A bit on hydraulic presses in the forge shop. I have been around presses in factories in both forge shops and in many other shops. I personally have designed and built myself presses from about 300# to 100 ton. Came up with concept and did project management on a portable 1000 ton straightening press for 24" x 250# wide flange. I’ve been around commercial forge presses up to 7000 ton. I've done the first aid, and the post accident cleanup and accident reconstructions for too many press accidents. Now that you understand that over the last 40 years I have designed, built, repaired and rebuilt many presses, lets get started.
-First a Harbor Freight press may move some metal but is NOT a forge press. They are ARBOR presses for pushing arbors and bearings and the like.-
So with that out of the way, what are the critical needs in a forging press? The monster has to be safe. that is critical requirement #1. The press needs to be fast for its tonnage. The hydraulics need to be durable and reliable. The frame needs to be rigid. A nice thing is to get these items in a press you can afford.
So what makes a press safe? lets put some items in a list
1. The frame must be able to withstand the load over a useful life.
2. The hydraulics must be as leak free as possible.
The least amount of hose must be used.
The controls must reliably and intuitively work every time.
3 The beast MUST have a big mushroom headed E-stop you can slap when the do-do hits the fan.
The press must sit stable and not be tippy.
The electrical controls need to be to code so YOU the operator do not become the ground path.
That said lets look at why these must be so. If the frame breaks and releases say 16 tons, the hot part may well be fired with 16 tons force and may come at YOU! Also a broken frame means no forging on that machine till fixed.
Leak free hydraulics are a pipe dream. ALL hydraulics leak. The only question is how much. If you use pipe threads in a hydraulic system you are setting your self up for failure. Pipe threads leak. Period. The only question is how much and when. Be aware that in my 40 years in factories the single biggest cause of leaks in hydraulics are hoses. They are a flexible rubber product and the rubber ages and fails. Not if but always when. Can start as a subtle ooze or be be a sudden spraying gusher. Usually starts as an ooze. So when those minimum length hoses show an ooze, replace then.
Pipe threads are a cut into the wall thickness of the pipe and weaken the pipe. Most threaders make really bad rough threads, and so you tape them up with Teflon tape right? Wrong! Teflon tape does not seal threads, it lubricates them and usually bits end up in your oil and clog stuff up. Use pipe dope instead, but always avoid pipe threads if at all possible. SAE style O-ring sealed fittings are better. They too will eventually leak. Write that down before you buy or build a press, it will leak, the only question is when and how much.
Reliable and intuitive controls, keep the beast in control. Nothing worse then the press making an un-commanded move.The intuitive part is so when bad stuff happens you can stop or move the press without thinking.
So what is this mushroom headed E-stop. It is a big switch that you can slap and the pumps STOP. This is great for an un-commanded move, or a sudden leak. I like to have a remote E-stop as well, where when you get a sudden spraying leak, it hits hot metal and now you have a thundering flame thrower, you can slap the remote switch as you EXIT the shop to consider if the remaining fire is fight able. See "A Bit on Fire extinguishers".
The stable thing should be pretty clear, these beasts are HEAVY.
The electrical controls to code, keep you alive and the code inspector happy if he visits.
So with that said what do you want in a press for good performance. You want a press that moves fast at rated tonnage. The dies pull a huge amount of heat out of the billet. A slow press cools the forging before much work can be done. A big press that can overcome the cool forging with tonnage may well tear the forging and make internal cracks. A good press will be fast AND controllable.
Ease of changing dies makes for a versatile press. When you pay as much as these things cost, you want versatile!
A quiet hydraulic system is a blessing. Hydraulics should not SCREAM. When you hear that it usually is a case of flow over the relief valve, which makes lots of noise and heat. If the machine always does this it usually indicates bad design.
A tip, especially when looking at an old press and especially a home brew one is to look for cracked or crazed paint at the welds. Easier to see then a painted over crack. If the press is old and freshly painted look VERY close that may be a hide the cracks paint job. Don't be afraid to ask to scrape the welds to look for cracks. They refuse to allow then take you money elsewhere.
Any hydraulic system should have filtration, and it should be easy to change and the filters easy to obtain.
I will NOT offer design tips as these things are killers if you are not familiar with the entire process. If you have to ask how big a cylinder you need for a certain tonnage, buy a finished press. If you can't figure the size pump and motor needed buy a finished press. If you can't figure the deflection in the structure buy a finished press. Life is too short to spend any of it Dead, injured or in jail.
Of the forge presses on the market currently I like the Coal Iron designs. They have a machine that meets the above.