By continuing to use this site, you agree to our use of cookies. Find out more
Forum sponsored by:
Forum sponsored by Allendale Jan 24th

Clamping force calculation

All Topics | Latest Posts

Search for:  in Thread Title in  
RAMA HEGDE01/05/2020 21:00:25
avatar
4 forum posts
3 photos

clamping force calculation_1(2).jpgHi, I need to calculate the clamping force. Details attached.

Robin01/05/2020 21:47:00
avatar
500 forum posts

I think we are all wondering what you are pushing against?

The answer depends on the angle of that driving face.

Approx 1 ton

RAMA HEGDE02/05/2020 01:45:31
avatar
4 forum posts
3 photos

The job is circular bar and it has been pushing against V- block.

not done it yet02/05/2020 07:06:18
6445 forum posts
20 photos

If nothing is moving the opposing forces, by Newton’s First Law of Motion, are equal. Direction is another matter.

One Pascal is one Newton / square metre.

Redsetter02/05/2020 07:51:01
192 forum posts
3 photos

I think we are all wondering what are you actually trying to do, and is that really the best way of doing it?

DC31k02/05/2020 07:56:09
586 forum posts
1 photos

Since you show a pin joint at the base of the middle arm, there will be no clamping force as you have drawn a mechanism. The horizontal arm will try to move to the left due to the wedging action at the right of it and will result in the piston tilting in the cylinder and all pressure being lost.

To make this statically determinate, you need an encastre joint at the base of the middle leg and to specify the angle at the right hand end of the horizontal arm.

Dave Halford02/05/2020 09:08:39
1820 forum posts
19 photos

The Vee block will move.

Michael Gilligan02/05/2020 09:33:32
avatar
19324 forum posts
964 photos
Posted by Dave Halford on 02/05/2020 09:08:39:

The Vee block will move.

.

dont know

The Vee block is shown as ‘mechanically earthed’

... Did the Earth move for you today, Dave ? surprise

MichaelG.

SillyOldDuffer02/05/2020 09:55:11
Moderator
7714 forum posts
1705 photos

Here's my attempt at the calculation, done with smath studio (free software) for which I am eternally grateful to Mr Duncan Webster of this Forum. Lots of good things about smath, in this case I use it to finesse the units automatically into consistent Metres/Kilograms/Seconds, and exploit built in values for pi and the gravitational constant (approx 9.81).

Ought to warn I am famously bad at maths! Much prone to silly mistakes, getting the wrong end of the stick and missing bits out. Double check everything, I'm liable to do things like get the lever the wrong way round. (Here I hope the lever reduces force on the job by 4/6...)

leverpressure.jpg

My answer: about two thirds of a metric ton. Hope it's right!

Dave

Edited By SillyOldDuffer on 02/05/2020 09:55:38

Steviegtr02/05/2020 10:00:50
avatar
2275 forum posts
313 photos

If your math is correct then I hope his centre fulcrum is pretty rigid.

Steve.

Dave Halford02/05/2020 10:12:28
1820 forum posts
19 photos
Posted by Michael Gilligan on 02/05/2020 09:33:32:
Posted by Dave Halford on 02/05/2020 09:08:39:

The Vee block will move.

.

dont know

The Vee block is shown as ‘mechanically earthed’

... Did the Earth move for you today, Dave ? surprise

MichaelG.

I can't remember

duncan webster02/05/2020 11:09:18
3598 forum posts
66 photos

SOD's sum gives the force acting vertically down, to get the force pushing the round bit into the vee block you have to allow for the angle of the end face. Then it gets involved in friction, which is never a known quantity, and I haven't had my weetabix yet. As Robin says, need to know the angle of the push face, and the exact relationship between the pivots and the bar, if they are not in line it changes the answer

Rod Renshaw02/05/2020 11:54:29
347 forum posts
2 photos

+1 for DC31k's analysis.

The system as drawn will not act as a clamp at all.

The "Centre Fulcrum" at the base of the vertical lever is shown as a pivot and is not rigid at all, so as the pressure in the cylinder rises the horizontal lever will press just a little on the work and then move to the left as there is nothing to restrain it from so doing.

Did I just repeat what DC31k said in less accurate language?

