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Thread: LV Twinscrew owners - How tall for the Jaws?

  1. #1
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    LV Twinscrew owners - How tall for the Jaws?

    I've found tons of LV twinscrew threads but cant seem to find what I'm looking for. I know you need a minimum 6" tall jaw height, but what are you using? Right now I'm planning a 4" workbench top that would need a minimum 8-1/8" tall jaw if I'm doing the math correctly and give me a throat depth of about 4-1/2". For some reason this sounds pretty tall and I'm wondering about thinning out 2 channels underneath the top for the screws (maybe down to 3"). What's everybody else using?
    Use the fence Luke

  2. #2
    My bench is 3" thick and jaws are 7.25"

  3. #3
    Hello Doug,

    You're doing the math right, depending on how you'll mount the nut flanges.

    Say it's a 4" top. If the nut flange (which is 3"x3" square) is flush up against the bottom of the benchtop, then the centerline of the main screws will be at 4" + 1-1/2" (half the flange height) = 5-1/2" below the benchtop. Then you need another 2-5/8" below the screw centerline to accommodate the thrust plate and its housing, for a total of 8-1/8". So that checks.

    Now you calculated the screw centerline at 4-1/2": To do that, you would need to mortise the nut flanges into the rear of the rear jaw (which is a good idea). Edit: Note that if you do place the screw centerline at 4-1/2", then the total jaw depth could be an inch less, or 7-1/8".

    I am using 8" deep jaws, with the screw centerline slightly above 4-1/4". This places the top of the steel studs (which keep the work off the greasy screws) at about 3-1/2"--so the gripping depth is 3-1/2". This works, but I wouldn't want the screw centerline much deeper, because you're beginning to lose gripping power at the top of the vise.

    Caution: Opinions follow....First, your idea of the 1" deep channels on the underside of the benchtop is very good--in order to keep the screws a bit higher, and therefore preserve a strong grip at the top of the vise. Second, LV's suggestion about mortising the main screw nuts into the rear of the rear jaw is a very, very good idea. What that does is provide direct support for the screw very close to the point where the screw exits the rear jaw--that is part of the solution to jaw sag. My third suggestion is to eliminate any clearance above the screws--use zero clearance. LV suggests 1/16" clearance, but that is going to let your jaw sag, and you can virtually eliminate sag if you eliminate the clearance. Zero clearance does not impair the screw operation, because the screw threads will run always in the same track, and they will burnish the track and run smoothly (they're greased). Eliminating sag is particularly important if this is an end vise. I have photos of the zero clearance installation if that would be of any interest.

    One other thought is that LV recommends putting a vertical taper on the inside face of the front jaw--approx. 3/32". This is important, in terms of taking up the slack in the mechanism as you tighten the jaw. For the somewhat deeper jaws you're describing, I would use 1/8". The method that LV shows to make the taper works perfectly, provided you or someone you know, has a lunchbox planer that you can put the jaw through.

    Wiley
    Last edited by Wiley Horne; 09-08-2007 at 7:26 PM. Reason: Clarification

  4. #4
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    Wiley
    Thanks for the detailed reply. There's some things there I wouldn't have considered. My 4-1/2" throat depth figure wasn't a calculation but a rough guess eyeballing the manual diagram. I was estimating the distance between the top of the screw and the bottom of the bench and adding in the other known values. I'd forgotten about the steel pins taking away some of that height though. I think I either missed the part about mortising the nut into the back or glossed over it as I thought it part of the instructions specific to mounting it on LV's thinner bench. I'll re-read that but it sounds like a good idea. The zero clearance idea sounds like a simpler alternative to the rub-strip suggestion in the manual. Maybe if the nut flange was mortised in I wouldn't even need the channels or maybe just a small pocket behind the flange? I'll have to measure and check the math and see what that means for the jaw height and throat depth (with the pins this time). One thing I definitely have to check is the size of that nut flange though. I could have sworn I measured that at 2-3/8" square today rather than 3".

