A Twin-Screw Vise Revolution

[George Neill]

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.

There are many different applications for sprag clutches. I know the miniature sprag clutch on my Kawasaki starter motor slides onto the starter motor's round shaft and the one in my friend's electric wheelchair is also perfectly circular.

[Mark Koury]

Only one problem: The more I think about it a one-way roller clutch can tighten but will not be able to loosen the wedged rack. So we are back to an oval shaft in an oval hole that can transmit rotational energy 2 ways - - or a keyway on the shaft.

[George Neill]

Only one problem: The more I think about it a one-way roller clutch can tighten but will not be able to loosen the wedged rack. So we are back to an oval shaft in an oval hole that can transmit rotational energy 2 ways - - or a keyway on the shaft.

An oval shaft in an oval hole wouldn't provide any more contra-rotation than a sprag clutch.

But contra-rotation isn't necessary. The physical jolt of un-doing the vice would be enough for the pressure to be removed from the train and the springs would then back off the clutches sufficiently for them to free the guide bars again.

[Mark Koury]

An oval shaft in an oval hole wouldn't provide any more contra-rotation than a sprag clutch.

Seems to me that oval in oval has equal torque in either direction — But, a roller clutch is no doubt one way.

[George Neill]

An oval shaft in an oval hole wouldn't provide any more contra-rotation than a sprag clutch.

Seems to me that oval in oval has equal torque in either direction —

Quite right, I was thinking of cams.

[Will Blick]

> The issue is how does the shaft move the small gear?


Well all have OCD disorder :-)


We all agree, the handle turns the pinion gear.... whether its a keyway, oval, sprag, etc. IMO, that is not relevant, and its not the brilliance of the design. There is many ways to make this portion functional.


We all agree the rack is angled, when the pinion gear moves the rack, the angled side of the rack pushes one side of the disc. (tighten function) When the disc is angled, it first bites the bar, then proceeds to push it further back. This is is the breakthrough IMO... its what separates this bench vise concept from all others...


I guess it's nick name should be "on-demand Quick Release vise"...as no matter what length the shaft, the system is always a 1/2 clockwise turn from fully tightened.


Now, more small stuff...

I would vote against the oval shaft, cause this makes the disc arbor hole harder to make and to remain free flowin after some abuse....hence why I think I keyway makes the most sense to turn the pinion gear.

The pinion gear must be cammed, or would be always fully engaged in the rack... I don't see away to escape camming it. No big deal...its all CNC'd anyway.

Anyway, what is the possible pitfalls? Its the disc on the shaft...to keep the vise trouble free, the contact point inside the disc must constantly bite and push the shaft, while at the same time, not damage it....cause the shaft must ALWAYS move freely through the two white bearings.

This leads me to beleive the contact point of the disc to the shaf is also key'd. Now, any roughness created by the constant bite n pull will be located internal in the shaft, i.e. not on its circumfrence.....and therefore NEVER will subject the white bearings to abuse. Quite clever.


My guess is, we are not seeing everything in the picture..... but if I was to design one after this thread, that would seem like the most sensible approach for a maint. free vise.

[George Neill]

The shafts must be cylindrical and not ovoid, otherwise the clutch discs (stack of three per side) would require internal holes to match the cross section of the shafts. The problem with that would be the threaded adjusters would not operate consistently. The clutch discs can't be keyed to the shafts either for the same reason.

If you watch the video as the drawer is tightened in the vice, as the left hand shaft is rotated, its profile doesn't appear to change, nor is there any sign of a keyway.

[Mark Koury]

The pinion gear must be cammed, or would be always fully engaged in the rack.

I believe it IS always fully engaged. The small gear doesn’t move, except to rotate. The rack only slides side to side. So full engagement should be the normal condition.

The idea of a keyway to engage the disk is interesting. That would prevent gouges in the surface of the shaft that would eventually destroy the white bearings. However, this would require the keyway to end up always at the bottom (as seen in the picture) because the screw that produces the counter leverage to the disk is always at the top and doesn’t move.

In other words if the shaft, when it is fully tightened, happened to end up with the keyway (that the disk rode in) at say 9 o’clock instead of 6 o’clock (where the leverage against the screw would be maxima) there would be loss of force.

I think you have hit upon the Achilles heel of this design. There will be gouges in the shaft (unless it is major league hardened steel) that will cause wear to the bearings over time. If the shaft is hardened I wonder how well a single clutch plate would work - wouldn’t it slip?

[George Neill]

I wonder how well a single clutch plate would work - wouldn’t it slip?

The clutch plates are in stacks of three.

[Mark Koury]

The clutch plates are in stacks of three.


Gee, looks like one in the picture.

[George Neill]

Have a look...

[Mark Koury]

OK - I agree.
Stack of three.

[Michael Peet]

This has been a very interesting thread, watching you guys reverse-engineer this thing. It looks like a cool concept.

Mike

[george wilson]

Some of you are over complicating this vise.Some are not comprehending how i said it works,and need to re-read my post.

The shaft,first of all,has the surface of an ordinary piece of cold rolled steel,which I work with all the time. It is not a machined surface,nor is it available in an oval shape,a very important consideration for his first prototypes. You'd have to order many tons of it to get it rolled oval,and it does have a rolled surface. Cold rolled steel is pretty accurate,+- .001",so it is good to go right out of the package.

Mark,the keyway has nothing to do with engaging the washers(there do seem to be 3).The keyway is only to engage the pinion gear.

UNLESS the keyway is made TOO SNUG a fit on the key,there would be no increased problem of jamming. As a machinist,I can tell you that.

Will,the gear always DOES stay engaged in the rack. Why would it not need to be? There is no cam,plain and simple.

If there are 3 washers,I have changed my mind about the function of the long,thin screw(LTS). Now I think it just bears against the top edge of the washer stack,preventing it from leaning over against the gear. There is a strong spring to keep the stack in tension sideways. At rest,I think the washers rest against theLTS,on their top edge,and against the tapered rack at their bottom edge. There may be a flat spot at the end of the tapered rack to keep the washers square when at rest,so the shaft will slide freely. When the tapered rack moves sideways as the vise is tightened,the spring forces the washers to stay against the LTS,while they lean sideways to pinch the shaft.

I also have re-thought this: multiple clutch clamps do not mar their rods,so perhaps there is enough of a grip from the 3 washers that the shaft is held well enough,and without being damaged.

I will also point out that IF the shaft were oval,its LONG axis(of the oval) would always have to end up vertical,or the washers would not grip it.

The main benefit I've gotten out of all the posts since my "discovery" post,is that there are 3 washers. I'm going back to the first or second page after I write this,and look at the better picture there. I didn't notice 3 washers there,though my eyes aren't what they used to be with these cataracts.

EDIT: now I went back at the better lit picture on page 2. I really cannot see that there are 3 washers in that photo. I wonder if the upside down photo from under the bench is a lighting aberration. It doesn't really matter,1 or 3,I really think my assessment of how the vice works is correct. It is a very clever bit of engineering,too. If there are 3 washers,the LTS could not be tapped into them,and would have to just be a stop,and now I think that it would in any case just be a stop with the spring pushing the washer(s) against it.

Here's MORE proof that the ends of the rack are tapered larger. Look at the above picture a few posts up. Look at how much wider the rack's base is closest to the camera. And,that's way too much to be simple perspective.

[Mark Koury]

I still vote for a slightly oval shaft - mated to the same oval hole in the gear. The disks would have a larger round hole that would allow the shaft to rotate in the disks. A slight oval shaft (though still oval enough to grip the mating hole in the gear) would not effect the grip from the disks - no matter what position the shaft was in.