Hey I have been looking at some shop presses recently and was wondering, is ther any reasons why i couldnt use a press from harbor freight like the one in the link?

 

https://www.harborfreight.com/20-ton-air-hydraulic-shop-press-with-oil-filter-crusher-65330.html

How fast does it move? What do you want to do with it?

speed is very important, wasted time doing a full stroke is not good, add a solenoid valve between the pump and cylinder and limit switches operated by the rod in the cylinder and make sure the rod cannot rotate.

quick change tooling is good so you can eject a hot tool and replace it with a cool one

a very large compressor if you want to use it for many repeated strokes ( I can get more than 1 stroke a second for 24 hours non stop easily, IF a HF one could do that the seals would not last an hour )

air over hyd jacks are made for slow lifting, maybe once in 10 minutes and a life of a year or so if used a few times a day, I have 400 pieces to bend tomorrow, with getting the press set up and getting the stock ready and putting it all away I expect about an hours work

The reasons not to use a HF press for forging are many.  Lack of speed, lack of stiffness, lack of replaceable parts, no limit switches, no safety shrouds on hydraulic parts (google hydraulic press flamethrower).

So many wide open questions in the original question.  Buy this book.  

Hydraulic Forging Press for the Blacksmith

By: Randy McDaniel

 

It's cheaper than a crappy press from HF and WAY cheaper than the mistakes, down time, injury, or worse from using the wrong tool.