Author Topic: Two bolt versus single bolt clamps.  (Read 5441 times)

Offline Anzaniste

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Two bolt versus single bolt clamps.
« on: July 18, 2013, 05:42:15 AM »
I recall reading or hearing that a single bolt clamp on a shaft was better (more efficient ) than a two bolt clamp for transmitting torque. By this I mean that the clamp ring has one split in its circumference or two splits.

Is this true?  and if so why?

For the purpose of this discussion I am assuming the clamps in both cases to be similar widths and thickness's.
Scrooby, 1 mile south of Gods own County.

Offline Lew_Merrick_PE

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Re: Two bolt versus single bolt clamps.
« Reply #1 on: July 18, 2013, 10:34:08 AM »
Anzaniste,

If I am reading your question properly, you are referring to circumferential split collar clamps.  Correct?

If so, then the advantage usually lies with the dual-split, 2-screw version.  The reason is that you can more accurately match the true round shape of the shaft and still make longitudinal adjustments.  With a single-split, 1-screw version the form taken defaults to a slight clearance between the collar and the shaft to allow longitudinal adjustment.  When clamped, you only (usually) get three points of contact between the collar and the shaft which reduces the overall area of contact over which friction works.

Hopefully I have answered the correct question.

Offline Anzaniste

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Re: Two bolt versus single bolt clamps.
« Reply #2 on: July 18, 2013, 11:33:31 AM »
Lew, thanks for your comments.
Yes, you are answering the right question.
The clamp in question would be bored to be a transitional fit on the shaft and in the one bolt case the gap would be temporally opened up with a wedge to position the collar along the shaft.
In case you are wondering about such a bonkers arrangement it is the fixing method for the sprockets on the back axle of a pre war chain driven Frazer Nash.
Scrooby, 1 mile south of Gods own County.

Offline Arbalist

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Re: Two bolt versus single bolt clamps.
« Reply #3 on: July 18, 2013, 01:17:25 PM »
Have you got any pictures/links for the two types?

Offline Lew_Merrick_PE

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Re: Two bolt versus single bolt clamps.
« Reply #4 on: July 19, 2013, 12:02:07 PM »
Arbalist -- If you go to the Ruland website (http://www.ruland.com/) you will see lots of examples.

Anzaniste -- The problem with wedging it open is that can (and often will) deform the collar leaving you with the 3-point contact I cited previously.

Offline Jonny

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Re: Two bolt versus single bolt clamps.
« Reply #5 on: July 20, 2013, 02:57:21 PM »
The clamp in question would be bored to be a transitional fit on the shaft and in the one bolt case the gap would be temporally opened up with a wedge to position the collar along the shaft.

That's the only sure way to grip shafts and items where you don't want to collapse tubes. I make my own and also do a product of similar idea.

Slightest nip on 1 screw they grip like a gorilla on almost the full circumference of the round. Of course need a decent fit and pays to wedge them open when sliding on. Caught me out recently wondered why there was some very very fine scratches on a pressure vessel, thought it were cracks.

Other similar way is to split a decent fitting bore open, same as above but this time the wall thickness very thin so forms to o/d of tube or round, still grips like a gorilla.

Now when using the two screw method, one either side you have two halves. When tightening up unless the two halves flex its only gripping at one place crushing round and tubular items.

Offline Lew_Merrick_PE

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Re: Two bolt versus single bolt clamps.
« Reply #6 on: July 21, 2013, 12:40:52 PM »
Now when using the two screw method, one either side you have two halves. When tightening up unless the two halves flex its only gripping at one place crushing round and tubular items.
First of all, the request deals with a shaft and not a (thin-wall) tube which means that crushing should not be an issue.  I design and manufacture such things with fair regularity for military and aerospace usage.  Such usage ends up requiring a visco-elastic test series as part of acceptance testing.  I have yet to pass a single-screw clamp under such conditions.  Dual-screw clamps pass easily.

There are no circumstances in which I would use an off the shelf clamp on thin-wall tubing (unless the longitudinal load was trivial).  It is a different issue with different boundary conditions which requires a different solution.

Offline Jonny

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Re: Two bolt versus single bolt clamps.
« Reply #7 on: July 21, 2013, 09:26:16 PM »
It is when you don't or cant afford to mark finished high value products done up excessively tight. That in itself will demonstrate it has a far greater circumferential grip at less bolt torque offering less deformation on product.

Two part clamps can only possibly crush the job or deform the clamp itself. That clamp has to flex and stretch which you are measuring or the material collapse to get anything other than grip at top and bottom dead centre. Even then it wont grip circumferentially even, whichevers softer will go first seen hundreds of disasters some on MOD stuff.
On the other hand if designed a two part clamp so it collapsed to form the exact diameter of intended it would fail your elastic tests.

Main advantage of two screw split open clamp is ease of use without disassembly of item its being attached to. Will also clamp wider tolerances.

Best comparison of two split screw type to single split is like a pair of mole grips compared with them rubber boas.
http://www.completecareshop.co.uk/products/large/Baby_Boa_Constrictor.jpg

Offline Anzaniste

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Re: Two bolt versus single bolt clamps.
« Reply #8 on: July 23, 2013, 04:45:37 AM »
http://farm8.staticflickr.com/7424/9347232717_700a476124_c.jpg

http://farm6.staticflickr.com/5542/9350017640_71bb7e7bfd_c.jpg



The top picture is the original design dating from some time around 1913 when no more than 25 hp was being transmitted. The lower one is what some of us have been using in recent years and In recent years 120 bhp is being transmitted by either method .

I have dithered between preferring one over the other for some time and it is interesting to see both of the arguments that I have been having with my self. The boa argument has marginall held sway in my mind which rather depends on the flexibility of the clamp and it's ability to wrap itself around the shaft.

Actually its difficult to envisage such massive clamps as those shown "wrapping" round an 1 1/2" or an 1 5/8" when pulled in by a 7/16 bolt.

The clamp manufacturer referenced by Lew claims the two piece clamp is more effective than the one piece and that is the view I am now tending to go with.

« Last Edit: July 23, 2013, 06:28:54 AM by Anzaniste »
Scrooby, 1 mile south of Gods own County.

Offline 75Plus

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Re: Two bolt versus single bolt clamps.
« Reply #9 on: July 23, 2013, 09:36:49 AM »
This appears to be a good application for a taper bushing system. The Q-D style would be my choice as it can be torqued tighter but the other styles do grip a shaft quite well.

http://www.daltonbearing.com/browning/browning-sprockets.aspx

Joe