Tuning for Controllability
Power hammers are truly amazing machines ... but they can be darned scarey too. This is especially true if they have binary controls: all on, or all off. The controls can and should be done so that the machine is easily and delicately controllable across its entire range of speeds; from a very slow tapping of the work to full bore, hell bent for election rapid pounding of the work. In fact, it's not really too difficult to do.
Here are the highlights of the process and the thinking behind it. If you don't think this is enough guidance to actually do the work, I would strongly recommend that you consider Sid Sudameyer's course on Power Hammer rebuilding. It's taught once a year and is a full "hands on," fix-that-junker-up endeavor in which the class actually does the work to a real hammer.
This guide will assume that your bearings are good and that the clutch assembly works properly. It will not address the issues of slack in the reciprocating assembly, the arms, the ram, or the guide. All these things tend to effect the power and precision of the hammer rather than its controllability.
Controllability is based on the smooth and even transfer of motion from the treadle to the fork which drives the saddle causing the clutch to engage. Guess what. This means some very simple, but very important things:
1) All of the holes in the arms that transfer motion are round.
2) All of the clearances are relatively small.
3) There is little to no flex in the pieces that do the transfer, and
4) That the surfaces that rotate to allow motion are smooth and well lubricated.
Let's start with the holes in the frame that have pins in them on which pieces of the linkage assembly actually turn. Unfortunately, these holes seem to have been cast in and were not cleaned up during manufacture. Fortunately there are only two of them. One is at the back base of the hammer and the treadle rides on a pin through it. The other is higher in the back of the hammer and it carries a pin that allows the roation of the control yoke.