Question about R8 tool holders

My only R8 collets that have a separate threaded bushing were made in USA and in England. Lyndex R8 collets all have threaded bushings. I have never seen a two piece on an R8 end mill holder.

When I was looking for a 3/4" R8 collet with minimal runout, the best specification that I could find was a Crawford, made in England, with a TIR of .0002". Lyndex collets run .0007" - .0011" TIR. Hardinge doesn't specify TIR on their website that I could find. Wholesale Tool has an RDX brand specified at .0004" concentricity. However, concentricity is not the same as TIR. Concentricity of .0004" means that an axis running through the center of a pin in the collet will be within .0004" of the spindle axis. Its associated TIR would be .0008".

A half thousandth TIR on an end mill holder would be great, IMO. An end mill holder, by design, must have clearance to be able to insert an end mill. When the set screw is tightened all that clearance is taken up on the side opposite the set screw. A class III fit for 3/4" would be equivalent to .0006" TIR.
 
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rgray said:
A 3/4" R8 collet "is" a 3/4' R8 tool holder. Why buy one with a set screw? Special op?
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Tool setting, every time you remove a tool from a collet you will have to reset its Z value when you put it back in, If you are doing 6 tool changes per part on 100 parts this is very slow and annoying at best.
 
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rgray said:
A 3/4" R8 collet "is" a 3/4' R8 tool holder. Why buy one with a set screw? Special op?
Click to expand...
When doing roughing work, I find that an end mill will occasionally slip in an R8 collet. I have bought other size tool holders with a set screw that hold an end mill with a Weldon shank, and they NEVER slip. Thought I'd add a 3/4" to my modest collection and not worry about it anymore. And for 20 bucks, to me it's worth it.

Regards,
Terry
 
I've been away from my computer for awhile working on another non-machining related project, so I'm only just now seeing the more recent posts. Thanks to all for your replies and the educational info from our experts. You guys are great resources.

I plan on using this tool holder with a coarse roughing end mill, so precision is less of a factor than would otherwise be the case. If it turns out to not fit my needs, I'm only out $20. Then we'll go to a plan B.

Regards to all, and thanks again,
Terry
 
I have several Shars R8 end mill holders that I have bought individually, and they run great. I don't think you'll be disappointed if you go that route. I'm content that these are capable of doing anything that I would encounter on a manual machine.
 
Got my Shars 3/4" tool holder yesterday afternoon. Looks great, but I won't get around to using it for a few days. I'll post comments then.

Thanks for all the counsel.

Regards,
Terry
 
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