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Page history last edited by Ron Bean 11 years, 4 months ago

 

Notes and information about CNC-related projects at bucketworks.org

These are preliminary notes for a CNC Router project that I had planned to build at Bucketworks (postponed due to the flood).

Each of these should probably have its own page.

Feel free to add stuff

 

See also: Useful Links

 

Working area:

2'x4'? Could be larger, but then the structure has to be stiffer and heavier.

 

Structure:

This is where most of the savings seem to be. In order of cost: MDF, high-grade plywood, aluminum, steel. I tend to lean toward

high-grade plywood, because the dust produced by cutting MDF is really nasty. Several options for gantry design.

 

Linear bearings:

Purchased vs homebuilt. I'm not sure how much savings  are available here, and there is some argument about the accuracy of the homebuilt versions. But the "best" ones are expensive, and not necessary.

 

If we can get some general specifications (travel, tolerance, load) I know a surplus dealer that can keep an eye out.  These would generally be at least an order of magnitude cheaper than new. (Jack)

 

Leadscrews & anti-backlash nuts:

V-thread, acme thread, ballscrews. Acme screws seem to be the best value; ballscrews are very expensive and not really needed. There is often a gear or belt reduction between the steppers/servos and the leadscrews.

 

Steppers/Servos:

Lots of controversy here. Steppers are cheaper, and position by counting steps from a known starting position. It's possible to "lose" steps by moving too fast, or at certain speeds that cause resonance (or by using steppers that are too small for the size of the machine). Servos cost more, and postion by feedback from a position encoder, which may or may not have to be calibrated periodically (depending on who you ask). Servos tend to be faster, if that matters to you.

 

[Later note: I've learned that high speeds can be useful for cutting wood or plastic-- if the cutting tool moves too slowly, it can build up enough heat to scorch wood or melt plastic. Several fast shallow cuts are better than one deep slow cut on these materials. Multi-start leadscrews can help.]

 

Stepper/Servo Drivers and Computer interface:

Single-chip stepper drivers have really brought down the cost of this part.

Also, Linistepper offers some well-designed 3-axis kits for $90.

 

4th Axis:

Could be useful in the future, so the controller should allow for it, even if it's not installed at first. Also, the X-axis will probably need two steppers/servos, depending on the design, so an extra driver will be needed for that.

 

Computer and software:

We'll need a dedicated PC (including display), most likely with a parallel port. I'd like to lean toward open-source for software, but there's a lot of stuff available for Windows. Maybe Linux with Windows in a virtual-machine. This is mostly outside my area of expertise, though.

 

 Spindles:

Could use a woodworking router, but there are other options, and spindles can be interchangeable.  A good option seems to be the Bosch Colt, available for $130.  It uses a 1/4" collet and can handle bits up to 1.25" diameter.  The 1HP motor has infinite variable speeds from 16,000 to 35,000 RPM.  There's a good review of it in The New Woodworker.  PreciseBits offers an upgraded collet kit for $70.  The 1/4" collet size may be somewhat restrictive for more intensive woodworking projects using larger router bits, where a 1/2" collet is desired.  I don't forsee that being a problem for our uses, and it could be replaced in the future.

 

An analysis done at CNCZone comparing Porter Cable routers with Bosch routers indicates that the Bosch routers have much tighter tolerances.

 

A consideration for the future would be running the spindle on a Variable Frequency Drive (VFD), which would allow automated and precise speed control

 

Soundproof enclosure:

Routers are some of the noisiest tools you can imagine, and I'd like to be able to run the machine while other events are happening in the building. This is also a good reason for not making the machine any larger than necessary.

 

Dust collection:

This is a good idea. A shop-vac might be adequate (although they tend to be noisy-- is there a quieter option?).

 

Useful Links

 


PBworks resources:

  • Learn what makes a good collaboration project and see how other PBworks customers are using their workspaces. Check out our PBworks educator community (not a support forum).
  • The PBworks Manual and 30-second training videos can help show you how to edit, add videos and invite users.
  • The best way to get your support questions answered is to click the help link at the top of this page.  Our support gurus will get back to you asap. 

 

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