Pneumatic clamp cylinder size?

[Brian Holcombe]

I’m in the planning stages for a pneumatic clamp setup for the mortising machine. In your experiences what bore size is typical for these sort of setups? I assume too big is typically better than too small but I’ll be working with a small compressor so I don’t want to greatly over do the bore size.

Ill probably wind up using two cylinders and putting them on an overhead bar then building some feature which allows them to slide.

The lever clamp is super annoying and always in the way for batch work.

[Bill Dufour]

Depends on force required and pressure of the air. Too much force can dent the wood. Direct acting is easy math to calculate the force applied, just cylinder area x pressure. Phi x R squared x PSI. I have seen 250 PSI as the recommended max clamp pressure. Of course that is PSI which depends on the area of the joint being clamped.
I have seen Bessy type bar clamps claiming 1000 pounds per clamp. at 100PSI that is 3.5 inch bore. That seems much bigger then what I have seen. I would guess more like 1-2 inch diameter but closer spacing.
What does the maker of the clamp you are currently using claim for force.

I just realized you are not gluing, just work holding, so my measurements are probably way too high.

Bill D

[Albert Lee]

I had those pneumatic clamps on my double mitre saw. they are not huge. they are about between 30-50mm bore. there are 4 of them.

on my Masterwood OMB1V there is only one pneumatic clamp but it is a lot bigger - probabbly 80mm-100mm bore.

There is no vertical hold down clamp on the OMB1V. the head of the machine locks down on the stock as you press the on button, its spring loaded.


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Regards

[Mark Hennebury]

What type of mortising machine?

[Brian Holcombe]

Mark, hollow chisel mortiser, I setup the Felder with a square chisel attachment.

Bill, 250psi seems right to me on gut instinct as well.

Albert, thanks for the bore size information.

[David Kumm]

You will want either the long throw small diameter Bimba type like Mac uses or the short large diameter short throw like you see on dovetail machines. Those would need to be mounted on a bar that you can adjust. You can also look at pictures of slot mortisers like Bacci, Bini, Balestrairi ( sp) etc. My Airtight clamps are set at 70-90 lbs pressure but you might need a little more depending on chisel size. Dave

[Malcolm McLeod]

You'll find lots of air cylinders with 1-1/8" (1.125") diameter bore. It might seem odd until you realize it is almost exactly a 1sq-in area, so the air pressure is effectively your resulting force (40 psi x 1 sq in = 40 lbs-f).

Not familiar with the equipment, but if the 1-1/8"dia will fit, it makes for very intuitive setups. Just make sure you have a conveniently located regulator w/ legible gauge on it.

[Brian Holcombe]

Thank you both. That’s what I was looking for. David, I’m thinking long stroke so that I can have a fixed height which is generally out of the way.

[Mark Hennebury]

Hi Brian, Can't really help on this one as i am not familiar with hollow chisel machines. I have alomost exclusively worked with swing chisel (Maka, Centauro, Lari & Lari) or slot mortisers like Balestrini and Greda.

[David Kumm]

Mine are 40mm diameter with about a 3" throw. There are different quality levels and some will disengage when hitting a non flat object like a finger. I've never needed that safety device but it is available. If you plan to use them in pairs, you want fittings that will operate both from one location. Dave

[Brian Holcombe]

Thanks David, I plan to use them in pairs. I'm thinking of building an overhead bar with some arrangement to allow them to slide into various positions across the width of the table. I'm thinking to mount the push button on the bar and mount a regulator on the side of the machine.

Hi Mark, actually I'm thinking to make them similar to Lari and Lari's setup. I have built a fence for the machine (FD-250) which does most of the work of keeping the piece in position, but with a big chisel and pressure to go into woods like hard maple it can cause the fence to slide. So, i had been thinking this may cure two issues as I don't like the eccentric clamp and it will alleviate some work that the fence is doing.

[Mark Hennebury]

Hi Brian, With a horizontally mounted hollow chisel mortiser it would appear that you need a a solid front and rear stops more so than a heavy top clamp, as most of you pressure is pushing and pulling.

Does your machine have any front or rear stop plates?


The swing chisel mortisers also have the lateral swing and therefore need solid ends stops. Lots of people use high downforce and extra clamps to compensate for no end stops and or dull blades with the Maka style. Dull chisels really shake the crap out of the Swing chisel machines.

[Brian Holcombe]

It does have stops, but the front ones need more heft. The rear stop is the fence and it's quite hefty. I've been debating a screw type arrangement for the back of the fence to adjust in and out.

I agree, it does not need a really high pressure setup for clamping, just enough to prevent the chisel from moving the work.

I've been following along with your thread on the Martin tablesaw and read your mention of that with swing chisel mortisers. I'm continually taking notes on swing chisel mortisers. I feel that will be my next step after a good shaper.

Anywho, here's a photo of my perpetual project. Please ignore the lack of fan cover, still working on that. I managed to get my hands on one for these motors but it doesn't fit this particular shape of motor. Please also ignore the lack of a standoff for the cord, also to be attended to shortly.

[Mark Hennebury]

Okay, now i remember.

It looks a little cluttered and awkward to me, do you find it so?

[Bill Dufour]

You have a choice of double acting, single acting with internal spring retract, or single acting with a spring somewhere outside to pull it back in. the internal spring will reduce stroke.
Bill D.