Possible causing my work being snatched out whilst cutting

This topic has 14 replies, 11 voices, and was last updated 12 December 2019 at 21:22 by Chris TickTock.

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12 December 2019 at 11:35 #9977
Chris TickTock
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@christicktock
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12 December 2019 at 11:35 #441325
Chris TickTock
Participant
@christicktock
Hi, I was working happily away on my Sherline lathe using a quality carbide right hand cutter trying to make a replacement arbour. one end completed having made the pivoy and reduced the arbour as needed I turned the stock around. First job I needed to do was create the pivot at the end and was nearly there when disaster. The tool felt like it dug in and yanked the stock out of the 3 jaw chuck decimating the work.

OK this happens but why? what I can tell you is the angle of the cutter was correct but what could be possible causes as it is not a happy moment when this happens/

Chris
12 December 2019 at 11:53 #441326
Emgee
Participant
@emgee
Chris

Were you holding the part by the short shaft end in the chuck when it broke free ? did the other end have centre support ?

Were the cutting forces towards the chuck ?

Emgee

Edited By Emgee on 12/12/2019 12:02:22
12 December 2019 at 12:25 #441328
Vic
Participant
@vic
Without actually seeing your setup at the time and knowing speeds and feeds it’s difficult to tell Chris.
12 December 2019 at 12:34 #441330
blowlamp
Participant
@blowlamp
You were holding the part by the pinion leaves in a three jaw chuck?
12 December 2019 at 12:51 #441334
JasonB
Moderator
@jasonb
Probably easiest if you pop it back into the chuck and take another photo so we can get an idea of what you ware holding it by and how much work was sticking out.
12 December 2019 at 13:49 #441342
Neil Wyatt
Moderator
@neilwyatt
The answer is almost always either the work is not held securely enough OR the cut was too aggressive for the work in hand (DOC or feed rate too great, sometimes speed too high for DOC or more likely too low for the feed rate). The other possibility is a blunt or poor choice of tool.

Posted by blowlamp on 12/12/2019 12:34:09:

You were holding the part by the pinion leaves in a three jaw chuck?

It also looks like the tool may have been used to face the work with quite a large depth of cut for such a delicate workpiece.

Neil
12 December 2019 at 14:00 #441346
Pete Rimmer
Participant
@peterimmer30576
Use a split collar to grip across those splines. It'll be much more secure in the chuck. Just take a piece of ally, drill it the diameter of the splines and cut a slit in it so the chuck jaws close it onto the part.
12 December 2019 at 16:47 #441374
Chris TickTock
Participant
@christicktock
Update

Hi guys, well some of you were spot on here. I got lucky and solved it myself and thought if I couldn't I would look for your ideas. well done guys you were spot on. the issue was the pinion wire would not centre in the 3 jaw but this time I got lucky in that it just fitted the 8mm collet. I was going to make a split ring up to that point, I take it brass would be better than steel?

Also I tried to see if my 4 jaw independent chuck would help, never got it out of the box till today and I would appreciate any one who has any tips on setting the 4 jaw up as it seems a pain in the but.

More lessons learned, still more to discover.

Chris
12 December 2019 at 17:00 #441377
Oldiron
Participant
@oldiron
Hundreds of video's on YouTube on setting up work in a 4 jaw chuck. Its all a matter of splitting the difference.

It comes to you quite quickly once you can see the operation. Have a look at Abom79 or Doubleboost's video's. They

show how its done.

regards
12 December 2019 at 17:06 #441378
Chris TickTock
Participant
@christicktock
Posted by Oldiron on 12/12/2019 17:00:25:

Hundreds of video's on YouTube on setting up work in a 4 jaw chuck. Its all a matter of splitting the difference.

It comes to you quite quickly once you can see the operation. Have a look at Abom79 or Doubleboost's video's. They

show how its done.

regards

Thanks for the pointer, yes I thought it would be something like splitting the difference but always pays to see how the experts go about it. Thanks for everyone's help greatly appreciated.

Chris
12 December 2019 at 17:37 #441387
I.M. OUTAHERE
Participant
@i-m-outahere
The way i set up my 4 jaw is to use the concentric rings machine into the front face of the chuck , if you get a rule and measure the diameter of these rings and note them down you will find it doesn’t take much thought to get the jaws close to the diameter of the piece you want to hold by lining up the jaws with these rings .

Another method is to measure the diameter of the chuck body and measure in from the outside diameter – chuck diameter minus workpiece diameter divided by 2 is your measurement from the outside diameter of the chuck to the inside if the jaw ( or outside if you are gripping internally ) .

I do have a design for a simple tool for this floating around in the back of my cranium – just got to find where i hid it !

Edited By XD 351 on 12/12/2019 17:39:01
12 December 2019 at 19:44 #441406
old mart
Participant
@oldmart
Another way to hold that pinion more securely would be to turn up an aluminium tube to just fit on the pinion, with a reasonably thick wall. Make an axial cut with a hacksaw to make the tube into a custom collet. The three jaw chuck will hold the work better. Take the time to learn to set up a four jaw independent chuck, they are always better than anything else. If you only have one chuck, make sure it is a four jaw.
12 December 2019 at 20:46 #441413
Howard Lewis
Participant
@howardlewis46836
A 4 Jaw will allow you to bring work absolutely on centre, more accurately than a 3 Jaw.

There are lots of places in books detailing how to centre work in the 4 jaw

There was an article in MEW some time ago, saying how to centralise work in a 4 Jaw.

The thing to remember is that you adjust the diametrically opposed jaws by half the run out shown on the DTI. You keep on checking and adjusting until the run out diminishes to whatever figure you consider acceptable.

(Often half a thou or less Total Indicator Reading is obtainable )

Practice will make perfect

Howard
12 December 2019 at 21:22 #441417
Chris TickTock
Participant
@christicktock
I appreciate the help and will note posts and hone my 4 jaw skills

Regards

Chris
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