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beanbag
06-20-2010, 03:52 AM
Short version:

I have a face mill with a shank that is .7486 at the base and .7483 at the top. The problem is that when I loosen the drawbar on the R8 collet, the face mill falls out instead of staying in place. I want to ghetto rig something up to help hold it in place with a little friction. I was thinking of machining a little groove and putting a retaining ring or o-ring in it, whose OD is a little larger than .75. Any other ideas?

Long version:

This is the same face mill that I used in the thread about getting a good surface finish. It originally came with a 1.25" shank and I turned it down to .75 to get it to fit in a R8 collet. My next mod for this facemill was to shim all the pockets to get the insert heights even. But before doing that, I decided to check whether I had originally turned it down perfectly concentric. It turns out that I was off by a couple thou.

One useful trick I learned today was that just because you turn between centers, does not mean that the piece is centered. To check that the two centers are actually interfacing coaxially with your piece, put an indicator to the piece, hold the piece steady, and turn the center, i.e. either the headstock or live center. If the center is off (like one of the live centers I used) then you can see the indicator move even when the piece is not turning.

In any case, to return the shank of my face mill back to center, I had to trim off just a tiny bit more, which leads to my current situation.

macona
06-20-2010, 04:53 AM
You could just go down to 11/16". Or get a 19mm collet. 19mm is .7480.

-Jerry

lakeside53
06-20-2010, 10:10 AM
yes, 19mm collet, or buy an "emergency collet" and bore your own.

If you're worried about the 3 10th's taper, polish it out with emery in the lathe.

danlb
06-20-2010, 12:10 PM
I would think that a face mill big enough to warrant a 1.25 inch shaft would be fairly heavy. I would expect a heavy tool to fall out of the collet when loosened.

Dan

gwilson
06-20-2010, 12:14 PM
So,lay a piece of wood under the tool when you loosen it. Won't hurt it to drop an inch or so.

Jack F
06-20-2010, 12:22 PM
beanbag,

Dan X 2.:rolleyes: The fact that you won't (can't?) hold it in while unscrewing the draw bar is a good indication that it will fall out from the weight.:eek:

Jack.

Black_Moons
06-20-2010, 01:11 PM
Use something soft to catch it :)
Box full of shop rags, Some UHMW plastic, etc.

saltmine
06-20-2010, 02:47 PM
Like a hand.


Every time I put a block of wood anywhere near my mill, I end up using it for a quick drill backer, and end up with a piece of artificial Swiss cheese.

Fasttrack
06-20-2010, 02:54 PM
You might try putting a groove with an o-ring in it. I personally don't really like the idea of using a metal ring, but a properly sized o-ring might do something for you.

Like others have said though, I'd just put a block of wood under it or hold it with your hand.

Tony Pratt
06-20-2010, 03:06 PM
Loosen the drawbar nut[or drawbar itself], support cutter with free hand and tap top of draw bar with spanner to free taper which will allow cutter to fall into your waiting hand.
Theres nothing simpler
Tony

Black_Moons
06-20-2010, 03:10 PM
Loosen the drawbar nut[or drawbar itself], support cutter with free hand and tap top of draw bar with spanner to free taper which will allow cutter to fall into your waiting hand.
Theres nothing simpler
Tony

Till you try it on a really big endmill with razor sharp edges :)

motorcyclemac
06-20-2010, 03:29 PM
Mill a flat on it and put it in a 3/4 inch R8 tool holder. If the cutter is that heavy...I wouldn't be content holding it in a R8 collet. I have a large 12 inch fly cutter that weighs in the neighborhood of 4-5 pounds. I always run it in a proper tool holder as having it slide down during a cut could be bad. I don't care for having to cinch a collet tight enough to assure that it won't fall out. If a snug draw bar isn't comforting enough to assure it won't slip...then it is probably not the right tooling for the job.

If you choose to cut a flat for the tool holder set screw, try to only allow enough width of cut for the screw to bear on and minimize any vertical slop when the screw is slightly loose. Once tightened the screw should prevent any chance of the cutter drifting in the z axis.

Another option would be to modify the cutter to accept a R8 shank that is key driven thus putting the adapter directly on the cutter. Make the fit for the adapter stub very snug or a slight press fit then secure the retaining allen screw with a drop of locktite.

In any case you will / should have to support the cutter when unthreading the draw bar. A piece of plywood on the mill table is a good idea when ever you change tooling.

I try to limit my use of collets to 3/4 inch diameter cutters. Above 3/4 inch I switch to using tool holders. I never run my fly cutters or face mills in anything but a tool holder.

motorcyclemac
06-20-2010, 03:32 PM
Till you try it on a really big endmill with razor sharp edges :)


Quite true! I normally change endmills with a rag in my left hand. Nothing like a series of razor blade cuts in your palm or on your finger tips to make one learn to protect your flesh. I always wipe my cutters down with a rag and spray them with LPS ...so I need the shop rag anyway. May as well fold the rag in my hand before I get cut.

Tony Pratt
06-21-2010, 06:45 AM
Sorry, I wouldn't insult peoples intellegience by stating the obvious but of course you shouldn't hold sharp cutters in your bare hands. I told this to my 18yr old son and he got quite irate as he said "he wasn't stupid!"
Tony

lakeside53
06-21-2010, 11:13 AM
Just loosening the draw bar should not allow the piece to fall untill you "tap" the end of the drawbar to loosen the collet in the quill. I loosen, hold a hand under, and tap the drawbar top. Except for solid carbide end mills (very slick), the tools rarely fall out unless undersized or I'm using a beat-up collet. Even my big drill chucks don't "drop out".

I never bothered to hold a hand underneath, but after a few sold carbide came out and chipped the tips, I finally learned:mad:

The OP - I bet a 19mm collet will hold your mill enough

lakeside53
06-21-2010, 11:16 AM
Mill a flat on it and put it in a 3/4 inch R8 tool holder. .


yes. In the OP case, he's already a 0.748 so the mill will now have 2 thou of runout. Of course, for a face mill, this may not matter though.. and if it did, a 1 thou shim on the far side from the screw might get it back.

lakeside53
06-21-2010, 11:22 AM
Sorry, I wouldn't insult peoples intellegience by stating the obvious but of course you shouldn't hold sharp cutters in your bare hands. I told this to my 18yr old son and he got quite irate as he said "he wasn't stupid!"
Tony


Funny thing is, I never use anything, but my bare hands. Mine are pretty tough from years of outside work, but the problem isn't the edges; it's tiny adhered (magnetic) needles from side milling!

madman
06-21-2010, 01:38 PM
Drill through facemill shank with a small drill (smaller than the ball bearing youre gonna stick in with a slightly larger hole for the bic pen spring followed by a drilled tapped hole for a set screw (use two of them in series to lock them) Now the small amount of the ballbearing will portrude through the shank holding it in youre mill without dropping and bustin your inserts up.you can change the tension on the ball spring arrangement by turning in the set screw more and or using a stiffer spring. Good Luck Mike

Scishopguy
06-21-2010, 02:10 PM
As Tony said, a hand under the tool is the way to go. I loosen the draw bar but do not totally unscrew it, tap it with my rawhide mallet to let the tool release the taper, and then unscrew it the rest of the way with my hand underneath the tool. That way there is no additional force propelling the tool out of the spindle. I still have a hand under end mills and fly cutters with straight shanks when I hit the drawbar as some of the shanks are slightly undersized. Nothing worse than having a ding in the table due to a sharp tool dropping onto it or having to chase that end mill across the shop in front of the boss. :D