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How not to use a clamp

Spotted on YouTube and thought it needed highlighting for beginners

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Martin Connelly22/01/2021 10:23:43
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1663 forum posts
179 photos

I found this example of someone showing how to use a mill for a model engine and thought this poor clamping practice needed highlighting for any beginners who may think it is acceptable.

2021-01-22clamping.jpg

The clamp is resting on the very top lip of the stepped block, the applied force is down and slightly outward due to the angle of the clamp. This is because good practice is to have the supported end of the clamp higher than the nose that is on the workpiece. The direction of the force vector is therefore both down and away from the clamped part. If you project this force vector it will be at the edge of the stepped block where it is chamfered and must be very close to being just past the support at which point everything will fall over.

Now imagine a small additional force from the machining operation pushing this force vector beyond the support, the result is a failure of the clamping setup when machining. Not a good outcome.

Better practice would be to put another smaller step block on the one being used and rest on that or to raise the step block on some other material so that the end of the clamp can engage with the steps much like the one to the left is being used.

Martin C

Oldiron22/01/2021 11:33:18
726 forum posts
23 photos

Pity you did not mention that this was a clamp on a very small drill operation and not a milling operation. The operator who is a very experienced machinist was drilling a pilot hole to affix the castingto a base plate for machining. The clamp was removed as soon as he had drilled the hole. No sideways forces whatsoever were involved. You should have linked to the video to allow people to make up their own minds.

regards

john fletcher 122/01/2021 11:39:50
669 forum posts

Small hole or not, why not use one of the other spare stepper blocks underneath, then the system can be used as was intended.. John

Oldiron22/01/2021 11:56:27
726 forum posts
23 photos
Posted by john fletcher 1 on 22/01/2021 11:39:50:

Small hole or not, why not use one of the other spare stepper blocks underneath, then the system can be used as was intended.. John

There is no reason that the clamp cannot be used on the top step. The forces are straight down in this instance. You would have to overtighten the bolt and bend the bar before it slips off. This is a case of selective reporting of which there is way too much these days. Taken out of context it seems much more dangerous than it actually is. We have all used dodgey clamping methods we would not admit toat some time or another.

regards

Tony Pratt 122/01/2021 12:30:22
1418 forum posts
6 photos

Clamp bar looks level to me so ok to use, what I don't like or do is put the step blocks straight onto my precious ground table, in industry & now at home I use surface ground 6 mm hardened steel plates to spread the clamping load, just a little foible of minewink

Tony

Oldiron22/01/2021 12:38:37
726 forum posts
23 photos
Posted by Tony Pratt 1 on 22/01/2021 12:30:22:

Clamp bar looks level to me so ok to use, what I don't like or do is put the step blocks straight onto my precious ground table, in industry & now at home I use surface ground 6 mm hardened steel plates to spread the clamping load, just a little foible of minewink

Tony

I agree Tony. I use strips of aluminium under clamps to save the bed.

regards

Circlip22/01/2021 13:03:40
1235 forum posts

Ahhh, the road to hell and all that. At least the clamping bolt is at the correct end of the clamp slot. Pulled off another popular forum years ago due to lack of safety considerations and the "BUT" excuse to justify their stupidity. One a long qualified "Machinist" showing a milling cutter mounted in a drill chuck, and a Phoenix who after a decade still hasn't learned how to clamp safely but is hacknolegged as a resident ex-spurt.

The use of stepped packing blocks would have been luxury had we not had to chase round finding suitable bits of packing in my industrial apprenticeship and sorry Oldiron, the fact the poster is "a very experienced machinist" does not excuse a potentially unsafe setup.

Sadly, when a photo is posted on t'internet, there is no discrimination for it to decide whether the viewer is knowledgeable or a dobbin waiting for an accident to happen.

Regards Ian.

not done it yet22/01/2021 13:23:25
5628 forum posts
20 photos

Was this demonstration supposed to be a means of “teaching beginners” (like recently came up in a thread?).

It does appear that one step on the clamps might have been in use. But seeing that, one might wonder why there are seven(?) steps provided? One might wonder why they provide so many steps? Beginners might not wonder at all?

Oldiron22/01/2021 13:29:00
726 forum posts
23 photos
Posted by Circlip on 22/01/2021 13:03:40:

Sadly, when a photo is posted on t'internet, there is no discrimination for it to decide whether the viewer is knowledgeable or a dobbin waiting for an accident to happen.

Regards Ian.

Without the back story who is say whether the setup is bad or not. My gripe is that the OP goes on about milling side forces etc etc when it has absolutly no relation to the setup. That is why the back story is important.

As I said just another fake news story.

regards

Oldiron22/01/2021 13:35:26
726 forum posts
23 photos
Posted by not done it yet on 22/01/2021 13:23:25:

Was this demonstration supposed to be a means of “teaching beginners” (like recently came up in a thread?).

It does appear that one step on the clamps might have been in use. But seeing that, one might wonder why there are seven(?) steps provided? One might wonder why they provide so many steps? Beginners might not wonder at all?

