ER collets again

[don-tucker]

I had a thought on er collets ,if you grip a short workpiece at the front of the collet what's to stop the back end closing further and therefore not gripping the workpiece parallel,I am talking about something about 1/4" long.It would need a short piece the same dia at the back.Amazing what you think of in bed,am I right :-\
Don

 

[Majorstrain]

Hi Don,
I'm no expert, but I have gripped a few short and thin walled pieces. 6mm dia, 6mm long and 0.25mm wall thickness brass.
I only had 3mm in the collet and had no problem with clamping or crush.
The only thing I would say is I didn't swing on it with the spanner, just nipped it up.

Cheers,
Phil

 

[bob ward]

You are right Don, a same size plug in the rear of the ER collet will do the trick

 

[ttrikalin]

but guys,

how much of a problem would that be? The collet is beefy enuf... and the collet chuck cannot apply more clamping force in the back rather than the front... :hDe:

short of using pencil and paper to draw, the clamping force is the normal force from the collet chuck's inner wall... and in a perfect collet and chuck the draw would stop immediately after the front part seized... Now is the taper is narrower back and wider in the front by a lot it will have an effect such as the one you fear...

Please, don't make me use a plug for the bottom part... :-\

tom

 

[don-tucker]

I think thats the answer ,if you want to hold something short use mimimum force,and Tom ,you have got to put a plug in the back ;D
Don

 

[arnoldb]

Guys, I'm with Tom

The design of the ER collets and chucks is such that it clamps down equally as much front and back, thus the reason for the increased clamping range you get from ER collets. In fact, on the ER collets with a small hole size, it has a much bigger hole at the back end, and only clamps to range on the front part of the collet. There is no need for stuffing something to clamp on in the back.

Regards, Arnold

 

[don-tucker]

That's what i wanted to hear Arnold,but the truth is they do close down at the back,I just took my collet chuck of the lathe gripped a 1/4" dowel by about 1/4" in at the front and the back closed down till the slots closed up tight,and that was by hand.
Don