View Full Version : Rotary shear

02-14-2015, 02:04 AM
Amongst 2,794 other projects, I'm currently involved in building a fiberglassing workstation. It will be two parts- one is a lamination press, and the other is a supply rack and cutting table. There will be a groove across the table at some point to guide a scissor. I have the fancy idea to make a more elaborate cutter.

What I have in mind is a section of heavy bandsaw blade wedged into one side of the groove, then a round blade on an arbor spring loads against the edge of the bandsaw blade. The round blade would be ground at an angle on the rim, and the exposed edge of the bandsaw blade would be ground flat. The round blade is pushed along on a track across the width of the table, all the while maintaining contact with the straight piece of bandsaw blade. Same action as scissors basically, except that it's one smooth motion across the table and no 'pumping' action as with scissors. The round blade rolls as it goes across, so there is a pinching action and a travelling intersection point where the shearing takes place.

I don't think I'll have a problem with the hss bandsaw blade- it should keep a decent edge well enough- but what can I use for the round blade? I'd like to use an old table saw blade. I'd cut or grind the teeth off, then turn the edge to true it up and put the angle on it, then perhaps flame harden the edge. I'm wondering if the typical blade steel would be good enough for this- or conversely, what could I use instead for this rotary part of the cutter?

Black Forest
02-14-2015, 03:16 AM
I have a rotary cutter made by Bosch. It has a driven rotary blade about 35mm in diameter. One of these blades would be perfect. Or you could just buy one of the Bosch cutters! You could just build a very low fence and run the cutter along the fence. I do that when cutting long straight pieces. Just clamp a straight edge and use that for a fence.

Here is a link to the professional model. I have the consumer model. It cuts 6mm thick leather great.

02-14-2015, 02:46 PM
The piece of bandsaw blade I mentioned would be the equivalent of the fence- and it would be simply a matter of running the cutter along that. That's the idea I had in mind anyway. I just wanted to be able to make a straight, clean cut across the full width of the cloth in one go-

I might just end up buying the Bosch tool, or another make, and make it run along a guide. Only problem would be reaching across the 53 inch width of the table. But then I could always make a fold-down handle to give the extra 2 feet or so for a comfortable reach.

If I go ahead with the original plan in some form or another, I'll have to decide what would be the smallest diameter for the rolling blade that will give a consistent nice cut without pushing the cloth. That's just a bit of geometry I can work out by testing with ordinary scissors. If you start a cut with the blades wide open, it tends to push the material away. At some point this effect disappears and the material is both held in place and sheared at the same time. Once I find this angle I can determine a degree of overlap for the disc against the fence, then determine a diameter for the disc. The blades in the rotary cutters seem to be no larger than about 3 inches, so I'll probably be good at about 4 or so. I've seen saw blades of that size that are flame hardened at the teeth, so the possibility exists for me to prepare one of these as my cutter.

But I'll look again at the existing powered tools-