As I post this the frame is just about complete, with the last side rail under semi-precision layout work right now in the home shop.
I'll post some pics of the actual work going into cutting/drilling one of these rails soon, before I paint it and fit it together.
Pics to come!
- regular NC threaded rod to be used
- ugly backlash eliminator to be designed machined & applied.
- 280 oz steppers from xylotex&board to be purchased
- Mach2, MC9.1(school version, of course)
- 2" square tubing galore outside from my dad's scrap pile
- cold rolled steel for the bearing surface
(photo: z axis incomplete, will take some bench work to fab it.)
It is hard to tell from your pics and drawings as to the size of this router. Ball screws are probably going to cost you a bundle. You have not given us a budget or expectations. Seems from your posts that you are leaning toward the cheaper side, and that is OK, but it makes a difference as to what to recommend.
If I got it right, your long axis is riding with skate bearings on unsupported rod (even if it is cold rolled). I would worry more about this than backlash. Backlash can be easily controlled with Acme screws or ball screws. Acme will be a lot cheaper and zero backlash nuts can be made by you or purchased from Dumpster. http://gonebowlin.com/dumpsterCNC/
Fairly cheap and affordable, but to work reasonably well.
I've been meaning to update the CAD pic that is found first thing in this post. At school I can't do that but I can describe a few changes to the design.
The design you see doesn't show everything in the plan. There will be holes drilled in the frame rails beneath the cold rolled shaft, with larger access holes directly beneath where adjustable support bolts will be mounted.
Hm, as for budget and expectations. . . well here is a rough estimate that I think would work:
- Misc. steel and aluminum (parts of the gantry alum, cold rolled shafts)
$200~ probably quite a bit less
- Steppers & control system, $430 CND shipped(xylotex system, 280oz)
- $80 ($5 a piece) 26OD 10ID bearings (one in photo)
- $30~ paint
- plenty of steel out back that can be used for general framing.
and of course, once it's built a $100 copy of Mach2 and BobCad/cam.
This is going to be a hobby machine, at least in the beginning. The machine will be used to route out complex contours and horizontal Z roughing paths. I already have a controller PC.
It's just that the way I see it, even a small amount of backlash is enough to kill your accuracy when controlled by stepper motors. Will check out that link.
oh, and for a size, I think the length of the frame in the pic is about 64". The width must me somewhere around 30", it happened to be the size of the steel that was already there.
I'm just a newbie, have to confess an older newbie, and don't know too much about CNC routers yet. But I do know that the backbone of lathes, mills, cross feeds, etc is the acme thread. This tells me that it is very capable of extreme accuracy!!