collet set sizes??

[jskeen]

Ok, I keep hearing that the metric 2 to 20 mm er32 collet set is preferable to a standard 1/8 to 3/4 set because the Standard set has gaps. I've taken a rough pass at the math, and I don't see it. So, one of you machinist types happen to know what gaps exist in a standard collet set, or ever ran into anything they wouldn't work on?

Thanks
James

 

[its_virgil]

I have the 18 collet fractional set and have never needed any other sizes. I use the collets a lot for holding various parts and pieces. This does not answer your question but may help in making your decision. I do not have the metric set because I've never needed other collet sizes.
do a good turn daily!
Don

Ok, I keep hearing that the metric 2 to 20 mm er32 collet set is preferable to a standard 1/8 to 3/4 set because the Standard set has gaps. I've taken a rough pass at the math, and I don't see it. So, one of you machinist types happen to know what gaps exist in a standard collet set, or ever ran into anything they wouldn't work on?

Thanks
James

 

[Tony Pridmore]

Check out this thread, especially post #24.

 

[JerrySambrook]

James,
This would be because of the range of grip for each of the individual collets.

a 3 mm will expand and contract from 2.5-3.5 mm. 3 mm is where it is made to be roundest, and where the best holding ability is
a 4 mm will expand and contract from 3.5-4.5 mm
a 5 mm will expand and contract from 4.5-55. mm etc etc

in an imperial set, there are non fractional sizes that may or may not get covered.

a 1/4 collet will range typicall from 15/64 to 17/64.
the next STANDARD (typically found) collet is 5/16 which goes from 19/64 to 21/64. so withthe typical set, you would not be able to hold a 9/32 object.

This is for sets, as we can always buy collets in 1/64 increments semi-readily, and in 1/124 if you want to spend the extra cash for a "custom" one.

Hope this explains

 

[Chthulhu]

Buy the set that has the most sizes you think you'll need, then fill in with appropriate metric single collets. A 7 mm collet's range includes 9/32" closer to the middle than the top. You can also buy individual size collets in a variety of sizes; you just need to get away from your usual sources. They do tend to cost a bit more, though ($30 each at McMaster-Carr for example).