Quick way to increase hold of flat smooth chuck jaws?

Cannonmn · Jul 2, 2017

We use an 8" buck chuck as a bench fixture to hold things requiring manual torque to unscrew two or more parts that after all the usual penetration methods, still need high torque. Hex items are of course easy to hold with this but many are smooth cylinders and unless the chuck is tightened to what is probably near the chuck-damage point, it won't hold some cylinders tight enough. My time budget for a fix is 1 hour. Don't want to replace jaws. So what do you suggest, epoxied-on coarse sandpaper, epoxy-on annealed file sections, or what? I'm sure many here have been faced with similar issue so what did you do? The flat area of each jaw is about 1.25" square.

specfab · Jul 2, 2017

I would likely opt for making some aluminum angle pieces that would function as jaw caps, and bond sandpaper to those, rather than to the steel jaws. From your query, I assume damage to the clamped items is inconsequential, so the abrasive marks don't matter. Another approach could be to take the jaws out and machine grooves in the clamping surface. Probably also would yield some marking on the workpiece.

dgfoster · Jul 2, 2017

Simply putting plain copier paper between the part and the jaw will double the coefficient of friction. Similarly aluminum shim stock or copper sheet will improve grip. For very coarse work expanded metal would actually provide some bite. Ther surely are several more methods----Cyano glue?

Denis

Cannonmn · Jul 2, 2017

Thanks good ideas. Anyone have any idea how much torque applied by the chuck wrench will break a chuck like this? I'm guessing the chuck body is the typical cast iron but I don't know about the scroll and jaws.

extropic · Jul 2, 2017

How about making 3 (aluminum??) V-blocks, 60º included angle, channel back to slip over jaw width and full jaw height (sit on face of chuck).

Limy Sami · Jul 2, 2017

This any good ? https://www.roehm.biz/fileadmin/content/pdf/products/en/Lathe_chucks_Independent_chucks_en_web.pdf

James H Clark · Jul 2, 2017

Simple, switch to a four jaw chuck. Several times the amount of holding power.

JH

TDegenhart · Jul 2, 2017

I have often wondered how a Ridgid pipe three jaw chuck can develop so much holding power with little more than a simple hand tightening. I wonder if they use a variation of the sprag clutch, where a roller rolls up a ramp at the work is tightened.

Tom

Mark Rand · Jul 2, 2017

How many different diameters are you regularly dealing with? If it's not too many, then turn up some 'soft jaws' with inner diameters a couple of thou smaller than the required diamerer and a full circle. Split the 'soft jaws' into three parts to fit the chuck (two parts works well with Aa bench vice). Then grip the parts in those. You can get a much better grip and not damage the parts that way.

At least, that's what's worked for me, exept I just use the two jaw bench vice and cut the 'soft jaws' from squares of 1/2" plate.

gbent · Jul 2, 2017

Quick but still robust would be aluminum shims for the jaws. Properly cut and bent around the jaws they should last dozens of times, if not hundreds. The softer the better. 3003 T0 is great, but I have used aluminum flashing from the hardware store before.

TDegenhart said:
I have often wondered how a Ridgid pipe three jaw chuck can develop so much holding power with little more than a simple hand tightening. I wonder if they use a variation of the sprag clutch, where a roller rolls up a ramp at the work is tightened.

Tom

On a Ridgid chuck the jaws have grippers that indent into the pipe. The tightening ring is actually a hammer to hammer the chuck tight as well.

Mud · Jul 2, 2017

dgfoster said:
Simply putting plain copier paper between the part and the jaw will double the coefficient of friction. Similarly aluminum shim stock or copper sheet will improve grip. For very coarse work expanded metal would actually provide some bite. Ther surely are several more methods----Cyano glue?

Denis

+1. Cardstock works even better, because it takes up more surface irregularity. Try just slipping a few business cards between the jaws and the part and see how much it improves. Strips of emery cloth, with the cloth toward the part if the surface can't be damaged.

Thanks good ideas. Anyone have any idea how much torque applied by the chuck wrench will break a chuck like this?

