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Carld
12-25-2009, 08:38 PM
I need an air cylinder with a hollow threaded ram for a machine I need to modify. It has to be double acting. I can't seem to find anything with a hollow ram, is there such a critter?

lane
12-25-2009, 09:10 PM
Check with SMC I seemed to remember using one from them years ago. Sorry I do not have a link.

Doozer
12-25-2009, 09:14 PM
Bimba.

--Doozer

Carld
12-25-2009, 10:30 PM
I have looked on about 10 web sites and just gave up and figured someone here may have seen or used one.

I guess I will have to go back and email or call each company. Oh well, it's sure easier now than it was 20 years ago. All we had was the Thomas books and now we have the net and ThomasNet.com

Geez, I hate making all those calls and emails and then end up making the cylinders myself. Since they have to fit into a compact area I suppose I'll be making them.

Ken_Shea
12-25-2009, 10:34 PM
Have 10 or 12 various size and makes of air cylinders, none have hollow rams, Carl, is the length such that it would prohibit drilling?

oops, over lap :D


Curious, what would be the use of one with a hollow ram?

JCHannum
12-25-2009, 11:08 PM
Lane's memory of SMC is a good place to start. Check the Yellow Pages for pneumatics & hydraulics suppliers in your area. There are a lot of options available that might not show up in an on line catalog search.

Does the ram need to be hollow the full length, or just female threads? I have a 4" X 3/4" pancake cylinder here with a deep 1/2" female thread on each end. It could probably be drilled through a smaller diameter for air flow. The problem with a through bore is the method used to attach the piston. If retaining rings are used, the diameter of the piston rod is reduced in this area.

Carld
12-26-2009, 06:12 PM
It's going on a welding table that rotates to tig weld tubes. I made some 3 piece collets to hold the tube so the screws don't deform the tubing. I uses 3/4" all thread for the screws and they have to screw them in and out a lot to remove the tubing. The boss got the idea of using air cyl. to move it in and out after they get it adjusted.

Now I have to figure out how to make it all come together. I'm not sure just how much stroke I will need but at least 2" on each cyl, maybe 3" to clear the flange on the tube.

If I make the cyl. I can shrink fit the piston on the shaft and use a double lip seal to seal both directions. Seals on the ends of the shaft is no problem.

The problem is the length and OD of the outside of the cyl. and I am not even sure if all this will work. It's a work in process but sure would like to find a cyl. the size I need. I don't think they will like the cost of doing this.

I am also looking at simpler ways to back the collets off and I have some ideas there.

mechanicalmagic
12-26-2009, 06:21 PM
Have you looked at Enerpac hollow Hydraulic cylinders?
http://www.enerpac.com/en/products/cylinders-lifting-products-and-systems/hollow-plunger-0
They seem to have many sizes.

John Stevenson
12-26-2009, 06:55 PM
Carl, when I have wanted something similar in the past I have finished up modifying an existing cylinder, in fact the last one I needed which was 6" diameter but only 1 1/2" stroke i just bought the tube from the local SMC agent and cast the two end plates as they needed to be very thick to carry part of the machine on them.

In my case it was easier to have them cast instead of machining them out of 7" square alloy bar which I didn't have anyway.

http://www.stevenson-engineers.co.uk/files/pencilstamp.jpg

The cylinder is just visible at the top of this machine.

.

Carld
12-26-2009, 07:08 PM
He wants to use air but I'm not locked on just air.

John, I am hoping to just modify an existing cyl. and I will check the sites suggested and some of the sites I found.

TGTool
12-26-2009, 07:37 PM
He wants to use air but I'm not locked on just air.

John, I am hoping to just modify an existing cyl. and I will check the sites suggested and some of the sites I found.

You can use air on hydraulic cylinders if you find one that otherwise fits your needs. OTOH, the hydraulic cylinder could give you the force you need in a smaller package. Air over oil might be an option at the detriment of more parts and cost.

Black_Moons
12-26-2009, 08:24 PM
Have you considered other methods to move bar?

Like say, a pnumatic cylinders on either side of the bar?

Id think the simplest non binding setup would be 2 cylinders to move it forward and back, and another 2 to actuate a clamp.
Of course if you only need to move one way, some kind of spring loaded knurled (rubber coated?) eccentric shaft could be used to make a simple (automaticly adjusting to diffrent diamiter) one way clamp.

Carld
12-27-2009, 11:45 AM
Spring loaded return would work and I have that in mind. One problem is I only have an area of about 6" long x 2" square to contain the cylinder in. Nothing can stick out to hang on the welders hands, arms or clothing and there is shields around the rotating table to deal with.

The more I have thought about this and read suggestions here. It may have to be a spring loaded cyl. for simplicity and compactness and I will probably have to make the cyl.

Black_Moons
12-27-2009, 05:36 PM
they make VERY small cylinders if the force required is low enough, like 1" diamiter is common.