C&P Platen Installation Mistake

So I came within 0.050” of printing this weekend. But the last 50 thou of adjustment on the platen bolts would just not budge! And I know why. Last winter I took off the platen to file and scrape it level (it had a big dished area in it). When re-assembling I was just too enthusiastic with the graphite/oil paste, sticking my finger in deep into each of the threaded jack-screw holes and smearing lots of the paste into the threads. Then the cleaned up jack-bolts pushed the paste ahead of the bolt into the blind bottom of the threaded hole and now it’s almost where I need it to be, but the hole is full of the paste and it will not compress. Argh! So one more dis-assembly, and printing next weekend?

Log in to reply   9 replies so far

That is a mistake that is so easy to make , there is a name for it too but it escapes me at present but it is a good point to remember .
In the past i had a problem with a heidelberg cylinder that used to back off impression nless it was always set on heavy form , eventually i collared one of the guys from heidelbergs service crew he just said wash the oil points through with an evaporating solvent and then just put the bare minimum of oil in the points , that solved it for us .
you have a similar problem so a fine artist brush with stripper like substance down the bolt hole and a rag too keep wiping the brush off should be an easy way to solve it .

Hugo, the word Peter is probably looking for is Hrdraulic(ing) , I have a 10 ton multi legged puller which acts on this very principle, I.E. grease is within the body of the ram, it is wound into/up to compression by turning the bolt up, in fine increments and then use of Copper, Hide or nylon hammer. The grease compresses to make the ram work, because the male/female threads are close fit, in essence exactly the problem you have (in reverse!) My suggestion would be, Beg Borrow, Steal or even Buy one Tap (as in thread cutting Tap) and run it in with light oil or detergent to “bottom” in your blind hole, because the “tap” has 2/3 flutes, the obstacle(s) dirt, ink, grease or whatever will come out trapped in the flutes!!! Obviously the “tap” will have to be the correct pitch, almost certainly, Imperial, and probably witworth, for that vintage machine??? N.B. as “taps” normally come in set of three, first, very fine taper to commence RE-THREAD from scratch, second, intermediate taper, (for progressive formation of NEW thread) and lastly PLUG “tap”, which by implication will clean your existing thread out right to the bottom of your blind hole!!! The Plug Tap is the only one you would need, because, as it is only cleaning and not re-cutting!! that “tap” is completely un-tapered and flat bottomed , to within one 1/4 of one thread for that very purpose.

I had a C&P in my basement shop for 30 years and I adjusted the jack bolts once when I first purchased it and never touched it again. I can’t see any need for any form of lubrication on the bolts. To make the final adjustment I set up 4 1/4” diameter dots in each corner of the chase and adjusted the platen so that the impression was even in all 4 corners, locked everything up tight and it should never need adjusting again. Dave

Are you talking about a floor model C&P or a Pilot? Either way, just remove platen and bolts, flush holes wih solvent from a sqeeze bottle, clean threads with brushes. A toothbrush will work for floor models. Good luck finding a bottom tap at larger C&P pitch: US standard, but before the automotive industry forced a change of standards. Not Brit Witworth or Wentworth which have a different thread structure. Pilots may use a thread still common.
These screws should not be so easy to move. I want to feel every bit of movement when adjusting. No more lubrication than is actually needed is a good idea (in general). Here you just are trying to prevent any future seizing, not making for a loose turn.
When a platen bolt broke on my Challenge-Gordon, a machinist made a replacement. He got the threads wrong; “close enough” won’t do, the threads must match perfectly, The bolt seized before it went all the way in. Had to adjust the other bolts and the packing to match. Getting another press solved the problem.

The bolts on the old C&P’s are not US standard (UNC).

The impression bolt you’re talking about is 5/8-12 tpi on one side (instead of the 5/8 -11 that is standard) and 3/4-12 tpi on the other side (not the 3/4-10 you might expect). The rest of the various bolts on the press are equally odd-ball. I have not found a single standard thread on either a 10x15 or a 14.5x22.

I wasn’t referring to any specific thread standard like USS, just that with a C&P the answer will be found in American practice not British.
The C&P was already fully formed when threads began standardization in the US in 1918, so they could have used thread specifications that are now obsolete. Why should C&P, or Mergenthaler, retool just because some mechanical engineering association wanted to simplify manufacture? Simplification wasn’t entirely possible. Your hardware store will have National- Fine and National-Coarse fasteners, but industry even now has other needs, and there are still many National-Special threads in use. And in this particular case, 5/8”-11 and 3/4”-12 were both listed as National Special in a 1935 reference, but gone in later specifications at hand.
It has been a while but I think I’ve replaced some C&P screws with others taken from Linotypes.

Intermediate Progress Report: Due to my disgust with the state of the platen I took a few days to get back to it. Also as pointed out, it is a miserable job turning the very tight jack screws from underneath the press. And remembering the last/first time when I removed the platen by myself (sitting on it), I hyper-extended my middle finger tendons due to the weight. So when I finally got the bolts loose, I set up some 2x4’s and a piece of plywood to flip the platen toward the delivery table rather than lifting it off alone. Next I determined the part of the bolts threaded into the platen are National Standard 1” (with a pitch of 10 to the inch). Today I found a place where I could order a tap to suit, as mentioned they are seriously out of date (the current NC is 8 threads per inch).
The taps are called taper, plug and bottoming (with roughly 5, 3 and 1 thread tapered). I ordered the intermediate, plug tap, taking into account the comments above about a likely intentional interference fit in the threads. I don’t want to make the platen loose. And the reason I need a tap is even after cleaning out the bolts and holes with brake cleaner they will not turn down to anywhere near where they need to be. They were tough as hell to come out originally, and I’m thinking there may be some metal parts left in the threads. Thanks for your interesting comments!

What size is your press?

For reference: My 14.5x22 uses 1”-10. My 10x15 is 3/4-12. Both new style.

Where did you find a tap for these? That’s a very handy tool to have when you’ve got your platen off.

Luke, my press is a 12x18 New Style C&P. For the tap I had to do a bit of calling and visiting machine tool suppliers. In the end Thomas Skinner Machine tools were most helpful and sourced the tap somewhere in Toronto. I will likely put the tap up for sale after I’m done (for 60% of my cost). I do not plan to go through this effort again.