Problem with .025 endmill in aluminum...

I am wanting to mill a slot .025 in wide and .025 deep in 6061 aluminum.

Equipment is less than optimal.

The piece is held by a dividing head, initally using the x-y to control initial cut then rotating the dividing head by hand to finish.

The milling machine is an old J head- with 2720 RPM max speed.

I was trying to blow out the chips with a can of dust remover. Later looked at it- it is using difluroethane as a propelant

I had two .025 carbide endmills- two flute, with the LOC possible at 0.75. Would have prefered LOC shorter- but that is what I had.

The first endmill broke shortly after starting- and shorly after I started feeding with the dividing head. I assumed my feed was too fast.

Tried again with slower feed in manually turning the dividing head and almost got done- then had a problem with my fixturing, turned off mill-- and snapped off endmill trying to back out of the cut. This was my mistake.

I went to inspect the slot I had cut- and found a .025 guage pin would not enter slot.

Got out a microscope- and found a lot of aluminum welded to the edges of the slot.

I can shift dividing head to Hardinge TM-UM with vertical head - which will get RPM up to 3700.

I will get some endmills with a shorter LOC.

What would be best for the chip welding? Would one of the mist cool systems work?
I am tempted to try a spray can of wd-40- but would prefer something I can turn on and not occupy a hand and require aiming.

Any other suggestions?

Jeff

Oh man, you are in for a world of pain. The feed rate for a .025 endmill at 2700 rpm is going to be so tiny you are going to have all sorts of problems. One unintended bump of the handle and snap! You need to get your spindle speed up. Options are spindle speeder and pneumatic attachments like a Vulcanaire.

Use coolant or some sort. WD-40 will help immensely. It will slow the chip welding down.

Use alcohol as a cutting fluid, it is the best for aluminium.

A plastic squeeze bottle and commercial denatured alcohol, keep it wet. Ideally the chips should be washed out, they will cause the tool to deflect and give an irregular slot, but if a pool of fluid is there the vortex from the spinning tool may sweep them aside.

- Mike _

Not quite sure of you application but a saw type cutter would work alot better. Like a keyway cutter.

If you are cutting a helix use a right angle attachment on the spindle and rotate to match the angle of the helix.

Good luck.

One thing I have found usefull when doing a problematic slot is: Try plunging in the "Z" to rough out the slot.
This take a bit of work, but it works very well. Make a plunge cut thru(or to depth), then jog table a little, and repeat. as many times as needed to get to the end of the slot.
Then after your slot is "roughed" then do the finish cuts as you would ordinarily do.(you would just be milling out the tits at this point)
I did not notice where yo mentioned the "length" of the slot, if is relativly long, this method may take more time that you would like(but it would still work very well....I think)

I hope this makes sense......

Spelunker said:

One thing I have found usefull when doing a problematic slot is: Try plunging in the "Z" to rough out the slot.
This take a bit of work, but it works very well. Make a plunge cut thru(or to depth), then jog table a little, and repeat. as many times as needed to get to the end of the slot.
Then after your slot is "roughed" then do the finish cuts as you would ordinarily do.(you would just be milling out the tits at this point)
I did not notice where yo mentioned the "length" of the slot, if is relativly long, this method may take more time that you would like(but it would still work very well....I think)

I hope this makes sense......

Click to expand...

This is especially good if you can go through because it will throw the chips, effectively being self clearing. A lubricant to avoid chip welding is an absolute necessity. Regular cutting oil will work as well as a lot of other things, but you must have something. I was showing a job applicant some of the items I had made, including a die with a 1/32" raduised ended slot in D2. The first thing he said was "how did you make the slot?" I knew right then I had a machinist. Later, the die cracked and he got to make a new one, on a CNC mill with the spindle running at the 5000 RPM max and a feed rate that took all morning to travel the few inches. There ain't no easy way.

Bill

I'd get a stub length 3 flute. Way stronger, more stable.

I'd probably take multiple passes at .005" deep.

Thanks for the responses.

Macona. I wish I had a speeder. Closes thing I have is one of the little Dumore tool post grinders- which will take an 1/8 shank bit. I have not bothered to check the runout. (Cannot true the endmill like you can a grinding stone)

HelEx. Will try the alcohol- I had not heard of using that.

Athack. This is a cut which has some jogs in it, so no way to use a cutter which cannot "turn the corner" when needed.

Spelunker and 9100. The cut is around the peripery of a cylinder. The cut is just a shade over 2.9 inches long. That would be a lot of plunges on a manual machine. Especially if I switch to the Hardinge, which has no quill.

John Will look for a 3 flute endmill. Will also look at more passes. I had wanted to minumize these as I have some angles which are critical.

I might try a mix of plunge cutting on the angles and multiple shallow passes on the rest.

Jeff

When rotating the workpiece with the cutter on rotation centerline, the material is rising into the center of the endmill. This can cause problems. If possible, offset your cutter so the leading edge is on centerline. Yes, I know, some part geometries will not allow this. But when its possible the offset is helpful.

Could you use some carbide circuit board drills? I could spare a few #75 and I have a lot of #78. You could use them to drill first and since they are free, you don't have to feel so bad when you break one. Especially with the 78s, the best thing is to get an Albrecht chuck with a sliding shank. You leave the quill fixed and use the ring on the chuck to feed with finger pressure. I had to drill lengthwise through the center electrodes of spark plugs and broke a drill almost every time feeding with a tailstock. After getting the Albrecht chuck, I never broke another.

Bill

You need a 45 deg, 2 flute endmill. I don't know anybody that makes one in 0.025" dia.

1. switch to a HSS 2 flute if you can find one. A little stronger and more chip clearance. More flutes will cut down on your chip clearance cause more breakage.

2. higher helix angle is better.

3. WD-40, or kerosene will work good for coolant. You need to keep the slot washed out.

Try Harvey tool for an endmill and suggestions.
http://www.harveytool.com/index.php
JR

9100- Thanks for the offer- but I will decline at this time. I do not have one of the sliding shank drill chucks- but ought to start looking for one.

This does bring up another thought. I do have a Hamilton Sensitive drill. It does have the speed for the endmills. I know it is not designed for the sidethust- but with this small an endmill that should not be an issue. I do not have an xy table, so would need to mount it on another machine. Will talke a look at that later.

JRIowa I have looked at the design, and can go up to 1/32 in diameter. May have more choices with this. I will look at the link when i have a chance.

Thanks again for the suggestions.

Jeff

Harvey sells a high helix 1/32" end mill with 3/32" DOC.
http://www.harveytool.com/products/...egory_id=1&product_family=Miniature+End+Mills

JR

Might check out what these guys have:

http://bitsbits.com/index.php?main_page=product_info&cPath=1_14&products_id=81

RPM = speed x 4 / dia = 32000 rpm for a hss cutter in Al. Anything slower than that and you have problems. To stop the chips welding themselves back onto the parent metal I have found Relton A9 to be the very best. the other cutting fluids work but A9 beats them all. You really need a speedier head and put the leading edge on center, bring the center in line for a second cut to get rid of the slight radius at the root. Cheap solution, fasten a dremel to the head. A carbide end mill is definitely not the cutter you should be using for this application, hss is called for. Peter

Another source for small endmills...

Here's another source for small endmills (down to .005). I use .023" endmills to cut fret slots with a cnc router. Have been pleased with the quality, price, and service from this supplier.

http://www.kodiakcuttingtools.com


Barron