Question about machining aluminum

[djmachinist]

I put together a Grizzly G1006 servo 3-axis cnc conversion
about 8 months ago. I use a Supertech controller with G320
Geckco's, 1028 in. oz. Servo motors geared 2 to 1. I also
use the Supercam software. The Z axis motor powers the
quill. I have pre-loaded ball screws on the X/Y axis.

I had a lot of trouble at first getting the table to run smooth.
The servo Motors would fault out frequently. With some help
from Dennis at Supertech with tweaking the Geckco,s and
taking the table back apart to lap the ways, I now have a
reliable system. I also honed my travel and cutting,slew and
ramp speeds with Supercam. I know nothing about cnc g-code.
What I do know well is Autocad. You load a autocad dfx file
into Supercam and you are making parts. No toolpath software
required. The machine can run at 100 IPM for travel and from
10 to 15 IPM in cutting mode depending on how deep the cut.
I machine dry using .125, .1875 and .250 end mills. I don't
push the machine. My cuts are 0.050 in. roughing and 0.010
for the finish cuts.

I machine mostly the aircraft grade aluminums: 6061-T6, 2024-T3
and 7075-T6. My question is at what speeds will give the best
finish cuts primarly running dry. I am aware flood cooling is the
way to go but I don't want the mess in my shop. Is there a type
of cutter that would be better for these conditions and at what
spindle and table speeds would be appropriate.

[Ken_Shea]

You should be fine at the 3000rpm limit of the Grizzly G1006 in cutting most any Aluminum, look for aluminum cutting carbide cutters, I began using 3 flute some time back and really like them, MSC sells them, Accupro 3 Flute 50 degree helix, for aluminum. More expensive then standard carbide but worth it in my opinion. Also checkout Discount Tools, they have a good selection of cutters at really good prices. With flood coolant in aluminum it is more about flushing the chips away from the cutter then cooling or lubricant.

Ken

[djmachinist]

Ken,
Thanks for the info. I'll try those cutters you recommended.
I'm not looking for a mirror finish, but something decent. I
found it helps to lock the quill for the finish cuts. I get less
chatter. I set up the tool direction delays in the software
to give me time to lock the quill and give the tool time to
settle before cutting. All I have to do is to remember to unlock
the quill before the Z axis motor trys to raise the tool out of the
material. I can also toogle to manual z operation for the finish cut.
This gives me more time to mess with the quill lock.

Maybe I'll replace my round column mill with a square column
mill or a small knee mill if I really get into this machining hobby.
Right now I'm just playing with a few RC car parts and race
bike parts for my friends.

Dale J.

[sdjdave]

If you want to cut dry, but still want to provide some chip removal, as well as cooling, try using a vortex chiller. It will provide you with chip removal, plus cooling without the splash and mess of flood or misting. If you are lucky you can find one on eBay that's mislabeled. I bought one for $5.00 (an Exair, $189.00 from Rutland Tool) because the person offering it called it an air amplifier and nobody knew what he was talking about. The only drawback is that you will need significant amounts of compressed air to run it. I bought a regular kit from Exair that allows me to run as little as 5 scfm, but I get the best cooling with the 10 scfm generator. I have tweaked it down as low as -17 F and use that for machining G-10 with carbide cutters. Since the chip removal is foremost and cooling is secondary, you just want to keep your aluminum parts cool while cutting, 5 scfm and a temperature 10 - 20 F below ambient should work just fine. You will notice an improvement in your finish, especially if you go to the three flute cutters Ken recommended (I recommend them too).

Dave

[djmachinist]

Dave,
I bought the Exair unit a couple of months ago. You are
right about the lots of air! My compressor just barely keeps
up with this thing. You say you put a regulator valve inline
with the exair unit. Where did you get the regulator. I have
not used the exair while I'm machining yet. I'll try it. What
cutters are you using for G10. I use G10 on my RC cars. I
also use some Carbon Graphite plate. I found some 1/8"
carbide cutters at discount tools that work pretty well
on composite plate.

Dale J.

[sdjdave]

Dale,

I use any good sharp carbide 2 flute cutter for G10. If you use your Exair, you can really remove some material in a hurry. I would use a 3/4" 2 flute cutter at a place I used to work to hog out big blocks of G10 for use as bed of nails carriers for testing flex circuits. They had a huge compressor system that allowed me to use the Exair at 20 scfm and still had enough pressure that I could drop the temperature way down. G10 generates a lot of heat, so the cooling is more important than the chip removal. Since you're making parts for RC cars, you aren't working large pieces, so crank the Exair down if yours is adjustable and use a nice sharp 2 flute cutter and a moderate feed. You'll know when the feed is right because you won't fray the mat as you cut, you'll just get a nice smooth, even green surface. I haven't cut any G10 in a while and the last thing I did was only a little .5" X .15" X.15" contact block for an optical sensor, so I haven't tried the 3 flute cutters on G10 yet. I'd be interested in hearing from anyone who has tried them. They're great on Aluminum, I'm wondering if they'll work as well on G10.

As far as a regulator goes, I used one when I was at my old work place, but at home, my compressor just keeps up with my 5 scfm generator installed. I can't get as low a temperature as I'd like, but I can still cool things down well enough to do the job. A bigger compressor is second on my list of things to get, but I'm really going to have to work to find a place for it.

One other thing, make sure you wear a respirator or some sort of filter mask when you cut G10. It won't cause silicosis, but the dust is pretty nasty and fibrous, and it can't do your lungs any good. I'd use something other than the painters masks, but they're better than nothing if you don't have anything else. Before I got a good Scott respirator, I'd take the painters mask and stuff it with cotton. After a good session, I'd find the cotton turning green next to the mask. That could have gone in my lungs. A mask is far cheaper than a lung transplant, so use it.

Dave