New base and packing

Our first windmill base was a 6 x9 from Elum. The packing math was straight forward. I use press blanket packing from my GTO. For a 20pt Lettra - tympan +a .04 draw sheet + (2) .010 sheets = 30pt approx. The 30pt packing plus the 20 pt stock = 50pt put me 10pts over so I did not have to increase pressure to much to get a good hit. Pressure was increased to taste.

I got a new 9 x 12 base but now my math does not work like it has in the past. Both bases appear to be the same height. Does a bigger base spread the compression area. I ended up packing to a 50pt plus the 20pt point for the stock (70pt build) and also had to increase the pressure a lot to get a good image. I tried another plate on different brand of 20pt cotton and the result was the same.

I always felt the base should set the image to type high. The packing was designed to bring the paper up to the plate and create an image. I have never put any packing behind my base. Should I only pack the area of Impression? Do I need to add packing behind the base? Do I need a softer or harder material to pack with?

Any ideas will be a big help, I am more than a little stumped

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Bass Height? The key to this must be to have the base and plate to type height so that that inking remains constant, too high and the roller setting will be lost. With tbe base, plate and rollers fixed, you can play with you stock and packing all you like.

Frank - thanks for feed back - Base height - We wondered that also but it is the same height as our other smaller base .875, plate I want to say is a QF95 - the same we have used all year long without incident. What troubled me was the packing math when I started with this new 9 x 12 base. I know that in the 1970 the idea was a kiss imprint, but not today. The stock and packing should equal 1/25 ( 40pt). I was afraid to over pack and / or over apply pressure. Recently we began adding or subtracting packing and the same with adjusting pressure looking for a contact print point in balance. It sounds silly but I always wanted to split the depth of my hit between greater packing and greater pressure. It sounds like we might be on the right track but want to be sure.

I started back in 1963 as a letterpress apprentice and as you say kiss impression was the order of the day. After 40+ years in administrative roles when I retired I felt the need to get fingers inky again. So for now I have a early 60’s Windmill and a 1950’s British Miehle Vertical possibly one of only 6 left in the UK and perhaps one of only 2 at present still printing.
So 6 years ago I entered a learning curve on how to print with a mixture of old and new materials. I am lucky enough to have a mixture of Honeycombe mount, cornerstone mount and Monotype 6x6 high quads. I tend to use 152 polymer plates and with 4thou d/sided adhesive these will mount directly onto both the high quads and cornerstone mount. for the Honeycombe mount I use a lead shim that was made back in the 80’s for mounting zinc plates and this works really well, but a modern alternative would be 2.5mm aluminum sheet with a 10thou d/sided adhesive plus a thin sheet behind the forme. This all adds up to keeping the plate to type height (.918) and enabled me to print the usual material including mixed formes ie type and plates, 4 colour process, and embossing, and yes even experimenting with deep impression.
Here’s an example of figures
Cornerstone honeycombe .748
2.5 aluminum .098
d/sided adhesive .010
polymer plate 152 .060
.916 + .002 sheet under
forme = .918
I am interested in you paper thickness descriptions in pts
which I am not familar with here in the UK as we use weight
to describe printing stock ie 300gsm, can you explain it to me.

I have always used caliper rather than GSM as a measure of stock thickness. To convert decimal-inch values into points, divide the average caliper by .001. The packing for the windmill says 1/25 inch. 1 divided by 25 = .04. Then take .04 dived by .001 = 40 ( 40 pt). A single point is equal to .001 inch. GSM uses length and breadth to determine a control measurement. You can have two stocks that are both 20pt in thickness but have different GSM values. We like to use both when have them. It tells us how thick a paper is and the GSM or weight gives us an idea of the calendering or compressed value of a stock.

Frank - I also ran a Miehle V50 in the 1980’s years before the current letterpress demand. The frame got cracked and we gave it away for parts. I have looked around for another one to run light weight work. The press was a heavy beast.

Western411:- thanks for the explanation