Newbie- new to cnc machining, need help.

[robotique]

I have a small shop cnc machine with a PC 892 router. I have been playing around with feeds and speeds off and on for a few months. I am getting closer but the main problem i am having is with heat. The material is .063 & .090 aluminum. I have just been using air with a slow feedrate. I sorta knew air would not be enough but i was really hoping it would work. :P I think a lot of the heat is coming from the router itself which transfers to the tool. The router will feel hot to the touch just by free spinning for a couple minutes at high rpm. I'm not sure if that is normal but based on this thread, it looks like i may need to get better bearings for it. The router is only a few months old with very little use.

Aside from the router running hot I need to figure out a good way to cool the endmill. I would really prefer not to use a liquid coolant as it would be messy and my computer/controller are very close to the machine. I have seen some air cooling systems but they seem in the $1000+ range which is high for my budget and i'm not sure if that would work or not.

Any advice is greatly appreciated.

[PhillyDee]

Sounds like you are rubbing the metal instead of cutting it. This will not help with the heat. You can cut aluminium without coolants, but it does reduce how long you can keep cutting it for. What speeds/feeds/ depth of cut are you running?

[robotique]

I am using an 1/8" 45* double flute endmill. The cutting depth is 1/16" (i think i will have to make two passes for the .090 with this size tool). I am milling/cutting the perimeter of 9"x11" rectangle for the largest piece. The router is running about 32k rpm and the machine is feeding at a very slow rate of 3 ipm (i usually end up slowing it down as heat builds up to try to save the tool). I think if i get the heat out of it i can feed faster. The router is maxed out on rpm. The perimeter is the main problem here being the longest continuous cut.

[robotique]

does the speed/feed sound ok for what i am trying to do? I did have the rpm at 16.5k but it acts like it wants more and it seems i can feed a little faster with higher rpm.

Also is there a general rule of thumb on the ideal temperature or a maximum temperature? I have a laser thermometer and going from memory I was trying to keep it below 90*F. I was using all the air i had last time to keep it at this temp and pausing to let everything cool down several times.

BTW, the tool is solid carbide.

[MChapman]

Seems kind of slow feed for a carbide endmill at that speed. rotors not spinning backwords right?

[robotique]

it is a right handed end mill turning in the right direction. It is a small router type machine and is not as rigid as a mill.

[RICHARD ZASTROW]

If the spindle motor is designed for liquid cooling, there will be inlet and outlet ports. You could try to have compressed air flow thru the motor. Be careful not to exceed the pressure the coolant was supposed to be limited to, might blow out some seals.

We did that on some Indramat spindle motors but they were lightly loaded.

Dick Z

[robotique]

The router is a standard porter cable 892, it doesn't have a place for coolant lines. I have considered trying to cool the router externally but not sure how to do it. I think a heatsink with some air on that may help, but this would probably need to be fabricated and i do not have the equipment to do that.

[grttt3]

Did you try calculating recommended feeds and speeds? Been a while since I've run a mill but those rpm's seem awfully excessive.

[robotique]

I have calculated using these formulas. I think they came from a forum but i dont remember where.

RPM = SFM / Circumfrence
Circumference = PI * Tool Diameter
*Tool Diameter in inches so divide Circumference by 12 before dividing into SFM

FR = RPM * T * CL

FR = Feed Rate
T = Cutter Teeth
CL = Chip Load

There was also a table for SFM (surface feet per minute?) values and it was 750 for aluminum with carbide tool and no coolant. For chip load I have tool diameter divided by 200. I think the 200 was a general rule of thumb or starting point.

So for my example:

RPM = 750 / (3.14 * 0.125 / 12)
RPM = 22,918

FR = 22,918 * 2 * (0.125 / 200)
FR = 28.65

Seeing this thing cut at 3 IPM makes that 28 look like a death sentence.

I wish i could remember where i got that information. I will see if i can find it again. Does anyone see anything wrong with my formulas or have better ones to use?

[DareBee]

Aluminum really needs lubricity to cut decent. Heat isn't as critical.

[LeeWay]

There are also different types of aluminum. 6000 series always cuts really well, but 5000 series can be gummy.
You can bend the 6000 stuff well too, but the 5000 will often crack.

Since you have such speed available to you and you are using such a small cutter, try running shallower passes at a much faster feed rate.

I cut quite a bit of aluminum on my router this way. It uses a PC 690 and I used WD40. Most of what I was cutting was 5052 and it had to have something to keep from welding to the bit. Heat was a problem that I had to keep an eye on. I would always rest it between jobs.

Spindle bearings on these routers aren't nearly what they should be for a spindle, but they will work with some work around. Probably why you would not think to go the full rate recommended by the formula. That is for a good spindle.