A Twin-Screw Vise Revolution

[Mark Koury]

Neat machine!
I’ll have to buy one.

How it works - my take.
In order to turn the small gear the shaft has to have a keyway (doubt this - old approach) or is machined slightly oval. Since the rotation used to tighten is less than 180 degrees (see movie) this would make sense. Once the small gear with a mating oval center is engaged by the oval shaft and begins to turn, the wedge-shaped rack moves and wedges against the oblique metal disk so that it becomes a clutch and clamps against the shaft to lock it. The screw seen at the top of this disk (on the picture) is to vary the amount of tilt and thus the clamping pressure of the disk on the shaft.
Mark
http://www.sawmillcreek.org/attachme...1&d=1278944715

[george wilson]

Oval would be very complex to make. I wonder if somehow when the shaft is tightened,it causes the sharp edged washer to tilt MORE,jamming the shaft against the washer.

That off center gear rack looks like it could move sideways a bit and run into the bottom edge of the washer,jamming the shaft in the tilted hole in the washer. HOW the rack moves sideways,I don't know. The pinion gear's teeth do not seem cut on an angle that would cause it to move the rack.

[Mark Koury]

George,

Follow the energy. First the shaft has to transmit rotational energy to the small gear.

It has to be an oval shaft or a hidden keyway. One other possibility, which I doubt, is a one-way tight fitting roller bearing assembly in the small gear. This would seem expensive to make and subject to wear.

In this day-and-age I think an oval shaft would be easy to make with a CNC machine. The small gear moves the rack. The rack is a flat wedge (see the other original picture). As the wedge moves side-ways it pushes on the lower edge of the disk forcing it to clamp on the shaft. The screw at the top of the picture is to vary the amount of tilt and thus the clamping force.

Interesting Problem!

Mark

[Will Blick]

Great contributions....

Mark, yes, I fully agree the shaft is probably keyed, I should have mentioned that in my first post, its the easiest way to engage the pinion gear while still allowing it to float (in/out) when the two gears are not meshed. Rounded shaft too costly and complex.... of course it makes sense this is not exposed in the pix - to avoid giving too much away....

>As the wedge moves side-ways it pushes on the lower edge of the disk forcing it to clamp on the shaft.


Agreed, this is very similar to what I expressed....except with the disc tilting method, the disc takes on both roles, t actually bites the shaft (holding force) and the rack is wedged as we all suggest.... so the rack pushes the disck backwards with a half turn of handle.... total movement probably even smaller than I first suggested, maybe only a 1/2".


If this is correct, the challenge is keeping that disc tight enough to the shaft, so over time, the tilt consistently bites the shaft without slippage. Very similar to a round bar clamps...... some have movable back jaws using this same premise. While in my experience they do slip over time (as both the disc and pipe wear), in this case, the clamp is not used for long term glue ups, like 24 hr expoxy holds....so even if it wears, a slight re-crank will keep the piece tight.... so good enough.... here is pix of tilted disc that bites a shaft....

[george wilson]

I think we are on the right track:the rack is pushed over to pinch the washer on the shaft.I still haven't been convinced how the rack is pushed sideways. Keep thinking,guys!!

I agree,there must be a keyway.

P.S.: Is this the blindingly brilliant solution I have been waiting for? IF the EDGE of the plate that the rack gear is sitting on is tapered,as the rack moves sideways,it would indeed press on and tilt the washer and bite the shaft. As the shaft is turned to tighten the vise,the shaft and the washer would be forced sideways . THE WASHER ITSELF WOULD MOVE SIDEWAYS A BIT ALSO,TIGHTENING THE VISE AGAINST THE WORK. The TOP edge of the washer's hole(which cannot rotate due to the little long bolt that is capturing it,could be rounded a bit,while the BOTTOM edge of the washer remains sharp. The shaft can slide past the ramp formed by the lower edge of the washer's hole IN THE DIRECTION OF TIGHTENING. However,the shaft would be bitten by the much steeper angle of the hole's edge if it tried to go BACK. There isn't much motion needed,as suggested. Just a little bit,since the vise jaw is brought into contact with the workpiece before tightening,as is a black plastic Irwin type clamp,previously mentioned by a member(of which I must have over 50) before the trigger is squeezed,but not used in the same way as the clamp. There is a small hole in the edge of the cast iron frame right where it would align with the side of the rack's plate. Wonder what it is for? A set screw to bear against?

The weak spot: Those white plastic collars(bearings) could wear after some use and screw up the whole operation,especially if the round shaft gets little nicks in it from the washers gripping it. I wonder how long they would last? I think reasonably close tolerances would be needed for this design to work.

If anyone thinks I'm wrong,study what I've written carefully,write your rebuttal on a $20.00 bill,and send it to me ASAP!!!

PS,I edited this several times,so I hope it makes sense,as I don't feel like writing it all over again.

[Mark Koury]

George,

The rack is engaged by the small gear and moved sideways. The issue is how does the shaft move the small gear?

I mentioned a roller bearing assembly before. Strange, but I ran into what I was thinking about, today on eBay. Does anyone recall the roller drive socket handles that were made 20 or so years ago? I found one for sale today and checked on the patent (no. 4408504). If you search for that you will find this diagram that I uploaded. This is a one way rotational device that would work in this situation allowing the shaft to slide in and out. If you recall the problem with these is that you have to remove the drive center and insert it on the opposite side to apply torque the opposite direction. The roller clutch only works one way. That, however, is perfect for this situation. Cost and reliability - - who knows?