No claim to teaching at all as far as I can see. Just a "this how I did it video" . I have not seen any hobby machinist video's that says "this is how youi must do it". In fact many point out that they do not know it all but it seems some on here profess to know how everything should be done. The back story should have been shown to put this into context.

regards

Douglas Johnston22/01/2021 14:28:28
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729 forum posts
34 photos
Posted by Oldiron on 22/01/2021 12:38:37:
Posted by Tony Pratt 1 on 22/01/2021 12:30:22:

Clamp bar looks level to me so ok to use, what I don't like or do is put the step blocks straight onto my precious ground table, in industry & now at home I use surface ground 6 mm hardened steel plates to spread the clamping load, just a little foible of minewink

Tony

I agree Tony. I use strips of aluminium under clamps to save the bed.

regards

I am glad that others , like me , use some form of packing to protect the mill table. I cringe whenever I see any abuse of the table.

Doug

Jon Lawes22/01/2021 14:53:59
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472 forum posts

I haven't used packing on the mill table in the past as it hadn't occurred to me, but I am very new to these things! A useful tip learned for me.

Mike Poole22/01/2021 15:06:55
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Moderator
2894 forum posts
68 photos

I cringe when people chuck spanner’s on the table of a machine, a table protector makes a useful place to put things down safely when setting up but once cutting is underway any tools left out will be buried in swarf. If cutting fluid is used then soft metal or plastic is better than wood.

Mike

Martin Connelly22/01/2021 15:20:06
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1663 forum posts
179 photos

Oldiron, I said machining forces not milling forces.

Any setup where the clamp can rotate the step block without the clamp being raised is a poor setup. By clamping on the steps further down the step block any rotation about the heel of the step block will try to push the clamp upwards, this is resisted by the clamp bolt. The top lip is not a good place to use on its own to support the clamp because it minimises this lifting of the clamp. The operation in the video was not brought up because in the end it is irrelevant, the point is this is an example of poor clamping practice that should always be avoided so that it is not used in machining where larger loads are applied to the workpiece.

I think we should always promote best practice.

Martin C

Steviegtr22/01/2021 16:37:47
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1912 forum posts
253 photos

Poor old ADE. I watch his video's & as already stated he took that off once he had fixed to the alloy plate.

Steve.

Allen Norris22/01/2021 17:02:19
9 forum posts

As a beginner myself I must say I found this discussion informative and Martin's explanation of the turning forces helpful. I am sure we all use set ups that are not ideal from time to time for expedience but unless someone points out the limitations this can easily lead to poor practice.

I am grateful to Martin for starting this discussion and I agree the more that the forum can do to promote good practice the better for us all, especially those with little direct metal working experience.

Allen

Andrew Johnston22/01/2021 17:14:00
avatar
5932 forum posts
666 photos

Irrespective of the merits of the original clamping arrangement I find that using clamps as illustrated is unstable. As often as not the clamp collapses when tightened. I'd have used another block on the first and rested the clamp on the second block.

The trouble with best practice is that everybody has a different view of what it is. I've never used shims under clamping blocks. There are enough variables without introducing more things that can move.

Andrew

old mart22/01/2021 17:16:16
2691 forum posts
176 photos

I hope I would not be tempted to publish a photo like that. It would have not taken much time to pack out the clamps so the serrations were in use.

David Colwill22/01/2021 19:01:11
725 forum posts
38 photos

One of the things that I really like about Youtube is that it is largely free of censorship. If you search around you will come across people operating at different skill levels doing things from the incredible to the downright dangerous. Long may this continue. Anyone who blindly uses it as an educational tool will sooner or later get more education than they bargained for!

It should be pointed out that this is a video made by a man in his shed. He doesn't have the resources of the BBC and isn't claiming to be any kind of authority on either machining in general or model making. Whilst I haven't watched this particular video, I have watched other videos by Ades Workshop and have thought that he seems competent in what he does.

He currently has around 100 hours of video on his channel, all there waiting to be scrutinised and picked over by the more learned amongst us.

I would suggest that before criticising one should consider making videos of their own, that way we can all learn something.

Regards.

David.

Oldiron22/01/2021 19:19:24
726 forum posts
23 photos
Posted by David Colwill on 22/01/2021 19:01:11:

One of the things that I really like about Youtube is that it is largely free of censorship. If you search around you will come across people operating at different skill levels doing things from the incredible to the downright dangerous. Long may this continue. Anyone who blindly uses it as an educational tool will sooner or later get more education than they bargained for!

It should be pointed out that this is a video made by a man in his shed. He doesn't have the resources of the BBC and isn't claiming to be any kind of authority on either machining in general or model making. Whilst I haven't watched this particular video, I have watched other videos by Ades Workshop and have thought that he seems competent in what he does.

He currently has around 100 hours of video on his channel, all there waiting to be scrutinised and picked over by the more learned amongst us.

I would suggest that before criticising one should consider making videos of their own, that way we can all learn something.

Regards.

David.

Here here David. I agree 100% Well said.

regards

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