Machinist

[Lawrence London <lfljvenaura@gmail.com>]

Usually supplied with soft collets so you can clamp them before machining.

That's a emergency collet, if you removed them then bored it out with the collet tight it would not shrink down and hold the part. They hold the collet open.

what are the 5c collet pins for?
http://www.practicalmachinist.com/vb/general/what-5c-collet-pins-296575/

Usually E collets are used to hold either thin stuff (so you need the backer of a land or flat bottom, IOW a reamer will not go through. Often E collets are machined to hold odd ball shaped, not necessarily round items. For instance, i have made a couple that are a rectangle for making different size Tee-nuts. That way I can c-drill, tap drill, tap, and chamfer very quickly on center, in the lathe with a turret. 4 ops and no set up or jaw creep as in a 4j chuck. Sometimes, the round part you are holding requires an off-center drill/tap/wobble broach, etc, etc. So the collet is made on the DH, off set the required amount. Ditto square and off-set square shapes.

If indeed the bore is through you can ream, but why? so much slower and not quite as accurate compared to boring. Even if the hole goes straight and concentric, compared to boring it is more likely bell-mouthed a smidgeon unless everything is perfect. And to get the reamer "perfectly" concentric and on size, you should bore the hole up to within a few .001's of reamer size anyway. It is your work, but why use a more complicated process, with more costly tools, that is more time consuming, to risk getting less accurate work?

smt

As Steven has already mentioned you may wish to bore the hole with a small boring bar to get the best concentricity out of the collet. However a spiral reamer should work if that is the best method you have available.

Those pins are only in place while the collet is being fabricated, to whatever size/shape is required.

Once that process is completed, the pins are no longer used, as when actually using it to hold a part in process.

The pins would be needed subsequently if the E-collet is being re-worked for a larger working diameter.