Shop Press - safe load?

[Hopefuldave]

On the "you suck" dumpster dive thread I revealed the channel I surfaced with, and intention to build a press, my question is: How much tonnage will be safe?

The frame will be built from 135 x 35 x5mm channel, the tapered variety, I'm looking at using two 28" lengths each for the top of the frame and the moving "table", the top bolted and welded to the uprights, the table sat on 20mm pins through the uprights' flages, a bit like this pic:

   

(Excuse the appalling Crap-O-CAD)

Close up the Channel looks like this:

   

So I guess my worry is, with a 25" span between the uprights, is it going to do a good imitation of a rubber crutch the first time I apply a bit of pressure?

Ay help or corrections from those who have built and not broken (or even know how much it took to break!) anything similar much appreciated!

[Vinny]

Mine is built with the same style channel measuring about 6.5mm on the thin part and 14mm on the thick. 5mm thick. I have a 21" span. Mine is not home made so it has an actual rating of 25 tons. The pins that hold the movable table are 3/4" 1018. Hope that helps some.

Edit: One difference between your drawing and my press is the way the channel is pointing. Flat sides are to the inside. not out.

[Hopefuldave]

Thanks Vinny, that helps and reassures - I was shooting for 10 tons from a home-made ram, I may consider a bigger bore and more tonnage!

The Fenner power pack I have has a cutoff switch at 2000 psi, so I'm basing it on roughly a square inch of piston per ton, I was originally thinking a 100mm bore would give me around 10 tons but could probably go to 150mm for around 20-22 tons although it would be pretty slow-moving - that may be an advantage, though!

If I could get 20 tons with a gauge reading of 2000 psi that would be pretty convenient for one so intellectually challenged...

EDIT: 136mm (5-3/8") bore would do it, 20 tons showing 2000 psi on the gauge, and I have stock big enough to make a 4" stroke ram...

[f350ca]

Dave
A quick calculation on your press frame.
The channel you listed in the Dumpster Dive was 5x1.75 which SHOULD be 6.7 pound per foot channel.
With the load in the middle of two 25 inch long channels as you've drawn it would carry 62,000 pounds before it permanently deformed.
With the 10 ton load you listed they would elastically bend 0.016 inches in the middle.
The vertical channels are 1.97 inches square area, so each one would carry 71,432 pounds tension, before they yielded. BUT that would have to be reduced by the metal removed where you drill for the pins. They should be safe.
Hope that helps.

[Hopefuldave]

Thanks Greg, I'm sure that's not a "quick" calculation! I think even with Machinery's at my elbow it'd take me a full evening...

It sounds like I could safely go to 20 tons, 44,800 pounds, I may scare myself first time I use it though!

Your advice is worth several times what I paid for it, by the way...

Now I need someone who knows hydraulic power packs to chip in, I've seen 1 gallon (US or Imperial? there's a 5:4 ratio...) per minute at 1500 psi per HP quoted, would it be safe to divide though, 3/4 gallon/minute at 2000 psi?

[f350ca]

Actually is quick now Dave, found a site with on line calculators that save me looking up the formulas.

[texx]

just looking at your sketch i would think you need to look at what the sheer strength of those 2 pins is ( what ever they are made from).

johno

[Hopefuldave]

Hi Johno,

I'll be going with 20mm pins (a little over 3/4", near as dammit 0.786") in the local equivalent of 4140 CrMo (709M40 aka EN19A, bluebell), hardened and tempered (I'm building a little HT oven at the moment, 5"x5"x12", designed to be fairly airtight so I can flood it with argon to prevent decarburising), the yield strength in tension would then (worst case heat treatment!) be a minimum of 26 tons, should give a shear yield strength of around 16 tons *per hole per pin*, so a total shear yield point (assuming, dangerous, equal loading) of around 64 tons, so it should give about a 3x safety factor - I think it's worth the extra on a decent alloy for the safety factor!

Earlier in the thread, Vinny described his (store bought) 25-ton press, which has 3/4" pins in a very similar frame, they're 1018 (aka "mild steel") with a considerably lower yield stress in shear, he didn't mention any snappages ;)

Anyone with better ideas, please feel free to criticise / constructively comment!

[Vinny]

Mine came without pins, I happened to have the 1018 so I just used that. The jack I have on mine right now is only a 6 ton, the 25 ton is on a shelf for when I need it for something else. I haven't had need to even max out the 6 ton yet.

[f350ca]

Grade 8 bolts or the metric equivalent would probably work and save the heat treat time.