Friday, January 29, 2010

New Tympan-Frisket Assembly

On my website, I write extensively about my 1st attempt. It turned out pretty well and Marya and I have been able to print all sorts of things with it, including multi-color and double-sided jobs. Nevertheless, I'm dissatisfied. The oak bars are 3/4" wide, so we end up losing 3" from the usable length and width of the bed, a pretty high percentage. It's also hard to duplicate, requiring some woodworking for the oak and metalwork for the hinges.

I had the idea of using carbon-fiber pulltrusions, since I knew they were quite stiff, available in convenient sizes, and pretty easy to glue together. I buy them from a company called CST.

My first attempt was unsuccessful. I built the tympan frame using bars 1/8" thick by 3/8" wide, using simple lap joints to fasten the corners together. The area for the glue joint (3/8" x 3/8") was too small and the glue (epoxy) joints broke.

While I could use wider bits of CF to increase the glueable area, one of my main motivations is to recover usable area in the bed of the press; wider bars would defeat that goal. I discussed the problem with a friend of mine, Howard Rush, who can build anything. He came up with the idea of using L brackets to hold the corners together. Not only that, he helped me build them!

First, we needed some raw material. We built a plate of CF-epoxy, 1/8" thick and about 5" square (a similar plate can be ordered from CST, but we wanted to get to work right away).

Next, we laid out the 8 required L brackets on a sheet of paper and glued it (with 3M 77 spray glue) onto the plate.

Following the outlines, we cut out the individual bits, sanding them to neaten up the edges. We used Howard's table saw with a diamond blade, but it would be possible to use a Dremel tool with an abrasive cutoff wheel (aka Dangerous Disk!). By the way, I also used the Dremel tool to cut the bar to length.

Here are the pieces of the tympan frame, ready to go together. Before glueing, we sanded all the mating surfaces, then cleaned them with MEK to remove and dust, oil, etc. that might interfere with the glue bond.

We layed it out on a slightly oversized scrap of shelving, then worked for a while to ensure all the corners were square before glueing.

We held the bars in place with hand clamps and remembered to add some teflon (wax paper would be ok) to prevent glue from sticking to the shelving.

Next we mixed up a batch of high-zoot epoxy (Loctite Hysol 9430), weighing the 2 parts carefully, and brushed a thin coat on the mating surfaces. Finally, we clamped the L brackets in place, lightly (too tightly will squeeze out the epoxy). A slippery job, but it turned out ok.

Finally, we let it dry for a week (until I had a chance to visit again).

Next, we need to build the frisket frame. Same process, just sized a bit smaller.



  1. Preston,this is really fine work you have done here. I have made some frames out of craft steel joined with pop-rivets that I have mounted on a large cast iron chase that fits fairly well on the bed of my Poco #1. I wish my work were as craftsmanly as yours, but it still achieves the basic objectives. I'm working on getting the typman surface at type high. So far I have not attachted the frisket frame. I'm considering sticking with the lazy man's masking tape solutions that I have used up to now. I've had enough drilling and riveting for now.

  2. Great! (But where are the pictures?)
    The tympan doesn't have to be exactly type high. I line the windows in the frisket with pieces of weather stripping and that seems to hold everything well above the inked type, but still crushes down neatly when the bed passes under the cylinder.

  3. You said you built a CF plate--how and out of what materials. I love the sleekness of your frame! I'm using a long piano hinge locked in with the furniture and screw a sort of frisket thing onto that but it's a little thick. This blog is very exciting!!

  4. The CF plate was built by laminating several (13?) layers of "carbon fiber prepreg". Which is a fabric woven out of carbon fiber, then impregnated with the proper amount of high-temperature epoxy. We just clamped the pieces together firmly between two flat plates (using a vacuum bag), and heated for a while. Howard gets this stuff from another friend; I don't know how.

    I would simply buy a plate from either CST or DragonPlate (google will find them for you). Not that expensive.