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View Full Version : Design help etc required with DIY CNC Router Design / Build



MikeyC38
06-10-2011, 03:25 PM
Hi All,

I don't know if this is the place for this but here goes.

After years of following this forum I am about to start my own CNC Router. I abandoned the idea of doing a metal version of the Solsylva design because of the potential problem
of getting 2 cheap ballscrews to be accurate enough in pitch to prevent crabbing of the gantry. I will now be using HiltonSteve's excellent design http://www.mycncuk.com/forums/showthread.php/1058-My-Build-I-blame-you-lot-for-this....!
Which is proven. However when I started costing it up, the cost for the Hwin linear rails and carriages alone is nearly 800 :sad:. The cost of 3 x FK12 and FF12 bearing supports comes to 200!! so my budget has been doubled.

So any suggestions on where I can source the Hwin linear rails and carriages more cheaply (HGW20)? Or do I need to look at 20mm round rail and linear bearings?

For the bearing supports, does any one on the forum make or know of a cheaper source bearing supports? I will be using Zapp 1605 ballscrews on all axes (1000 x 650 x 300 mm) and can source the double-row angular contact bearings for the fixed end of the ball screws and single row bearings for the floating end.

Does anyone do Nema 23 stepper motor mounts?

There is someone on e-bay called CNC4YOU has anybody dealt with them and can tell me about the quality of the ballscrews and stepper motor drivers?

Many thanks everyone

Mike

Jonathan
06-10-2011, 04:35 PM
Interesting that you consider the pitch error causing crabbing of the gantry to be a significant error. For C7 ballscrews the error is up to 0.05mm per 300mm, and it's not simply cumilative - it is greater over longer lengths but the relationship is not linear so it's not too bad. I would have though 0.05mm is absolutely negligible, you'll get greater errors from other sources.

There's quite a few profile rails on eBay if you hunt around. 15mm rails and bearings will be fine.

If you havn't already look at linearmotionbearings2008 on eBay. His ballscrews seem good, lots of us have bought them and the bearing mounts are cheaper than england...though I'd just make them.
The ballscrews there will be MUCH cheaper than Zapp as you get the end machining for practically nothing and from what I've heard the quality is the same.

Consider using RM1610 ballscrews on X and possibly Y if you want it to go really fast...lower screw inertia and speed with 10mm pitch but half the resolution but that's generally not important.

I can do Nema 23 motor mount, here's some I made earlier:

47084709

http://www.mycncuk.com/forums/showthread.php/3621-Nema-23-motor-mounts

Altering the design to suit your requirements is no problem...
I can also make the bearing mounts if you send me a drawing / requirements.
(Hmm, looks like you've already noticed them!)

Ballscrews from CNC4YOU are probably the same as Zapp/eBay.

blackburn mark
06-10-2011, 04:52 PM
i would say it is worth splashing the extra cash..... however you need to do some lurking on ebay and bide your time so that your NOT spending 800 on rails n bearings... they do come up cheep from time to time, even new ones.... dont fixate on any perticular brand or size, see what comes up... i bought THK HSR25's for my X and Y axis, massive overkill but the price was good and its no real hinderance over engineering your kit (unless you want to keep the thing portable:smile:) its worth changing your search settings on ebay to include a worldwide search when looking for things like linear rails and the like

linearmotionbearings2008 on ebay is the place to go for your ballscrews etc
he is based in china and will machine them to your spec, im pretty sure there are plenty of us on this forum who bought from him with no complaints :smile:

i think jonathan has done a few mounts for people, he did some 1605 nut mounts for somone, not sure how much he charged but im pretty sure i would have saved a few quid if i could have twisted his arm to make a few more, i paid top dollar for mine from one of the retailers you mention, it broke my heart :sad:

EDIT: hahahaa!!! beat me to it jonathan, do you ever sleep eat or work ? :)

MikeyC38
06-10-2011, 06:57 PM
Thanks Jonathan and mark for the useful posts. I will hang on hunt for some "bargins". I've seen the linearmotionbearings2008 on e-bay. Zapp and CNC4YOU have an ebay presence and seem more reasonable price wise on the ballscrews than previously.

