|Chris TickTock||12/12/2019 11:35:33|
|291 forum posts|
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/
|1320 forum posts|
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 ?
Edited By Emgee on 12/12/2019 12:02:22
|2374 forum posts|
Without actually seeing your setup at the time and knowing speeds and feeds it’s difficult to tell Chris.
1218 forum posts
You were holding the part by the pinion leaves in a three jaw chuck?
16877 forum posts
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.
|Neil Wyatt||12/12/2019 13:49:16|
16933 forum posts
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.
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.
|Pete Rimmer||12/12/2019 14:00:17|
|536 forum posts|
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.
|Chris TickTock||12/12/2019 16:47:27|
|291 forum posts|
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.
|343 forum posts|
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.
|Chris TickTock||12/12/2019 17:06:03|
|291 forum posts|
|XD 351||12/12/2019 17:37:31|
1384 forum posts
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
|old mart||12/12/2019 19:44:33|
|967 forum posts|
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.
|Howard Lewis||12/12/2019 20:46:54|
|2588 forum posts|
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
|Chris TickTock||12/12/2019 21:22:00|
|291 forum posts|
I appreciate the help and will note posts and hone my 4 jaw skills
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