Lets talk multi part soft jaws

I’m new to soft jaw fixturing and have 3 parts that will be needing 4 side machining from a single piece of stock… The plan is to mod vise clamp raw stock and do my top side operations then cut soft jaws for back side facing and chamfer.

My question is how much bigger should the pockets be milled? I know to clamp a spacer in the jaws before milling them but need a good ball park to shoot for.

Any help would be great.

I’m not an expert and I’ve never used real soft jaws (but I did 3d print a pair to machine a coin once) but since no one else replied I’ll offer my opinion…

I think the offset you use for the soft jaw really depends on how accurately you are machining your parts and how accurately you are machining the first side of this specific part. If your end mills have been carefully measured and calibrated you’ll need a very different offset than if you are using end mills that are smaller than their nominal dimensions…

Because it depends so much on your tooling and machine, and your needs (can you tolerate some slop in the fit in the soft jaws or does it need to be super tight?) it’s hard to give an answer.

That said, is there any chance to run different operations and avoid the soft jaws altogether? From the two pictures, it looks like you have some nice parallel edges for securing the parts in the vise. What does the final part look like?

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I do not, yet, have enough experience to effectively comment. I did learn from some NYC CNC YT videos. Here is a link to one of them.

And another.

My experience has been to use your part to make a cutout in the softjaw for the tool paths and then make sure you have a way to get inside corners (like you have in your image) the tight/exact fit has always worked best for me on all the one I have built. I too like to watch and learn from the NYCNC guy. Overall a tight clearance fit will work best to hold solid. I even cut some of my soft jaws for the 2nd side opps with a 1mm holding lip if I need too and they work solid with the SMW vises

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