Tuesday, April 11, 2017

Swivel Head Attachment

Swivel heads are what goes on end of the screw in a C-clamp.  I need something like that which screws on to 1/4"-20 bolt once it is through the threaded hole.  Swivel is not required.  I could also make it myself from a small cylinder with a tapped hole.  Suggestions.

Called toggle pads, about $6 each.  May have to make my non-swivelling version.  Probably use a parting tool on the lathe to make 1" cylinders, then drill and tap 1/2" deep 1/4"-20 threads.
Made one pretty quickly.
Some of you reminded me that on a screw, the length should be twice the diameter.  Is this for tension, or compression?  This won't ever be in tension  Good news is that I estimate there is 15 seconds of labor making these if I do it in quantity.  Material cost is near zero, so at $20/hour, about eights apiece. 


Will said...

1/2" thick should be ok. Is it a thru hole, or blind? Either way, the screw should be locked in some manner, especially if the screw end is close to the outer (working) face. If the screw tip bottoms out, you could potentially distort the face, leaving you with a high spot that could reduce your clamping force.

How close to full face contact do you need on that? Unless the screw can wiggle in some manner, you are unlikely to get good contact. Too many variables to get consistent surface engagement from part to part. Drill, tap, and parting off on a lathe would help to make the cylinder consistent, at least.

What about using a chair/stool foot that uses a swivel pad?

Clayton Cramer said...

Will: Blind hole.

Will said...

On second thought, you are more likely to dimple the face by running the tap end into the bottom of the hole, but a standard tap won't let the screw get all the way to the bottom. You don't want to run a second (bottom) tap into the hole, probably. (more time, effort)
Consider grinding the tip of your tap to a flat or gentle radius, so it will be less likely to create that dimple. You could use some sort of travel limiter on the tap, instead.

Tension or compression, the threads won't see any practical difference.
What is the foot/pad going to be sitting against? How much force is involved? If it loses tension and things shift around a bit, is that a problem? If it marks/dents the surface? Basically, I'm bothered by the fact that the pad can't accommodate for any misalignment of surfaces.

Since this is for clamping force, you really don't need the pad to be threaded to the screw, you just don't want the pad to fall off during installation/adjustment/removal. I'm wondering if you could use an o-ring to capture the screw. Drill the oversize hole on the lathe, then cut the groove for the ring, and then part it off. Consider pressing a ball bearing to the bottom of the hole to distribute the clamping force. This won't deal with large angles like a true swivel joint, but it should be much better than a fixed pad, and it won't tend to rotate with the screw.

Clayton Cramer said...

Will: Dimple not a problem. Small dimple makes a tiny mark on the wood, quite acceptable.