Axminster Medium Duty Bench (BENCH2)

[Alf]

:lol: :lol: In this instance it's when the front vice jaw isn't parallel with the rear jaw, but rather "on the skew". It comes about when the jaw is exerting lots of pressure at one end (on the work) but with nothing to do at the other end (hence the spacer).

Cheers, Alf

 

[Chris Knight]

The term is used for situations as Pete basically describes in frames that become a parallelogram instead of a rectangle. Also to eg drawers that twist slightly sideways and get stuck as you move them in or out. A vice can rack if one side grips something and the other side is left free to move.

Basically racking is bad!

 

[RogerS]

Ah..more or less what I intuited but one thing still niggling. If you have a single screw vice and you mount something vertically to the right of the screw thread then surely ANY vice is going to rack since the left hand side is empty?

Roger

 

[Alf]

Yes. Unless you place the work centered over the screw. But some are worse than others.

Cheers, Alf

 

[CHJ]

:lol: :lol: In this instance it's when the front vice jaw isn't parallel with the rear jaw, but rather "on the skew". It comes about when the jaw is exerting lots of pressure at one end (on the work) but with nothing to do at the other end (hence the spacer).

Cheers, Alf

Alf
Sorry to spoil such a sensible answer, :lol: but why is it that when you divide the load/force applied by the vice jaws to the workpiece by 2 by adding a 'spacer' it holds, but if you had slackened the vice jaws to achieve the same resultant load on the workpiece without the spacer it does not :?:

The answer has serious implications re possible unseen damage to you workpiece I think. (and Roger
a reason for always balancing the jaw width on delicate jobs)

 

[Alf]

Anyone? :shock:

I'll have to think about that one. I suppose "it just does" is not sufficient explanation...? :lol:

Cheers, Alf

 

[CHJ]

Anyone? :shock:

I suppose "it just does" is not sufficient explanation...? :lol:

Cheers, Alf

No.

 

[Anonymous]

something to do with vectors, i suspect...

With the spacer, the force is applied to the workpiece at a 90 degree angle to the bench, with the force spread across the whole width of the workpiece.

Without the space, the vice jaw racks - this results in a non-90-degree angle of force on the workpiece, and also the force is being applied to a smaller area on the workpiece - the vector of the force applying at 90 degrees is lower. To acheive the same gripping force in a racking vice, you have to actually INCREASE the vice pressure, not back it off.

If I could work out how to make pretty pictures and upload em to a web site, I'd do so to illustrate (cos I've noticed my verbal explanations aren't very clear, of late! lol)

Of course, I could be spouting a load of rubbish - it's happened many times before, and will many times in the future

 

[Jake]

The racking has the effect that the vice is only exerting pressure on a very small area of the workpiece. Add the spacer and the surface area (and friction) goes way up as the jaw is now parallel to the workpiece and should have full contact. So you are much more likely to crush the workpiece if the vice racks, as you are concentrating a lot of pressure on a small area (and it will, inevitably, be the corner, too).

That's my take, for what it is worth.

 

[mudman]

Sorry to spoil such a sensible answer, :lol: but why is it that when you divide the load/force applied by the vice jaws to the workpiece by 2 by adding a 'spacer' it holds, but if you had slackened the vice jaws to achieve the same resultant load on the workpiece without the spacer it does not :?:

It isn't the force that's being applied but more of the resultant geometry.
If there is no spacer, then the unpacked side of the vice is free to move. This means that a pivot point is formed on the edge of the workpiece about which the vice jaw will try to rotate. Upshot of this is that the direction that the force applied by the vice will actually tend to push the workpiece out rather than hold it. You also end up with a the total area of the piece in contact with the jaws, very much reduced. So, as soon as you try to do anything with it, you find that the situation ain't stable and it moves.

Does that make sense?

 

[RogerS]

Is it something to do with keeping the jaws perfectly parallel and so the load is applied evenly to the workpiece? I know that with my workmate (which has two screws .one at each end) if I am trying to clamp something up (especially if a fairly short piece of work) then keeping the jaws as parallel as possible is essential otherwise the piece of work slips as you apply pressure to it.

So putting something in the other side of the vice (a spacer) will keep things paralell. If you slacken off the vice as suggested then the work is going to slip when you apply a load ?

May be it also has something to do with whether it is an all metal vice or a wooden one. For example, you know with an all metal vice (single screw) that the jaw is going to stay pretty much at right angles to the thread and so the only slop, allowing it to not grip evenly, is going to come from the thread. If you take a vice made from, say the York screw thread from Axminster, then there is going to be additional slop between the wooden jaw and the thread ...in addition to that from just the thread.

Does that make sense?

EDIT - This crossed with the other posts !

 

[CHJ]

EDIT - This crossed with the other posts !

Yes, everyone seems to be quick off the mark today, something to do with the weather prompting browser time perhaps.

Espedair Street, Jake, Barry glad to see that the schooling wasn't wasted.

Hope your explanations prompt others to think about that pretty little box next time they clamp it in the vice.

 

[RogerS]

What was that old adage about the correct torque setting?

Tighten up until the nut shears and then back off half a turn

 

[Alf]

Dammit, I actually started typing surface area but time was pressing and I didn't have time to explain myself properly so I went for the comedy answer. :roll: Didn't allow for everyone and their lunch hour stepping in and making me look like a klutz in the meantime! :lol:

Cheers, Alf