Parts slipping in 5C Collets ?

It sounds to me like you may have some collets that aren't up to spec. I've been using 5C collets in both lathes, a spin indexer, and other fixtures for nearly 40 years and never had one slip. I do have a complete set by 1/64". The vast majority are Hardinge with a few fill ins from Shars. The Hardinge collets have a grip range of +/- .007". The Shars have a grip range of. +000"/-.015".

Any threading I do on stock 1" diameter or less is with the collets. I've never had one slip and ruin a part.
 
I could be suffering from age related brain fog but I could have sworn this came up recently and a member said an old hand where he worked said they used Dykem on the part then put it in the collet. Can’t remember if it was wet or dry but said it worked.
 
I remember seeing the Dykem trick too but can't remember the original post
 
dansawyer said:
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. )
Click to expand...
Is the 5c collet closer a lever type . Where you can feel the pressure as you close the collet.
 
Yes, the collet mechanism is the lever type. It pulls firmly on the collet, however I would not bet very much that it could use adjusting. I will take a photo and post it. It sets firmly and the parts feel secure. However they do slip.
 
Does the closer have the “taper chuck” (for lack of a better word) in the spindle? Most collet closers or drawbars use a small taper assembly in the spindle. When the closer lever is activated it pulls the collet against the taper to close it.
 
projectnut said:
Does the closer have the “taper chuck” (for lack of a better word) in the spindle? Most collet closers or drawbars use a small taper assembly in the spindle. When the closer lever is activated it pulls the collet against the taper to close it.
Click to expand...
Yes. If I understand you correctly there is a 'cone' that fits in the spindle. It is a clean, solid taper fit. This cone adaps the spindle to 5C. The closing mechanism attaches to the back of the spindle. (This is a bit of a process to attach. If it is not carefully placed then the mechansim is out of alignment and introduces wobble. ) I haven't checked the cone to collet surface in a while I will check that for proper contact.
 
dansawyer said:
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. )
Click to expand...
I have been machining for over 60 years and have never seen parts slip in a 5c collet that was set up correctly. I think if I had this problem I would collet a large bolt in the collet and use a torque socket wrench to see when grip fails. It is probably the collet set up.
 
Update: After yesterdays bad outcome I started again. I removed the collet closer and cleaned everything and reinstalled it. I slowed the machine down and took care to take smaller cuts. There are three steps in making the part: 1. turn 2 inches of a 1 inch rod to 3/4 inch, 2. rotate the rod and insert the part into a 3/4 collet, then turn the 1 inch rod to .95 inch, 3. finally cut acme threads in the .95 rod. All went well until the very last step.
I had cut the threads with a carbide insert to about the 98 percent complete point. On the last cut when the full insert made contact it grabbed the part and it spun. I was able to stop the lathe and slowly retract everything. The insert was not broken and everything was OK except where the insert locked onto the part. The part simply spun in the collet. I was able to reset and clean things up.
Could this be heat related?
If I were to test the torque in a 1/2 bolt can any one estimate the torque I should expect?
 
Below is a picture of the closure mechanism. I stopped the insert while the fingers were on the top of the ring. Normally the fingers are a 1/4 inch or so the right. Any thoughts on the mechanims or it adjustment would be appreciated. Thanks, Dan 20220930_172308_1.jpg
 
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