Chuck jaw truing tool

[olderdan]

Do you have a worn chuck that is only gripping on the back of the jaws, here is a way to fix it.
This simple tool will do the job if your chuck has hardened jaws, by gripping the jaws by the front only (where most work is done) while allowing a grinding wheel access though the length of the chuck.
My 50 year old 5 inch 3 jaw will grip a 5 inch long test bar with the same run out at the end as at the jaws (usually within a thou) after this treatment.
You would think that working in a tool room everything would be looked after but sadly not so, I have seen chucks tightened with extension bars and metal being torn out of 3 jaws when 4 jaws should have been used (laziness is the common culprit), this obviously renders them useless for accurate work unless the jaws are ground true. I am not suggesting that anyone here would do these things but maybe you have an old chuck that could be reclaimed.
On the subject of trueness of 3 jaw chucks I have used a method which is is a little unusual and may not meet with everyone’s approval. I have turned the backplate register -.008 thou to allow a small amount of movement for final adjustment if needed, after which the mounting bolts are tightened, I can almost here the disapproval but I can say I have never had the chuck move while in use, indeed all faceplate work is clamped so why not a chuck. If you don’t like this idea I find that a few taps with a soft drift on the offending chuck jaw to settle the scroll before final tightening will often do the trick.

[DIYer]

Thanks olderdan! We've added your Chuck Jaw Truing Tool to our Machining category,
as well as to your builder page: olderdan's Homemade Tools. Your receipt:

Chuck Jaw Truing Tool by olderdan

tags: chuck, truing

[C-Bag]

Thanks olderdan for posting this. I'm not a trained machinist so there's no disapproval here. But my impression of being a machinist is not only a constant creative application of what you have to do the job at hand, but also to make the tooling to repair and improve your equipment.

So this is to me a novel way to true the jaws. I saw Mr. Pete take a ring and put it on the outside of the jaws and open them to tighten then grind them. As a FNG/noob can you give details how to make your rings because they obviously need to be done accurately. Or is that going to be in your plans for sale?

[olderdan]

Thanks C-Bag, not a lot wrong with your definition of a machinist.
No need for great precision in making the rings as they only have to stop the the jaws from moving and simulate gripping a diameter.
You could at a pinch make one from tube with the cut outs sawn and filed, the accuracy comes from the chuck itself.
You mention using a ring on the outside to do this, the problem with that is the jaws tilt inwards at the front whilst grinding, ending up with the condition you started with of only gripping on the back of the jaws when holding a shaft.
Hope that makes sense.
I dont intend to sell plans , I would rather just pass on what I know and further the cause of home engineering.

[Paul Jones]

Thank you! Your chuck jaw truing tool is brilliant and easy to find the raw materials compared to other designs I have seen using round steel plates with holes precisely drilled to catch the chuck jaw edges. If you have time, I found it is a good practice to dismantle and clean the 3-jaw chucks before grinding the jaws to help ensure repeatable jaw clamping. It is amazing how much gunk gets into the scroll plate behind the jaws and can affect the jaw positions.

I too have turned the backplate register on my mini lathe chucks to be slightly smaller than what comes from the factory. These are bolt mounted so an easy modification and never found any slippage. The ER32 collet chuck now runs with almost no measurable TIR.The larger lathe and chucks have a D1-4 mounts and already run extremely true. However, I do use a 0.0001" division indicator to measure the chuck OD run-out after mounting to makes sure I didn't get a chip lodged on the D1-4 surfaces.

Thank you for sharing your designs and experience with chuck jaw truing.

Regards,

Paul

[C-Bag]

Having never worked as a machinist but as a mechanic there are still some common concepts/lingo to machining that I'm going to have to bone up on. Like register. I think I get the concept. Like what taper is to X axis, but in the Y axis?

But in the shops I worked in the machines that were used by everybody were always suspect. Alignment racks were a good example where you give up a precision machine to the horde and always with a bad outcome. Especially with the electronic racks. All it took was for one of those wheel sensors to not be mounted right and it hit the floor and you were no longer doing a real alignment. Same thing with the valve grinding equipment, line boring, even brake lathe. So I can't even imagine sharing a lathe or mill.

Both my Chinese hobby lathe and mill/drill were owned by several people who thought they were improving them. So all this kind of info of checking and possibly correcting problems is invaluable to me. As I learn more and do more precision work it points up sometimes the limitation of the machine but more often than not shows a botched "improvement". And probably why I was able to pick it up so cheap

My problem is you can't probably drop it down to a low enough gear for me to get all the nuances. Like, your test bar. Obviously you have to buy one, but is that what it's called? Sorry for all the stupid noob questions.

[brianhw]

Post withdrawn by brianhw.

[olderdan]

Hi C-Bag
There are no stupid questions, only stupid answers, an inquiring mind will always get there.
A register usually refers to a radial location diameter where a taper is not used I.E. screw on chucks, the thread hold it on, the register aligns it.
The test bar can be anything you know to be parallel and straight, the one I use most often is a 1/2 inch dowel 5 inches long, these are centerless ground and case hardened and quite cheap
Hope that helps.

[milomilo]

Do you have a worn chuck that is only gripping on the back of the jaws, here is a way to fix it.
This simple tool will do the job if your chuck has hardened jaws, by gripping the jaws by the front only (where most work is done) while allowing a grinding wheel access though the length of the chuck.
My 50 year old 5 inch 3 jaw will grip a 5 inch long test bar with the same run out at the end as at the jaws (usually within a thou) after this treatment.
You would think that working in a tool room everything would be looked after but sadly not so, I have seen chucks tightened with extension bars and metal being torn out of 3 jaws when 4 jaws should have been used (laziness is the common culprit), this obviously renders them useless for accurate work unless the jaws are ground true. I am not suggesting that anyone here would do these things but maybe you have an old chuck that could be reclaimed.
On the subject of trueness of 3 jaw chucks I have used a method which is is a little unusual and may not meet with everyone’s approval. I have turned the backplate register -.008 thou to allow a small amount of movement for final adjustment if needed, after which the mounting bolts are tightened, I can almost here the disapproval but I can say I have never had the chuck move while in use, indeed all faceplate work is clamped so why not a chuck. If you don’t like this idea I find that a few taps with a soft drift on the offending chuck jaw to settle the scroll before final tightening will often do the trick.

I have done the same thing to my back plate except I drilled and tapped the chuck for three 5/16" set screws to make adjusting the chuck easy and it can not move after you tighten the set screws.

[olderdan]

Thanks Chris
I would have installed set screws as you have done but the register on my old chuck is only 1/8 deep.
I used to operate a Myford cyl grinder with a griptrue chuck which had three tapered screws to bear on the register, I always wished it had four so it could be adjusted as you would a 4 jaw chuck.