    One other thing I noticed after posting earlier was that there doesn't seem to be any mention of a suggested jaw width distance outside of the screw holes unless I've missed that too. There doesn't seem to be a dimension given on how far the cover plate extends past the centerlines either. I was trying to work backwards from
    (bench width) - (suggested distance from jaw ends to centerlines) = center-to-center spacing I'll need to use. I better get the tape out and do some calculating there too.
    Use the fence Luke

  5. #5
    Doug,

    I'm going to interline with your post.....

    Quote Originally Posted by Doug Shepard View Post
    ...I'd forgotten about the steel pins taking away some of that height though. I think I either missed the part about mortising the nut into the back or glossed over it as I thought it part of the instructions specific to mounting it on LV's thinner bench. I'll re-read that but it sounds like a good idea. "

    LV's instructions mention the mortising as a way to increase the jaw-opening distance. When you do the math, you will decide that it ain't worth mortising to get an extra inch of jaw opening, when you already have a bunch. BUT--if you are concerned about jaw sag, that inch becomes important. Remember that you've got a heavy front jaw cantilevered out beyond that nut. As you open the vise, there is less and less length of screw supported behind the nut, and more and more screw cantilevered beyond the nut. It makes a material difference to get that nut as close to the rear jaw exit as you can--IF you care about jaw sag. By the way, the above reasoning is also why it is useful to have a rear jaw that is close to minimum (1-3/4"), rather than making it big and heavy. The thicker it is, the longer the cantilever, unless you mortise.

    "...The zero clearance idea sounds like a simpler alternative to the rub-strip suggestion in the manual."

    I am suggesting that, even if you use a rub strip, to let the top of the screw actually rub on the rub strip. That 1/16" clearance that LV recommends just gives the screw license to do that much sagging. But if you snug the screw up against either the bottom of the bench, or whatever spacer you end up needing--you can just about eliminate sag, especially if you do the mortising thing along with it.

    "... Maybe if the nut flange was mortised in I wouldn't even need the channels or maybe just a small pocket behind the flange? I'll have to measure and check the math and see what that means for the jaw height and throat depth (with the pins this time)."

    The screw diameter is a tad over 1". So it is possible, with the screw directly laying against the underside of the bench, to put the screw centerline at 4-1/2". My vise works OK with a 4-1/4" centerline, so yours will work OK with a 4-1/2" centerline. The mortising would allow you to use 4-1/2". You would end up with a throat depth above the steel studs of 4-1/2" - 1/2" (to top of screw) - 3/8" (approx. offset of steel stud) = 3-5/8", say 3-1/2", which is plenty, believe me. I believe you would be happier long -term if you use the channels, but it is a complication in a couple of ways, and the vise will work with the 4-1/2" screw centerline. But please use 1/8" taper on the front jaw.

    "... One thing I definitely have to check is the size of that nut flange though. I could have sworn I measured that at 2-3/8" square today rather than 3". "

    I just went and checked mine. Bumped my head a lot in amongst the drawer runners. Anyway, I get 2-3/4" square, not 3". LV's drawings show 1-1/2" as the distance from screw centerline to outside of flange, because they're assuming you'll give yourself 1/8" leeway. My vises are a few years old now, so things could have changed.

    "One other thing I noticed after posting earlier was that there doesn't seem to be any mention of a suggested jaw width distance outside of the screw holes unless I've missed that too."

    Doug, this is an interesting observation you've made. It's hard to discuss this one in detail without knowing if you're doing an end vise or a front vise installation (I have twin screws for front and end vises). But basically I have found that clamping space outside the screws is very beneficial. I know that the intuitive thing is that you'll be clamping inside the screws. But for many applications, I've found that one of the best things about the twin-screw is the ability to clamp outside the screw. Bottom line: don't be afraid of having clamping room outside the screws. Is your vise front or end?

