Rookie Lathe Soft Jaw Questions

All discussion about lathes including but not limited to: South Bend, Hardinge, Logan, Monarch, Clausing and other HSM lathes, including imports

Moderators: GlennW, Harold_V

User avatar
rmac
Posts: 515
Joined: Tue Jun 26, 2012 12:48 am
Location: Phoenix, Arizona

Rookie Lathe Soft Jaw Questions

Post by rmac » Wed Jan 05, 2022 7:13 pm

I was browsing online the other day and stumbled on a site where they were selling soft jaws for lathe chucks. This surprised me. I have yet to try soft jaws, but I figured when the time comes I would just grab some aluminum and make my own jaws to mate with the master jaws on my 3-jaw chuck.

So a few related and semi-related questions:
  1. Are lathe chucks standardized enough that it's common to buy soft jaw blanks rather than make them? If so, how do you know which jaws to get? I don't think my chuck says much more on it than "Made in Poland".
  2. Aside from the time savings, is there any reason to buy the soft jaws rather than make them?
  3. If you're only planning to run a few parts, is there any reason to use steel for the soft jaws rather than aluminum?
  4. When you're machining the jaws to hold a specific part (after they're installed), it seems like you'd need to preload the chuck in order to keep everything stable. I guess you just put something behind the soft jaws so the master jaws clamp down on it. Correct?
  5. Another thing I read recently (nothing to do with soft jaws) was that you should always use the same socket on a scroll chuck to do your final tightening. That didn't make any sense to me. If that's not just a myth, what's the reasoning behind it?
Thanks,

-- Russell Mac

bill jones
Posts: 38
Joined: Thu Jan 28, 2010 7:20 pm
Location: salt lake city, utah
Contact:

Re: Rookie Lathe Soft Jaw Questions

Post by bill jones » Wed Jan 05, 2022 7:30 pm

---here's a link back to some discussion about soft jaws a while back--and I have posted some photos of one set of my largest soft jaws---made from aluminum
---I have built something like 14 sets of aluminum jaw sets---all for two piece hard jaws that have two bolt holes in each of the jaws
---also have several older one piece that are steel--where I have welded some dedicated jaws like for gripping pistons in the oil ring grooves

---since I learned the virtues of the aluminum soft jaws I seldom ever use the original outer hard jaws any more


viewtopic.php?t=110015

----------------------------------------------------------------------------------------
http://www.ryanbrownracing.com/Bill_Jones_Page_21.html

---this link shows what I have done with the old one piece hard jaws & their chucks---making them into dedicated piston holding pieces and attached the chuck to a sturdy tilt table so I can cut valve notches using my mill

User avatar
rmac
Posts: 515
Joined: Tue Jun 26, 2012 12:48 am
Location: Phoenix, Arizona

Re: Rookie Lathe Soft Jaw Questions

Post by rmac » Wed Jan 05, 2022 9:45 pm

Thanks for the link to the old discussion, Bill. Looks like a lot of my questions are answered there.

-- Russell Mac

User avatar
SteveM
Posts: 7605
Joined: Mon Jun 27, 2005 6:18 pm
Location: Wisconsin

Re: Rookie Lathe Soft Jaw Questions

Post by SteveM » Wed Jan 05, 2022 11:41 pm

rmac wrote:
Wed Jan 05, 2022 7:13 pm
Are lathe chucks standardized enough that it's common to buy soft jaw blanks rather than make them? If so, how do you know which jaws to get? I don't think my chuck says much more on it than "Made in Poland".
The chuck you need to have for this is one where the jaws are two pieces, a top and and a master. Only the top is soft.

There are several systems, but the most prevalent are American standard tongue and groove and serrated (usually goes by the brand name Kittagawa). The serrated ones seem to be used more on power chucks.

If you measure the hole distance, the width and the size of the key, you will find a match in any lathe chuck catalog.

There are options on the size of the jaws for a given chuck.

If you are going to machine them to hold work that goes thru, you want a lot of material at the end so that you can get a lot of machining operations out of them.

If you are going to put part in the face of the jaws (think holding a train wheel in a recess cut in the face of the jaws) you might want deeper ones.

