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hornluv
08-03-2006, 11:35 AM
I'm making a small, very light duty vise and was thinking of just pressing an Acme nut into the fixed jaw (which is CRS). Should I turn the nut down a bit so there is more contact or can I rely on the points of the nut to hold it? Is the nut going to be hardened? How undersized should the hole be? As an alternative, how difficult is it to tap acme threads?

Thanks,
Stuart

pcarpenter
08-03-2006, 12:26 PM
I am having a hard time picturing the design you are attempting to build. I have a Bridgeport vise and a Kurt vise and in both cases, the nut is in the movable jaw and the leadscrew is held fixed.

I have another milling vise in which the "nut" is at the tail of the leadscrew and the screw moves through the body of the vise pushing the movable jaw forward.

Still can't picture the nut in the movable jaw because as you move the jaw, you end up with lead screw sticking out of the jaw.

All that having been said, something, a pocket and a roll pin, or something has to hold the nut in place. Otherwise the forces you make with the vise will just press it back out. I would look at a round bronze nut of some sort. There is no need to go with a hardened nut as the threads on the lead screw will just be the next weak link. Usually something softer is used and the nut is treated as a wear-replaceable item.

You may want to look for bronze acme nuts on McMaster.com The cheap way to go may be to buy a bronze or brass acme hex nut and turn it round on the outside.

Paul

Evan
08-03-2006, 12:26 PM
You will need to fasten it somehow or what you will discover is that you have made an acme nut puller. For a light duty vise pressing it in and then brazing it should work well. You can make the hole about .020" smaller than the point to point diameter of the nut. It will broach grooves in the hole when it is pressed but still needs to be held by something more secure.

Tapping acme in steel requires a LOT of force and a good tap.

Mike Burdick
08-03-2006, 02:30 PM
Stuart,

There are numerous ways to accomplish your objective – just depends on your requirements and loads. For example: one could machine the nut round with a flange on one end. That way the nut could be inserted into the vice such that the flange would take the compression force when clamped. To keep the nut from turning and coming out when the vise is opened, one could either fit it with a keyway or simply install a set screw such that it fits into a ‘dimple’ on the nut. This way no welding is needed and the nut can be any material desired.

JPR
08-03-2006, 03:05 PM
To continue on Mike's idea of using a flange. Once pressed together, drill an 1/8" hole where the nut and the body meet (a simple key way) and insert an 1/8" pin into the hole. You can stake the hole or use locktite to keep it from coming back out.

http://img.photobucket.com/albums/v228/jpr2004/nutinstalled.gif

hornluv
08-03-2006, 08:06 PM
To answer Paul's questions, I guess it isn't really in the jaw, but more like the threaded hole inthe back of a drill press vise. The vise is going to be on a bending jig I am making. The part with the nut pressed in it will be fixed to the edge of a steel plate and the movable jaw will hold a piece of tubing against a block attached to the center of the plate. I was thinking I would have the nut pressed in and facing the movable jaw so when it is tightened, the nut is pressed in, so it won't come out. If that doesn't make sense, I'll provide a drawing or two. In the meantime, all of you have answered my questions. Thanks a lot.

Stuart

C. Tate
08-03-2006, 11:41 PM
I would suggest tapping the hole. If you want to save the expense of tapping then turn it round and press from direction oppisite the most force. Leave a shoulder for the nut to seat against. This will allow you to tighten the vise and lessen the chance of pulling the nut out. Remember it will still be possible to push it out. The dutch key will prevent turning but will not prevent the nut from being push or pulled. You could fix it place by placing a button head screw over the edge of the nut.

Evan
08-04-2006, 12:04 AM
I still say silver solder or brazing. It has a shear strength about the same as steel and will become one with the force. :D

giddingm
08-12-2006, 12:06 AM
It's just like anyother tap but much longer to gradually give you the full thread form. An Acme tap is quite expensive....If money is a concern it would be cheaper to just buy an off shore vise. If you turn a small shoulder the nut will sit nice and square to the axis of the screw.

LarryinLV
08-12-2006, 05:27 PM
Drill your through hole no larger than the diameter of the screw that will extend through it.

Broach a square hole perpendicular to the through hole about 1/8" in from the end. The broach should be the size of the distance across the flats of your nut.

Drop the nut in the broach, capture it with your screw. It'll stay there forever or until you unscrew from it.

Edited: I suppose it could be easier to toss your nut and just make a mini T-slot at the end. Then just slide a piece of flat stock in the groove - drilled and tapped of course.