Perils of using small endmills

[rotate]

I was using 0.02" solid carbide endmill to do some pcb milling. I needed 0.5mm tracks. My mill has maximum speed of 1900 rpm, which is way way too slow, but I only had 24 straight tracks to do, so I thought I'll take it nice and slowly. After all, it was just a thin layer of copper.

After doing 3 tracks, I got a little cocky and increased the feedrate and to my utter horror, the tip of the endmill just dispapeared!!

Lesson learned, albeit an expensive one ($18). I have a whole new respect for these little endmills. I can't imagine using these little bits for milling steel let alone soft metal.

[Bruce Griffing]

I solve that problem with one of these. Mine is the straight shank model.

http://www.macrotechnologies.com/hig...r_spindles.htm

Having the beast in hand, I think you could use one of the Horror Freight pencil air die grinders for the same task. Not nearly as durable and low in TIR as a purpose built spindle, but it would probably work for what you are doing. Turns out to be on sale right now for ten bucks. Might be worth a try.

http://www.harborfreight.com/cpi/cta...emnumber=47869

Mounting would not be as simple as chucking up a purpose built spindle, but it shouldn't be too hard.

[Mcgyver]

I can't imagine using these little bits for milling steel let alone soft metal.

smallest i use is 1/16 in steel. hss gives you a bit of fighting chance, sometimes you can even see it flex - that'd be a busted cutting in carbide. like any endmill, too much load and away she goes. the feed rate to end up with whole and complete cutter at the end of the job is tedious though.

[mechanicalmagic]

I made a solid Aluminum block, clamps onto the quill. It holds a slightly modified 1/4" air die grinder (20,000 rpm), or a 1/8" pencil grinder (60,000 rpm).

The grinders are located at a known, precise location from the spindle, so I don't need to edge find them, for moderate work. (Just dial in the flat on the block.)

.020 endmills are fragile, 90 degree point, carbide engraving tools are cheaper, although you will cut .014 deep at the tip. (Well, they were cheaper the last time I bought for that kind of project, maybe different now.)

[Swarf&Sparks]

For small carbides at a good price, check out this outfit.

http://www.carbidebur.com/18shank/scminiburs.htm

I use the 1/8 in a high speed air spindle on my CNC router.
Usual disclaimer.
Cheers, Lin

[ptjw7uk]

Talk nicely to your local dentist (if you can) I got several carbide burrs and some diamond points, they usually just bin them my dentist autoclaves them for another patient to use but gave me a supply also an old air drill runs at 60000 rpm just need find a way of fitting to a mill.

Peter

[Evan]

I recently had to mill a keyway in hardened steel to make an adapter for my horizontal mill. All I had that would do it is a 1/16 carbide mill. My mill goes to 6200 rpm which actually gave decent rate of cut but I twitched or something on the handwheel and the bit went "tink". I pulled out another and finished the job without incident. At least I can grind the stub to make a nice D bit for board milling. 1900 rpm just isn't fast enough for hand feeding. The required feed rate is too slow to do reliably by hand.

[Swarf&Sparks]

Same here with dental tools, Peter. But they are limited to "point" work. Dentists don't seem to use endmills

I also hafta make a collet so they'll fit my air
spindle (one day). Just use em in the Dremel for now. Diamond points are great on glass.

[Boomer Mikey]

These Proxxon units are very popular as a high speed spindle too. The 3/4" spindle nose (#1) makes it easy to adapt it for use in a mill or lathe. These are industrial quality with quality collets and cutting tools from Germany. All metal 5,000 to 20,000 rpm ball bearing spindle TIR .001" or less guaranteed for two years.



Boomer

[Nick Carter]

Yeah, copper adds to the problem as well. I cut a lot of Sterling silver dry at 10k rpm (CNC Taig) with a 1/32" HSS endmill and I still keep my feedrate down to about 3 ipm - if the flutes load up with chips then the endmill snaps...coppper cut the same way and half the time the cutter snaps anyway, probably will try 2 ipm as I have to make some more copper earrings...
If you can use coolant (I can't it makes the parts come off the carpet tape) things are easier but copper really likes to stick to the flutes.

Nick