Hi Martyn,
I’m not sure if the following is relevant to your situation other than in terms of the slideways clearance. However, while serving my time in the toolroom in the 50’s, we had a 24″ shaper mostly being used by a very elderly gentleman.
The machine (I can’t remember the make, but it was pretty old) had a Whitworth quick-return linkage, as opposed to a hydraulic ram drive. Changing speed and clutch operation was via large joy-sticks emerging from the side of the machine.
Occasionally, the shaper became available for use by others. None of these people, including myself had little if any problem cutting large slabs of (mostly) nickel chrome steel. Incidentally, I did have to stand on a box to reach the top slide handle.
Anyway, the machine had one problem when set for a finishing cut. There was a few thou wear in the main (ram) slide. In use, this was taken up by a film of oil, which meant that the last (finishing) cut had to be continuous, and the machine had to be left to run across any workpiece until the cut was complete. If, for any reason, the machine stopped mid-traverse and was left for a period of time, the next stroke would be deeper by the amount of oil missing from under the slide. The usual practice was to leave the finishing cut either until after lunch or to take a late lunch break.
If you look at the basic forces involving the ram, and depending upon the style of cutter already discussed previously, these forces would tend to cause the front to dip and the rear to lift. Could this relate to your problem?
In closing, I’m reminded of one unfortunate chap who was using this same shaper to put a 15 deg bevel across the edges of a steel blank. Rather than tilt the work-piece, he chose to set the top slide over by 75 deg and then hand feed across and down the slope.
Sadly for him having carried out this setup, and with the machine on bottom speed, he inched the ram back again to start his first cut. What he didn’t realise was that the overhang of the top slide was perfectly in line with the body of the machine. There was a slight noise as the `T’ bolts ripped away the `T’ slots on the head of the ram. The whole top-slide weighing a good 50kg dropped onto the work-piece with a thud, leaving the poor guy scratching his head.
Good luck.
Sam