My droopy leg vise

[ok_in_iowa]

This past winter I finally built a real woodworking bench, with a killer leg vise.  I got the screw and nut from Lake Erie Toolworks, and the Crisscross mechanism from BenchCrafted.  It worked perfectly, I could run it in and out with one finger on the cross bar.  When the humidity got serious this summer, it started getting harder to work, and then got nearly impossible to turn.  I think I have two issues going on.  When I put a straight edge against the screw, it is showing a very slight bend.  I think that probably accounts for the fact that it gets a little harder to turn for 1/2 of a revolution.  The other thing is the sag.  When I take the screw out, I can see a wear groove in the clearance hole in the leg:



I took a rasp and opened up the clearance hole until I couldn't see the groove.  I put the screw back in and ran it in and out a few times and the problems returned.  It got extremely difficult to turn, and it was a little more difficult for 1/2 of the revolution.  The pic above is after the rasping and re-fit.

Here are some pics of the installation.  This is a shot of the nut installation.  I think the nut is in there solid.  I had to use a mallet to seat it, and I thought the lag screws were overkill. But maybe it has loosened up since then.  I can't wiggle the nut by hand.  I haven't tried removing the lag screws to check the fit.  


Here is a side shot to show the Crisscross installation.



So now, what do I do to fix it?  I figure I can live with the warped screw if it doesn't get any worse.  But the sagging is a show-stopper.  The ideas I can come up with are:

1)  Move the nut to the front side of the leg.  I'm not convinced this will solve the sagging issue.  It might just transfer it from one end of the clearance hole to the other, and I might not be any better off.

2) Buy a second nut and add it to the front of the leg (and they're proud of those nuts, $50 each).  I'm thinking this might be the best bet.  It will provide two points of support instead of just one.  It will be a little tedious getting the two nuts clocked with each other, but should be do-able.

3) Abandon the wood screw and go with a metal screw.  Ouch!  That's a lot of re-work and expense, but could be a solid fix.  I suppose I'd have to plug the existing clearance holes and re-drill to install a steel screw.

Do you guys have any other ideas?  Has anybody here had a similar problem?  I've been watching the forum for quite a while and don't remember seeing any problems like this.

thanks,
Steve

[Karl1163]

I don't have one, but I'm pretty sure the crisscross is supposed to keep the vise level (according to Benchcrafted's explanation).  If the screw is sagging, it seems that your problem is in the crisscross, not the nut; I can't see exactly how it is mounted, but check to see if there's been any movement in the crisscross mounting, holes wallowed out, pins bent, etc. The bend in the screw might be from failure of the crisscross causing the weight of the vise jaw to hang on it during the hot, humid summer- so once you fix things, you may be able to steam-bend the screw back to a straighter shape.
Karl

[Boatman53]

I agree I think the problem is with the Crisscross. Are the jaws still running parallel? If not then something is bent or perhaps some crushing where the lower part of the arms bear. The screw on a leg vise is capable of tremendous force, more than people realize. I haven't tried to do the math for that mechanism but it could easily be upwards of 1000 pounds where those lower arms bear.

Jim

[ok_in_iowa]

Thanks for the replies.  The pins that hold the Crisscross bars are still fairly snug.  I can just barely push them by hand.  I haven't checked to see if one of them is bent.  The chop is still parallel (mostly) with the leg.  When I installed it, it toed in slightly at the top, with maybe a 1/4" gap at the bottom of the leg.  It still toes in slightly at the top, I can't tell that the gap at the bottom of the chop has changed any.  The chop still lines up flush with the edge of the top (although the top of the chop is now slightly below the top of the bench), and it still grips work as well as it ever did.  It's just that turning the screw is so difficult that I'm afraid to use it now for fear of damaging the screw or the tommy bar.

[Karl1163]

It looks like the lower arm ends of the crisscross are made to ride against the wood in the bottom of the slots of the jaws, right?  From the pictures, it seems your moving Jaw is oak, but the stationary one (the leg) is Doug Fir or similar soft wood - use a depth gauge or combo square to see if the slot bottom has worn/ crushed in - at that distance from the screw, just a little bit "off" may lever the screw a lot. If that's the problem, you could fix it by milling out the slot evenly (again) to allow you to place a mild steel bearing plate in the slot so the lower arm end doesn't dig into the softwood.  That's the way it looks over the Internet at least - good luck
Karl

[theoldfart]

The criss cross lower end of the arms ride on a steel plate on both side so that should not be an issue. I have the same set up as yours but the hole in leg is much larger than yours. My bench is DF for the legs and oak for the top. The chop is maple and cherry laminated.

[ok_in_iowa]

As OldFart says, there is a metal plate at the bottom of the groove where the leg rides.  If you look closely at the pics above, you can just barely see it at the bottom of the groove.  I didn't let the metal plate into the bottom of the groove, I just dropped it in the groove and attached it. 

I've been trying to figure out how the force vectors would all work out, but it's a fairly complicated system.  There are multiple support/pivot points: the four Crisscross bar ends, the center pivot point and then the chop hanging from the screw, which is a lever with a pivot point at the nut.  I can't figure out whether the Crisscross could actually resist sag, and if so, where would it need to be adjusted to correct the problem?  Should I try shimming the bottom Crisscross bar contact point on the leg side?  Would that counter-act the sag?

thanks for the responses,
Steve

[AUswimKC]

I believe the answers to your problems are laid out in the crisscross instructions.

http://www.benchcrafted.com/PDF%20Files/...pr2013.pdf

A quick once through of the instructions shows there are a few different reasons and solutions.  I would read and re-read and re-read them very carefully. Their instructions are very through and you're the only one looking at the bench in the flesh.

Don;t give up, I went through several iterations with my leg vise and crisscross too

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shimming the bottom will counteract the sag well - only at that specific jaw opening depth. Could cause other problems throughout the screw travel

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from Benchcrafted: "Here's a critical step: You need to position the vise
s nut and fasten it to the bench leg so its in
line with the movement of the Crisscross."

Sounds like an easy solution is to drop the nut

[theoldfart]

I would shim the leg side, that should bring the chop up. I would think a 1/16" should do it. Also check that the base of both crisscross morrises are paralell too each other as well as the contact surfaces. Make sure the shim underlays the entire steel plate.

[Adnick]

I have the classic version of the crisscross and at first I installed at the height recommended by one of the famous workbench books, the screw handle was way too low so I then put a much larger chop on mine and raised the screw hole.

In the first instance I did not install the little support bearing/ring that the screw rides on, and it worked fine, but my thought is that without that support bearing/ ring the screw hole would wear at the bottom.....I have a huge chop, it weighs almost 50 lbs and rides just a few thou off the floor, with no sag issues at all.

I'm would bet that's what's happening on your vise. Would not shim the crisscross arms unless you cut the slots too deep, the vise requires toe in to work properly.

I can take pictures of the support system if you need them