The jaws are not the problem... the scroll wear is the problem.. thats why I prefer the 4 jaw independant chuck. Grinding the jaws at a particular diameter will do no good if the scroll has wear elsewhere as the jaws wont be concentric at THAT spot... A better solution for 3 jaw chucks is to fit / make mild steel soft jaws & skim them when ultimate precision is required. This is what I did... 😎👍☘🍺
Peter is correct in saying The problem is in The Scroll as everyone knows people tend to lean a little too heavy at times when tightening 3 Jaw Chucks on Lathes which tends to Stretch or deform The Scroll. I worked for A Government Facility making Rifles for Armies of Many Countries & never had any Success in Grinding Jaws for 3 Jaw Chucks as they worked at the diameter at which they were ground then when you open The Jaws for a different size you still have The Original Problem
One of the advantages of the Grip-Tru chuck is as it is adjustable for run out the jaws can be re-ground on a surface grinder and the flat profile is maintained. And with care the jaws can de ground pretty exactly the same.Would it have been a good idea to have set the OD of the chuck body true to start with?
Hi Alan, great method with the bush turned around so you can grind the back also. Is that a Pratt Burnerd adjustable 3-jaw? I have one of those that needs a regrind. I wondered if you took any special measures to centre that adjustment mechanism up before grinding, or maybe you don't use the adjustment at all? Cheers, Craig
I may have missed something. The front of the jaws are reduced by the amount ground off. Therefore, the chuck will close to a different (smaller) diameter than it was when the bushing was held in the back of the jaws. How did you account for this when you ground the back of the jaws? Also, the center of the jaws still showed red marker, so that area was untouched. Without running an indicator along the ground faces of the jaws, how do you know if they are all flat and true? Again, I may have missed something, but it seems that this method might settle for clamping using only a portion of the jaws.
Hi Tim I ground the front first then marked the jaws with the red pen and held the bush at the front. Grind the back until the pen marks show the grinding. The red pen mark in the centre was under the bush and had already been ground. Then I used the test bar to check the run out you can put some micrometer blue on the bar hold it in the chuck and check the jaws are touching all along the jaw.
Thank you for sharing. I have been contemplating doing the same thing but have not proceeded as I have a couple of points that cause me worry, I don't know if it is valid however.... When you grind the jaws you are obviously grinding the bore of a cylinder, admittedly it's an interrupted cut. So you grind the jaws true. When you use the chuck to grip a diameter smaller than the ground diameter all would seem well as you are getting line contact on each jaw. If however you grip a diameter much larger than the ground diameter you are effectively getting two line contacts on each jaw. My concerns are firstly, will these lines dig in and mark the workpiece? Secondly as you are getting these line contacts on the edge of the jaws will they wear out or get damaged quickly and cause run-out. I'm probably worrying about nothing, has anyone had any problems after grinding jaws?
Hi When new the jaws had a flat face so you had line contact, as the jaws wear the front gets bigger in my case one jaw was out giving me a run out every time I held a part.
You can see the runout at 10:02... nice work and I like this method but it doesn't appear that you can get the jaws perfect without taking a full pass from back to front on the jaw? Using this method it seems like in the middle of the jaw you will have a small hump and the front part of the jaw won't be the same as the rear. I have a small recess that I created on the front of my jaws for holding washers and boring holes while sitting flat against the back of the jaw. It's actually similar to how the jaws step down moving out from the center I have one step down moving into center (hope that makes sense). Using a ring in this location gives the best results of all the methods, you can load the chuck like normal and make a complete pass.
Clearly the small red patch in the centre of the jaw is where the second applications of red marker has overlapped the front surface. To suggest that Alan has missed a portion of the jaw or just left a random high spot is ludicrous.
The problem of course is we end up with a radius inside the Chuck or on the jaws .I've come to the conclusion that it makes sense to make that radius large and be able to ALMOST make it flat.if u know better way let me know..that's why I bought a 4 jaw Chuck to have flat jaws.i don't mind having to use an indicator.thks for vid
I think you're right. It needs to be an iterative approach. The initial bush installation at the back is on worn jaws (admittedly less worn than the front will typically be but worn nonetheless) and that wear will show up in the front grind. Doing it in multiple stages might help that significantly.
I don't see how this method gets the entire jaw surfaces on the same plane. Since you ground the front and then the back and not the middle to the exact same plane, I don't see this as a great way to get the jaws aligned up to make it run more concentric. I think an other ring where you force the jaws against and then grind the entire length teh same would yield a much better concentricity. JMHO
I did grind the front and the back all the way along the jaw. I ground the front marked the jaws red to give a visible guide then ground the back until it just removed the red. the jaw with the red on had already been ground.
The jaws are not the problem... the scroll wear is the problem.. thats why I prefer the 4 jaw independant chuck.
Grinding the jaws at a particular diameter will do no good if the scroll has wear elsewhere as the jaws wont be concentric at THAT spot...
A better solution for 3 jaw chucks is to fit / make mild steel soft jaws & skim them when ultimate precision is required. This is what I did...
