Q on mill arbors (R8)

[Greenbuggy]

Just bought some misc tooling off of ebay, one is a 3" face mill, one is a 2" indexable shell mill, both take a 3/4" arbor which was included with the face mill.

If I pull the bolt from the face mill, the arbor fits into the hole on the shell mill, up until it gets to the slot where the two blocks (I don't know what to call them) that keep the face mill from rotating on the arbor, they fit into the face mill just fine but will not fit the shell mill, on the shell mill the anti-rotation slots seem to be just a hair smaller than the blocks that need to fit in them.

What are these blocks called? They are held in with screws, do they come in different sizes? Lastly do I risk anything by just clearancing them enough to fit? I pointed out what I'm talking about on a pic of a very similar arbor I found on ebay

[GWIZ]

I don't know what they are called, I would call then shell mill drive dogs.

I don't see any problems if you re-size the dogs as long as the fit is not sloppy, BUT be careful when using over-sized tooling as the added torque may shear off the R8 index pin inside the spindle.

[precisionworks]

be careful when using over-sized tooling

+1

For any small mill (Bpt or mill/drill) 2" is the maximum size face mill. I've seen people run larger, and the spindle bearings will tolerate that for a little while, but they are not made to withstand the radial load of a tool above 2".

The good news is that Class 7 bearings for a Bpt spindle cost only $400 per matched pair

[Lu47Dan]

Barry, for future reference if 2" is the maximum shell mill in a BP with R8 spindle what would be the maximum size for a shell mill in a mill with #30NMTB spindle?
Dan.

[precisionworks]

what would be the maximum size for a shell mill in a mill with #30NMTB spindle?

30 taper is much more capable of handling the radial loads from a face mill. 2.5"-3" is a good number. As diameter increases the number of inserts usually increase and (assuming the same DOC) the horsepower requirement also increases. Sometimes with a larger diameter face mill, the DOC will need to be reduced, depending on the hardness or toughness of the material.

40 taper can handle 4"-5"

50 taper ... about as big as you can find

[Greenbuggy]

Originally Posted by GWIZ

I don't know what they are called, I would call then shell mill drive dogs.

I don't see any problems if you re-size the dogs as long as the fit is not sloppy, BUT be careful when using over-sized tooling as the added torque may shear off the R8 index pin inside the spindle.

Ok, good to know. I figured I would only be able to take small cuts with this baby anyway without knocking the whole works out of tram.

Next question, if sloppy fitup is a concern would I be better off filing the opening slightly larger on the shell mill? Because it occurred to me that if I clearance the drive dogs there will be slop if I put that arbor back onto the face mill. And I'd rather not buy a new arbor to dedicate to either piece of tooling.

[akabull]

Why not make a new set of dogs for the shell mill?

[GWIZ]

As akabull said make a new set of dogs, that is best.

I don't think you can file the shell-mill, I assume the mill is hardened throughout.

The problem with sloppy is if you start getting chatter it may unscrew the bolt holding the shell-mill.

[precisionworks]

I just looked at my 3 face mills that use a drive arbor. The slots vary from .323" to. 337". If the slot in your face mill is not at least that big you may want to enlarge it.

[coleasterling]

Originally Posted by precisionworks

+1

For any small mill (Bpt or mill/drill) 2" is the maximum size face mill. I've seen people run larger, and the spindle bearings will tolerate that for a little while, but they are not made to withstand the radial load of a tool above 2".

The good news is that Class 7 bearings for a Bpt spindle cost only $400 per matched pair

Now, I'm not claiming that it is good for the mill, but we constantly use a couple of 3 and 3.5 inch face mills in the shop and the mills seem to do just fine with it. Pretty much everything else about them sucks, but the spindle bearings aren't in bad shape.