NEWB - Need advice on kit/plans for aluminum cutting

[piperpilot]

Hi,

I have been lurking for a couple years. A few years ago, I actually bought a set of plans and some other parts to start building a router to cut PCBs. Due to children, work, etc. I never really got started on the build. I now have some time on my hands and a need for something that can cut Aluminum front panels for enclosures.

I already have a working (assembled a couple years ago):

Unipolar Microstepping HobbyCNC Pro Rev1 Board

and

3 x HobbyCNC 23-84-DS - 84 Oz-in 1.8 Deg 6VDC 1.2Amp 5R steppers

I'd really like to reuse these if possible.

What I'm looking for is advice on a kit, plans, turnkey system, that will meet my needs. I'd like to spend around $600-$800 max on the rest of the parts, etc. I'd like it to be easy to assemble...I'm not good at tapping screw holes, etc. I know myself, and if it is going to take me more than a couple weeks to build, it will end up on a shelf and not get done.

As far as size, I am space constrained in the garage, so smaller footprint is fine. The panels I am initially cutting are small...in the 3" x 5" size range, but I'd like to have maybe 12"x14" capability.

Anyways...if anyone has any recommendations, I'd really appreciate it!

Regards,
PiperPilot

[awerby]

Aluminum requires more rigidity than wood or plastics, which most of the machines that have plans available are geared to cutting. So you're probably best off developing your own plans from scratch. A moving table design is more rigid than one based on a moving gantry, although it takes up more space.

If you're only cutting panels, then you don't need a lot of Z axis travel, which is good, since the higher the Z the less rigid the machine will be. I'd suggest making the base of the machine from steel, as well as the (fixed) bridge that the Y and Z axes travel on, and the rest of it from aluminum. A wooden or MDF machine may be cheaper and easier to build, but it's inherently less stable. Use supported rails only, and good-quality Acme screws. You can get anti-backlash nuts for them that will help your cut-outs stay in spec.

I don't know anything about that control board, but those stepper motors sound too weak to contend with the cutting forces you'll be dealing with. If that's the strongest motor that board will support, you need another one; otherwise use it with some 23-frame steppers which will hold 200 oz-in or so. For a spindle, consider a 1 hp or better router, controlled with the Super-PID circuitry that's been discussed here on the Zone (don't even think about doing this with a Dremel tool or similar...)

Andrew Werby
ComputerSculpture.com — Home Page for Discount Hardware & Software

[Fish4Fun]

piperpilot,

Everything awerby said is quite valid. The elephant standing in the room that he didn't mention is your budget. While it may be possible to find "salvage" parts that total < $1k for your build, I seriously doubt you will be able to source them in a reasonable time frame. Realistically to reliably cut aluminum with a spindle you will likely have ~$500 in your rails/bearings, $600+ in your steppers/driver(s)/PS, and likely a couple hundred in your frame/lead screws/hardware and this is fairly optimistic as a bare minimum investment in parts and assumes you have the tools/skills to assemble the parts into a viable machine. Even a used manual mill/drill is going to cost more than you have budgeted. You would likely be much better off simply outsourcing your work to a shop equipped to handle it, or revisit your work envelope. If you reduce your work envelope considerably you MIGHT be able to build a machine in your budget, though I think 84oz-in steppers are going to be too weak unless you gear them down.

To stay within your budget, you are going to have to use unsupported rails, bronze bushings with an MDF frame and acme lead screws likely with cast nuts. This type of construction is typically NOT considered suitable for aluminum milling, but in a small enough format machine many have had decent results with light cuts in aluminum. I would STRONGLY advise you to read John's (microcarve) threads:

http://www.cnczone.com/forums/diy-cn...p_machine.html

http://www.cnczone.com/forums/diy-cn...ans_files.html

John has likely designed/built more viable machines than anyone who is not a manufacturer, and probably more than many manufacturers. His designs have evolved over a couple of decades into very robust and capable machines. He is meticulous in his work, modest with his claims and freely shares his knowledge and advice. I feel certain he would suggest everything awerby said, but several people have reported success using his "A4" design with light cuts in aluminum. Careful study of his plans and materials MIGHT lead you to a design that will perform well enough for your needs close to your budget; the more you reduce the work envelope the more rigid your machine will be. For 3in x 5in aluminum work, I would suggest you scale his A4 design down to 4in x 6in x 1in travel. It is important to remember that EVERYONE is going to suggest a metal frame/supported rails for any machine intended for cutting aluminum, by going with an MDF frame/Unsupported rails you are definitely "leaving the reservation"; keep the work envelope as small as possible.

As a final note, you need to give serious consideration to cooling early in your design process. With an MDF table/frame flood cooling is not a good option, so you should consider forced air cooling directed as close to the tool as possible. With a typical spindle speed of > 10k RPM you are not likely to have enough travel speed/force to come anywhere near meeting the tool's requisite feed rate; this means your tool/work will build heat very rapidly reducing tool life and degrading the cut finish unless you can adequately remove the heat. Planning for this early will prevent headaches and expenses later.

Good Luck with your Build!

Fish