Grinding An R8 Taper

[JoeLee]

I have an R8 arbor for a face mill, the taper is galled, you know the usual radial galling from slipping in the spindle.
It was given to me, it didn't slip in my machine. There is no sign of damage to the key slot where the pin would be, so it must be who's ever machine it was in when it slipped didn't have a pin, probably what saved it, or why it slipped.
Anyway, I want to clean it up in my T&C grinder, no problem. I can zero it in by setting it up it in my 4 jaw chuck.
What I would like to know is if I grind .005 off the dia. of the taper how much further up in the spindle will the taper seat???
As it is now after I stoned the galling best I could when fully seated in my BP there is about .125 of the taper exposed.
My guess is I can get away with it seating .040 further up with out any issues.
I don't want to have to remove the arbor from the grinder to check it and then try to set it back up again. I would like to do this in one shot and know where I will be when done.

JL....................

[TGriffin]

According to Bridgeport, an R8 taper is 16.85؛. If you make a right triangle with an angle half that or 8.425؛, the short side .0025 to represent material removed and the long side (X) the distance the arbor will move, then Tan 8.425؛ = .0025/X. Solving for X yields a move of .0169". I'm sure if it's wrong, someone will gladly correct me.

Tom

[macona]

Those arbors are so cheap they are hardly worth messing with.

[MichaelP]

Short side is the radial reduction. Opposing angle is half of the included taper angle. The hypotenuse will represent the amount of forward movement needed. The answer is 0.017".

You can use the following formula:

X= D/2*sin(T/2)

where

X is the additional forward movement needed after grinding to engage the taper
D is the diametral reduction (by grinding, etc.)
T is the included taper angle, in degrees

P.S. Removing only 0.0025" deep of material sounds very shallow for the purpose of elimination of clearly visible grooves. But without seeing it, it's hard to tell.

[JoeLee]

Short side is the radial reduction. Opposing angle is half of the included taper angle. The hypotenuse will represent the amount of forward movement needed. The answer is 0.017".

You can use the following formula:

X= D/2*sin(T/2)

where

X is the additional forward movement needed after grinding to engage the taper
D is the diametral reduction (by grinding, etc.)
T is the included taper angle, in degrees

P.S. Removing only 0.0025" deep of material sounds very shallow for the purpose of elimination of clearly visible grooves. But without seeing it, it's hard to tell.

Thanks for the help. I just used .005 as an example, I'm not exactly sure how much it will take to clean the arbor up, maybe double that but at least now I know what to expect as far as depth of seat. If I grind .010 off the dia it should seat about .035 deeper. Plenty of room.

This is an 1 1/2" arbor for a 5" face mill, they aren't really that cheap.

JL.........................

[flathead4]

I don't want to have to remove the arbor from the grinder...

Can you remove the chuck with the arbor still in it to check the fit? I do this sometimes when machining something on my lathe to fit another machine in the shop.

Tom

[lakeside53]

If you don't remove the arbor to locate the original center points , how do you intend to accurately center it?

[Mike Amick]

I just sent a millrite B&S#9 out to the index wells boys to convert to R8, they had
to have the quill with it. They grind it while its spinning in the quill to prevent/limit
runout.

Got it back .. looks good.

[JoeLee]

Flathead, good idea to remove the arbor for a fitting check in the BP without taking it out of the 4 jaw. My grinders work head has a B&S #8 taper and it always centers up perfectly.

Lakeside,
The way I will set this up in the work head of the grinder is to chuck up on the part of the arbor that goes into the 1 1/2" pilot hole of the face mill. This will insure that taper is on center with the pilot part of the arbor. I'm going to have to indicate off the taper during set up. No other way really as with those big block keys on each side of the arbor there wouldn't be any room to sneak a dial point in.

JL......................

[krutch]

I hope you realize the arbor will draw further into the spindle after grinding the taper. Some arbors might not have very much material to remove before it is too deep in the spindle to hold properly.

[Royldean]

I hope you realize the arbor will draw further into the spindle after grinding the taper. Some arbors might not have very much material to remove before it is too deep in the spindle to hold properly.

This was the original point of the thread.

[edit: whoops, thought this was the second set-up thread]