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js530
02-22-2005, 11:49 PM
I've been reading the forums for about a week now, and I want to build a CNC router. I want to be able to do light work, such as plotting PCB's for chemical etching, and the heavier type of work, ie. plastic molds from aluminum billet. The gantry will be moving with a station table. Three axis, 18" by 12" by 6" travel. I will use aluminum channel and a homemade linear bearing for the gantry slide. I will use some cheap 1/4"-20 couplers welded to the other axis. The stepper/threaded rod coupler will be some flexible tubing.
1)Initially, I would like to use 1/4" 20 threaded rod, and eventually buy some preci$ion acme threaded rod, if it's worth the expense. Will it be difficult to upgrade?
2)I have the stepper motors, three 24 volt 200 s/r. When I tested the steppers holding torque, I could not rotate by hand (1/4" diameter shaft).
3)For the frame, I would like to use some aluminum square tubing. I have the ability to weld aluminum, but should I? Would I loose precision if I welded the frame using a right angle clamp instead of bolting it together with some hardware?
4) How should I connect the threaded rod to the bearings? I don't have access to a lathe.

Hobbiest
02-23-2005, 01:38 AM
1)It shouldn't be difficult to upgrade to the acme, you will just need to turn/have the ends turned down to utilize your bearings, and stepper coupler, and supply a new nut for each axis. Make sure to give yourself enough clearence from your linear assemblies for the larger acme.
3)for the frame, ultra precise is not necessary UNLESS locating your slides, and motors/leadscrews/bearings is dependent on high precision to line up properly. In other words, do yourself a favor and make things adjustable. Other than that, you just need to be certain that the axis' move 90 deg from eachother.
4)If using skateboard bearings (I never could understand why they are always called "rollerblade" bearings, but then I skateboarded before I ever rollerskated or rollerbladed)wrap som 22ga bare copper wire around the lead screw where it sits inside the bearing. Keep wrapping until the fit is snug. Or, use a nylock nut on both sides of the bearing, facing eachother. The side with the nylon lock is round and slightly tapered so that it sits nice in the inner race and centers the lead screw.

Get all of that? I am quite long winded sometimes, but I hope that helps. Good luck, and keep the posts comming!

js530
03-02-2005, 06:59 PM
I've decided to buy a few old printers from a computer store, for the slides. For mounting the slides and the threaded rod bearing, I will use a plate with four screws at the corners to adjust the position. I'm starting to think this will be too hard to make....

Hobbiest
03-02-2005, 11:15 PM
Make sure to get the biggest, ugliest, heaviest printers you can get. They are generally the ones with the best parts. Its not that hard dude. You can do it if you take your time, and keep trying at it.

js530
04-06-2005, 11:15 PM
I now have a source of FREE precision leadscrews with steppers attached, four 12" lengths with steppers coupled. And these leadscrews are fast. Only problem is the leadscrew ends are suspended in the air, so I'll have to put some skateboard bearings on it. This steppers are fairly big, but I don't have any specifics. AFAIK, there are no hardened steel rods or linear bearings in these assemblies. X will be the table, Y and Z will be on the tool. Might even that extra stepper for an indexer.

js530
06-10-2005, 07:47 PM
Update:
Here are some pictures of what the router is looking like. I'm using acme threaded rod, with some delrin anti-backlash nuts. The linear bearings will be jgro style, I'm waiting for a center drill bit so I can drill the holes in the al. angle with some precision.
http://members.thegeekgroup.org/~js530/cncrouter/images.html
and
http://members.thegeekgroup.org/~js530/cncrouter/images2/images.html

js530
06-22-2005, 11:53 PM
Finished and mounted the linear bearings tonight, and attached the X axis motor. That hole saw was smoking, even drenched in wd40. Still don't know how to mount the leadscrew nut. The bottom of the table is about two inches above the leadscrew, and I have no idea how to attach it. Any suggestions? I was thinking about using two pieces of MDF screwed to the table, but that might have too much flex.

js530
08-12-2005, 02:58 AM
After three months and a few hundred dollars, the plotter is finally working. A Z axis still doesn't exist, but it can plot. The pictures were taken during a rebuild of the X axis, but it does work.

http://members.thegeekgroup.org/~js530/cncrouter/images3/