I had a project to build a device that would provide a measurable level of pulling force to preload a bearing assembly...I used a 12T bottle jack on a 4:1 lever to get there...but I was to cheap to buy a jack that was pre-drilled for a pressure guage cuz they were about $150 more than a standard jack, so I used a HF 12ton jack for $29 and found a 5000psi guage at HF (in the air fitting section) for another $9.99.

Here's the tech if you want to install a pressure guage in your bottle jack:

Use a pipe wrench to get the big nut off the top...the piston will come out with it. It's easier if you open the release valve for this. After the piston is out, all the oil will probably have spilled, but if it hasn't, dump it out...the outer shell (reservior) will probably fall off while you're doing this because it is held on by the big nut you just took off with the piston.

By now you probably think it's pretty simple...just drill through the boss in the base casting and catch the bottom of the cylinder....wrong.

From the looks of things I thought the cylinder was sealed buy the pipe threads, but there is a machined seat on the end of the cylinder that seals against a gasket...which of course I drilled right through on my first try, and the jack bled down. You need 2 holes, one straight down in the cylinder into the base casting, and another through the casting boss to meet the first hole. Measure measure measure. You need to keep as much meet around the hole as possible, so make the hole as small as possible. If you drill in the wrong position and make the casting too thin under the reservior gasket...it will crack under 4000psi + and bleed down. That was my second try.

Third try was a charm. Good thing HF jacks are cheap....

Clean the shit out of everything and reassemble.

Picts?

I've read the threads where folks used a jack with a port, fitted it with a gauge and used it for a scale. I've been looking for jacks with the port (with no success) and was wondering where exactly to drill. Seems you could have a set of 4 scale jacks for pretty cheap if you got the ports and conversions just right. What was the size bore that you used? Also you said this was to mesure PULLING force?

The 6 ton jack I started out with had a bore size of 1.3333". The 12ton I have now has a bore size of 1.74something inches.

pi(r²) x psi = force exerted by the jack.

I've got the jack pushing up on the long end of a lever and the short end pulls on a drawbar with 4 times the force exerted by the jack. It's not to measure pulling force, it's to replace a less consistant and reliable fastening method for the purpose of testing certain qualities of a double tapered roller bearing unit.

I'll take some pictures tonight.

always wondered how difficult that would be. glad to hear its possible. would love to see pics.

Here's the jack all taken apart

http://img.photobucket.com/albums/v201/machschnelGTI/IMG_2436.jpg

You can see the boss where I drilled my hole.

Here's a couple more pics of the inerds
http://img.photobucket.com/albums/v201/machschnelGTI/IMG_2435.jpg

The outermost ring machined into the base accepts a flat rubber gasket that seals against the bottom of the reservior. It's not a very deep groove.

The center area is the bottom of the pressure chamber. You need to measure and determine the distance between this surface and the bottom of the cast base, then put your hole right smack in middle, or somewhere close, and drill it perfectly horizontal. I went about 1/4" in to the chamber area with my horizonal hole, then drilled another hole to come down and meet it.

This is a 10T jack that I fawked up on...you can't even see the hole because after drilling and tapping for 1/4"NPT, I drilled upwards at an angle to hit the bottom of the pressure chamber...but I went at too much of an angle and drilled through seat of the cylinder that mates against the seal, which is hard to see because it's clear plastic.

I kinda suck at explaining stuff sometimes, so ask questions or request different pictures if you want.


http://img.photobucket.com/albums/v201/machschnelGTI/IMG_2436.jpg