Parts slipping in 5C Collets ?

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dansawyer

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The machine is an older Colchester lathe with a 5C collet attachment. The project is to make a hob from W1 tool steel. The first part that slipped was 1 inch in diameter. I managed to complete that step and moved on to the second step which involved cutting threads. The second step used a 3/4 inch collet, the tool acually caused the part to turn in the collet. Needless to say this ruined the part.
I have used these collets in the past without issue. The closing mechanism is set 'firm'. I did use oil as coolent in the turning process, it is possbile that some oil was on the part, I did wipe them with clean paper towels before installing.
Any advice or experience would be appreciated. (I am about to go back to the 3 jaw. )
 
The 5C collets do not have that good of holding power and any coolant/lube at the collet part interface will make it slip. I try to clean the oil off of the collet portion interface with the work holding, if you need coolant maybe some form of deflector/barrier may help. I use a 5C collet chuck and crank down hard when threading stock to prevent movement. I am not sure if you can achieve the same holding power with a lever style collet closure.
 
The ER platform by design seems to hold much better than 5C
5C is a wide open collet system. Lots of tooling is available.
The obvious question, how is the fit?
I don’t have a 64ths’ set, you get a better clamping range for sure.
 
What is the actual size of the parts you were gripping? If they are too much undersize, that could be causing the slipping.
 
My first reaction was also to recommend ER collets. For lathe work especially.

I sure hoped I'd hear some good tricks for getting 5C collets to grip. There's got to be some amazing reliable way to up your grip using cockroach spit and carbide dust.
 
You can also use a collet stop if the part does not extend past the length of the back of collet.


Cutting oil is my blood.
 
Ischgl99 said:
What is the actual size of the parts you were gripping? If they are too much undersize, that could be causing the slipping.
Click to expand...
Good quesiton. The raw material is 1 inch and the collet is a 1 inch. It is a firm fit. The first cut is to turn one end to 3/4. That end is placed in a 3/4 collet. The fit was close, not loose. Both slipped. It was the 3/4 that slipped while cutting threads. They were good fits.
 
pontiac428 said:
My first reaction was also to recommend ER collets. For lathe work especially.

I sure hoped I'd hear some good tricks for getting 5C collets to grip. There's got to be some amazing reliable way to up your grip using cockroach spit and carbide dust.
Click to expand...
I thought about light knurling? Would that make is better or worse?
 
I am apparently not the first to have this happen. Would a 3 jaw provide better holding? I used the collet for accuracy, not speed or ease of set up.
(I can also use a 4 jaw. It would be a bit strange to see a 1 inch part in a 12 inch chuck. )
 
dansawyer said:
Good quesiton. The raw material is 1 inch and the collet is a 1 inch. It is a firm fit. The first cut is to turn one end to 3/4. That end is placed in a 3/4 collet. The fit was close, not loose. Both slipped. It was the 3/4 that slipped while cutting threads. They were good fits.
Click to expand...
Sounds like that was not the issue then. I use a collet chuck and not that familiar with a closer, so unfortunately can’t help with anything related to that.
 
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