Fixing Ralph's Chucks

[Bogstandard]

I know Ralph would have liked to write this post himself, but unfortunately, he will only be able to take pics of just a couple of operations at most. So while I was preparing to get everything ready for the repairs, I serialised it as I went along. Maybe you could leave long questions until the end, then both of us can answer your queries if needed.

I am not a great believer in regrinding chuck jaws, purely because they will only ever be perfect in the position they are ground in, and also, you lose some of the gripping size, you will only be able to grip slightly larger things than you are maybe used to. There is a fix for that, and if it is viable at the end of grinding, I will see if we have time to do it.

But seeing as these are three jaw self centring, they will usually end up better on the runout stakes than original, which can be almost anything up to 3 thou runout. If these turn out less than that in their closed up position, I will be happy.

So a little history as to what is going on here.

A few weeks ago, Ralph asked me if he could true up two of his fairly new chucks, the reason for the truing is Ralph's business, I am here just to get the job done. I said that really we need a dummy spindle nose making, but not having the time, we tried to set one up in the four jaw and grind it up. The results were abysmal as far as I was concerned. So he went away with the ground up chuck and left me the smaller one so that I could prepare for him coming back tomorrow, when both chucks will be reground.

So this post is my preparation and explanation of why I did things the way I did.

There are a couple of things that need to be done before hitting the jaws with a grinder, so if you are going to try this yourself, follow along.

The first thing you need to do is to expand your jaws until they are just inside the thru hole in the chuck. This is so that when you actually grind the jaws, they will have the largest radius on the end as you can get, they should really be flat on the end, but because we are using a rotary mounted point, we have to settle on an arc.




The next job is to make a clamping ring that just fits over the outside of the jaws. If you are to be grinding the chuck you are using, you will have to fudge things up so that you make the ring in the chuck first. What you want to aim for is a ring that is faced and bored from one side only, that will give you the optimum ring.

I found a bit of brass that was an offcut from a previous boring job, and was ideal for what was needed. You could even use a bit of thick wall pipe if it could be bored as suggested and end up with the jaw faces in the correct position.




The ring is fitted with the faced side to the chuck jaws, and the jaws are opened up until things go solid. No need to go overboard with the tightening, nipped up is just fine. You don't want to distort anything that then might get ground into the jaw faces, and when the ring is removed, they won't have straight faces, but tapered front to back.

As far as I know, Ralph has already made the ring to fit the other chuck, so it will be ready just to screw onto the spindle nose.

This is the stage, if the chuck is already fitted to your spindle, you can grind up your jaws with confidence that this is the best you are going to get.

I will be showing how I grind them up tomorrow.




If you are doing as I am, truing up a chuck that won't fit my lathe, then you will have to convert your lathe to take the chuck.

This is now what I am about to do.

First off, I chose a bit of some sort of steel bar, and machined up a spigot and shoulder on the end that will be gripped in my chuck.




The spigot was then gripped in the chuck, and from now on, the chuck and spigot will not be touched until all machining jobs on the chucks to be done are finished. I am basically turning this chunk of metal into a clone of the nose on Ralph's lathe.




First off the chuck tenon and back face are machined perfectly to size and squareness, then a runout slot for thread cutting and the area for cutting the thread were made. It needs to be 39mm x 4mm pitch.
You need to measure up the chuck backplate to get the correct lengths and diameters to make everything to.




The thread was easily knocked up using my swing up threading tool, it took no more than five minutes, and fitted the chuck backplate perfectly.

So now my lathe has a perfectly sized nose with no runout at all. As long as my chuck isn't slackened/tightened or taken off, it should stay that way




Chuck fitted, ready to have the jaws reground.




See you again tomorrow, if Ralph gets here.


Bogs

[Divided he ad]

Leaving in 10 John   



Cool start 



Ralph 

[Ned Ludd]

Hi Bogs,
Sorry to butt in  before you have finished your write-up and please don't take this as any criticism of the way you are describing how to do the job, but have you seen the device in the picture?
I read about it years ago and thought it was a good idea, so I made one. I have not yet had a need to use it, yet, but I see no reason why it should not work.
As you might imagine the three jaws go into the slots and the hole in the middle is to give access to grind
them. I am afraid I cannot remember who's idea it was, so I can't give credit where it is due but if they should read this, Thanks.
Ned
 

[Bogstandard]

Ned,

There are many ways to get a cat to give up it's skin, both yours and mine are viable, plus most probably a dozen other methods as well.

There is very little that we do that can be written in stone.


Bogs

[Ned Ludd]

Hi Bogs,
I agree 100%, and where would the fun be if we all had to do everything the same way. I repeat no criticism was meant or intended, you know I respect your work greatly.
Ned

[Bogstandard]

You can criticise all you like Ned, I never get upset over it, because no matter how a job gets done, if the end result is correct, then the method must also be.

