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Can Toggle Clamp Joints Have Bearings?

09/28/2009 11:55 PM

I am designing a toggle clamp device. Due to design considerations it is little heavy.

I am driving it through lead screw. As you know to make the screw self locking I have to keep efficiency less than 50%.

And since I am driving the lead screw manually, I was suggested to put needle roller bearings at toggle joints to reduce driving torque (theoretically its 10 N.m).

Now, my doubt is that, if I use bearings at toggle joints, will they creat problems in toggling action.

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#1

Re: can toggle clamp joints have bearings

09/29/2009 1:23 AM

I am not sure of the concepts here, especially the 50% "efficiency" criterion. If the angle of the lead screw is less than the inverse sine of the coefficient of friction (minus safety factor) , the screw should hold its position. Also, if the toggle mechanism incorporates an over-center feature (as would be normal), the bearing can't hurt, and it will almost surely help. A drawing would clarify matters.

If the lead screw angle is very small, it will take many turns to advance the screw. In this case, a split nut may be useful. (Spread the nut to move the clamp close to the work, then engage and lock the nut, and then tighten down the clamp.)

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#2
In reply to #1

Re: can toggle clamp joints have bearings

09/29/2009 1:37 AM

yep,

screw will definitely hold its position & wont rotate/move unless rotated manually.

Actually its inverse tan of coefficient of friction

So, I think this will not pose any problems.

If the mechanism reaches to toggle position then even if there are bearings in joint the lead screw wont let move.

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#3

Re: can toggle clamp joints have bearings

09/29/2009 2:09 AM

You might be right about inverse tangent rather than inverse sine, but the screw would slide along the hypotenuse, which is why I am thinking sine. At small angles, say <= 10 degrees, these numbers are nearly equal. The over-center issue will probably dominate over this consideration, anyway.

If the cycle rate will be high, I would be inclined to include the needle bearings as originally suggested.

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#4

Re: Can Toggle Clamp Joints Have Bearings?

09/30/2009 1:31 AM

Needle bearings are for precision applications and require precise alignment in operation. That is; no cantilever forces via say shaft bending or mount deflections. Secondly, all 'rolling' bearings have less load capacity than a plain bearing of equal dia & width.

Your application 'runs up to contact' at 'no load' then exerts a large force at virtually 'no movement'. What you should consider is "PermaGlide" aka Teflon alloy bushes. For a 'slow', 'very high force', 'imperfectly aligned' motion, these are "perfect".

The coefficients are available from most bearing suppliers, and are far more toward a greased rolling bearing than 'self lubricating' bronze or similar used conventionally in such clamps. Be mindful you DO need a 'polished' shaft for these bushes to perform and last.

Re the screw; have a look at how "Hi-Low" vices work. This might 'solve' run up speed - if this is an issue.

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#5
In reply to #4

Re: Can Toggle Clamp Joints Have Bearings?

09/30/2009 3:20 AM

thanks for your reply.

As far as bendng forces are concerned, I dont see any problem as the pin lengths are very small & have high FOS. So Needle bearings can be used.

And again in toggle action my clamp (having rubber pad at clamping surface) will be pressing against an object, pressing the rubber pad by 3 mm, so very high force wont come.

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#7
In reply to #5

Re: Can Toggle Clamp Joints Have Bearings?

10/01/2009 8:26 AM

"very high force" is in the context of the mechanism bearing load resolution.

Ref "the pin lengths are very small & have high FOS"

In typical 'toggle', pins are 'left and right' so separate.

Are they 'always in line' ?

In Solid Works animator - yes.

In life - not so likely.

This might be equivalent to "bent shaft"?

I recommend more thought.

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#6

Re: Can Toggle Clamp Joints Have Bearings?

09/30/2009 3:21 PM

Check screw jack come with most cars.

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