    "There doesn't seem to be a dimension given on how far the cover plate extends past the centerlines either. I was trying to work backwards from
    (bench width) - (suggested distance from jaw ends to centerlines) = center-to-center spacing I'll need to use. I better get the tape out and do some calculating there too.
    I have the metal cover plate on mine. It extends approx. 2-1/2" (laterally) beyond the screw centerline on each side. I don't see a 'suggested distance from jaw ends to centerline', but I may have missed something. My advice would be, if the post placement is not controlling, to use at least 4" outside the screws just because this is very useful clamping real estate. However, there are other considerations: For example, if it's a front vise, you might want to limit the vise length, in order to keep more of the bench front unobstructed. Whereas if it's an end vise, you want the jaw running from end to end. Hard to get past these generalities without knowing a lot more about the bench design.

    Wiley ..... apologetic to have run on so long (it's a favorite topic

  6. #6
    My bench top is 4" and 8 1/8" sounds about right for my jaws without measuring, installed per the instructions. I have not had any problems.

  7. #7
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    Wiley
    As long as you keep doing all the hard work for me, feel free to run on at will. The twinscrew is going to be my end vise. I've got a Tucker going on the front LH (Geez Rob Lee's been getting a lot of my money lately ). At the moment, I've got my bench length nailed down at 78" (at least I think it's finally nailed down) but am going through the mental gymnastics to get the width figured out. For right now, lets say it's 26". It's also going to sit on a set of Noden Adjust-A-Bench legs which are 17" wide. I'd like to not center the legs under the top, but set them back as much as I can. The screws will straddle the Noden leg panels. So the setback legs would want a wider screw spacing for the sake of the rear screw clearance, but I also like the idea of having a bit more wood outside the screws. So I've got a few variables to juggle that could include possibly going a bit wider with the top, or having the legs be a bit closer to center than I would have otherwise liked. I think all the help you gave me plus doing a bit more measuring and cipherin should let me get the width figured out tomorrow.
    I'll check that nut flange again tomorrow and let you know if I was off or whether they're making them smaller now.
    Use the fence Luke

  8. #8
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    Max and Kelly (your's slipped in while I was typing the last reply) - Thanks for the measurements.

    Wiley
    You're right. It's 2-3/4" not 2-3/8" for the nut flanges.

    Still doing the rest of the math on figuring out the bench width, location of the legs on the width, and the jaw width.
    Use the fence Luke

  9. #9
    Doug,

    My friend Konrad Sauer has had a Tucker vise for a while now, and he's pretty ecstatic about it. Money well spent.

    One more thought on the clamping space outside the screws, and how it relates to doing dovetails....

    It turns out (for me at least) that the best place to transfer marks from the tails board to the pins board is at the corner of the bench, using the end vise. You can clamp the drawer front (to be marked) vertically outside the screw, bringing the end grain flush with the bench top, or a hair proud. Then lay the drawer side with tails to be transferred over top of it, and clamp it down. Tap the tails board with hammer to get exact adjustment, then give clamp one more quarter turn. Then mark, with everything cinched down.

    Point: The clamping space outside the screw of the end vise turns the corner of the bench into a great place to do joinery operations (for me, at least.

    Wiley

  10. #10
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    Well I've been monkeying with the figures most of the afternoon and it looks like I'm going to end up with a 28" bench width and the screw centers at 22-1/2". That's only going to give me 2-3/4" past the centerlines on the end but will allow me to get the rear screw into a 3-1/2" space on the back side of the Noden leg and gives me a 7-1/2" offset from the front of the bench to the front of the Noden leg. The only way I was even able to make this bench fit in my limited space is to use the single rail brackets and the under-bench area for storage with the bench raised to max height while not being used. Without the off-center leg mounting, there's just no depth to that storage area. Oh well - a compromise driven by needing to share my shop with a vehicle.
    Use the fence Luke

  11. #11
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    OK - with Dave Da-Man Richard's help, I got the basic geometry of this sketched out and have another question.
    For right now, I haven't decided on the joints for the hardwood edging and am just showing these butted but will probably go with dovetails for the LH end. I'm wondering about the RH end that is also the rear twinscrew jaw though. I'm wondering whether I should avoid gluing it on and just use the method LV's instructions show, using the cross dowel nuts to bolt it on? Or could I (should I) go ahead and glue it on as well as dovetail it to the long edges? I'm not sure I like the idea of a thinner glued on table edge then the thicker jaw bolted to that, but if that's what I should be doing, I want to figure that out now as it will affect the plywood core length.
    For right now I'm just showing the jaw height without implementing any of the other earlier height issues. And the strange notch in the left front corner is where the Tucker will reside so that the rear jaw face is flush with the bench.