That is why I usually say something like 'this is the way I do it', because I know for sure, someone will have another way to achieve the same result.

In fact it can be good, people showing different methods, then the ones with less experience will have a choice, and will find which way suits them the best.


Bogs

[madjackghengis]

Hi Bogs, a small question, when I bought my first Logan, with a threaded spindle, I bought the cheapest three jaw universal, and a threaded back plate.  I machined the back plate to fit the chuck, and machined it on the machine it was used on, and ended up with a chuck which holds less than half a thousandth at a number of different diameters, still, twenty years later.  When I switched it to another Logan lathe with the exact same spindle, it was no longer accurate, but taking it off the backing plate, machining the plate on the new lathe, with a fresh spigot sticking in the back of the chuck and a fresh facing, it returned to the same level of accuracy to the extent I can grind Harley valves with 3/8ths stems, and have them run true to two tenths every time.  Every chuck I've ever put on with its own backing plate has been less than acceptable in accuracy, and each trued up when the backing plate was machined in situ, so it may end up needing to be trued up on the lathe it will be running on.  It helps a lot when the owner of the chuck is the only person to use it, as goes with all machine tools, I think.  More often than not, it is the spindle which has unique qualities which cause a chuck to be less than accurate, particularly with threaded spindles.  While I still have both my '42 Logan and my '48 Logan, I can't swap chucks between them and if I need to swap a face plate and the work needs dead on accuracy, I've got to take a couple thousandths facing cut.  Just to put my two cents worth in.  Good luck and hope things come out accurate mad jack

[rleete]

One question:  WHY?  Was runnout too great?  What was the reason for the fix in the first place?

[NickG]

Good method John, this is what one of my chucks needed but I didn't have the tools required to do it so I bought a new cheap Axminster chuck as I did on my previous lathe. Once the back plate was trued up it gave very good results again. I am sure a lot of people will require this work carrying out so a useful thread. Nick

[Dean W]

John, thanks for this thread.  I know of the method, but seeing it done is always great for a guy like me.
Glad you are getting some shop time.  Hope things are going well in your corner of the world.
Will be watching for your second part.

Dean

[Bogstandard]

Jack,

I am doing a rescue here, and by making the spindle nose perfectly true, as I did, is the only way it could be done. We all know that it is always better to use the original machine, but in this case it was just not possible. Anything will be better than what the chucks are like before the fix.


rleete,

Ralph told me he will be answering your question later.


Anyway, back to getting the job done.

So Ralph eventually arrived, clutching his duff chuck, plus a few other bits as well. Choccie scoffed, drinks drunk, gums well beaten, and then we got going into the shop.

I was going to be grinding the first chuck, and with a little instruction, Ralph will be doing the second.


The first job was to mount up the toolpost grinder and to dress up the mounted point to run true and be true to the bedways. Very slow power feed will be used during the grinding exercise.




This is the shot from the other direction, showing how the stone is fed down into the chuck. As you look at it, the stone is rotating clockwise and the chuck in it's normal direction, anti clockwise, at a speed of 65 RPM. The initial cut feed was 0.01mm, and the stone was turning at around 25K RPM




This is a much closer shot, action stopped by using flash. At the 1 o'clock position at the top of the chuck face you can just see a spark burst. It took 0.3mm before all jaws were sparked out down the whole depth, slightly more on the second chuck, mainly because of the bodge job I did a couple of weeks ago.




Here is a very rare shot of Big Ralph, happily sitting there, twiddling a knob and pushing a handle every so often. It seems like he has found a job that isn't too strenuous.



This shot shows the finish obtained on the jaws. On checking with a DTI and test piece before taking them off the stub spindle, the first, much less than 0.001", the second, a little more, and as I told Ralph, I suspect the scroll has been damaged slightly somehow, because it sparked out perfectly, but when the jaws were closed down to fit the test piece, the jaws moved out of position from each other. But still within expected runout tolerances.

Rescue done and dusted.




But before I finish, this does prove that Ralph did occasionally move.

He will kill me for showing this. Click the picture.





So anyway, the job got done on time, hopefully Ralph is happy, and we spent a few hours afterwards just beating our gums, putting the world to rights, hence the late timing of this post.


Hope you enjoyed this short journey with us.


Bogs

[ozzie46]

  Enjoyed it a lot Bogs. Thank you.


  Ron

[John Stevenson]

John,
I was told when grinding chuck jaws you had to load up in the direction they are closing because of any differences in the scroll.
Using a ring on the outside of the jaws is forcing the jaws open but you are grinding the part the is the closing element.

We were told to put the ring inside on the bottom of the jaw teeth, doesn't matter if the ring doesn't run true the jaws will do. This way you still have clearance to get all the way thru to clean the jaws up.

