End Mills

Maplehead said:
I dab motor oil on it but it doesn’t seem to help much.
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Motor oil is not cutting oil, and would be of little help; I use TapMagic for nearly everything in my shop.
Also, I have to agree with the other writer, if it is a mini machine, the 3/8" Diameter cutter would be much better; a reasonable RPM for it would be around 700 - 1,000 RPM. Brown & Sharpe's calculator recommends 70 SFM as a starting point for (relatively) soft steel of 200 BHN, and 150 SFM for 100 BHN; with a light machine, I'd thing to err on the conservative side.
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I agree with the comments above; 3k rpm is much too fast for ¾ end mill in steel, I'd keep it under 1k.
Also, it sounds like you are milling a slot? for this you should use a 2 flute end mill a 4 flute will tend to chatter.
Another thing you can do to help with plunge cutting, pre-drill a hole, smaller diameter than the end mill so the center of the end milll doesn't have to cut, a task it's not great at doing.
 
With a benchtop,mini mill, .125" depth of cut in one pass is asking for trouble in my humble opinion.(especially in mild steel)
how I would do your cut in my shop is .030" DOC , with a center cutting 3/8" 3 flute EM at ~800 RPM.I would also lock the Y and Z axis.and of course use some magic tap as well. but I'm sure there are wiser members who might have a more aggressive milling approach than mine but this method has always been safe and free of any drama for me.
 
Thanks all, I’m going to try these suggestions this Saturday.
Does the cutting oil dry after use or will it stay wet on the machine?
 
it stays wet. unless cutting brass, cast iron, bronze... etc, you should use cutting oil. On aluminum you should not use cutting oil, but use a fluid like wd40 or my preference usually Tap Magic for Aluminum.
A it prevents galling (welding chips to the cutting edge) . B it helps cool the cutter .

The oil or fluid is easily removed with a rag, and then a your choice of cleaning fluid. I use simple green on stuff, or WD on ferrous metals.
 
I agree with Ken from Ontario about depth of cut. on a Bridgeport machine I usually limit depth of cut in steel to 30-50 thou. The light attached to your machine will usually tell you if you are taking too big a cut or have too high a rpm, the shade of the light will vibrate, especially if its a long arm light.

Somewhere on the Web is a Sherline milling manual that is quite good. Its worth searching out and reading if you are struggling with milling on a light mill or any mill for that matter.
 
It may be too late for that end mill. sounds like it rubbing now, hence the shrieking. If it is still ok, try ramping into the cut, that has worked for me.

As others have said, 3/4 SEM on a mini mill is probably a no go.
 
As said many a time, too fast, use cutting oil or coolant! Also, however fast you're running it, the centre of the endmill's cutting edge is running at effectively zero FPM and plunging is trying to force it into unyielding metal (a lot like the web of a drill bit) - the suggestions of ramping in or drilling a "starter" hole to lower the centre of the cutter into are both good, as you'll be cutting with a moving tool edge - and a micro/mini mill hasn't the strength to push a cutter that big, even the suggested 3/8 may be a bit beyond its capabilities!

A good rule of thumb* is that a mill with HSS cutters can remove up to a cubic inch of mild steel (e.g. HRS, CRS) per minute per horsepower, many of the micro/mini mills are around 1/4 HP (delivered to the spindle, power consumption considerably more) so aren't going to do quick work...

Dave H. (the other one)

* for a large, heavy, rigid industrial mill running flood coolant, and taking cutters as disposable/consumable items - reduce drastically for a hobby machine
 
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