Subject : laminations warping Posted : 2020-03-20 8:01 AM Post #37916
Hi and thanks for allowing me to post.
I’ve been using your poly vac bag, glue etc for about 20 years. To date, I’ve done flat panels and some simple curved work such as curved drawer fronts. All successful, so far.
I’m attempting to make laminated splats four Chippendale-style chairs. The splat profile (edge view) is a flattened ‘S’ shape. The mold is solid plywood. Unibond glue applied with a small roller. The vac pump is set for 25 # and cycles between 20 and 25 #. There are several hours between cycles. I use an electric blanket to keep the bag and contents at 90 degrees for 24 hours. The laminations are 4 pieces of 1/8” maple, 24” x 7”. I’m not using a caul over the laminations. Relative humidity in the shop is about 35%. Leftover Unibond from the glueup is cured and brittle, as expected.
All looks good when the laminates come out of the bag. Over a few weeks the laminate starts to warp. Hoadley calls it ‘twist’. I’ve made two sets of splats so far. The first set twisted so I made a second set. They are also starting to twist. I have them clamped to slow down or stop the twisting motion but don’t know if that will help.
I’m puzzled that the splats are twisting. Any guesses as to what is happening?
Subject : RE: laminations warping Posted : 2020-03-20 10:02 AM Post #37917 - In reply to #37916
Its hard to say without being there and seeing them first hand. There’s nothing your doing that jumps out at me as being a real issue. A couple of suggestions though, the more lamination the more stable the final shape. Consider going to 6 laminations instead of 4. If you are resawing them from the same board I would make sure you flip/flop the laminations so the annual rings oppose each other for more stability.
Subject : RE: laminations warping Posted : 2020-03-21 7:07 AM Post #37921 - In reply to #37920
Thanks Darryl and Don for your suggestions. I'm using Unibond 800. Wood moisture content is around 7 %. My meter lights are fluttering between 6 and 8. Shop rh was mid 30s on the most recent batch. The first batch (in May 2019) was 50% rh or more at a guess.
I like the idea of more plies. I'll look into the skateboard kits mentioned in another post (Serpentine Laminations) or make my own from maple veneer. I'll let you know what happens. I do work (very) slowly so it might be a while before I check back in.