Weld Fixture Design — Practical and Easy Clamping and Clamp Arm Ideas for Beginning Machine Tool Designers and CAD Drafters

A while back a reader asked how do we determine how much clamping muscle (pounds of force) we need to hold the production parts in place while they are being assembled and welded.

Good question!

For the slide show on clamp arm creativity, scroll down to the slide show. But if you are interested in getting the full answer… keep reading.

You need to know, for example:

1) How heavy is the part you are holding in place;

2) Other than heat distortion while welding, what other forces will be pressing on the part your are holding in place.  For example, in an assembly fixture, there might be some rotating forces while things are being bolted together, there might be some tugging, pulling, pushing;

The weight of the part is easy. Central Steel or McMaster Carr will tell you how many pounds the material weighs. You just have to figure out how much of the material is in your part and do the math.

You should figure that the clamp should at least be powerful enough to hold the part in place if the machine was turned over, such as in a trunion-mounted weld fixture.  Each clamp usually holds only one part.  But occasionally a clamp will need to hold more than one part.  Then the weight of all the parts held need to be added together.  But that isn’t enough.  You need to add some for safety.

So how much is too much?

Well, other than cost of the clamp itself, that isn’t a factor.  I have seen tiny parts held by huge clamps.  Some companies have a standard size clamp they use in all applications and to go smaller you need to get special permission.

Why is “too much pressure” not a problem?  Because, clamps have a stopping point on their clamp arm swing.  Once it reaches it’s stopping point an adjustment in the part of the clamp assembly that touches the production-part can increase or decrease the pressure on the production-part.


Words words words!  Watch this slide show and get the full picture of what the words are trying to say.


For Fun…

Announcing a new page on Rentapen’s web site!  Shim price comparison we conducted in February showed that Rentapen’s RAPid Shims(tm) won every time!

Check out this cool picture of Rentapen’s founder’s trike that he rides to works sometimes.

Catrike Expedition Custom Painted


’til next time…

The Queen


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