file Frage Best Linear Track Design for a CNC Machine?

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25 Mär 2017 11:13 - 25 Mär 2017 11:18 #45850 von Doug
I'm not trying to suggest that Stepcraft completely overhaul their basic design here :lol: , I was just wondering what users consider to be the ideal solution for engaging the moving assemblies with the tracks on a theoretical CNC machine. Stepcraft's brass roller solution doesn't seem to be optimal either for a self-assembly CNC machine kit or a turnkey solution.

I.e., if you were to design your own 'ideal' CNC machine, what solution would you choose? My ideal machine configuration would not have a larger XY footprint than the 2/840 machine I already have. Myabe a little more Z axis travel would be useful, but I don't need much for milling guitar bodies, necks and other 2.5D parts from plastic or aluminium.

For the Y axis in particular, I was thinking of a central ball screw/ball nut for the linear drive mechanism coupled to one powerful NEMA stepper motor (at least a NEMA 23) with a rack and pinion either side and a locating bearing with some built in float at the opposite end. The ball nut would be mounted at the centre of a rigid axle, probably within a housing with aluminium tube sections either side would suffice to keep the weight down.

Would this be subject to alignment challenges do you think? I guess it depends on the rigidity of the transverse axle and amount of pinion tooth engaged with the track.

I see from a quick Google search that the EZ-Mini from EZ-Router.com operates with a rack and pinion drive on both X and Y axes:

http://ez-router.com/products/cnc-router-systems/ez-mini.html

Has anybody else designed and/or build their own CNC machine? Possibly not the best forum to be expressing these ideas or asking these questions on is it? I guess www.cnczone.com is better but I'm not about to join yet more forums right now, my digital footprint is already far too large. :ohmy:

Doug

Stepcraft 2/840, StoneyCNC industrial HF spindle, 4th axis, TurboCAD 2016 Professional 64 bit, MeshCAM, GWizard feeds & speeds calculator, UCCNC
Hobby use: guitar building (luthiery), www.facebook.com/DougShortGuitarBlog/
Letzte Änderung: 25 Mär 2017 11:18 von Doug.

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21 Apr 2017 14:55 #46538 von MMorao
MagLev!!!

Clockwork Orange is a S600 with 4th axis, Kress 1050. Software is UCCNC, DeskProto, Rhino, DraftSight. Also a Silhouette Cameo for vinyl, plastic card, etc.
Folgende Benutzer bedankten sich: Doug

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21 Apr 2017 19:46 #46551 von Doug

MMorao schrieb: MagLev!!!

:lol: Chortle.

Stepcraft 2/840, StoneyCNC industrial HF spindle, 4th axis, TurboCAD 2016 Professional 64 bit, MeshCAM, GWizard feeds & speeds calculator, UCCNC
Hobby use: guitar building (luthiery), www.facebook.com/DougShortGuitarBlog/

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16 Jul 2017 22:06 #48810 von Radford
Doug,
I'm in agreement with you on the size of the machine, but I differ in the type of guides for the axes. I think that linear bearings on all axes is a better choice. Also, for the gantry style routers, I believe two motors (one at each gantry leg) is probably the best solution, a single, central, drive would require that the entire bed of the machine would be moving, which adds more complexity than the two motor solution.
I've never cared for rack & pinion systems, they invariably have backlash that affects the accuracy & repeatability of the machine.
I really like the looks of this piece of equipment: www.probotix.com/CNC-ROUTERS/COMET-CNC-ROUTER , although I'm a little apprehensive about the acme drive screws. A design like this, with the ball screws replacing the acme screws, would be my idea of an ideal solution.
I am afraid that I've made an expensive mistake in purchasing my 840. I have yet to get the machine operating correctly, and I have fears that I may never do so. It's not that I am without knowledge or talent, I have been a professional CNC programmer, operating & working (including complex repairs and retrofits) on CNC equipment for over 15 years.
The machines construction, as you point out is less than optimal. On top of that, since I now am aware of it's deficient nature, I cannot, in good conscience,bring myself to sell it to someone else. And I can't find any info on Stepcraft's site about return policy, I've sent them an email, so we'll see. I blame myself for not doing sufficient research, of this forum and other reviews, before I purchased the machine. We live and learn, however, this looks to be an expensive lesson.

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