will open end of Feb after their Chinese new year... hoping to order soon :)


Attachment 17516Attachment 17518Attachment 17519

Which drives are you going for when you say 60V AM882 or EM806 about 68V would be better.

If I am not mistaken 90 x 45 and 180 x 45 work better with the BK/BF bearing blocks. But Dean probably chime in with the correct size

Quote:

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Originally Posted by Clive S

Which drives are you going for when you say 60V AM882 or EM806 about 68V would be better.

If I am not mistaken 90 x 45 and 180 x 45 work better with the BK/BF bearing blocks. But Dean probably chime in with the correct size

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Clives correct Bosch Rexroth 45 x 90 slot spacing matches the hole spacing in the BK/BF12 bearings. If using Item section then you'll need spacer plates.

10mm Ali is too thin 15mm is the minimum I'd use. 20mm prefered.

Thanks - Will look at the difference in specs and price for the AM822 and EM806 - any recommendations ?

I'll look at the 90x45 & 180x45 - thanks!

When you say 10mm is too thin - I agree in some part, but let me try explain my thinking...


Attachment 17520

On the Y Side plates, most of the "force" will be stopping the X beam flexing, and moving in the Y direction, so on Y1.
The forces on X1 (if the X is bolted down on the bottom plate properly) will be minor.

On the Z axis gantry, the back plate - I agree - 15 or 20mm. It will flex, although the blocks should support it, apart from the 30mm gap between them, so only "bend" that will apply will be on the small 30mm bit inbetween the blocks... Whats bend like on 30mm of 10mm plate?

On the front Z plate, the plate will be bolted to the square rail. Surely the 20mm rails will stiffen up the 10mm plate?

I don't want to put extra weight on it if I don't need to - but you guys know what works and what doesn't....

I like to match the spacing, so will change the design to 90x45 - The BF/BK blocks will be on spacers...so the bolt will go through the BF/BK, through spacer and into profile. :)

I'll then swap out the 120x40 with a 180x45. This will also give me more cutting (working) space.

Currently (according to my calcs and drawings) the Z has the ability to travel at least 120mm.

Thanks!
Jacques

Quote:

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Originally Posted by Jacques

Thanks - Will look at the difference in specs and price for the AM822 and EM806 - any recommendations ?

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The EM806 is upgraded AM882 but there's not a massive difference between them in performance terms. The AM882 can be bought much cheaper so I'd go with those.

Quote:

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Originally Posted by Jacques

On the front Z plate, the plate will be bolted to the square rail. Surely the 20mm rails will stiffen up the 10mm plate?

I don't want to put extra weight on it if I don't need to - but you guys know what works and what doesn't....

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Yes to some degree they do but that means they are also under bending forces and linear rails don't tolerate much error and will bind. The Z axis is THE MOST IMPORTANT piece of the machine so if you skimp here then you will regret it later guaranteed.

The bearing plates you could probably get away with 10mm but why bother just buy one plate size for all key areas it will be cheaper or not much more money.

Will amend my design with the changes.

Thanks JazzCNC

Can anyone recommend a good supplier for 45x90 & 45x180 profiles ?

Also cut to size Aluminium plates 15mm & 20mm ?

I can't help with profile suppliers but you can cut those shapes with basic tools. Cut the aluminium on a bandsaw close to size and then finish the edge using a hand held router and carbide cutters. You need a template or straight edge to run the router edge along. Your shapes are main rectangles or triangles so should be OK.

As for 10mm vs 20mm I know aluminium is expensive so you are trying be economical so here are my suggestions on the minimum areas to use 20mm on, and why.

Z plate
as Dean says. Don't use the rails to add the stiffness. No worries about weight either - the steppers will lift more than you think once they are driving a ballscrew.

