Tympan Bale missing & enlarged hole

I acquired an 8x12 C&P that needs a bit of work before it can print. It’s missing the uppermost tympan bale. I was about to ask on classifieds if anyone has a spare they’d be willing to sell when I noticed that the hole the pin would fit into is larger than its matching one on the other side.

I’m assuming the hole size might be an issue with holding the tympan taught… If so, what would be the best approach to fix/work around it?

image: cphole.jpg


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after a certain length, most machine bolts have a shoulder. find a good diameter for the existing hole, tap it to the size of your new bolt, then cut off threads of bolt enough to allow the shoulder to bottom against the platen. i would use grade 8. locktite in place.
metric or sae thread really would not matter here.
drill your tympan hole to allow easy pivot.
otherwise you could drill the hole to match the next size up rivet that would work.

ericm has given good advice. As I understand it, you also need the bale. The existing bale is held in place with two pieces that are like short bolts without threads, or like rivets. They are in there as a friction fit. The bales are steel and you cannot easily break them unless you use a lot of force.
Use the much abused screwdriver to get between the bale and the platen and see if you can make the pin work out a bit. Get on the head of the pin with a Vicegrip and wiggle the pin and work it out. Same for other side.
Either with your skills, those of a friend, or a machine shop, fabricate a new bale. Note that the bale is curved in as a bow so it will be force tightened against the tympan sheet.

You could always just tape the tympan paper to the platen until you get a new bale.

We used to repair thread loss with a product called Helicoil, The coil was oversize and allowed you to thread in the helicoil in the oversize hole that you put thread into with a tap and then insert the helicoil and you have have a replacement thread.

those holes do not have threads. the rivet just taps in and stays. if the hole is worn, the original rivet prob won’t stay in there. thus the need for a larger rivet, or threads.

Thanks for all the info. I’ll see if I can buy a spare bale from someone first. If that fails, I’ll take the one I have to a machine shop.

This is not a hard fix, if you go to a machine shop it will cost more than a new press.

I called two machine shops in Houston, Texas to drill new holes and put the screws back in to hold the tympan bale on my 8x12 C&P.

Both gave me a song and dance, that it would take 4 to 5 hours to fix and the cost would be $250 and up.

Last night a retired machinist came to my shop I unbolted the four bolts and we removed the platen, a less than 5min job. He took a drill and enlarged the holes a little tapped out the holes for new bolts, we put the tympan bales in place and returned the platen to the press.

Less than an hour job. Cost $125.

That right there is a guy worth knowing!