Cant see how this can work??

[optima21]

for all that effort turning the ring and drilling the chuck jaws, you could have just used a heavy duty cable tie to load the jaws. I think the reasoning for the ring and pin approach is just to take up the play in the grooves in the side of the jaws too.if a ring is used on the outside jaws, they may not be parallel when clamping on round bar if the grooves are worn and sloppy.

if you want it accurate, either use a collet chuck or independant chuck

 

[Wallace]

Would a cable tie not be loading the jaws up against the wrong side of the scroll? I see the ring and pins loading the jaws up as they would if clamping a round bar.

 

[bigbadbugga]

I think some of you are missing the point of the exercise.

He is re grinding the jaws of the 3 jaw chuck, the chuck just needs to be tightened against something to take the backlash out of the scroll.

You could put the washer in the chuck directly and grind the jaws but you wouldn't be able to grind the last bit were the washer was held, therefore you do it the way shown. I don't see how the positioning of the holes is relevant as long as the jaws are being forced outwards in a similar manner to when they are gripping a workpiece while in use.

 

[brightspark]

wouldn't it be just better to make a ring and hold it on the outside of the jaws?... doesnt make too much sense to me in this configuration...

no it wouldnt its not just the jaws that wear its the scroll as well .it must be held as ilustration and the pins do not need to be totaly accurate as the chuck is self centering

 

[AdrianH]

OK I have to add something here, this grinding of the 3 jaws as far as I can remember from my youth is correct, but, and this is the big but I remember is that the ring has to be so sized that the 3 jaws are in the same position to when they are holding work.

The main problem with 3 jaws is that the scroll starts to wear were you use it the most. So you true up the jaws in one position of the scroll and if you use on a larger or smaller bar you end up on a different piece of scroll so the grinding of the jaws mean nothing. To me is a quick way to start knackering up your chuck. OK do it if the jaw faces become damaged but otherwise.

Use a 4 jaw if you want accurate and true up with a dial gauge, use a larger piece of bar in a 3 jaw and turn down to size, if you need to remove and reinsert later then mark the bar so you can refit at the same point, lastly. Most 3 jaw chucks I have seen will have a stamping next to a chuck key hole, that is the one you are meant to tighten up on for the best accuracy.

Trying to remember all my lathe training , but it was years and years ago.

Adrian

 

[slim_boy_fat]

no it wouldn't its not just the jaws that wear its the scroll as well .it must be held as illustration and the pins do not need to be totally accurate as the chuck is self centring

Thanks, that answers my question [I think ]

 

[shedfull]

I'm going to do this to one of my chucks when I get the chance

 

[ukracer]

OK I have to add something here, this grinding of the 3 jaws as far as I can remember from my youth is correct, but, and this is the big but I remember is that the ring has to be so sized that the 3 jaws are in the same position to when they are holding work.

The main problem with 3 jaws is that the scroll starts to wear were you use it the most. So you true up the jaws in one position of the scroll and if you use on a larger or smaller bar you end up on a different piece of scroll so the grinding of the jaws mean nothing. To me is a quick way to start knackering up your chuck. OK do it if the jaw faces become damaged but otherwise.

Use a 4 jaw if you want accurate and true up with a dial gauge, use a larger piece of bar in a 3 jaw and turn down to size, if you need to remove and reinsert later then mark the bar so you can refit at the same point, lastly. Most 3 jaw chucks I have seen will have a stamping next to a chuck key hole, that is the one you are meant to tighten up on for the best accuracy.

Trying to remember all my lathe training , but it was years and years ago.

Adrian

Its not so much I need to true a chuck up to turn accurately its the fact its bell mouthed. I am talking about £600 to get a replacement or buy second hand and buy the same problem back again (potentially).

I do have a 4 jaw if I need precision. But much of my work is jobbing and to be honest I think I would be better getting a collet chuck if I was to pay £600.

Hope this explains things a little more.

 

[ukracer]

I'm going to do this to one of my chucks when I get the chance

Dont suppose you have a bigger picture . I cant actually enlarge it or read it!

Cheers.

Andy T

 

[shedfull]

I'm buffering........

