Parts slipping in 5C Collets ?

[dansawyer]

I just had another idea: I will test the collet to the spindle adaptor using Prushin Blue and test the part to the collet the same way. If the adaptor is not spot on that could cause a point contact. If the collet is not contacting the part evenly ditto. Anything to look out for while doing this?

 

[dansawyer]

Well that did not find anything. The collet to spindle blue was a near perfect uniform smear. The rod to to collet blue was also uniform.
That said, the inside of the collet is scratched, it shows signs of slipping. (is there anyway this can be 'repaired'?)

 

[Winegrower]

I spent two days fussing with my collet closer, which looks much like yours. Finally I understood how it actually works, and it’s pretty clever. When the spool is pushed to the right, to release the part, the fingers relax inward and quit pressing against the spindle, thus releasing the collet clamping pressure. When the spool is pulled to the left, the fingers expand and as they open, the back side of the fingers lever against the spindle with a lot of leverage and go over center, giving the pop and locking the part. Twisting the collet closer shell pulls the collet into the nosepiece…if not far enough, no pop. If too tight, there is also no pop and no locking. When the collet is engaged, a pin can lock the shell to the spindle preventing loosening.

Maybe somebody can explain better. Please!

 

[dansawyer]

I spent two days fussing with my collet closer, which looks much like yours. Finally I understood how it actually works, and it’s pretty clever. When the spool is pushed to the right, to release the part, the fingers relax inward and quit pressing against the spindle, thus releasing the collet clamping pressure. When the spool is pulled to the left, the fingers expand and as they open, the back side of the fingers lever against the spindle with a lot of leverage and go over center, giving the pop and locking the part. Twisting the collet closer shell pulls the collet into the nosepiece…if not far enough, no pop. If too tight, there is also no pop and no locking. When the collet is engaged, a pin can lock the shell to the spindle preventing loosening.

Maybe somebody can explain better. Please!

Thank you for that explanation. My question is: Is there an adjustment that will increase the distance, i.e. pull on the collet before the mechanism reaches its end of travel and the fingers go 'over center'. This will help explain if I have a collet closure mechanism problem or a collet problem.

 

[Winegrower]

Is there an adjustment that will increase the distance, i.e. pull on the collet before the mechanism reaches its end of travel and the fingers go 'over center'.

Kind of. On mine, there is a collar on the shaft the spool rides on, and is held in place with a couple set screws. I moved that back a bit to give a bit more pull distance, but it seems to me the closer is designed around parameters for 5C collets that define the loose to tight movement range, so once the collet is installed and screwed down by the operator, the lever arm caused collet motion is pre-determined.

 

[Jimsehr]

I am sending you 3 pics of collet set up in my lathe. One pic shows collet in relaxed open position and the 3 slots measure about .06 thousands wide . Next pic shows collet tightened ,with the slots now measure about .035 wide. This slot width is what you should check to see if collet is closing enough.

The other pic of collet set up shows an adjustable bolt set up for keeping the collet balanced as it runs. One adjustable bolt on the top and one on the bottom.
You adjust these bolts with machine running and use a lock nut once set.

So check and see if your collet slot closes down to about .035 wide. If not the set up is wrong.

Sending a pic of collet adjustment screws #4 pic.

 

[twhite]

Something you mentioned about your collet being scored on the inside. That is never a good thing for any collet. I would replace that collet.

Just to be clear. Your part in the collet is pushing back in the collet or spinning? If it is pushing back. The solution is as simple as using a collet stop if the part bing machined is shorter than the length of collet.
I have this type and a few others I use. This one allows the longest part to be inserted into the collet.

Cutting oil is my blood.