😎👍☘🍺
Peter is correct in saying The problem is in The Scroll as everyone knows people tend to lean a little too heavy at times when tightening 3 Jaw Chucks on Lathes which tends to Stretch or deform The Scroll.
I worked for A Government Facility making Rifles for Armies of Many Countries & never had any Success in Grinding Jaws for 3 Jaw Chucks as they worked at the diameter at which they were ground then when you open The Jaws for a different size you still have The Original Problem
Bell mouthed jaws are not a consequence of a worn scroll.
One of the advantages of the Grip-Tru chuck is as it is adjustable for run out the jaws can be re-ground on a surface grinder and the flat profile is maintained. And with care the jaws can de ground pretty exactly the same.Would it have been a good idea to have set the OD of the chuck body true to start with?
Hi Nathan I set the chuck OD true to start but did not video it
That was a great tip, Great contact and as always, Thanks.
Hi Alan, great method with the bush turned around so you can grind the back also. Is that a Pratt Burnerd adjustable 3-jaw? I have one of those that needs a regrind. I wondered if you took any special measures to centre that adjustment mechanism up before grinding, or maybe you don't use the adjustment at all? Cheers, Craig
Hi Craig. yes its a Bernerd true grip chuck I set the out side body of the chuck running true to start
I may have missed something. The front of the jaws are reduced by the amount ground off. Therefore, the chuck will close to a different (smaller) diameter than it was when the bushing was held in the back of the jaws. How did you account for this when you ground the back of the jaws? Also, the center of the jaws still showed red marker, so that area was untouched. Without running an indicator along the ground faces of the jaws, how do you know if they are all flat and true? Again, I may have missed something, but it seems that this method might settle for clamping using only a portion of the jaws.
Hi Tim I ground the front first then marked the jaws with the red pen and held the bush at the front. Grind the back until the pen marks show the grinding. The red pen mark in the centre was under the bush and had already been ground. Then I used the test bar to check the run out you can put some micrometer blue on the bar hold it in the chuck and check the jaws are touching all along the jaw.
Enjoyed the video two tenths of a thou run out is a great result.
Thank you for sharing. I have been contemplating doing the same thing but have not proceeded as I have a couple of points that cause me worry, I don't know if it is valid however.... When you grind the jaws you are obviously grinding the bore of a cylinder, admittedly it's an interrupted cut. So you grind the jaws true. When you use the chuck to grip a diameter smaller than the ground diameter all would seem well as you are getting line contact on each jaw. If however you grip a diameter much larger than the ground diameter you are effectively getting two line contacts on each jaw. My concerns are firstly, will these lines dig in and mark the workpiece? Secondly as you are getting these line contacts on the edge of the jaws will they wear out or get damaged quickly and cause run-out. I'm probably worrying about nothing, has anyone had any problems after grinding jaws?
Hi When new the jaws had a flat face so you had line contact, as the jaws wear the front gets bigger in my case one jaw was out giving me a run out every time I held a part.
Interesting Allan,my 3 jaw needs doing.
You can see the runout at 10:02... nice work and I like this method but it doesn't appear that you can get the jaws perfect without taking a full pass from back to front on the jaw? Using this method it seems like in the middle of the jaw you will have a small hump and the front part of the jaw won't be the same as the rear. I have a small recess that I created on the front of my jaws for holding washers and boring holes while sitting flat against the back of the jaw. It's actually similar to how the jaws step down moving out from the center I have one step down moving into center (hope that makes sense). Using a ring in this location gives the best results of all the methods, you can load the chuck like normal and make a complete pass.
Clearly the small red patch in the centre of the jaw is where the second applications of red marker has overlapped the front surface. To suggest that Alan has missed a portion of the jaw or just left a random high spot is ludicrous.
The problem of course is we end up with a radius inside the Chuck or on the jaws .I've come to the conclusion that it makes sense to make that radius large and be able to ALMOST make it flat.if u know better way let me know..that's why I bought a 4 jaw Chuck to have flat jaws.i don't mind having to use an indicator.thks for vid
Show us how to make a piston return spring , or a set of muffler bearings for our lawn tractors. Keep machining, forever.
I think after you grind the back, one needs to grind the front a second time - just a touch up. After the back is ground, the jaws won't sit the same.
I think you're right. It needs to be an iterative approach. The initial bush installation at the back is on worn jaws (admittedly less worn than the front will typically be but worn nonetheless) and that wear will show up in the front grind. Doing it in multiple stages might help that significantly.
The bushhh. Let's count.
I think the grinder is too large, in this case hi must go out of the jaw for perfect accuracy.
Greeting from Algeria
I don't see how this method gets the entire jaw surfaces on the same plane. Since you ground the front and then the back and not the middle to the exact same plane, I don't see this as a great way to get the jaws aligned up to make it run more concentric. I think an other ring where you force the jaws against and then grind the entire length teh same would yield a much better concentricity. JMHO
I did grind the front and the back all the way along the jaw. I ground the front marked the jaws red to give a visible guide then ground the back until it just removed the red. the jaw with the red on had already been ground.
Looked like you missed a good 1/8" in the middle !
Hi Steve when I moved the bush from the back to the front I marked the jaws red again then ground the back the red you can see is on the ground jaw.