I was recently trying to set the form (inking) roller height on an SP15 and found that I was unable to properly set the gear-driven one (nearer the impression drum). There was no way the back end (closer to the gear) could drop down far enough. I measured the rollers and found that, instead of being 2.5″ diameter as they should be, they were 2.382″. The back end of the form roller could not drop down because the drive gear was bottoming out in its rack.
Other than being the wrong diameter (inexplicably so) the form rollers were in good condition. Having the rollers recovered would have cost $270, although I could have got away with half that by just recovering the gear-driven one.
I found a less expensive solution, though: replace the gear with one that is the right size for the roller. This worked out in this case because the roller height mechanism has enough range to hold the roller axes 1/16″ lower than normal, and also because the actual roller diameter corresponded to another gear size.
The standard gear is a 40-tooth, 16 DP, 14.5° PA gear, with a pitch diameter of 2.5″ (40/16) to match the standard form roller. Applying the 16 pitch to 2.382″ diameter comes to 38.112 so a 38-tooth gear with the same pitch and pressure angle would do the trick. A gear this size is not generally available with a hub (like the original gear) but is is available as a “change gear” (usually used in machine tools to adjust the speed ratio between two shafts). This is a flat (hubless) gear with a 3/4″ hole and 2 keyways. I also bought a 1/2″ hub (for welded-on pulleys and sprockets), and used my lathe to fit the hub to the gear with a press fit. The combined parts look just like the original gear (except for the tooth count, of course) and the press now inks properly.
The slight difference between the ideal tooth count (38.112) and the actual tooth count (38) will cause a slight amount of slurring, but the amount is very small, about 0.05″ total slippage over the full length of the form.
Total cost: about $43, plus my time on the lathe. Of course, if I had to pay someone to do this, getting the roller recovered would likely have been cheaper.Kevin Martin the Papertrail Handmade Paper & Book Arts New Dundee, Ontario, Canada