Have a look at Don Fogg's page and don't miss the 5 or 6 other pages with links at the bottom of the page.
http://www.dfoggknives.com/hydralic.htm
There is a booklet he sells there too which runs through specs and designs by an actual engineer.
-the Baston book
A pre made shop press is usually unsuitable because it achieves its high power with a large cylinder at a very slow stroke speed
A forging press is usually recommended to have at least 1 or 2 inches per second stroke speed so you can move metal while it is still hot.
If you start doing calculations you will see that it is easy to get a high tonnage, but at a slow stroke speed because of the volume of fluid required.
This takes a large pump and motor.
You may have to reach some sort of comprise on a slightly smaller 5" cylinder instead of 6".
It starts costing real $ to up your pump volume, motor HP and wiring size above 5 hp
Is 50 tons twice as good as 25 ? probably not as good as a fast 25
The larger size will allow you to run larger dies and keep the same PSI at the die level...but there must be a practical limit..
in the numbers Billy gave he is running 2200 psi is 21.5 tons
Buy the book , look at what others have done and do the calculations with what you can buy locally.
I would tend to stay with 5 or 6 inch cylinder, go larger on the pump volume and keep the pressure down to keep the stroke speed up so you can get more squeezes per heat in.
When the steel is hot, you wont' need huge pressures to move the steel and are better served by gradual reductions to preserve your patterns.
the difference between the pump volume at 5" and at 6" is significant.
Don Fogg's specs
10 hp dual pump hydraulic station pushing
16 gallons a minute at 1500 psi.
5" double acting hydraulic cylinder with an 8" throw.
Works out to 14.7 Tons
Indian George
SUPPLIER PART# DESCRIPTION COMMENTS
NORTHERN 1053-C161 BARNES 2 STAGE PUMP -11GPM
2010-C161 PRINCE STANDARD 4-WAY CONTROL VALVE
4051-C161 7 GALLONS HYDRAULIC OIL TANK MUST CLEAN THE INSIDE WELL
4022-C161 RETURN LINE FILTER
4010-C161 SUCTION STRAINER THIS GOES INTO THE TANK
FITTINGS AND HOSES YOU WILL NEED 3 HI- PRESSURE HOSES AND LOW PRESSURE HOSE FOR THE RETURN.
53606-C161 GLYCERIN FILLED GAUGE 0-3000PSI
SURPLUS CENTER 10-1485 ELECTRIC MOTOR I USE A 3 HP AT 3250 RPMS
09 4954 HYDRAULIC CYLINDER I USE A 4 1/2" BORE X 8" STROKE WITH THE PUMP AND MOTOR SHOULD GENERATE 24 TONS
"If I ever build another one it would be a H press with a minimum 5" cylinder."
__________________
Eric Fleming
WIP with automated stroke timing
http://www.bladeforums.com/forums/showthread.php?t=648250&highlight=press
Material list
http://www.bladeforums.com/forums/attachment.php?attachmentid=137813&d=1247009168
Motor – 7.5 HP
Pump – Single stage 5.2 GPM (Single stage is necessary to get repeatable timing for an automated stroke)
Cylinder – 5” X 8” Stroke
calculations.
http://www.bladeforums.com/forums/attachment.php?attachmentid=133500&d=1243476166
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220V motors are practical in these sizes