Lams slipping under pressure. Help?

[Mike L.]

I’ve had a hell of a time with alignment issues on the last two builds.  This one, every time I applied pressure, the back glass and veneer slipped in opposite directions.  I think that previously, I used a much thicker limb veneer, so I was able to push it back into place.  The last bow I thought the problem was my core lams were a little wider than 1.5”, and the bow ended up being just over 1.25” after I got everything surfaced.  Is this just being careless with the hose alignment or is it normal, or do I need to use an index pin?  I’ve heard them described in the forums, but I’m not sure how to employ it with a one piece bow using heat strips. 

[Mike L.]

I found this under the heat strip.  Awhile back, I used carpet tape to affix a thin strip of rubber to the surface of the press.  After the last glue up, I didn’t take the heat strip off, so I didn’t notice this, but it seems the carpet tape didn’t hold up well under the heat and the rubber strip shifted.  I wonder if this and hose alignment is the problem.  I think this one is lost.  To get to the edge of the slipped veneer, it will bring me to 1.125”.

[Mike L.]

The shop is a train wreck.  It’s a small garage I’ve got packed with a full shop worth of tools; cause I thought it’s a good idea to buy a house in the city.  And cause I’m messy. 

[Mad Max]

I use a self centering drill jig to drill a hole into the center of the riser, lams and the form (1/4" wood dowel 1/2" deep). I use furniture wax in the form hole and around that area
Then I pin the belly lams to the ramps with a 1/8" wood dowel.
They will be covered with a overlay of cut off on the belly ramps

[Mike L.]

You think I could get away with doing something like that but shearing it at the surface of the glass?  So as not to put a hole through the silicon heat strips? 

[Mad Max]

 

[Mike L.]

It seems like it would do the trick.  I’ll give it a shot.  Thank you for the tip. 

[kennym]

On my TD form, I drilled the stop pin hole a bit deep and put a spring under the pin so the pressure strip pushes it down to limb glass level. Works  really well. Maybe you could do that?

[Mike L.]

Kenny,

I’ve read where you describe that before, but I don’t get how it keeps the stack lined up.  It’s under the pressure strip recessed into the press?  I know I’m missing something. 

[kennym]

On mine it is the pin on a one limb form for a 3 piece take down but it could work same as Max described with a pin hole up thru riser .

Hole in form is deeper than pin and the spring under it pushes it up but can compress when your pressure strip goes on down to glass level. Then your heat strip goes on top of pressure strip?

[Shredd]

  Is the top part of your form bolted tight with sturdy 1/8" thick straps??  Is your top form too close to the bottom form??  Another words is the air hose in too tight a space?? The cross section of your air hose should look like an oval race track... If the space is too tight and the cross section of your air hose starts resembling a dog bone everything is gonna go sideways...

[Mike L.]

Here is the pic of the dry run and glue up of the previous bow, which I had trouble with too, and one of the press with everything but a bow.  I took off the rubber pad and it seems everything is square.  It might have been the problem, but I would like to figure out how to use something to keep things aligned. I put a block in there to separate the heat strips so you can see them. 

These dowels that are bigger than I usually use to close the ramps, but they seemed alright during the dry run.   As I applied pressure, I noticed the veneer on the bottom of the stack was slipping out from the front of the press, and the fiberglass was visible under the riser on the back.  So I dropped pressure and tried to push everything back against the washers on the back side.  I should have taken the whole thing down at that point and figured out why.  I felt like I was getting the hang of it, but I think some kind of alignment solution is going to improve things going forward. 

I would like to figure out a way to put an index pin in there or something like it.  The heaters are between a metal pressure strip and Formica on both the top and bottom, with the metal strip toward the stack. 

[Mike L.]

Some of my pictures are upside down, they’re not that way in the phone.  I don’t see a way to rotate them.  I also have 4 short pieces of Velcro to keep the hose attached to the top of the press so I don’t drop it all over the stack when I’m installing it.  I wonder if that’s keeping it from centering properly.

[Flem]

Sorry for your troubles, that whole set-up looks like a pain in the a$$. Can you use some painter tape and put that mess into bondage before mounting on the contraption?

[Mike L.]

I used to tape the hose to the top press.  I thought this would work better.  Doesn’t mean I was right about it.  I always think Velcro is a lot more useful than I give it credit for.

[Mike L.]

The Velcro might be keeping the hose off center. 

[garyschuler]

Wax the form bottom, lay Saran wrap over the form, put on your glued layup.
Take strapping tape and start at the center, push down on riser as you tape. Do each side as you go, push down and tape to the ends of limbs. Put on another layer of saran wrap and tape that down with painters blue tape. 3-4 spots are good. Instal your pressure strip and hose. Put on top form and add air in 5-10 psi at a time until 40#psi ( my pressure) and check gaps and alignment as you go.
It looks like you have to big a gap between your hose and form. I do not use any shims or spacers in the fadeout areas. Strapping tape will help stop side to side slippage of glass and lams. I also use a C-clamp on the center of riser before tapping as that helps to keep things from moving and ensures you center line dies not move on riser to lam center marks. Hope this gives you some ideas.

[Mike L.]

It does.  I could see how clamping the riser and taping down each side as I go might do the trick.

[Shredd]

  Silly question but are those keeper washers tight up against the lams?? They look as though they might be shimmed out...

[Mike L.]

The ones on the front are obviously useless I think. The ones on the back are shimmed out by a cut off of a lam that’s about 1/32”.  I think that was a hold over from some build along ages ago that used roofing nails. All the ones on the back have screws now, so they have enough tension to stay up.  I recon I should take the shims out now.  That makes sense.