Hello! I have been wondering about proper packing on my SP-20. I have a Galley Bed Plate with 040 cylinder undercut. I have Vandercook Tympan, .003 packing sheets and a Mylar sheet.
Everything I can find as to how much packing you need does not mention if the thickness of the bed plate is involved or not.
If I use one piece of Tympan, the mylar and 5 packing sheets. Its not enough to make an impression in 80lb lettra.
I'm worried that if I add any more thickness to the packing I may be counterproductive. and of course I do not have a micrometer (Yet)!
Any advice would be great.
Firstly, your bed plate shouldn't matter to anything, as long as it's level and brings your type/plates up to type high.
Vandercook recommends no more than .03 over the undercut--so you'd want you paper and tympan/packing thickness to total .43. I find that with Lettra (because it's so soft), you want a bit more than that--closer to .50.
(I'm not sure what Lettra you're using that's 80lb. Is it the text weight?)
Lettra 110# is .021
Tympan is generally a standard .06
I don't use mylar, so I can't speak to its thickness, but you should be able to find that info on the packaging and/or the place you purchased it.
With 110# Lettra, I use 1 tympan top sheet (the diecut piece that goes under the gripper bar and around the tightening rod), plus 3-5 tympan packing sheets, depending on the amount of impression I want, and whether the printing is double sided.
Hope that's helpful!