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External Jaws for a 3 jaw

MashingMetal

MashingMetal

Well-Known Member
Last weekend I picked up a 10” 3 solid jaw Cushman that fits my Colchester with the L1. Of course no external jaws with it. There is a set on fleebay which would work out to $100 Canadian to my door. I know with a 10” they won’t get used much and I do have a big 4 jaw. Convince me one way or another please.

Thanks! Mark
 

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If they are for the same chuck then the scroll should match.
Personally I would want outside jaws. I know I've used mine a fair bit.
 
MrWhoopee said:
^^^This^^^

If you have actually found the orphaned jaws to fit your chuck, you should not only buy them, you should also buy a lottery ticket.
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I know, Been looking for Jaws for my jawless Rohm chuck 20 years, i am not spending $700.
I have 3 sets of orphans here, two are Asian external, 6” if anyone is interested in me measuring?
 
How hard are your existing jaws? If you can, think about drilling and tapping them for some custom add-on external jaws you make yourself.

Mine are reversible, so it's basically the same thing. Then you can turn the new jaws in place so they are centered properly.
 
They feel like they have to be the high 50’s Rockwell. My chuck is their heavy duty series what ever that means. I am sure Cushman has the specs somewhere. Probably carbide would be the only thing to touch it. Good idea if it was Asian I would go for it.
 
MashingMetal said:
Last weekend I picked up a 10” 3 solid jaw Cushman that fits my Colchester with the L1. Of course no external jaws with it. There is a set on fleebay which would work out to $100 Canadian to my door. I know with a 10” they won’t get used much and I do have a big 4 jaw. Convince me one way or another please.

Thanks! Mark
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Heck it's your money not mine so I'm a firm go for it. :D
 
A hundred bucks doesn't get a fella very far these days...

FWIW, I went down that same shiny path a fair few years ago, bought a new-in-the-wrap Pratt-Burnerd Gri-Tru, with a Myford back plate, at an auction, that had had the outside jaws sitting next to it on the table. The Jaws were not there when I went up to pick up my purchase...
Eventually found a set on eBay out of England, clicked the buy it Now button, and never regretted it! Even at that, I got a three jaw chuck with two sets of jaws, for about 20 percent of what Pratt-Burnerd wanted for a single set of jaws, so I was still pretty pleased.

But, Hobby Stuff, eh? If it isn't cutting in to other budget items, I figure $100 to the door is a pretty reasonable price.

Personally, I am pretty happy to use a three jaw chuck, (but certainly am well versed in getting a four jaw dialed dead nuts too!) you DO have to plan your work flow around that you pretty nearly need to do any work that requires a degree of concentricity, all in one set-up.
A set of outside jaws, just gives you that many more options as tools! :)
 
Thank-you. I am not the only victim of the disappearance auction thing, it’s happened to me more than once. Glad you were able to get replacements. I am fine with using a three jaw too knowing it’s limitations. I have pretty much decided to pull the trigger.
 
MashingMetal said:
Thank-you. I am not the only victim of the disappearance auction thing, it’s happened to me more than once. Glad you were able to get replacements. I am fine with using a three jaw too knowing it’s limitations. I have pretty much decided to pull the trigger.
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I honestly don't think you will be regretful for the money spent.

Even, in the odd off chance, if you have to make some fairly major mods to the Jaw surfaces to make them work, I think it'll be worth it.

For what it's worth, I would suggest digging through Stefan Gotteswinter's YouTube channel, and find the video of him making a set of custom Chuck Jaws. LOTS of maths, then there is dealing with that the pitch of the threads is different on the outside and the inside of the scroll, so that the jaws will actually close as they get closer to center, as well as when they are at near full extension... Badly phrased, but...

I'm pretty sure I would work myself into starving to death, if I ever got it into my head to start making one-of, custom jaws sets! :)
 
trevj said:
I'm pretty sure I would work myself into starving to death, if I ever got it into my head to start making one-of, custom jaws sets! :)
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Me too Trev......

In my mind, it's a lot easier to figure out how to add internal jaws to the existing external ones. Drilling and tapping hard jaws isn't easy, but it's gotta be WAY easier than making new scroll parts.

But then again, if @MashingMetal can find the coin is a lot easier to just buy a whole new chuck.
 
Susquatch said:
Me too Trev......

In my mind, it's a lot easier to figure out how to add internal jaws to the existing external ones. Drilling and tapping hard jaws isn't easy, but it's gotta be WAY easier than making new scroll parts.

