My CNC Router Adventures

[mangozac]

I did some real 3D routing today!

First up, I did the backlash tests correctly (using just a single movement) and discovered 2thou of backlash on the X-axis only. The other axes didn't have any measurable backlash so I left them as is.

Rhino has been purchased but for some strange reason they don't let you download. So I had to pay 15 bucks to get it posted and now have to wait...

And now for the good stuff. Here's the 3D model drawn in Rhino (with identifying marks censored):

And here's the result cut in high density insulation foam (left over from making terrain). The part is 100x120mm:

Obviously the finish is pretty ordinary, but I didn't want to have it take three days to machine! Initial roughing was done with a big 5mm endmill, with detailing done with a 2mm ball ended cutter. It took about 1.5 hours to machine. Considering the relatively coarse final pass, the result is quite acceptable for the purposes of demonstrating to the client what I want them to spend a lot of money on tooling for! Obviously running with a much smaller cutter and closer passes could give a very nice result, at the cost of much longer machining time.

For the record too, USB CNC hasn't missed a beat thus far!

Oh and I found a new program for toolpath creation: . It's WAY faster than PyCAM (it took about 5 minutes to do what took PyCAM 1 hour!) and have given much more consistent, correct results. And it's still free!

[Bar]

Very nice. This is looking sweet!

[Lane]

A couple questions on the machining:

What is the smallest (internal) radius, not counting any text, does the part have? You may have been able to use a larger diameter cutter for most of the finishing. Switch to a third, smaller, tool for things like text.

What size of stepover are you using between passes? Using a slightly smaller step could greatly improve the surface finish without increasing time that much. Using a larger cutter could allow the same or larger step and still get better finish.

[mangozac]

Thanks guys!

At this rate Bar I reckon we'll be making parts in no time! I found out about this stuff called Model Board (UK) or Tooling Board (Oz) that is a dense polyurethane foam great for making masters out of. From what I've seen though it's both hard to get and quite expensive so I was looking for alternatives. Personally I'd love to find a super dense styrene based foam so that it can be detailed easily. The benefit of the foam based materials is that they cause much less wear on the cutting tools.

Lane:

1. Well the 3D model wasn't as finished as I'd have liked (I will be redrawing it from scratch once properly once I get my working copy of Rhino) so there were a couple of 90 degree angles, but other than that I don't think I did anything less than 1mm radius. For stuff like this I don't expect I'd want to go larger than the 2mm ball end that I did this with. From what I've seen it should be pretty easy to restrict the toolpath generation to a specific area for doing just the text with a fine tool. For the record the text is just one big blob as is (the 2mm cutter was way too big for it).

2. On the 2mm cutter I was using a 1mm step over. I would imagine that a 0.5mm stepover would have given a much better result, however would that not double machining time?

Oh another thing I need to sort out is a better tool change procedure, possibly with a tool length touch off sensor. Afte changing the tool I've just been manually correcting the Z-axis to suit; this works fine for large stuff like the lens, but for doing models it will be no good.

So I'm going to have to get myself some tiny cutters. Like 1mm and maybe 0.5mm. Any suggestions as to the best/cheapest place online?

[blind pig]

[mangozac]

Yes and in fact you can get wax specifically for that purpose. My understanding is that it's very fragile though. And then you'd have to mould and make resin duplicates to do any further work with them. It's not cheap stuff, so adding in the cost of silicone duplicating them means that overall it would be relatively expensive.

I was told that Roberto Cirillo did much of his Quantum Gothic terrain on a CNC router, and that while originally he was using styrene blocks, he switched to pouring blocks of resin and machining them up. I'm not so sure about doing that though - could you imagine all of that nasty, irritating resin dust generated? The dust from cutting the foam today was bad enough (I had to have the vacuum cleaner running for most of it).

[blind pig]

Resin would be the easy solution. Adding a filler like fine talk would cut down the cost too, buy using 20-25% by weight of talc to resin.

Make a form from LEGO and use Klean Klay to line the sides and rough-out the mould to close to what shape you will eventually need, to minimise wastage and time lost getting rid of the bulk of the resin to cut the shape.

[Bar]

How about blue foam?
http://www.infolink.com.au/c/Austech-Ex ... ts-n822378

[Lane]

[mangozac]

[Bar]

Right. I have some pink foam here(Well, they call it that, but it's closer to orange). It's light as all hell(It's only foam, lol), and very strong.
It's designed as heat insulation for homes, and i use it with a hot wire cutter(You can see my sheets stack up ).
If you want me to send you some, i can pop a slab in the post to you for you to try.

[mangozac]

Yeah that looks to be very similar to the stuff I used here (which I'm now out of incidentally). Thanks for the offer but I'll see what this company comes back with.

So now that I can manipulate the 3D models and print them out did you have anything particular in mind to try machining?

[Bar]

I have no personal preference. I'd just love to see more of your work. It's the way froward!

[blind pig]

Austec is where I buy my high density foam from.

It is near the brisbane airport and a 2.4x0.6M x 50mm board is less than $60 from memory.

Take a cross-cut saw or box cutter to cut the bugger up so it'll fit in your car, or see if they will cut it for you. Don't go there around lunchtime, as the manager is useless at using an EFTPOS machine without the Receptionist there.

[mangozac]

Oh nice that's handy. Thanks for the tips

How dense is the blue foam you used? Could you compress it by hand?