Pneumatic Derimming Pres for 22lr cases .... Design and Fabrication Thread

[featherhead]

I'd like to start a discussion on the design and fabrication of pneumatic presses built to derim 22 long rifle cases. The process requires a huge force to get that pesky rim off the case. So I spent a good lot of time and effort working on a design and came up with some interesting features that I'd like to share.

I'd appreciate if we could keep the thread on topic and focus the discussion on the building and function.

Here is the first press I built. Has a 4" cylinder bore with a 2" stroke.

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Here is a video

http://s136.photobucket.com/user/franketrozzo/media/derimpress.mp4.html


The second press used an RCBS partner press. 5" cylinder bore with a 2" stroke.

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Also got a video on it.

http://s136.photobucket.com/user/franketrozzo/media/Untitled.mp4.html

[303british.com]

I'd like to ask a couple of questions about your presses. First, is about the compressors needed to run the press. Could you recommend some general specs for them? What is the minimum a person should get?

Secondly, connecting the dies. Are the cases pushed all the way past the constriction by the punch? If so, would a section of vacuum hose (or similar) work to contain the newly formed jacket and feed it into a bucket?

On a side note, I dropped the money order for mine in the mail this afternoon. The lady at the post office says it should be there within a few days. :)

[featherhead]

The cardinal rule on compressors is Clean dry air. Use a filter and water trap. Cylinders need to be kept dry inside. All compressor manufactures exagerate and hide the real output from the buyers. CFM is what to look at. Whatever the brand says it produces in CFM, reduce it by 40%. They do give ratings for CFM @ 90psi and 40psi. Any compressor will produce 90psi and run the cylinder. Small ones will kick on quicker and run continuously. Big ones will take an hour for the cylinder use enough air to kick the compressor on and they will recover and shut off sooner while the cylinder is in continuous use. Even if a compressor keeps up with the cylinder but is under sized, it's irritating to hear it running continuously. Anything in the 30 gallon tank range will work, and kick on about every 5 minutes and maybe run for 15 minutes while the cylinder is in constant use. In the 60 gallon range, belt driven models will kick on after maybe 8 minutes and finally recover and kick off in 8 to 10 minutes. Anytime you take a short break the air supply will build back up in minutes. I have a 60 gallon hooked up in tandem with another 60 gallon reserve tank from my last compressor that died. So I have plenty of air volume, but at 7 CFM the unit will run for 5 to 10 minutes before it kicks off while I'm running the cylinder constantly.

The dies are push through out the top design. I turned down the neck on my die to accept the Lee sizer kit container bin shown on the presses above. Some guys will cut a hole in a tupperware container and slip it over top. You could run the press on its side anf let em fly into a bucket. And they will fly. Cases will also feed out of a hose that leads into a bucket. There a lot of options available to suit your likes.

[303british.com]

I like the idea of sliding a hose over the top of the die. I'm basically lazy, so a little gun tape to hold the hose in place and I'm good to go. I dug my Corbin.com derimming die out and I'll head over to the hardware store for 4 to 6 ft of clear hose. When the press gets here, I'll put everything together and put up a picture.

Do you have a preference in cylinder size?

[chuckbuster]

https://www.youtube.com/watch?v=G6ffy_kLJms

[featherhead]

Do you have a preference in cylinder size?

Before I learned the formula for cylinder force I built a press under a 2" cylinder exerting 300 lbs. The ram hit the die and came to a dead stop. I reworked it with a 4" and 1200 lbs did the trick. A 5" will apply 1800 lbs and a 6" 2800 lbs.

[DukeInFlorida]

Thanks, chuckbuster, for linking that video.

Featherhead, I also made a preliminary mistake with the air cylinder on this press. The 2" cylinder isn't big enough. The 3 1/4" cylinder should be considered the minimal size for this job, and a 4" or 5" is a good size. You have to keep in mind that 1200 pounds of pressure or 1800 pounds of pressure is a LOT of pressure. Certainly enough to break steel and break body parts if some part of the structure fails. As has been discussed many times in the past, keeping fingers out of the way is a CRITICAL safety consideration.

[featherhead]

You have to keep in mind that 1200 pounds of pressure or 1800 pounds of pressure is a LOT of pressure. Certainly enough to break steel and break body parts if some part of the structure fails.

The task associated with derimming involves drawing a spent 22 case measuring .230 down to .220 as it exits the die in addition to removing the rim. Since the force between 2" and 4" cylinder ranges 400 to 1200 lbs we know derimming requires less than 1200 lbs. Unless I build a 3" cylinder I won't know if 800 lbs is adequate. So liberally I'd say 1000 lbs will derim a 22 case. That translates the power of the press to a half ton jack. If I were to weld a metal square out 1/4" steel and slide a 1/2 ton jack into it and start jacking, I wonder if it would break the steel? I think a typical O style cast press body will tolerate slow steady pressure of the ram and the 22 case. Then there is that moment of abruptness when the rim strikes the die that could for a fractional second increase the force to the cylinder max. That is if the pressing movement stops or come to a near stop. As I watch cases derim I don't see any of that happening.

[Capt. Senile]

I built my de-rimming press just like this one.
http://castboolits.gunloads.com/showthread.php?196918-Derimmer-Made

The only difference is my air cylinder is a 4" stroke, 4" bore. I'm also running a 20 gal compressor at 125 PSI and have no problems de-rimming cases. .22 magnum cases will de-rim, but the punch needs to be about 1/2 an inch longer to push the case fully into the die.
The whole setup weighs around 25 pounds and sits on the bench top.

[featherhead]

That's slick Cap. If you mill grooves into the channel, you could slide the cylinder to and from the die for adjustability.