    Benchtop3a.jpgBenchtop3b.jpg
    Benchtop3.skp
    Use the fence Luke

  12. #12
    Doug,

    Is there a hardwood benchtop over the ply core? I'm assuming so....

    I suggest dovetailing the hardwood edging into the rear jaws. For a coupla three reasons. First, it strengthens the assembly a lot, aligns it, and provides an interlock which takes some load off the rear jaw bolts. That is, if you dovetail, with the tails on the long boards and the pins on the rear jaw, then the vise load against the rear jaw is resisted not only by the bolts in the rear jaw, but also by the dovetail joint plus the bolts in the edging. Essentially the dovetails unitize the rear jaw with the edging. As a bonus, that corner at the jaw is a very functional place on the bench, and the dovetails lock it up tight and square and plumb.

    Second, glue on the ends is inevitably going to be long grain to end grain, which doesn't do much for you. And you have the hardwood top moving cross grain to the end cap, so if you glue top to end, something may have to give depending on climate. Dovetails kinda solve that problem: At least in my climate, the dovetails have just enough give to accommodate the cross grain movement through the seasons. Whereas if you had steel fasteners tying the rear jaw to the edging, you might need a special slotted washer assembly to accommodate the movement (depending on your climate in the vicinity of the bench). Plus the steel fasteners through the rear jaw would end up probably 4 inches into the edging boards, and it's kinda nice to have a doghole in that edging close to the end of the bench, and if you dovetail, you can put it where you want it.

    Now if you do decide to dovetail, please don't glue the joint. First off, you want it to have just a little give. Second, if it's a nice joint, you're going to need to hammer it home with a good-size mallet (given those thick boards), and it'll hold just fine without glue. In fact, it'd be quite a job to get it apart, even without glue. But if you do use glue, once it's halfway home, forget it--nothing to do but get a bigger hammer when it starts slowing down on you. So if you go dovetails, don't use glue, just do a nice sawing job, and put it together once and that's it. I think tails on the long boards, because that creates max. resistance to the load on the rear jaw. You'll be amazed how stout that jaw is on there with dovetails plus the bolts.

    Oh, and it looks cool, too. My 2 cents.

    Wiley

  13. #13
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    Wiley
    No hardwood top. It will look like the one Sam did on this thread
    http://www.sawmillcreek.org/showthread.php?t=22081
    The DT's like the one's he used were also what I was thinking about using. I also forgot to mention that the black slabs are representing the Noden Adjust-A-Bench legs this will sit on, and I don't have the connecting rail or it's mounting brackets shown on the sketch yet. I'm going to read through the rest of your reply while at work today to make sure I got it all.
    Thanks
    Use the fence Luke

  14. #14
    Oh, OK. The Baltic birch ply will make a fine top, and I agree to just do what Sam did. Since you'll have no expansion in the core, gluing the dovetails just becomes a practical matter for you to decide. On my bench, I was dovetailing apron to rear jaw, and both boards were 8" x 2-3/4" in cross section. Glue was neither needed or wanted. But with the ~4" x 2" cross section on these boards, two tails and one pin, I would glue it, and it won't present the problem I kinda overstated above.

    That's a nice design!

    Wiley

  15. #15
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    OK. This SU stuff is sloooowly coming to me. I managed to get these done. Dont have the changes in centerline height from the earlier feedback done, but I mainly wanted to check the screw and leg panel proximity. Managed to get my horizontal ply layers cut today as well as strips for the verticals out of what was left. Need to figure out how much I need for vertical strips and pick up some more.

    Here's a shot underneath. It's just gonna fit.
    Benchtop5a.jpg

    From the end.
    Benchtop5b.jpg

    And got rid of all the ugly butt joints.
    Benchtop5c.jpg
    Use the fence Luke

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