soft jaws for raw stock and fitting news hard jaws on old chuck

[GG917]

Hello !

two questions about clamping raw stock on lathe chuck. We run quite a lot of steel in (at least for me) quite big diameter, 150 to 200mm. Not too long pieces (max. 150mm) but stock have rust, scale and is not too round. My boss told me to use soft jaws bored to the stock diameter, clamping on 10 to 20mm. Since we don't have external hard jaws for this machine it makes sense. It works but the jaws take a beating from the stock, as it is clamping on raw surface.

Does it makes sense to you to use soft jaws on raw stock? To me not really with the scale and rust, unless it is ground stock ("clean" stock) but my boss is in the "soft jaws for everything" camp. But I would prefer to have some hard jaws like these :

I am right ? those should be more versatile no ?

Our lathe tooling guy came this morning, I asked for the hard jaws "claw" type and he told me there is a chance they will not run true on the machine. Well they are hard jaws so I don't expect these to run like freshly bored soft jaws, but he told us to use new master jaws for the new claw jaws. It does not make sense to me, this is a hydraulic chuck not a wear-out scroll-type chuck. I asked him if after changing the master jaws I will have to re-bore all my soft jaws he told me no. So I am a bit lost on this one. As anyone fitted new hard jaws on an old hydraulic chuck (SMW 315 to be precise).

thanks !

 

[Mtndew]

You definitely want hard jaws, unless the raw stock only has a very small amount of stock on it from the finish size.
You're looking at about $500-$600 for a set of 3.
I would go with this style bs the style you posted if you can, they're a lot more versatile.

https://www.usshoptools.com/Custome...yMCUzRCUyMCdIQVJEJTIwSkFXUyc=&IsDynamic=false

 

[guythatbrews]

New master jaws? Never heard that one before.

No reason to need new master jaws unless old ones are worn out. And if they are worn out likely the whole chuck is worn out.

Soft jaws will work in a pinch or for a few pieces, but hard jaws will hold much better and will hold more than one size. The only reason not to use hard jaws is your boss doesn't want to cough up the money, even though it will save in the long run.

Your boss is penny wise and pound foolish.

Another reason for hard jaws is security. A piece that big flung out of soft jaws is a dangerous and costly thing.

 

[GG917]

thanks for your replies.

You definitely want hard jaws, unless the raw stock only has a very small amount of stock on it from the finish size.
You're looking at about $500-$600 for a set of 3.
I would go with this style bs the style you posted if you can, they're a lot more versatile.

https://www.usshoptools.com/Custome...yMCUzRCUyMCdIQVJEJTIwSkFXUyc=&IsDynamic=false

Yes in some cases the finish size is close from the raw stock, 169mm finished for 170 raw (more like 171 when measured...) but I can get around that by altering the process. Sort of shouldered flange, I can grip on where the shoulder side for op1, turn the short 169mm diameter and then clamp into that. Other parts have shoulder on both side, so no problem. I don't know how deep the claw jaws bite into the material actually, how much to removed to get rid of the bite marks?

I had those stepped external hard jaws before, don't really like them. OK when gripping on the biggest diameter but when I had to use the smaller one the stock was too deep inside the jaws and I had to use longer stock... That's the reason I am more inclined to claw jaws, in some case I only have 5mm to clamp onto (smaller parts).

New master jaws? Never heard that one before.

No reason to need new master jaws unless old ones are worn out. And if they are worn out likely the whole chuck is worn out.

Totally agree ! I was quite stunned by the distributor comment that new hard jaws needed new master jaws as well ! the chuck is from 2007, same as the machine, but not worn out. No visible defects, no big maks onto it from crash (second hand machine). He said he's seen it before that new hard jaws weren't running true at all on old chuck, but on scroll chuck. Mine is hydraulic, not problem with worn out scroll (or I am missing something?)

Soft jaws will work in a pinch or for a few pieces, but hard jaws will hold much better and will hold more than one size. The only reason not to use hard jaws is your boss doesn't want to cough up the money, even though it will save in the long run.

Your boss is penny wise and pound foolish.

Another reason for hard jaws is security. A piece that big flung out of soft jaws is a dangerous and costly thing.

That's what I think too. At my old job I almost never used hard jaws as i used ground stock already to the finish diameter. So soft jaws not to leave marks on the parts, that's what I learned. But here I grip onto raws stock, so hard jaws. And yes part security, I haven't brought this argument yet but will do.

My boss is actually great, were have the same way of doing work. Very knowledgeable as well. He's the former lathe guy, I'm replacing him. Not stingy (that's the CEO!), just like "I alway used soft jaws, don't like hard jaws".