But then again, if @MashingMetal can find the coin is a lot easier to just buy a whole new chuck.
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One of the 'available' things I never quite pulled the trigger on, though tempted, was a set of Soft Jaw Bases, essentially a set of chuck jaws with the tops shaved off flat, and a couple bolt holes to be able to bolt on any manner of suitable raw stock which could then be bored or machined, to fit the work as required.

If you have a set of jaws with reversible tops on them, it's not that hard to steal the same idea and make your own upper jaws! Best of all, you can make them of the most machinable crap you can lay hands on, and, since they are bored out in place, they are accurate anyways!

In the particular case of mine, the outfit was making aftermarket jaw bases for the Myford sized P-B chucks, and you simply cut slices off a piece of brass or bronze Hex Stock, to get three usable blanks (rotating the unused point of the Hex towards center before boring to size in-situ).

If I already had the hardened base Jaws, I am pretty sure I would just swallow hard, and pay what the nice gentleman with the multi-axis EDM was charging to have some threaded holes burnt in to those.
 
trevj said:
I honestly don't think you will be regretful for the money spent.

Even, in the odd off chance, if you have to make some fairly major mods to the Jaw surfaces to make them work, I think it'll be worth it.

For what it's worth, I would suggest digging through Stefan Gotteswinter's YouTube channel, and find the video of him making a set of custom Chuck Jaws. LOTS of maths, then there is dealing with that the pitch of the threads is different on the outside and the inside of the scroll, so that the jaws will actually close as they get closer to center, as well as when they are at near full extension... Badly phrased, but...

I'm pretty sure I would work myself into starving to death, if I ever got it into my head to start making one-of, custom jaws sets! :)
Click to expand...
I have seen Stephens video of that and would recommend it too. Another video I would most highly recommend is CàLems video in which makes his own six jaw chuck. Simply amazing.
 
trevj said:
I honestly don't think you will be regretful for the money spent.

Even, in the odd off chance, if you have to make some fairly major mods to the Jaw surfaces to make them work, I think it'll be worth it.

For what it's worth, I would suggest digging through Stefan Gotteswinter's YouTube channel, and find the video of him making a set of custom Chuck Jaws. LOTS of maths, then there is dealing with that the pitch of the threads is different on the outside and the inside of the scroll, so that the jaws will actually close as they get closer to center, as well as when they are at near full extension... Badly phrased, but...

I'm pretty sure I would work myself into starving to death, if I ever got it into my head to start making one-of, custom jaws sets! :)
Click to expand...
This topic comes up fairly often. I have made scroll chuck jaws - my recommendation is to buy jaws, if it is reasonably possible. Especially on a smaller chuck - just get a whole new chuck. I think the OP is on the right track, spend the $100.

The teeth on the scroll jaws are not particularly difficult to make (there is still the rest of the jaw features - the width, the slide key, a loading ring, cutting the grip surface - a set of jaws is a bit of work, not hard to do, just time - the teeth are no different). The pitch is constant across the entire face of the scroll and the same all the way along the jaw. The curvature of the scroll tooth is generally a little bit different on the inside versus the outside of each tooth (it doesn’t have to differ, but you get a bit stronger tooth) - the scroll only contacts a relatively small amount of each tooth. Still each tooth will be the same along the whole jaw.

I made two sets of 3J jaws for my 13” chuck (I made them as two piece jaws - sort of pointless except the material was sourced from a scrap bin and was not large enough to make one piece jaws). The chuck had only the outside grippers when it came to me - good jaws, but not the ones you want if there is only one set. I don’t claim any wizardry in figuring out the jaw teeth - I found it well explained by Harold Hall http://www.homews.co.uk/page99a.html

My method to cut the teeth was different than Harold’s but accomplished what he had explained. He used manual machines. I used a CNC mill, so I took the approach of a spiral (helical interpolation), matching the scroll curvature of the largest radius of the scroll for the inner surface of the teeth and matching the scroll curvature of the smallest radius of the scroll for the outer surface of the tooth. I suppose circular interpolation would work too(?), but the helical is no more difficult and takes advantage of the change in radius across the width of the jaw (slightly stronger? maybe slightly larger contact patch?). The result was very satisfactory - gets used quite a bit.
 
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Thanks everyone for your replies. I have watched Stefan Gotteswinter’s jaw making video before, amazing really what can be done. My reality is the time taking away time from projects started and cost of the good steel for a heavy 10” jaw really isn’t worth the $100. I have ordered them. I am thinking of mounting a smaller 6 jaw chuck at some point. I want to take on the challenge of making an L1 I have watched This Old Tony make his L0. Going back to time, I would rather finish up my metal shaper to make the keyway on L1 mount.
 
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