Locking up a form in the chase


Ok i don't know if i did this right. I was advised the quions should NOT touch the metal, that it should have wood on both sides. My question is, should the whole chase be filled with furniture or just enough to make it all lock up?

here it is in action:




2 comments:

Mattlabs said...

From Ross ....

"Your lockup is pretty dicey. I know you don't have a lot of furniture and leading to work with right now, so given that, it's not horrible, but I'd hate to print a long run with that. Using that one long thin one on the right is pretty risky. What you want to try to avoid is your forme bowing out - a poorly done lockup might start to bow - to rise up slightly in the middle - as you tighten the quoins. Try this - Take your chase out of the press, and rest one edge on the table, and push on the back of your lockup. If the form starts to bow out, it's a good sign that the lockup is not going to make it for a long run. You should almost be able to smack it hard and not have it budge."

brad said...

Hi Matt

I'm reading this about 2 months after your post, so my information may now be redundant. If not, then I hope it helps, and apologies in advance for the length here... always easier in person, or with a visual aid.

Ross' comments about bowing are absolutely true, and can be mitigated with more furniture around the forme. The most important practice when locking-up a forme (or wood-mounted mag cuts, or a photopolymer base, etc.), however, is a trick called "chasing the gap." The idea behind it is that you never want your furniture on one "side" of the forme to touch the furniture on the neighboring left- or right-hand "sides." When these bits of furniture touch each other, you run the risk of the applied pressure on that "side" countering the pressure being applied to the adjoining side, which can result in both bowing or improper tightness to the forme.

So, to avoid this, chase the gap: start with your forme in the position where you'd like it, then lay-in furniture on one side only. The piece that buts-up against the forme should be as close to the same width as the forme as possible, always erring on a wider piece of furniture over a shorter piece. For demonstration purposes, say your furniture is exactly the same width as your forme. Lay it in right against the forme, perfectly flush corner to corner. Now, move the furniture just a bit to the right, about the distance of two quarters side-by-side. Now, build a pyramid of furniture, starting with this first piece, and build out toward the edge of the chase; if this "side" happens to be the side that includes the quoin, then fit it into the pyramid.

Once this side is complete, I always like to put furniture in on the opposite side... so you'll be laying-in furniture in the same "direction," just on the opposite side of the forme. Lay it in exactly the same way, and again create a gap, but this time, put the gap on the opposite corner of the forme. Then build-out that final side with furniture, pyramiding-out to the edge of the chase.

You always want a little bit of play, once you've got all your furniture in, so that when you tighten your quoins, their first movements apply the pressure to fill the play, and so you can ensure that none of the furniture in any one direction impedes or touches the furniture in another direction. Then, incrementally tighten each quoin, tapping the surface of the forme with a planing block.

Another good test, once you're done locking-up, is to tap down on each corner of the chase; if there's any see-sawing motion on the chase... if the chase "rocks" at all, then you've either overtightened, or there's some wonkiness in the lockup.

My final test, before proceeding to move the chase to the press, is to take a piece of furniture, lay it on its side, and then picking up the chase just a bit to rest on this piece of furniture. Then I tap firmly, as if I'm playing the piano or typing on a manual typewriter, on the forme, simulating the application of pressure to the forme, to make sure that it's solid and won't move. Check this by peeking under the forme, while it's still resting on the furniture, to see if it fell down or moved at all. If it did, you'll need to tighten your quoins, or check the forme to see if there's something weird in the layout causing an uneven distribution of pressure. If it didn't move, then you're golden and ready to move to the press.

Now do the same thing for the side of the forme that'll include the quoin for that direction: make the initial piece of furniture, the one that sits against the forme, the same width as the forme in this direction. Insert a gap, again, by moving the furniture to the right (as you face the forme from this new "side"), then build a pyramid of furniture out to the quoin, then out to the edge of the chase. Finish-off by laying-in furniture to the final "side," again inserting a gap at the opposite corner.

Cheers,

Brad
Smokeproof Press

 
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