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sbmathias
12-07-2010, 03:23 PM
In an unusual situation, I need to INcrease the friction on some threads. I have a couple of homemade wooden clamps (similar to those at http://www.justclamps.com/wooden_hand.htm). Some of them loosen by themselves when I clamp them down. This makes them pretty useless. It seems that the pitch is too great, but they are standard 3/8-16 single start threads. They appear to be galvanized.

Anyone have any ideas on how to increase the friction? I've thought of pouring sand into the nuts, or epoxy, but none of those seem to be very good options.

John Stevenson
12-07-2010, 03:31 PM
There is a grease that achieves this, can't remember the name but we bought some once, or my customer did to help some micrometer adjusters from working loose all the while.

Sorry can't be of more help.

BillTodd
12-07-2010, 03:43 PM
There is a grease that achieves this, can't remember the name but we bought some once, or my customer did to help some micrometer adjusters from working loose all the while.

Sorry can't be of more help.

Try a search for Traction oil or grease. The stuff is formulated to increase friction when squeezed, for metal on metal traction drives etc.

However given this is a wooden clamp, how about some rosin? (as used on violin bows etc.).

Bill

Frank Ford
12-07-2010, 03:47 PM
Are you sure the threads are unscrewing by themselves - i.e. is the handle turning? I'm just remembering that it took me a little while to learn to use that kind of "hand screw" clamp effectively. . .

The corrected link:
http://www.justclamps.com/wooden_hand.htm

TRX
12-07-2010, 04:06 PM
Hmm, the link came up "page not found."

Anyway, if the body of the clamp if thin enough, you can deform the threaded section with a vise, a hammer, or a punch, to create something similar to a self-locking nut.

If there's a thick section you can drill into, you can drill, tap, insert a piece of lead shot or plastic, and then run a set screw down on top of it; tighten the screw until the feel is to your liking.

Otherwise, you might be able to put a hardware-store coil spring between the main body and the foot, to preload the threads.

Rich Carlstedt
12-07-2010, 04:27 PM
On the side opposite the starting side for the thread, take a ball bearing and set it in the tapped hole and hit it with a hammer.
This will make the last thread deformed enough to create drag, but not enough to destroy the threads or make it impossible to use.
The ball should be about 50 % larger than the thread.

This is a trick apprentices use to make the instructor think they have a great thread fit !

Rich

MotorradMike
12-07-2010, 04:41 PM
On the side opposite the starting side for the thread, take a ball bearing and set it in the tapped hole and hit it with a hammer.
This will make the last thread deformed enough to create drag, but not enough to destroy the threads or make it impossible to use.
The ball should be about 50 % larger than the thread.

This is a trick apprentices use to make the instructor think they have a great thread fit !

Rich

Now that is a brilliant but deeply flawed idea!

Alistair Hosie
12-07-2010, 04:57 PM
I have a number of these clamps and have both medium priced and expensive ones and never had a problem.Frank is correct though you need to think about how to use them properly as twisting one handle tightens and can slacken at the same time depending on the angle of the piece being clamped.Alistair

sbmathias
12-07-2010, 05:41 PM
Yes, I do know how to use them. When I tighten both on a part, the handle furthest from the part does rotate and loosen itself. A strategically-placed vice grip is my temporary fix.

One minor problem is that these are difficult to disassemble and get to the nut threads. The handles are glued on tightly, so will take some messing around to remove. May have to make new handles. Anyway, I'll try some of these solutions. I like the rosin suggestion, although I don't have any lying around. Thanks for the many good ideas.

Sorry about the bad link. Looks like the "automatically parse links" picked up the adjacent close parenthesis.

lynnl
12-07-2010, 05:42 PM
What I'd be tempted to try, is painting a thin coating of linseed oil on the screws and let that dry.

But I'd probably do a test first to make sure it didn't gum up too much.

Forrest Addy
12-07-2010, 06:54 PM
Nah! Rosin and alcohol. Paint a little on your wood clamp threads and no more slip. It will squeal and creak like hell, though. Works good on leather soled shoes too. Go to a music store and buy a chello rosin thingy. Crunch up a little piece and dissolve it in alcohol or just sprinkle the dust and mall crumbs on the threads.

Frank Ford
12-07-2010, 07:12 PM
For a quick/easy semi-temporary way to increase drag, just wind a big rubber band around the clamp body and threads of the offending screw.

I do try to keep the jaws parallel as I tighten, but I typically give a last turn on the outboard screw to get a little more grip out at the ends of the jaws. Mine have pretty loose fitting screws, but I've never seen one unscrew itself.

Peter.
12-08-2010, 09:08 AM
If the clamp is similar to those in the link could you not drill & tap a hole in the end of one of the pins and fit a thumscrew to lock the clamping screw. a small brass or nylon end would stop the threads getting marred.

whitis
12-08-2010, 12:01 PM
On the side opposite the starting side for the thread, take a ball bearing and set it in the tapped hole and hit it with a hammer.

