I seemed to have missed this topic. Great idea John. I've been wanting some punch tongs and tools for them for a while so I can get my hand farther away from the hot stock. I don't like wearing a glove so I thought they would be a good alternative.  I really like the cam idea. I haven't tried making any because of the problem with variation in sizes of the tools and jaws as you pointed out. You've found a pretty elegant solution. Kudos. 

Pnut

Thank you!

For special purpose tongs, such as these, why couldn't you rivet an offset handle to one of the reins so that, in holding larger material, there is almost a second Rein that can comfortably be held?

 

That is a very interesting thought. Before I do that, however, I want to see if adjustments to the jaws and the reins will eliminate the problem. I just need to get another cylinder of oxygen for the oxypropane torch first.

I like your thinking, though.

Overdue update:

On 10/12/2020 at 2:08 PM, JHCC said:

It occurs to me that these might be good for upsetting under the treadle hammer, for holding workpieces that are on the short side. Hmmm....

This turned out to be quite true, and reason enough to leave these tongs as-is. Another pair for smaller tools is on the project list.

New developments!

I was discussing these with Willow Zeitman at Prospect Hill Forge, and she had the bright idea to make a twist-tong version from 1/4” x 1/2” flat bar. I then had the idea that the loop of the outer V-jaw could be made by bending the bar the hard way and fastening it with the same rivet as the pivot for the tongs. 

And of course, the proof of the pudding is in the punching, and it worked great.

You can see not only the twist in the reins, but also the integral loop at the end to hold them shut. 

Very nice work.  Looks like something I'm going to have to knock out soon.

Those are so neat  it makes me want to make a whole set.  Maybe when I retire. . . 

Meanwhile, I have a (relatively) simple idea for an adjustable rein, if anyone's interested.  Cut off the rein for the inside jaw, leaving a stub a couple of inches long.  Make a new rein, split so it will straddle the existing joint; drill it for a longer rivet.  Offset the new rein so it will sit outside the stub rein, and drill and tap it for an adjusting screw that will bear on the stub rein near the end.  

A variation would be to make the split nearly as long as the stub rein, and thread the stub rein through so it ends in a flat section that extends a little below the crutch on the outside of the split.  Then set up the adjusting screw so the head pulls the stub rein in toward the split one.

I’m having trouble envisioning what you’re describing, Mike. Could you post a sketch of what you mean?

I think the answer is "no, I can't," but you can "draw" your own conclusion.

The outside jaw/rein is orange, the inside jaw and "stub rein" are dark gray, and the "split rein" is blue.  In addition to the leg you see, the split rein would have another blue leg on the back of the joint, with the split ending somewhere between the joint and the bend (as drawn).

The other version I suggested would have the gray stub rein running inside the split (which would extend further down the blue rein).  The end of the gray stub would emerge on the right to pass under the head of the screw.

And I haven't quite decided, but I might go with a right-hand screw 

 

I don't see how it works Mikes, maybe sketch it in different positions of adjustment so we can see what changes? Right now I see a pair of tongs with an adjustable stop and from your description that's not close.

Frosty The Lucky.

I think I get what you're saying: the dark gray and the blue together make up a composite tong half, where the thumbscrew adjusts the angle between the cam arm and the rein. In other words, if you're using a thicker punch, you adjust the screw to allow the rein to close more, and if you're using a thinner punch, you adjust it to keep the rein from closing too much. Sound right?

That makes more sense, I can see the idea working, worth a little experimentation for sure.

Frosty The Lucky.

Yep — that’s it. 

One other thought, though this may have become obvious when you adjusted the tongs:  In the current configuration, the inner jaw moves almost parallel to the outer jaw when it closes on the punch.  This gives a high mechanical advantage and a very tight grip, but it also makes the rein position very sensitive to punch thickness.

If these were set up like conventional tongs, with the concave jaw and the cam facing each other above the pivot, the two bits would move directly toward each other and there would be a lot less mechanical advantage.  Of course, apart from weakening the grip, that would mean that the punch was aligned with the reins, making the tongs useless for their intended purpose. 

But you could try something in between, for example by moving the business end of the concave bit a little closer to the joint and adjusting the angle so the punch was perhaps 70 degrees to the reins instead of 90 degrees.  That would reduce the mechanical advantage some and make the grip somewhat weaker.  But it should also permit the tongs to reasonably hold a wider range of punches.  You could put bends in the reins themselves (i.e. on the side of the joint closer to where you hold the tongs) to bring them back to 90 degrees.  

Of course, the trade-off between grip and versatility might or might not be worth it.

Nice brainstorming Mike, I LOVE brainstorming. 

We're striking the punch which conduces the force to the work, the tongs only need to hold it firmly enough not to move till you strike and prevent it from getting away from the user afterwards. 

I've been thinking of different "cam" configurations so all the user needs do is make contact with the struck tool and any movement in the direction of impact tightens the grip without added effort from the user. 

An eccentric is as easy as cutting a round disk with an off center the axle. What John forged as the cam jaw is the same principle and a lot lighter than a disk or a section of one. 

The question we're playing with now is how to make the close jaw eccentric enough to grip a range say from 5/16" to 3/4" while only rotating on the tong pivot maybe 15* for the purposes of discussion.

Frosty The Lucky.

This may not matter in the end, but I'm a little skeptical about the "self tightening" concept.  It seems like the object should be to keep the punch from forcing the tongs open, not necessarily to wedge it into the jaws as tightly as possible. 

 

What seems important here (maybe) is that when the punch wants to twist in the jaws, it's trying to push the inside jaw directly back into the pivot (which it obviously can't do), rather than pushing the bits apart as it would in conventional tongs.  That seems to me like the aspect of the geometry we should focus on. 

The cam would squeeze the punch into into the jaw towards the pivot IF the punch moved at all.

I've never experienced tongs being spread holding a struck tool, punch, chisel, even some of the really odd chisel and punch shapes. The only "special" feature is a half round groove across the bits of otherwise pretty standard round stock tongs. 

If I we still interested in making tongs I'd maybe give John's design a try once he tweaks it a bit. Were I to make another pair like my current ones I'd make them much smaller than standard working tongs.

Frosty The Lucky.

23 hours ago, Mike BR said:

I'm a little skeptical about the "self tightening" concept.

Don't be; experience has shown it to be a real phenomenon. Basically, you want the tool pointing in the same direction that the cam jaw moves as it closes. This means that the force of the hammer blows will tend to pull the cam farther into the V, tightening the grip. 

On the other hand, if you position the tool so that it's pointing in the opposite direction, the hammer blows will tend to push the cam out of the V, loosening the grip. I have observed this many times.