Problem with R8 collets tightening properly

[Buffalo21]

Does it happen with just one 3/8” end mills or all 3/8” end mills, have you tried that end mill in a different collet. I bought a couple of end mills recently, when the shanks were .008” to .011” undersized. Which caused a few moments of what the hell??

 

[Tozguy]

If the 3/8th collet does not hold a 3/8ths (.375'') end mill then the collet is defective. An R8 collet has little range. A .375'' dowel should just barely slide into the 3/8 collet and then take very little tightening to hold it. The lips are not normal and are another sign that there was a screw up at the factory.

 

[Technical Ted]

Is there any way you can slide a feeler gauge or some other thin piece in the slots when the collet is tight to see if those lips are hitting and preventing the collet from closing up properly? Maybe cut a narrow piece of shim stock that's only a few thousandths thick to slide in to test?

Just a thought,
Ted

 

[Bob Korves]

All collet threads have been chased. Will not perform any material removal until everything else has been checked out. Temps are in th high 90s today so shop environment is not conducive to long stays.

Did you check the shank diameter of the end mill?

 

[Low tech]

I just went out to the shop and checked . All of the Bridgeport brand R-8 collets (1/8 through 5/8 ) have that extra heavy web built in .

 

[Cadillac]

I also got around to checking a lot of mine but not all are like that. 5c and r8. My r8 collets are Bridgeport’s and hardings. My 5c are encos. On my 5c collets I have acouple with holes and I’ve seen some with pins which I do not know what their use is for?

 

[Asm109]

The collets with holes or pins are soft collets.
You put dowel pins in the holes and tighten the collet onto the pins.
Bore the collet to the size of the part you want to hold.
Remove pins, insert part and tighten up.

 

[Canus]

The mystery is solved! After carefully measuring all of my 3/8 end mills I came up with readings from .3745 to .375. All is good here. Tested each end mill with the collet in the mill and none would tighten. Added a washer under the head of the drawbar nut and no luck there as the drawbar wouldn't even engage the collet. Out comes the washer and the drawbar was removed from the mill and tested for thread engagement in all my collets. Even though I had chased the threads in all my collets it now became evident that the threads in my 3/8 collet weren't deep enough. Out comes the 7/16-20 tap and the Anchor lube. For those who haven't been here, the material these collets are made out of is harder than a woodpeckers lips. Managed to add a few more threads and problem solved. Now the question remains as to whether the lip/web is supposed to be in the smaller collets. I am inclined to agree with some of the other fine folks who posted in this thread that they are supposed to be there. Looks like they are needed to provide a larger contact surface for the smaller end mills and to prevent over collapsing the collet. I would like to sincerely thank all who posted as much good information was received. You're a great bunch of guys!!

 

[Cadillac]

I am 100% confident that the lips are intentional. Collets are the only thing between the spindle and tool. Collets are precisely made even the cheap ones. No way would a manufacturer expecially more than one forget or accidentally not cut the whole slot.
Good to hear you got the mystery sorted out!