Mark

[george wilson]

Mark,re-read my heavily re-edited explanation. I'm sure my idea is correct. The small gear does not need to be moved,except to rotate. That could be done via a key way we can't see in the picture.Nothing fancy. The whole trick is the tapered rack's edge. The gear's rotation moves the tapered rack against the washer.

Having a one way clutch mechanism in the gear accomplishes absolutely nothing. Think about it.

[Mike Brady]

George is very close to being right on this issue. I don't believe the shaft has a keyway at all. We have seen the shaft from above and below in the videos and stills. The oval shaft theory works, as does this mysterious clutch mentioned above in the ratchet wrench post.

That set screw looks like it prevents the tilting washer clutch from over rotating and thus damaging itself or the shaft. It obviously is an adjustment to limit the travel of the clutch.

One hitch: Wouldn't a 1981 patent still be in force?

[george wilson]

It would be very easy for the inventor to hide the keyway in each photograph. Something has to turn the shaft and gear,and an oval shaft,and an oval hole in the gear would be the most expensive way to do it.

However the gear is made to turn,I'm more interested in how the vise tightens,and I do think I figured it out. It was a nice bit of engineering.

P.S. I have re-read all the posts,and Will mentioned "wedge" a few times,but he was not specific about what was a wedge. He seemed to think the gear teeth were angled. I think he was nibbling around the edges of the secret.

Mike,you explain to me how a clutch mechanism in the gear would accomplish anything.

[Mark Koury]

George,

I agree! But, that’s really what I’ve been saying all along. The small gear doesn’t “move” except to rotate. Now, what makes it rotate? You say a keyway. That’s surely possible but the other explanations are more elegant. The gear slides the flat wedge shaped rack that then bears on the bottom (in the picture) of the disk and forces it to tilt and clamp on the shaft - locking it. The screw at the top limits the tilt of the disk and thus the force against the shaft. The shaft doesn’t interact with the disk except to be clamped by it as the disk is forced to tilt against the shaft. Thus, when the shaft is turned to the left - the rack moves, releasing the wedge against the disk. The disk is no longer tilted and the shaft can then slide in and out. The same clutch mechanism as noted before that is seen on a pipe clamp. The only thing fancy here is: what moves the small gear?

Mark

[Mike Brady]

You said it yourself: "Something has to turn the shaft and gear". The shaft also has to slide in and out in the quick release action. I think the key and keyway are too prone to jamming to be reliable. I think that a splined shaft would work but clearly there are no splines present.

I wasn't too impressed with the robustness of the vice at the chop. I couldn't tell if there is a garter arrangement of any type. I also would find to two spinning handles to be a pain. I suppose one could be eliminated.

Another potential problem is that if you don't close that vise evenly on your workpiece, the "timing" of the tensioning action could be off and your workpiece could be loose on one side or the other. I don't think that the "screws can be tensioned separately, can they?

I will be particularly interested in the Chris Schwarz evaluation. I just finished installing a Lie-Nielsen twin screw on my new bench. I'm not worried about that one failing in any regard.

[George Neill]

It has to be an oval shaft or a hidden keyway. One other possibility, which I doubt, is a one-way tight fitting roller bearing assembly in the small gear. This would seem expensive to make and subject to wear.

As I mentioned a few posts back, they are called sprag clutches and would cost a few dollars for this size. They are used in everything from motorcycle starter motors to heavy lifting cranes.

[George Neill]

Another potential problem is that if you don't close that vise evenly on your workpiece, the "timing" of the tensioning action could be off and your workpiece could be loose on one side or the other. I don't think that the "screws can be tensioned separately, can they?

Funny, I was just looking at the photo of the unit again and I am now in agreement that it is the rack bar that provides the wedging movement that activates the clutch disc and no cams on the back faces of the pinions. If the rack bar moves the clutches, then it can't go out of timing.

A clue to the wedging action of the rack is visible in the photo: If you look at the cast housing, on the far side of the rack there is a wider gap between the rack and housing. Surely that is to allow for the width of the tapered bar which is also on the correct side for the necessary action to move the clutch.

George, the plastic bearings would be one of the longer lasting items of the whole design.

[Mark Koury]

Looks like a sprag clutch has essentially an oval shaft.

I admit I don’t know how the socket handle that I noted works. I suspect that it too has an oval center drive portion and similar to your sprag clutch has one way roller bearings. Seems to me that a less complex solution would be simply an oval hole that the oval shaft goes into. Since this is not a motor or a transmission the constant torque doesn’t have to be managed, so a simple oval hole in the small gear should work.

[George Neill]

I think I'm now ready to make one of these vices (once I get a foundry to cast and mill the housings! ).

The guide bars slide freely within sprag bearings in the pinions, but when the guide bars are rotated clockwise, they activate the sprags which rotate the pinions. The pinions move the rack latterly and the tapered section of the raqck bar acts against the clutch discs, which grab the guide bars, locking them within the cast housings.

The threaded adjusters and lock nuts keep the clutch discs on the cusp of grabbing the guide bars so that very little movement of the clutches is required to lock it all up.

When the guide bars are rotated anti-clockwise, the wedging force is reversed and the springs on the guide bars return the clutch discs to the neutral position allowing the vice chop to be moved at will.

I believe the expenses of the whole set-up (in order of cost) would be the machined castings, the rack bar, the hardened guide bars, the clutch discs, the pinions, the sprag clutches, the plastic bearings, the threaded adjusters and the springs.