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isaac338
10-27-2008, 09:08 AM
When I bought my compressor (for dirt cheap), the guy I got it from had an old Brazilian-made (iirc) vise sitting on the floor. Apparently his kids had used a cheater bar and stretched the screw, and he was tossing it out. He let me throw it in my truck.

The vise works for most of its travel but in the last 3-4" it binds up and won't close any further. I haven't gotten around to measuring the screw but it sure sounds to me like it's stretched around that point. It's not visibly damaged, however.

My only ideas for fixing it are making a couple of really thick (like 3" or more) jaws to take up the slack (which isn't the best because I'll lose that capacity), or buying a new screw. Is there anywhere to buy replacement vise screws? Are they generally all the same size (for a 6 or 8" vise), or do I have to take some measurements and shop around?

I could just go buy a new vise but I'm a poor university student so I've gotta make do with what I've got.

lynnl
10-27-2008, 09:38 AM
I dunno about buying a replacement vise screw, but I'm sure most of the mail order suppliers sell acme threaded stock, usually in 3' and 6' lengths.
I know I've seen it in Enco's catalogs.

Just measure the size and pitch (tpi) of your screw - probably somewhere in the neighborhood of 5/8" to 7/8" for a 6-8" vise (just a WAG on my part), and order some. It's been awhile since I've looked at one of those ads, but I recall it being pretty inexpensive.

Of course you'd have some machining to do on it to use it in your vise. ... maybe a retaining ring on one end, and a knob on the other to engage the movable jaw. ...or you maybe could weld on the old knob.

ptjw7uk
10-27-2008, 10:08 AM
Sounds more like the screws bent remove it and see if its bent.
Then have a go at straightening it with a big hammer - you have nothing to loose.
If the thread was stretched you shpuld see signs of where it is binding.

Peter

SGW
10-27-2008, 10:27 AM
You'll probably need to make it, and it might be a metric thread....but metric threaded rod can be had, too.

As others have said though, the first thing to do is take it apart and find out exactly what is going on.

isaac338
10-27-2008, 11:06 AM
Yeah, I've had it apart and I can't see any visible stretching on the screw. I'm thinking maybe it's stretched just enough to mangle the threads but not enough to be obvious (I didn't think about measuring the diameter in a few spots when I had it apart).

I'll take it out again and check the diameters and see if it's bent, and see if I can track down a source for acme threaded rod in Canada. Guess I'll be buying some acme thread pitch gauges :D

bruto
10-27-2008, 12:04 PM
Before you go too far with the screw, make sure the vise closes properly with the screw removed. It doesn't take much to make a vise bind if something else is bent.

isaac338
10-27-2008, 12:36 PM
Before you go too far with the screw, make sure the vise closes properly with the screw removed. It doesn't take much to make a vise bind if something else is bent.

Yeah, thought of that - I think it works well without the screw, but I honestly can't remember actually checking, so I'll check again. Thanks!

biometrics
10-27-2008, 12:39 PM
Once disassembled, does the nut spin freely on the screw when not attached to the vise? if so, the jaw is somehow binding in its ways or slots... find the bind and eliminate it. If the nut binds on the screw under these conditions and the jaw moves cleanly... then buy or make a new threaded rod and matching nut to get the vice back in operation. It would be a good weekend project.

isaac338
10-27-2008, 12:57 PM
Once disassembled, does the nut spin freely on the screw when not attached to the vise? if so, the jaw is somehow binding in its ways or slots... find the bind and eliminate it. If the nut binds on the screw under these conditions and the jaw moves cleanly... then buy or make a new threaded rod and matching nut to get the vice back in operation. It would be a good weekend project.

Maybe I'll call Visa, get a credit limit bump, and go to princess auto and pick up a 9x10 lathe ;D

Your Old Dog
10-27-2008, 01:23 PM
$5.00 says it's bent and not stretched. Think about it, you got a 4 foot cheater bar on it cause you can't find the 7 foot cheater bar, if the movable end of the vice is suspended and/or held on one side only it pulls in a canted position. Long before you would stretch the screw on a normal vice you would bend the screw. YMMV.

dp
10-27-2008, 02:29 PM
There's a possibility the screw is twisted. If so put that 7 foot cheater bar on there and unwind it a smidge.

Scishopguy
10-27-2008, 02:40 PM
A simple test you can perform to check out the screw thread is to put a little spotting blue on the threaded shaft and run it up to where it binds. THe threads are usually a pretty loose fit in most bench vices. If you don't have any spotting blue you can also use a sharpie marker. Where it binds you will see the marker rubbed off. This will also work on the slide. Sometimes the cause of these things will surprise you.

isaac338
10-27-2008, 04:41 PM
Well, the screw's not bent as far as I could tell (just by quickly laying it on a relatively flat surface and checking for light underneath). It is, however, stretched a bit - the diameter goes down by about .6-7 mm where it binds, and the thread pitch goes up by about .30-.40 (I don't remember the exact numbers).

Looks like I'll be finding the administrator of the machine shop at school and trying to bribe him to give me some lathe time :)