R8 Collet will not hold tight!

[bgolash]

Hi
I purchased a mini mill assembly and some R8 collets from the littlemachine shop. I just ran a 1/8 end mill in one of the new 1/8 collets and for some reason it just will not hold the bit tight. Is it normal for the 1/8 diameter collet to measure more like 3/16 before the cutter is inserted. As a test I used some plastic clamps to pull together the three kerf cuts in the end of the collet and inserted the bit. The kerfs contact one another before the 1/8 diameter squeezes the bit. In my old spindle I had C5 collets and never experienced a problem even with aluminum. This problem is occurring with pine, so there are minimal tooling pressures. I`m wondering if the collet is junk.

Thanks and Regards, Barry

[mxtras]

Sounds like you may have gotten a mis-marked collet. The ID of the collet should be very close to the diameter. Many that I have (all old and well used) hold the tool against gravity without any compression - the tool expands the collet just a tad when inserted.

I think you got a bum collet.

Scott

[lakeside]

-Your drawbar my need to be shorter to pull in the collets in

[bgolash]

Your drawbar my need to be shorter to pull in the collets in

Good Point. I did try a 1/2 collet and was machining steel with no problem.
As a result, I believe the problem is the collet itself. You did make me think,
I made my own drawbar to get up and running. They were back-ordered

[bennett71]

mxtras & lakeside both have good points. If your 1/8 collet measures more like 3/16 that is too big. Did you try a 3/16 drill in that collet? In our mass produced world, I wouldn't doubt if you have mis-marked tooling. I was looking for a .186 pin out of our new starret pin guage set last week & it was marked .187. After mumbling to myself about the careless person that put the pin back in the wrong spot, I discovered that the .186, .187 & .188 pins were all marked .187. The pins measured right according to there locations in the box but were all marked the same lol.

[Mcgyver]

A quality R8 collet like say a Hardinge is designed so there is enough spring that even when loose, a cutter won't fall out of the collet or move significantly while being tightened, a very handy feature as having tooling fall out while tightening the spindle is obviously not going to do any good.

I don't know what littlemachineshop is selling, but suspect they may be bottom of the barrel india/chinese stuff. The CDN equivalent, busy bee, lured me in once, and I bought some collets that had several thou run out. back the went and I've never darkened the doorstep again.

your call, but your might find better quality tooling is more economical. It doesn't have to be $$$$ Hardinge, for example you can get a Bison or Lyndex from kbc which are both decent for $16 & $22 respectively

http://www.kbctools.com/can/Navigati...m?PDFPage=0417

just buy the sizes you need and it will cost less than a set of cheapo's

[mxtras]

Excellent points, McGuyver.

I have an old set of collets but I only have maybe 4 or 5 that are kept out at the machine - the rest hide in a drawer and are almost never used.

I am still thinking the collet in question here was mis-marked - it sounds like a 3/16 collet but was marked 1/8".

Scott

[john robin]

I Always Use An End Mill Holder When Using A End Mill. It Seems Do Hold Without Every Getting Loose.
John

[Mcgyver]

Scott you may be right, still I submit the supposition that the frequency of mis-marked collets is inversely proportional to the price.

in this case, better off with a good R8 imo - end mill holders are great but mini mills don't have much daylight and it puts extra strain on already light bearings.

[mxtras]

Don't go pulling all that high level math stuff on me, McGuyver.....I have enough trouble with 3/16 and 5/132 and all those other English fractions and stuff.....





I don't care for end mill holders, either....never have. They may have their place, but collets work for me - the tool is closer to the support and is more rigid with less chatter potential.

Scott