My views on soft jaws

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EdK
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Re: My views on soft jaws

Post by EdK » Mon Jul 26, 2010 1:11 pm

Very interesting write-up on soft jaws. Nice job Harold :!:

This was my second read of this thread and I got more out of it this time. It helps to concentrate on what you're reading. :wink:
I ran across this document about soft jaws.

http://www.prattburnerd.com/products200 ... Blanks.pdf

This paragraph in particular caught my interest.

"As an aid to improving concentricity it is better when loading the workpiece if the chuck is positioned with a single rather than two jaws at the bottom. Simultaneous location on two jaws can cause a trapping effect on large diameter workpieces as the workpiece is lifted to contact the third jaw. This may be detrimental if very accurate concentricity is demanded."

Ed
Vectrax 14x40 lathe, Enco RF-45 clone mill, MillerMatic 180 MIG.

Harold_V
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Re: My views on soft jaws

Post by Harold_V » Mon Jul 26, 2010 9:55 pm

EdK wrote:Very interesting write-up on soft jaws. Nice job Harold :!:
Thank you. I hope you found points of interest that will aid you in their use. It's a system that's hard to beat.
"As an aid to improving concentricity it is better when loading the workpiece if the chuck is positioned with a single rather than two jaws at the bottom. Simultaneous location on two jaws can cause a trapping effect on large diameter workpieces as the workpiece is lifted to contact the third jaw. This may be detrimental if very accurate concentricity is demanded."
I'd certainly agree, particularly if the item being chucked was large and heavy. By raising with a single jaw, it is free to "hunt" for true center, which may not be the case if the weight is spread on two jaws, each leaning slightly. It's not a lot different from using a spider that loads the jaws unevenly, side to side. Most jaws have at least a minimal amount of clearance in the slide-so they don't necessarily stay in the same orientation when under load.

Again, not much of an issue unless extreme concentricity is of concern, but certainly good to know.

Harold
Wise people talk because they have something to say. Fools talk because they have to say something.

stevec
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Re: My views on soft jaws

Post by stevec » Wed Mar 27, 2013 7:35 pm

Just to add, I recently decided to use an older redundant Cushman three jaw chuck as a "soft jaw chuck learning experience".
Cushman didn't reply to my query for jaw possibilities so I thought about machining the existing ones. The jaws laughed at my file test. The file lay trembling in the file drawer.
So, with the recommendation of a buddy (on another forum) I put the jaws in the coals of my now constantly burning airtight stove.
Removed them to the constantly at hand ash can 20+/- hrs. later and the next day, slowly cooled the file had it's revenge.
Here's the progress so far.
ready for soft jaws and backplate.JPG
.
Next step is the backplate.
This is all your fault Harold :wink:

Harold_V
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Re: My views on soft jaws

Post by Harold_V » Thu Mar 28, 2013 12:17 am

stevec wrote:This is all your fault Harold :wink:
I am not to be trusted, as, by now, you likely know. I've been responsible for the ruination of any number of otherwise well minded folks, who have paid attention to my ravings.

Welcome aboard! :lol:

It was a good idea annealing the jaws. However, I think I'd encourage you to have them re-heat treated now that you've machined the desired configuration. I expect the teeth for the scroll will thank you, as will the threads for mounting the soft jaws.

I don't think I'd tackle the heat treat myself, unless I had access to a controlled atmosphere furnace. it would be desirable to limit the amount of scaling involved in the process, and more than a good idea to draw to a specific hardness. Knowing the alloy would most likely make that a lot easier, so persist with your inquiry with Cushman.

If push gets to shove, maybe one of the readers who has a Rockwell tester can test a Cushman jaw and relate the hardness to you. Too hard and may be prone to failure from shock. Too soft and it's prone to failure from distortion (clamping and machining pressures).

I have the testing capability, but I do not own a Cushman chuck. Be happy to test one from my Graziano if it would help. Let me know.

Well done!

Harold
Wise people talk because they have something to say. Fools talk because they have to say something.

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SteveM
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Re: My views on soft jaws

Post by SteveM » Thu Mar 28, 2013 11:03 am

stevec wrote:Just to add, I recently decided to use an older redundant Cushman three jaw chuck as a "soft jaw chuck learning experience".
My soft jaw chuck was a Hardinge chuck with 2-piece jaws where the tops were missing. Got the chuck for cheap and made my own aluminum jaw tops. Also picked up some steel soft jaws on closeout from Wholesale Tool.

Nice work on the jaws. You're half way there.

Steve

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GlennW
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Re: My views on soft jaws

Post by GlennW » Fri Mar 29, 2013 6:44 am

I checked a Cushman Master Jaw and it was 55RC.
Glenn

Operating machines is perfectly safe......until you forget how dangerous it really is!

mikeehlert
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Re: My views on soft jaws

Post by mikeehlert » Fri May 29, 2015 11:11 am

New member. Read this discussion with great interest. It has served to harden my opinion that when machining long soft plastic parts, I need to switch from my three jaw chuck to soft jaws as the parts should run truer and not pop out of the jaws under tool pressure.

Machining a 1/4" radius on the end of a molded cup (1 7/8" OD x 2 1/2" long with 1/8" walls). My lathe is a Grizzly G4000 9 x 19. No that probably wasn't the best purchase I ever made but it was a good start.

Was gripping the ID with a slip on reinforcement ring. Now gripping the OD with a slip in insert. The OD grip method seems to work a little better but I just don't have enough grip depth.

Unfortunately the jaws are one piece and I have not been able to locate 2-piece jaws for this chuck. Is there another chuck with 2-piece jaws available or does anyone have experience making machinable covers to clamp onto the existing jaws?

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SteveM
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Re: My views on soft jaws

Post by SteveM » Fri May 29, 2015 2:30 pm

mikeehlert wrote:...or does anyone have experience making machinable covers to clamp onto the existing jaws?
Yes.

Image

The back face of those shoes are machined for the step in the jaws.

Steve

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steamin10
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Re: My views on soft jaws

Post by steamin10 » Fri May 29, 2015 9:03 pm

(chuckle) Where did you get the square drill?
Big Dave, former Millwright, Electrician, Environmental conditioning, and back yard Fixxit guy. Now retired, persuing boats, trains, and broken relics.
We have enough youth, how about a fountain of Smart. My computer beat me at chess, but not kickboxing
It is not getting caught in the rain, its learning to dance in it. People saying good morning, should have to prove it.

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SteveM
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Re: My views on soft jaws

Post by SteveM » Fri May 29, 2015 11:09 pm

You can use a watts drill:

Image
Image
http://www.ohgizmo.com/2009/10/07/squar ... s-my-mind/

Or, drill 4 small holes in the corners, rough with an endmill, finish with a file.

Steve

mikeehlert
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Re: My views on soft jaws

Post by mikeehlert » Sat May 30, 2015 9:52 am

SteveM:
Those look slick. Guess I know my next project.
That watts drill is something I had never heard of.... will have to look into it.
Now to figure out how to get access to the mill i don't have....

Thanks
Mike

redneckalbertan
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Re: My views on soft jaws

Post by redneckalbertan » Sat May 30, 2015 2:51 pm

There are some amusing videos of the watts drill bit on YouTube:

https://youtube.com/watch?v=ALiqAXiTQBg



https://youtube.com/watch?v=2brs_wR63Rs


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