Inverting an hydraulic jack for a workshop press.

[tonyfoale]

hello tony, seems to me the frame is a fabrication too, i imagine you`re really busy but if not much trouble can you comment on material and size? i`m about to make a press and would like to get on the correct path regarding to this. thanks man.
been following your work for years (and i mean years... )
regards

Rigidity is of the utmost importance in a press, especially if you are using it to insert or separate interference fits such as crank pins in a built up crankshaft. If the the press is "springy" then instead of a nice smooth action it will "stick-slip" as the spring winds up and releases. Therefore, use material for the frame with the thickest sections that you can find or afford. As shown in my previous photos the was a little too much flex under high pressures and I soon braced the bottom and top sections. I'll take some photos of the current arrangement and post them here. I'll also check what section sizes I used, and let you know.

[penca]

thanks tony, i saw the bracing in the pictures you posted, i`m thinking the ideal shape for the top of the frame would be a triangular form so the members are in tension rather than flex but that`s armchair engineering. i better ask first.
i`m worried about the casting of the base of the jack i`m planning to use not being strong enough to cope with any side load if there is misalignment while pressing something. i`ve used a different design in which instead of drilling holes for adjusting the height of the "table" there are tabs welded to the frame, looks easier and faster to make although a bit clumsier to operate.
i`ve experienced the chattering you mention and thought it was flexing within the pieces but makes much more sense what you`re saying, flexing of the press frame.
i`ll wait for your reply and thanks for taking your time to answer
pete

[Cascao]

Rigidity is important for safety reasons too.
More rigidity means less energy stored. Les chance of thing flying around.
When you feel your press flex, it's time to release pressure and start to heat or freeze something.
You're the Tony who wrote the book Motorcycle Handling And Chassis Design?

[tonyfoale]

You're the Tony who wrote the book Motorcycle Handling And Chassis Design?

I have to plead guilty. Details can be found here TONY FOALE DESIGNS - Home page

[tonyfoale]

thanks tony, i saw the bracing in the pictures you posted, i`m thinking the ideal shape for the top of the frame would be a triangular form so the members are in tension rather than flex but that`s armchair engineering. i better ask first.

Pete,

Here is a pic. with the bracing that I put on after the previous photos were taken.



As to size of the members. basically some 100 x 100 tube with 3 or 4mm wall. I'd prefer thicker but it is what I had.

[penca]

thanks tony, the picture helps a lot, hope to finish the tool soon and i`ll post.
i definitely prefer the bracing to the ginormous sections
thanks again
happy new year - feliz año nuevo
pete

[janders1957]

Brilliant! Have never liked the usual econo shop presses. This is going to be high on my list as I rebuild my shop.

[Hans Pearson]

Well done Tony, my sentiments on hydraulic presses entirely. I did almost exact what you did some time back and needed about four modifications to get to where I am now with it. I went a different route (eventually) with the pump. I mounted a cut-off hydraulic power pack pump remotely on the side of the press stand and take the pressure into an adapter mounted into the press pump position. (I used steel brake lines for high pressure). Unfortunately the piston of the power pack is a bit bigger than the jack's piston so I only get about 7.5 tons instead of the theoretical 12 tons. I still use the jack reservoir for the oil supply with a return line to the remote pump tank. On the subject of the frame work, it is nice to have a wide press but it puts tremendous forces on the cross members, so watch that width. There is a way of using a second low load jack as a remote pump - the pumps are all the same capacity - come back to me if anybody wants the instructions for that mod.

[tonyfoale]

Hans,

I have been thinking of removing the outer reservoir cylinder and feeding the pump directly from the header tank and taking the outlet of the release valve directly back to the tank. This is not high on the priority list.

[Hans Pearson]

That would be possible, you would then take your return from the pressure release valve, but would have to close off the return to reservoir port in the base. I think working a supply into the inbuilt pump would pose a problem. I have an adapter that replaces the jack pump and feeds directly from the remote pump. It still returns into the reservoir but another low pressure pipe leads back into the power pack reservoir, a pressure relief filter high in the jack relieves air pressure build up and protects the piston seal. Perhaps I should post a series of pictures of my setup. My pipe connections are a copy of the high pressure couplings used on older models of Citroen cars. A very simple and effective system that easily withstands over 2000 psi.