All that wasted maths!

Rod

not done it yet02/05/2020 12:23:41
6445 forum posts
20 photos

Dave(SOD),

Unfortunately it will be accelerating (well, something will) - according to Newton’s Second Law. if accelerating, by definition its velocity cannot be zero (for very long, anyway)!

duncan webster02/05/2020 12:27:01
3598 forum posts
66 photos

The base of the pivot point is clearly shown as grounded (slanty lines underneath), it won't move anywhere as long as it doesn't snap. We must assume the base of the cylinder is similarly prevented from moving down, but I think that is a safe assumption.

Steviegtr02/05/2020 12:43:16
avatar
2275 forum posts
313 photos
Posted by not done it yet on 02/05/2020 12:23:41:

Dave(SOD),

Unfortunately it will be accelerating (well, something will) - according to Newton’s Second Law. if accelerating, by definition its velocity cannot be zero (for very long, anyway)!

Across the workshop floor probably. Not a good method of clamping. Must be a better way than that.

Steve.

pgk pgk02/05/2020 13:06:11
2367 forum posts
293 photos

I'd go with SOD but if one wishes to be difficult then it's point contact so the force expressed as pressure per area is infinite. Indeed the piston needn't be round and the whole thing could be end on for a long system....

pgk

RAMA HEGDE02/05/2020 13:08:20
avatar
4 forum posts
3 photos

Hi,

Here I am giving little more details.

Please find the image. Initial condition

duncan webster02/05/2020 13:15:30
3598 forum posts
66 photos

Ah just had another look at the sketch, I'm in error. Because there is a little link between the lever and the fixed pivot all the side load will be applied to the top of the piston rod, which has no sensible means of resisting it, so it won't work.

Strange how you sometimes look at something and see what ought to be there, not what is there.

SillyOldDuffer02/05/2020 13:19:05
Moderator
7714 forum posts
1705 photos
Posted by duncan webster on 02/05/2020 12:27:01:

The base of the pivot point is clearly shown as grounded (slanty lines underneath), it won't move anywhere as long as it doesn't snap. We must assume the base of the cylinder is similarly prevented from moving down, but I think that is a safe assumption.

 

I agree about safe assumptions!

For completeness I assumed:

  1. the title 'Clamping force calculation' indicates the drawing is to identify dimensions rather than being an engineering design.
  2. The cylinder & piston is round rather than square.
  3. The piston can't tilt.
  4. All the fixed points are firmly grounded on Planet Earth. (But the answer in Newtons is OK for other planets!)
  5. Friction is zero, ie the piston and joints are all 100% efficient.

But your other post mentions the angle of the lever on the rod as being relevant. I missed that!

So, if the angle at the end of the lever is 20°, what is the force F on the job, and F1 and F2 on the V-Block?

job.jpg

Back at school my mathematical humiliations were only in front of the whole class. Now I'm messing up on the internet!

smiley

Dave

PS This post crossed with Rama's clarification.  I guessed 20° correctly!  Amazing.

Edited By SillyOldDuffer on 02/05/2020 13:21:57

Edited By SillyOldDuffer on 02/05/2020 13:24:27

All Topics | Latest Posts

Please login to post a reply.

Magazine Locator

Want the latest issue of Model Engineer or Model Engineers' Workshop? Use our magazine locator links to find your nearest stockist!

Find Model Engineer & Model Engineers' Workshop

Latest Forum Posts
Support Our Partners
rapid Direct
walker midge
JD Metals
cowells
emcomachinetools
Warco
Eccentric July 5 2018
Eccentric Engineering
Subscription Offer

Latest "For Sale" Ads
Latest "Wanted" Ads
Get In Touch!

Do you want to contact the Model Engineer and Model Engineers' Workshop team?

You can contact us by phone, mail or email about the magazines including becoming a contributor, submitting reader's letters or making queries about articles. You can also get in touch about this website, advertising or other general issues.

Click THIS LINK for full contact details.

For subscription issues please see THIS LINK.

Digital Back Issues

Social Media online

'Like' us on Facebook
Follow us on Facebook

Follow us on Twitter
 Twitter Logo

Pin us on Pinterest