There are even pie shaped jaws that are great for holding thin round parts.
rmac wrote:
Wed Jan 05, 2022 7:13 pm
Aside from the time savings, is there any reason to buy the soft jaws rather than make them?
I made a set for my lathe, and it was an interesting exercise, but the reason I did it was that they were too expensive to buy.

Now you can get them cheap from usshoptools.com .

You can also buy them on ebay.
rmac wrote:
Wed Jan 05, 2022 7:13 pm
If you're only planning to run a few parts, is there any reason to use steel for the soft jaws rather than aluminum?
I made mine out of aluminum and I haven't found a reason why they would not work. I do have a pile of steel ones. I suppose most of it is the time to machine them
rmac wrote:
Wed Jan 05, 2022 7:13 pm
When you're machining the jaws to hold a specific part (after they're installed), it seems like you'd need to preload the chuck in order to keep everything stable. I guess you just put something behind the soft jaws so the master jaws clamp down on it. Correct?
You can take a nut, drill and thread on three of the sides (alternating) and install socket head cap screws. Hold that with your finger and stick it far enough in the jaws that the screw heads will contact the master jaws and clamp the jaws down. That will give you your preload. Note that you should set the screws to preload the chuck just slightly smaller than the finish size you need so you don't need to machine a half inch off your soft jaws.

You can get one of these to hold the jaws:
JBR_on_chuck[1].jpg
They are a couple hundred, but you might find one on ebay for less.

The bee's knees is one of these:
TL_JawBoringRing[1].jpg
TL_JawBoringRing[1].jpg (9.25 KiB) Viewed 2957 times
You set the chuck to just undersize, install this in the holes, crank it to where the pins are tight in the holes and then tighten the chuck jaws. The original is the Revellica Outlock and they are almost a grand. US Shop tools sells these ones for about half that.
rmac wrote:
Wed Jan 05, 2022 7:13 pm
Another thing I read recently (nothing to do with soft jaws) was that you should always use the same socket on a scroll chuck to do your final tightening. That didn't make any sense to me. If that's not just a myth, what's the reasoning behind it?
If you have three pinions, you will find thru experimentation, that one of them is more accurate and more consistent. Mark that one with a dab of paint and use it. Check it every once in a while, because as it wears, another one might end up better.

Steve

Harold_V
Posts: 19351
Joined: Fri Dec 20, 2002 11:02 pm
Location: Onalaska, WA USA

Re: Rookie Lathe Soft Jaw Questions

Post by Harold_V » Thu Jan 06, 2022 2:45 am

rmac wrote:
Wed Jan 05, 2022 7:13 pm
[*] Another thing I read recently (nothing to do with soft jaws) was that you should always use the same socket on a scroll chuck to do your final tightening. That didn't make any sense to me. If that's not just a myth, what's the reasoning behind it? [/list] Thanks,

-- Russell Mac
This is something you can verify for yourself.
Chuck a round object (like an end mill shank, a dowel pin, or a drill blank if you have them), using one of the sockets of your three jaw, which has been marked so you know which one was used, then run a DTI on the chucked item. Note where the high spot is, and how much runout you determined. To do that, I'd suggest you make a mark on the chuck and note the degree of runout in thousandths. Now repeat, using the next socket on the chuck. Repeat yet again, using the third socket.

You should find that each iteration yields a slightly different amount of run-out, and that the runout isn't in the same place each time. That's due to the slack in the scroll being taken up in a different place, according to which socket was used. It is for this reason that one marks a socket and uses it for soft jaws, ignoring the other two. Some universal chucks have but one socket, which eliminates the problem.

I don't like to promote the things I've posted, but if you'd like to spend a little time reading, I spent considerable time posting on soft jaws many years ago. I did it in such a fashion that a novice could glean enough information to pursue their use successfully. If you're interested, here's a link that leads you to the thread. viewtopic.php?f=44&t=4266

H
Edit: I don't know how anyone who operates a lathe can get by without soft jaws. They answer so many questions and make life so much easier that it's hard to believe that they aren't in use by everyone.
Wise people talk because they have something to say. Fools talk because they have to say something.

