Your C3 31 is similar to my MinMax CU300 in that the planer table is supported by a single column.? It's hard to tell by looking at the pics, but it looks like there are 4 bolts at the bottom of the column...? ?So, have you checked to see if the 'table' is level/parallel with the cutter head?? (I had to shim the bolts on mine using copper shim material that I bought from Amazon).
Same thing with the shaper.? I had purchased a brand new set of Freeborn cope and style cutters and was getting a 'loose' fit.? I even sent the cutters into Freeborn to have them checked.? Turns out the shaper spindle was not perfectly perpendicular to the table and again, it needed some shimming.? I think anyone who purchases these types of machines needs to invest in some good straight edges and something like the Betterley Una-Gauge