Regards
Mike

MikeyC38
21-10-2011, 01:08 AM
Thanks John and everyone for your advice. I am about to source my bits 1605 ballscrew and nuts, bk/bf12 etc. Using supported round rails 350/750/1150 on heavy gauge 40x80 aluminium profile. Is 16mm enough or should I go with 20mm for the round rails with the linear slides?

Jonathan
21-10-2011, 09:37 AM
I am about to source my bits 1605 ballscrew and nuts, bk/bf12 etc

From Chai / linearmotionbearings2008 on ebay?


Using supported round rails 350/750/1150 on heavy gauge 40x80 aluminium profile. Is 16mm enough or should I go with 20mm for the round rails with the linear slides?

I definitely wouldn't use any less than 20mm rails. I currently have 20mm rails on Y/Z (900/400mm) and 25mm rails on X (2000mm). The 25mm rails do seem better, i.e. much more rigid with less play. This is no doubt partly due the 25mm bearing blocks having one more row of bearings, which evens out the loading a bit and is obviously stronger overall...
Theoretically the load ratings for the 16mm rails are plenty, but in practice people use more. Bear in mind that though the rail is supported that support is not perfect - they can flex upon the support, but only in one direction not all directions like with unsupported rails.

I should also mention that I do have 15mm profile rails which I will soon fit to the Y and Z as they are clearly much better.

John S
21-10-2011, 09:38 AM
Best to go for 20 on the long axis with 16 on the rest.

MikeyC38
21-10-2011, 11:47 AM
Thanks John and Jon for the guidance. better get my order changed!

MikeyC38
21-10-2011, 03:37 PM
I got the order changed . Am ordering the bits from linearmotionbearings2008, which many have spoken of well. I'll get a drawing done so the more experienced on the forum can critique. The long axis design should be ok with the vertical loads on the rails, but on the short axis with supported rails not too sure here - as there are torque and vertical loads from the z-axis carriage and router to account for - the top bearing carries vertical and torque and the bottom bearing carries the torque loading only. I'm sure you guys will steer me appropriately

Thanks
Mike

Jonathan
21-10-2011, 04:16 PM
on the short axis with supported rails not too sure here - as there are torque and vertical loads from the z-axis carriage and router to account for - the top bearing carries vertical and torque and the bottom bearing carries the torque loading only

You can resolve the forces and moments on the bearings, I did it here:

http://www.mycncuk.com/forums/showthread.php/2739-Calculating-forces-on-linear-bearings-...

But it doesn't really achieve much except for deriving the obvious (space the bearings out as far as you can afford to, and minimise overhang) and showing what I said in my previous post.


I got the order changed

Excellent - what did you change it to?

John S
21-10-2011, 05:07 PM
Excellent - what did you change it to?

Two bacon butties, dill pickles and a side order of chips..............

MikeyC38
21-10-2011, 05:48 PM
You can resolve the forces and moments on the bearings, I did it here:

http://www.mycncuk.com/forums/showthread.php/2739-Calculating-forces-on-linear-bearings-...

But it doesn't really achieve much except for deriving the obvious (space the bearings out as far as you can afford to, and minimise overhang) and showing what I said in my previous post.



Excellent - what did you change it to?

Changed to 20mm supported rails on the long axis - 1100mm, shorter axis (700) 16mm , Z (300) 16mm. Chai seems to be a good guy and altered the order on my request. The primary use for the machine is to cut hardwoods for guitar bodies and the secondary use is for carbon/glass fibre and light (6060) alloy. Aiming for a cut area of the machine of approx 900 x 600. My initial calcs for the maximum static deflection on the long axis, assuming a 30kg carriage of 0.12mm. The supported rail should stiffen this - but I could be wrong.

Thanks for the link - I'll examine this in more detail tonight

MikeyC38
21-10-2011, 05:50 PM
Two bacon butties, dill pickles and a side order of chips..............

Hi John S - If only! only allowed 1 bacon butty a week on my diet!! -:)