 

[brightspark]

if its bell mouthed get grinding then as long as its reasonable the job becomes accurate as soon as u take the 1st cut and if u need to take it out clock it up put it back in thats when u need the 4 jaw

 

[ukracer]

if its bell mouthed get grinding then as long as its reasonable the job becomes accurate as soon as u take the 1st cut and if u need to take it out clock it up put it back in thats when u need the 4 jaw

Thats the plan but I was taking my time researching how and why and what is the BEST way to give me 99% chance of getting the best result..

 

[AdrianH]

I can understand grinding if the jaws are bell mouthed.

Now you probably would have checked this, but with the jaws out of the chuck and on a flat surface, piece of kitchen granite or plate glass, or the flattest surface you have. Put them in turn with each other with the jaws touching and see if the jaws are worn on the outer ends just to prove if the wear is on the gripping faces. In one of the oldest chucks I have on a dividing head it is a mixture of the jaw slides that have worn, so as the jaws tighten up the wear in the slides allow the ends of the jaws to splay out. It looks as though my old dividing head used to hold small pieces in the ends most of the time, the jaw faces were not worn as they are hardened but the chuck guides or slides took most of the wear on the inner ends.

What type of chuck do you have and what size is it, some of the older and larger units one used to be able to get replacement parts.

Adrian

 

[MrFluffy]

Ive done this for myself, I was going to make the clausing grinding preloading jig as pictured above but I just drilled the jaws & loaded it up with a ring and ground the jaws insitu with a proper tp grinder on their inside faces as the chuck was scrap at this point anyway. If you want to do the outside of the jaws, you have to grip something inside the chuck once they are trued and grind the OD to suit also.

I ground my jaws in a jig on the surface grinder to get them near, but they were miles off on the chuck itself as that doesn't account for wear in the chuck body, scroll or slideways.

The chuck afterwards will be very accurate, at the same diameter it was held for the grinding operation. The further away from that diameter, the worse the accuracy gets.
I was going to bin this chuck as its so bellmouthed it was unusable and it rattles when its span unloaded its so bad, but Ive got another couple of years out of it and it will end up on a positioner instead of the bin when I get my hands on a good unworn replacement as at least now it can hold things firmly.

 

[ukracer]

I can understand grinding if the jaws are bell mouthed.

Now you probably would have checked this, but with the jaws out of the chuck and on a flat surface, piece of kitchen granite or plate glass, or the flattest surface you have. Put them in turn with each other with the jaws touching and see if the jaws are worn on the outer ends just to prove if the wear is on the gripping faces. In one of the oldest chucks I have on a dividing head it is a mixture of the jaw slides that have worn, so as the jaws tighten up the wear in the slides allow the ends of the jaws to splay out. It looks as though my old dividing head used to hold small pieces in the ends most of the time, the jaw faces were not worn as they are hardened but the chuck guides or slides took most of the wear on the inner ends.

What type of chuck do you have and what size is it, some of the older and larger units one used to be able to get replacement parts.

Adrian

Actually no I had not thought that could be an issue.

THe chuck is a 10 inch chuck and it has no name on it. Its possibly a Colchester iif its original.

 

[MrFluffy]

Cover your way's up well if you do, and you have to dismantle the chuck afterwards to clean it out inside.
I use neodynium magnets to stick dampened paper towels and rags over surfaces during the grinding, stick the lathe in a lower speed and start the tpg up, then gently wind back and forth using the saddle until it stops sparking on all 3 jaws right along their lengths. The tpg is homemade, but it is a commercial grinding spindle with a motor and mount added, so came with close tolerance bearings where it matters etc.

 

[CRB]

As if to kill two birds with one stone post #367 shows this operation on a Cazeneuve HBX360.

Not so sure about the towel MrFluffy. I think newspaper would be a safer choice.

I have seen more of those tool-holders too recently, nice.

 

[ukracer]

wonder how much one of these would cost to get made. and how would i measure it all up

 

[CRB]

Anything with a hole big enough to get the grinding stone into the jaws would suffice. The fancy shapes are not really necessary. Even the accuracy of the grinder holder does not have to be stunning, you are, after all, putting a small circle into a larger circle, it will only touch one place.

 

[ukracer]

Anything with a hole big enough to get the grinding stone into the jaws would suffice. The fancy shapes are not really necessary. Even the accuracy of the grinder holder does not have to be stunning, you are, after all, putting a small circle into a larger circle, it will only touch one place.

Damn i thought i understood now i dont again lol