User avatar
neanderman
Posts: 879
Joined: Mon Jan 09, 2012 7:15 pm
Location: Cincinnati, Ohio, USA

Re: Rookie Lathe Soft Jaw Questions

Post by neanderman » Thu Jan 06, 2022 4:42 am

Earlier topic bookmarked!

Thanks, Harold.
Ed

LeBlond Dual Drive, 15x30
US-Burke Millrite MVI
Atlas 618
Files, snips and cold chisels

Proud denizen of the former "Machine Tool Capitol of the World"

User avatar
SteveM
Posts: 7605
Joined: Mon Jun 27, 2005 6:18 pm
Location: Wisconsin

Re: Rookie Lathe Soft Jaw Questions

Post by SteveM » Thu Jan 06, 2022 8:21 am

Harold_V wrote:
Thu Jan 06, 2022 2:45 am
They answer so many questions and make life so much easier that it's hard to believe that they aren't in use by everyone.
They answer questions you don't even know you had!

Steve

User avatar
rmac
Posts: 515
Joined: Tue Jun 26, 2012 12:48 am
Location: Phoenix, Arizona

Re: Rookie Lathe Soft Jaw Questions

Post by rmac » Thu Jan 06, 2022 10:03 am

Thanks again to SteveM and Harold for the extra hints. I haven't yet finished reading the entire thread that Harold referenced, but I bet it answers all of my questions, and more!

Thanks again.

-- Russell Mac

PS to Harold: I don't think you should feel bad about "promoting" your own posts. A quick link like you provided above sure beats duplicating your original effort, and it sure helps somebody like me who would never have found that info otherwise.

RSG
Posts: 1439
Joined: Fri Feb 04, 2011 9:59 am
Location: Ontario, Canada

Re: Rookie Lathe Soft Jaw Questions

Post by RSG » Thu Jan 06, 2022 10:39 am

Russell,

Harold has an excellent thread dedicated to the topic but if I could add my experience with soft jaws, they are vital to my operation. Whether its for one part or many. I suppose you could buy them but it has been my experience that aside from the money savings aspect of making your own it will also bring you closer to the desired profile faster. I have three chucks dedicated to soft jaws and since they are all the same chuck configuration I can leave the jaws attached to the main scroll jaws and move them from the lathe to the mill without having to realign an entire chuck for each application.

As far as setting preload, if you are working with large diameters then the spider Harold mentions will work great, my sizes don'y allow anything that big so I use a set of aluminium discs I made in .05" dia increments and put them int he soft jaws directly. Sometimes I can push them far enough back so they don't get cut but sometimes I don't have that luxury and they get sacrificed. And if I can't use the inside of the jaw I'll use metal rings I've made up to preload from the outside.

Soft jaws are awesome and once my friend taught me about them many years ago I rarely ever use a 4 jaw chuck now.
Vision is not seeing things as they are, but as they will be.

earlgo
Posts: 1711
Joined: Sat Jan 29, 2011 11:38 am
Location: NE Ohio

Re: Rookie Lathe Soft Jaw Questions

Post by earlgo » Thu Jan 06, 2022 12:31 pm

If one doesn't have a lot of heavy machining to do one can get away with the poor man's soft jaws made from bar stock.
Soft Jaws from round stock.jpg
Soft jaws made from round stock
Soft Jaws from round stock.jpg (23.97 KiB) Viewed 2892 times
small soft jaws.jpg
In use for smaller work.
--earlgo
Before you do anything, you must do something else first. - Washington's principle.

pete
Posts: 2518
Joined: Tue Feb 10, 2009 6:04 am

Re: Rookie Lathe Soft Jaw Questions

Post by pete » Thu Jan 06, 2022 3:26 pm

Now that's really clever Earl. Simple, fast and cheap to do when it will work with the machining forces and part size your holding.

RSG
Posts: 1439
Joined: Fri Feb 04, 2011 9:59 am
Location: Ontario, Canada

Re: Rookie Lathe Soft Jaw Questions

Post by RSG » Thu Jan 06, 2022 6:44 pm

Very smart Earl!

I like the cross slot idea, usable on all four sides as a result
Vision is not seeing things as they are, but as they will be.

Post Reply