Re: Centroid CNC
 

things I've made:
- engraved aluminum (1/4th 6061) keychains (they're kinda cool, wish I had a picture). This was the most challenging as we had to drill reference holes to face/mill/engrave on both sides. I've never spoken to a machinist, and if I did, I'd ask them how to cut things out without damaging the table. We put another aluminum plate under it to solve that. Worked for us, might not be the right way. Another note, about roughing. DO IT! Aluminum likes to be cut with slow spindle speeds, highish feedrates, multiple shallow cuts (roughing), and lots of lubricant/coolant. We kept dumping oil on it, which was effective, but probably not the best solution.

- aluminum mounts for the CIMs. Also 1/4th 6061. Above holds. The thing about the Prolight is that it is, if anything, overpowered. If you make a mistake, and the spindle's going too fast, or the cut is too deep, or your feedrate is too high, it will just keep pushing. It CAN and WILL melt the aluminum to the bit if you do this. Result: ruined and/or broken endmill/ballmill, and the lubricant will eventually start burning (almost happened, once). We now keep a fire extinguisher on hand.

- Various things of balsa. Mostly 3D milling, for a challenge. A mockup of an injection-mold for a vase. We don't have an injection molder yet, but we want one.

- Red lexan tetra clovers! That was fun. We cut 12 at a time (3 tetras cut from 4 stacked sheets). Wear ear protection, or go slow.

- Others. I don't remember them very well.

general guidelines:
- Stick with manual control of the spindle speed.

- Make sure the E-stop button works. If ours didn't, I'd have broken the machine a couple times.

- I've never cut steel, can't talk about that.

- Don't make heavy cuts with low feedrates and high spindle speeds on aluminum. It makes very sharp, very fine shavings, which pile up and resemble steel wool. Combined with the oil, it would make a very, very nasty fire.

- Having an overhead winch helps. The machine weighs around 350 pounds. Move it as little as possible.

- Try to shield your computer from aluminum shavings for obvious reasons. We had two hard drive head crashes last year, which may or may not have been because of shavings getting in the hard drive.

- Oil your linear bearings and ballscrews with a light oil (WD-40 works), and do not let shavings get on or in them. It will destroy the accuracy you have paid for.

- Clean the machine. Not only does this serve a practical purpose, but a psychological one as well. No one wants to use a dirty machine, and you'll be much more careful if you've put a lot of effort into maintaining it. That's how I feel, at least.


George

Re: Centroid CNC
 

Thanks for the advice, now i cant wait to get the machine running and try all sorts of things. Im definatly making a keychain :D
The best way to clamp pieces which youre gonna cut out is using step blocks and clamps (Grizzly sells a cheap yet effective set with 3/8-16 threads to fit the table). If that scrap piece of Al moves under the work piece, thats a good way to ruin a project or break an endmill.
And, btw, machine oil really isnt the best lubricant for Al. Ive heard old machinists say kerosene which does work well, but im a fan of the synthetic cooltoolII for all sorts of metals. Its a great lube/coolant, isnt waterbased so it doesnt rust the machines and doesnt become a sticky mess when hot as ive found Tapmatics Aquacut does.

Re: Centroid CNC
 

Yep. Holding wasn't the problem (we were using step blocks and clamps, big ones too), and the scrap under it was larger, and clamped as well. It wasn't really a problem, just a (maybe) odd/different way of doing things.

We didn't use machine oil. Sorry I didn't make that clear. It was not a heavy oil, but it wasn't a specialized cutting oil either.

George

Re: Centroid CNC
 

Actually, the couple professional machinists I know generally run aluminum jobs at a very high spindle speed.

Re: Centroid CNC
 

High compared to steel and other metals perhaps - but compared to plastics and woods (things likely to be milled in a school shop), no. It's relative. Consider the context - a 12'' x 6" x 9" mill intended purely for education.

One note I forgot in my above comment:
- I don't remember what we were cutting at the time, but we had a shard of something fly up and shatter the splash guard. We took a heat gun, bent up some polycarbonate, and replaced it. I'm not sure if they've fixed that problem by now. Lesson? Wear safety glasses, because you SHOULD be watching the machine.

George

Re: Centroid CNC
 

Actually compared to wood and plastics, yes you can do aluminum at very high speed. Wood if fibrous, which doesn't let the shavings come out as well as aluminum ones, and thermoplastics which can melt have their speed limited in that manner also.

I've see aluminum roughed at 20,000 rpm spindle speed, and 1,000 ipm feedrate (yes, one thousand ipm), with a 3/8" endmill. I don't know the depth of the cuts or the step rate, but it wasn't exactly real light... For that machine, it was actually faster to do it that way than to take a few heavy cuts with a hog cutter. If that's only relatively fast for you, I want to see your setup :D

Oh and for work-holding with a key-chain, and other small things, at our work we used a lot of "soft jaws" they were pieces of extruded aluminum that you would bolt to your vice, and mill out as you needed to hold your work.

For a key-chain, I would have it sized so the step holds your stock to at least half of it sticks up above the top of the jaw. In the first step, it roughs out and engraves the top half. You flip it over into the next spot, which is a negative of the top of the key-chain, and you cut out the bottom and engrave it. If your interested I'll draw up a sketch or something. Not exactly the best for one-off stuff, but if your doing key-chains, I would guess your doing a bunch so it would work fairly well for you. Just put the pieces in, tighten the vice, tap them down, run the cycle, flip the piece over to the next op, tighten the vice, tap it down and run the cycle again. But step blocks and clamps are definitely great for single pieces.

Re: Centroid CNC
 

How much coolant? I'm curious - we don't pump coolant continuously onto the work, because we can't.

Re: Centroid CNC
 

We do it in our school but I have never used master cam, I have just never Had a chance to. PM rees2001 if you wanna know more he is my teacher.

Also, i have heard to use vegetable oil based lubricants, i heard they work good and clean up easy.

Re: Centroid CNC
 

I dont have GPM figured but it was coming from 2 nozzles a little under 1/2" and it would travel a good foot horizontally before it got any noticable amount of sag in the stream (we didnt keep them like that I was just fiddling aroud with the nozzles before we got the wash down hose hooked up...) so definitely quite a bit of coolant.

For our coolant we used Blaser Blasocut, mineral oil based, and doesn't stink, like our old stuff does.

What are you working with that you cant use coolant continuously?

Re: Centroid CNC
 

Aforementioned Prolight 1000 . I could probably rig something with a bilge pump and some filters, as the machine does have a chip tray, but I haven't because we're leery of modifying the machine (buying another isn't really an option if we break something...). I'll see what I can do - we do after all have a pump or two lying around, and the coolant could speed our machining greatly.

George

Re: Centroid CNC
 

ahhh ok... I was thinking it was a material restriction and not a machine restriction

Rather than a streaming coolant check out something that puts a mist of the coolant onto the work area. Even a bit would be better than none.