I was thinking the same thing. Don't get too enthusiastic with the hammer, though. It is quite possible to make the threads too tight. Have a tap handy in case you overdo it. If you don't have a ball bearing, you can use a cone shape, a pin punch, etc.

Evan
12-08-2010, 01:21 PM
"Lubricate" the threads with a bit of honey. It will stop slipping.

drof34
12-08-2010, 05:33 PM
Unscrew the threaded rods completely and screw a 3/8-16 lock nut to near the handle, place a flat washer on the rod and screw the rod back in.

Weld a 1/4" dia. x 2" long rod to the nut to eliminate the need for a wrench.

It might be beneficial to rotate the internally threaded rod ( in the wood )180* so the long threaded rods are pushing against unworn threads.

Paul Alciatore
12-09-2010, 05:46 PM
I used a simple trick to keep the height adjustment screw on my quick change tool holders from changing position. I simply lay two or three lengths of fishing line in the hole and then put the screw in. It takes up the space between male and female thread and seems to last for quite a while. You may have to renew it more often in an application like a clamp. But fishing line is dirt cheap.

Of course this assumes that the screw is removable.

Another thing you may try is a small amount of cooking oil. It seems to gum up quite nicely. Probably the cheaper, the better. Use sparingly.

dp
12-09-2010, 06:35 PM
You want damping grease from Nye Lubricants.

http://www.nyelubricants.com/products/damping.shtml

Evan
12-09-2010, 07:35 PM
Oil or grease of any type is the wood worker's enemy. You don't want to be contaminating the wood with even a trace of grease picked up from a clamp. That is why I suggested sugar in the form of honey. It does a wonderful job of making the lid on the jar hard to remove.

h12721
12-09-2010, 08:37 PM
What kind of Pitch is used on the thread so that it unscrews it self?
You mention Home made!
I have about twenty of these clamps and non ever came loose.
H12721

thebigron
12-09-2010, 08:47 PM
I used to have a bathroom door that shut itself on occasion. It depended on the exact location it was left in and whether or not the air conditioner ran forcing the door shut with air, and of course being a bit out of plumb. I solved the problem with a bath of Coke-Cola on all three hinges. It becomes a bit sticky when it dries a little. Worked for 10 or more years and now we had it off the hinges for a new wooden floor that was added last year. After cutting the bottom off 3/4 ", I can't get it to stop creeping toward a closed position. It's not near the problem now as it will only go to the 1/3 closed position and stop. Good luck!

sbmathias
12-09-2010, 09:37 PM
What kind of Pitch is used on the thread so that it unscrews it self?
You mention Home made!
I have about twenty of these clamps and non ever came loose.
H12721

Yeah, it's pretty weird. The clamps are homemade only in that I bought the hardware somewhere (Rockler?) about 30 years ago, and made the wooden jaws. Saved a ton of money, no doubt. Anyway, the threaded rods are about 3/8" threads, but are double-start, after closer inspection. Not sure if this is standard for this kind of clamp, but obviously it is a bad design in my case.

dp
12-09-2010, 09:49 PM
Oil or grease of any type is the wood worker's enemy. You don't want to be contaminating the wood with even a trace of grease picked up from a clamp. That is why I suggested sugar in the form of honey. It does a wonderful job of making the lid on the jar hard to remove.

I thought the clamps were wooden - don't think it was specified what material they would clamp. In any event I misunderstood the original post. I thought the threads were loose, not coming loose as in unwinding. Grease won't help. He needs a square or buttress thread.

Paul Alciatore
12-09-2010, 10:48 PM
I think you need to clarify what the female threads are made of wood or metal and what kind of whichever it is.

You say "threaded rods", "galvanized" and about 3/8" diameter and to me that implies metal, probably steel. But even if the rods are metal, the female threads could still be wood.

Toolguy
12-09-2010, 10:59 PM
It's probably the double start thread. In a 3/8 - 16 that equals a 3/8 - 8. Too coarse of a pitch. They probably did it that way so you don't have to twist all day to open or close. If you change that to a 3/8 - 16 single start they probly won't come undone on their own.

sbmathias
12-10-2010, 03:02 PM
Boy, this is getting confused. The clamps are wooden jaws, as shown in the illustration link. The screws are steel, and they go through steel nuts that are cylindrical, with the (two-start) acme threads transverse through them. So, all the threads are steel. The cylindrical nuts pivot in holes in the wooden jaws. And, they do unwind after you tighten the clamps - the fit of the threads is fine.

I agree that the problem is the double-start threads - this makes the pitch pretty steep. However, not all of my clamps, made from similar hardware kits, have this problem. I don't have any other commercial clamps to compare the threads with, so don't know if this is common or not. Changing the threads to single pitch would involve making all new screws (each has right- and left-hand threads) and new nuts.

Evan's suggestion of honey is attractive, although it might also be attractive to the local ants we have occasional invasions of. They found the sweet in the threads of the cough syrup lid in the bathroom just a few days ago!

Paul Alciatore
12-11-2010, 12:08 AM
So it is steel on steel. I repeat my suggestion of cooking oil, inexpensive brand. Just a drop or two on each one.