Screwless vise screw stripped, why?

After looking at all of your pictures, I suspect you need to get into the habit of locating the nut so the screw engagement is only about one diameter. I think you have been trying for maximum screw/nut engagement which makes the screw too vertical and causes the interference.

Also, for any given vice design, there is an optimum screw length, so you might take a look at whether or not a different screw length would be advantageous.
 
extropic said:
So the screw is not being stripped at all. Instead, a couple of threads are being damaged because of interference with the moveable jaw.

Does your vise include the hemispherical washer?

I think that kind of damage can be caused by the operator trying to get too much jaw movement without resetting the the nut into the next slot. That would be my guess here.

Alternatively, the clearance hole for the screw may need to be slotted a bit to allow more angle on the screw.
You could also just turn the threads off of the screw in the area of interference. Turn that area leaving a witness of the thread root. The screw will not be weakened.
Click to expand...
Yes. Exactly!

Yes.

Quite likely. The issue happened once every 2 months or so, but it did happen 3 times. Not trying to be greedy ;) on hole position, but sometimes it happens. When the vise is mounted it's not easy to tell if the nut is in the more "correct" slot. Seems I mess it up once every 2 months! I suppose if I used a longer stud and nut the angle of the threaded element would be more obvious.

My easing of the edge is making a little more clearance for the screw. It is easy to take more off if required.

Deliberately turning the threads there is an interesting idea.

I'm going to monitor the thread condition and see if there's any further evidence of wear. Guessing that the removal of the sharp edge and easing will eliminate the issue.
 
extropic said:
After looking at all of your pictures, I suspect you need to get into the habit of locating the nut so the screw engagement is only about one diameter. I think you have been trying for maximum screw/nut engagement which makes the screw too vertical and causes the interference.

Also, for any given vice design, there is an optimum screw length, so you might take a look at whether or not a different screw length would be advantageous.
Click to expand...
I could go a length smaller in the screw, say from 40mm to maybe 35mm. Don't want to go too short or the nut will fall off too often. That's a royal pain to get the screw back in while the vise is bolted to the table.
 
Converting to using a stud and nut solves all the problems. Easier to to see the angle of the stud and the stud will be providing a handle.

Besides, then you will NEED to make a nifty looking custom nut. :grin:
 
Sounds like a project in the making :)

If I'm going to implement your suggestion - might as well upgrade the nut down below. The cross pin appears to have gouges in it. At the very least I need to replace the pin. I'm going to have to machine off the pin since it doesn't easily press out. I removed the set screw, but the pin doesn't budge. I'll try a punch, it that doesn't work then I'll machine it and then use a punch.
What material should on use to make the pin? O1? 4140? Something else?

What steel is suitable for the nut? Would 1144 be ok or do I need to go to an alloy steel?
 
Considering that you intend to use a stud in new nut, I would have no reservation using 1144.

I recommend using a hardened steel dowel pin for the cross pin in the nut.

McMaster-Carr sells metric 12.9 threaded rod for your stud. Don't change the diameter from the original screw unless you want to wrestle with clearance problems.
 
The pin that was there wasn't hardened. It is rather beaten up. I was just looking at dowel pins on McMaster. Wasn't sure if I needed to use the hardened version or not. Is the alloy 52100 the correct stuff?

Grade 12.9 stud M8 50mm long = $18, 100mm long = $19, 300mm long = $22. More expensive than I thought it would be. May spend the extra $4 to have a few spare pieces.

Have enough 1144 to make the nut, both top and bottom one if necessary.

Goodness, I was using this vise to make a part to fix my lathe. Once I finish that, I need my lathe to make a part to improve the vise. Going around in circles, like a dog chasing his tail ;)
 
WobblyHand said:
Is the jaw edge machinable with a carbide end mill? Or is that just flushing money? It's no fun to break end mills.
Click to expand...
I'm not sure how consistent the hardening is for different parts of the vise & throughout, may also vary from different manufacturers & batches. But I was able to machine part of one of my vises with a carbide end mill (was just a minor plunge cut though). The first slot was not drilled properly so I fixed it.

Third subject in post #49

20200310_165137.jpg
 
Installed the new hardened dowel pin. Looks to be much better than what I had.

Finished fixing my lathe (different thread) so I can make the stud and nut mod. Have the Grade 12.9 M8 all thread. Think I will make the nut first, then cut the stud to be ~15mm longer.
 
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