[Divided he ad]

Ok.... Firstly.... Thanks for the debut video appearance John     


Now, to answer a few queries... I screwed up the 80mm chuck long ago when not having a clue I tried to remove the runout and true up the jaws with a carbide tipped boring bar    I know!


The 125mm chuck was not running as it should, probably me and my over eager need to "secure" stuff in the jaws!?  (it was perfect to within all tolerances when new... There's a thread out there somewhere of me fitting it!) and had picked some steel up badly on all jaws, attempts to remove said welded matter were not good and ended up in poor condition (to be conservative with language) of the jaws. Marking all of the work I was producing.


So, chucks well and truly bu663rd, I asked John if he could help me get them into a better shape.... Else new chucks would be purchased. (not what I wanted to do without trying!)



The rest... You can read above. 




Very happy with the process myself. The test of runout was well within tolerances on the little chuck and pretty close on the big un... (as said... Probably me screwing up the scroll!  )   will prove if it worked or not on my lathe, I'll be testing them hopefully tomorrow evening.... I'll tell you all about it if you want?





Thank you John for being so patient and sparing me so much of your workshop time    For those who would doubt it.... A proper gent  (even if he did record me sitting on my ar53!  )






Ralph.

[Sorekiwi]

Thank you for a very imformative thread.  I have a chuck that I need to do this to, just havent had the Ba11s to do it yet!

Quick question, any reason why I couldnt use the inner race of a big roller bearing instead of the brass ring that you made? 

[Bogstandard]

John,

Could you please elaborate a little. I couldn't understand where the ring is supposed to fit. Did you mean right down the hole, at the back, where the scroll is?

I will always bow gracefully if a new and better way is shown to me. 

Sorekiwi,

I would wait for John's answer first, his method might be a lot better.


John

[Stilldrillin]

John B.
I was taught to nip on a ring/ disc, held behind the working area of the jaws, inside the chuck bore.

Never thought to do it any differently.......

David D

[John Stevenson]

John, You need to get thru with the grinding wheel so you can't grip on the holding part of the jaws or you get a step so the only part you can grip in is the bottom of the teeth of the jaws, often these are relieved back a bit which makes it easier to slip a ring in.

John S.

[NickG]

I was thinking the same as any backlash in the scroll is taken up in the correct way it would normally work gripping on the inside of the jaws. You could grip something right at the back and relieve it afterwards but as Bogs said, you don't need to go mad with the tightness so I guess gripping with the teeth should be ok.

Anyway, this way worked well and as bogs said, it only corrects it for the position you grip in, the rest is down to the accuracy of the scroll and Jaw teeth. Just over a thou run out is as good as it'll get I would have thought.

Nick

[Davo J]

John,
I was told when grinding chuck jaws you had to load up in the direction they are closing because of any differences in the scroll.
Using a ring on the outside of the jaws is forcing the jaws open but you are grinding the part the is the closing element.

We were told to put the ring inside on the bottom of the jaw teeth, doesn't matter if the ring doesn't run true the jaws will do. This way you still have clearance to get all the way thru to clean the jaws up.

That's the way I have always done it, though I see plenty doing it this way.
Over here they sell these for CNC aplications.
https://www.machineryhouse.com.au/Products?stockCode=L763

Dave

[John Stevenson]

I use soft jaws a lot and the ones I have do have a recess at the back just for holding a ring to allow you to machine the jaws,
I'll get a pic later and post it.

[madjackghengis]

Just to toss my two cents in, I've had to drill the end of each jaw with a pin hole, and made a ring which fits inside the diameter of the pins sticking out the end of each jaw, and that way get the scroll pressure in the right direction, while keeping the ring clear of the grinding.  I was taught to do everything possible to get the chuck running true before even considering grinding, as usually the problem is in the way it's mounted, and in the back plate, unless it's like a couple of chucks I've got which just have had too many things slip in the jaws, and worn out the grip surface.  mad jack

[NickG]

Bogs,

Was it necessary to take a skim of the other angled faces of the jaws to get it to close up smaller or did they close up small enough? Guess if it was only a few hundredths of a mm it would still be small enough?

Thanks

Nick

[Bogstandard]

Nick,

Taking some off the jaw angles was discussed in length by Ralph and myself, but Ralph said he would try things out first, then if needed, he could just bring the jaws back here to have them taken down a little. No big thing with doing that.


John

[philf]

I have successfully reground a few chucks - mainly to rectify wear at the front of the jaws. I turn a tube with a 1.5mm to 2mm wall thickness, the OD of which easily fits into the bore of the chuck. Then I machine 3 slots in the tube wide enough for the chuck jaws to protrude through the slots. This preloads the jaws in the correct direction.

Cheers. Phil. (My 1st post - hope the photo appears.)