You can't break it with that ratchet. We made a 32" long ratchet to tighten some 10" chucks we use on VMCs. that gets really reefed on for some ops, all that has happened is the jaws are no longer parallel because the body of the chucks have distorted. That would be bad for you, because the tilted jaws would have less holding power than parallel jaws. In our case we have carbide grippers screwed into soft jaws so the distortion hasn't hurt.

Wild West · Jul 3, 2017

Instead of copy paper like one poster said, use 400 grit wet/dry paper.

DDoug · Jul 3, 2017

Standard HF $50 1/2" drive impact wrench should do the trick.... :rolleyes5:

HuFlungDung · Jul 3, 2017

A scroll chuck probably has as much internal friction as it does actual holding power, so maybe you get half of what you think you're getting when really reefing on the wrench.

For grabbing stuff like solid shafts, I like to use a stacked pair of aluminum vee blocks (vees facing each other) in the hydraulic press. This means working with the part axis horizontal in aspect, but that doesn't usually matter to a nut and wrench. The aluminum is soft enough to deform to fit the shaft without raising dents. 10 or 20 tons of pressure provides pretty good grip. No fancy Vee's required, they get messed up anyways. Cut the vees with a bandsaw if you have such available. The 'natural' angle of Vee blocks that have been used extensively for shaft support in a press seems to squash out to about 115 degrees (started life at 90°).

If you really need a vertical axis, maybe rig up something with a couple of support pads opposing a portapower cylinder ram.

Mud · Jul 3, 2017

HuFlungDung said:
A scroll chuck probably has as much internal friction as it does actual holding power, so maybe you get half of what you think you're getting when really reefing on the wrench.

+1. I once put my hydraulic chuck pressure gage in a manual chuck to see, and was sorely disappointed in how little pressure I could make on the gage, even leaning with an extended handle on a 12" 3 jaw. IIRC I could hardly get past 500 lbs and CNC chucks go to 3000 or more.

jim rozen · Jul 3, 2017

Your chuck, sir, has removeable soft aluminum jaws. They're designed to be machineable to match any particular
workpiece.

Those jaws have been used up pretty much, and were left in a state that is poorly-suited to holding round stock securely.

Buy a new set of jaws. Machine them to match the items you are trying to hold. You won't need any paper or magic
unicorn poop if the jaws are shaped better than they are now.

Mark Rand · Jul 3, 2017

jim rozen said:
Your chuck, sir, has removeable soft aluminum jaws. They're designed to be machineable to match any particular
workpiece.

Damn! Even if they're actually steel soft jaws, rather than aluminium, I hadn't noticed them.

Yes:- get/make some new soft jawa and machine each set for the diameter of the part you want to hold.

Cannonmn · Jul 3, 2017

Mark Rand said:
Damn! Even if they're actually steel soft jaws, rather than aluminium, I hadn't noticed them.

Yes:- get/make some new soft jawa and machine each set for the diameter of the part you want to hold.

Thanks but every item we use this to hold is different so the expedient solutions such as card stock or emery cloth, for example, seem more attractive. We'll also try Presses with Al V-block type jaws/feet, I think
That has some of the best potential, and most of the workpieces we need to unscrew would be easier to work in horizontal orientation anyway, especially when we use a chain wrench. The idea of using a different chuck is a good one for us, there's a box with many (20?) spare chucks of various types and sizes, it just isn't near the bench, but I'll be moving some there this week.

jim rozen · Jul 4, 2017

Cannonmn said:
Thanks but every item we use this to hold is different so the expedient solutions such as card stock or emery cloth, for example, seem more attractive.

Attractive fine. The jaws you are using RIGHT NOW are the exact type I would use if I wanted to avoid holding a part
securely. At least go get some stock jaws and profile the tips so they're at least reasonable shaped. You can use all the
unicorn poop you want but it's gonna be marginal at best.

Cmsmoke · Jul 4, 2017

Some valve grinding compound on the jaws or part may do the trick.

Quick way to increase hold of flat smooth chuck jaws?

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