Y axis upper and lower bearing plates
Several reasons:
1. If you use 10mm plate you will have to use very small bolts into the side to mount them to the Y plate. So could probably only fit say 6mm bolts to connect them and this is just not good enough. They will bend and you can't get much torque into them to get a good clamping load

2. The 10mm plate has a small footprint onto the Y plate so is much more likely to bend up and down at the joint.

X axis bearing plates
1. They hold the gantry and stop it rotating. The triangular plate on the sides transfers this load down the outside to the bearing plate, but the X bearings are in the middle of the plate. This means that the unsupported corners on the inside will bend. Therefore they should be 20mm.
You could add another triangular plate on the insides as well but it is a bit awkward to attach back to the gantry front face.

2. You will need to counterbore the bolts which hold the X bearings onto the X bearing plate so that the gantry can sit flush. I'm guessing these are around M6 so need ~6mm of counterbore depth. In 10mm plate this leaves just 4mm of metal holding the bearing to the plate. This is a bit thin in my view, whereas 20mm still leaves 14mm of metal.

3. The triangular plates on the side will bolt onto the edges of the 10mm X-bearing plate and you will have to use fairly small bolts (~6mm) which is a bit small.

Finally . . .
X ballscrew drive plates
The strips which drop down to mount the X ballnut to are quite thin. They will twist when the load is applied as it is offset. A thicker plate with a pocket for the ballnut would be better, or at least some support, but it sounds like you have limited tools so you could build it like this and use the machine to make some beefier parts.

Another finally . . !
I don't think you can assemble the Y axis and Z axis can you? I think you've done the classic 'lock-out'. Walk through the steps of bolting it together in your mind and make sure it is possible and there is a build sequence.
As you are using packing pieces to mount the Z bearings to I think you will have to extend them (and the Y axis plate) say 15mm below the level of the lower Y axis bearing plates to be able to bolt from the back. The top is OK as it already extends above the level of the upper Y axis bearing plate so you can bolt through from the back.


Attachment 17522

Quote:

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Originally Posted by Jacques

Can anyone recommend a good supplier for 45x90 & 45x180 profiles ?

Also cut to size Aluminium plates 15mm & 20mm ?

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How about this http://www.motedis.co.uk/shop/Slot-p...91_999994.html they cut very accurate to size

Thanks Clive!

Yeah - I've been looking at a German company: http://www.dold-mechatronik.de/Alumi...er-i-typ-b-typ

Turns out, the link you posted get their stock from the site above :)

Thanks for the advice re bolting it all together. There is one bit that has a 'locked-out'

I've already started on the 20mm adjustments.

The spacer blocks will be there until I have the ability to machine out the Z plates. (and as you suggested, the brackets that hold the ball nut to the Y plate supports.)

Thanks again.

Will post next version soon... (no use calling it final.... ever, no such thing hahaha)

Ok,

Re-Designed so all plates are 20mm (except motor mounts, those I have at 6mm - might end up as 10mm...)

I did what Clive suggested and put each piece together as I would.

I should be able to get away by having recessed bolts for the entire Y/X axis, and being able to bolt everything without tapping :) [Y will need tapping]
[ The bolts holding the X plates and bearing support (160mmx50mm) together, can be bolted from the back to the front ]


Attachment 17541Attachment 17542

I 'think' I'm getting nearer to finally placing an order of exact lengths of components :)

Thanks all!

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I did what Clive suggested and put each piece together as I would.

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I can't take the credit for that I think it was routercnc.

Not sure why you need the spacers on the Z plate as it would be better to recess the front plate and that would get the spindle nearer to the gantry.

edit it looks like you have the BK bearing at the bottom end of the Z screw

Quote:

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Originally Posted by Clive S

Not sure why you need the spacers on the Z plate as it would be better to recess the front plate and that would get the spindle nearer to the gantry.

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That would be the long term plan - but unless I grind out the recess.... I won't be able to do it now.

Unless... I could rig up a temporary motor mount and bolt the linear rails to it and do it by hand.... hmmm...
Another idea is to rig up something and do with the hand held router.

Suggestions?

For now, I've gone with mostly square cuts, (that's how they are supplied), and then once the machine is up and running, start cutting bits and then replacing them. Although, I will try do do most of it by hand with the router.