OT- Clamps for bent laminations

nektai · Post by **nektai** » Mon Dec 07, 2009 3:37 pm

I have a commission to revisit one of my pieces with a number of bent parts. I put in a quote to get the biggest ones steam bent but the price was a tad off the mark. I was looking at 1000 bucks per bend! They are complicated but not that crazy.

Here is my thought. I will do the laminations myself. I will build special clamps to help me do this without having to wreck my hands.

This is out

And I will try to make a version of this work

The 'clamp' is going to need to be flipped so the threaded rods dont conflict with each other. I set it up like this so I could use my impact wrench to drive the screws. It seems to have worked. There was little deflection

I am going to need to buy stock for this so I could beef up the system. Before I proceed does anyone have a strong reaction against this half assed clamping system?

blackcreek · Post by **blackcreek** » Tue Dec 08, 2009 8:41 am

Hey Nico,

A bag press would work well for this application if you have one. You would want to use a pallet sized to the form and fill the void at the center of your form so the bag does not get sucked in at that point. Another option, favored by some of my fellow school alumni, is a fire hose filled with water and a loose but fixed negative form. Fill the hose which is sealed at one end to create an even pressure. The hose would have to be as wide as the lamination. A well cut negative form lined with cork would also work if the lamination are relatively thick. This would require many fewer clamps to obtain even pressure.

Good luck,

Tom

nektai · Post by **nektai** » Tue Dec 08, 2009 9:20 am

Tom,

is a bag press the same thing as the bag i use for vacuum pressing?

Thanks for the suggestions.

preston · Post by **preston** » Tue Dec 08, 2009 12:09 pm

These approaches to lamination all look good. But steam bending's not so very difficult either. Certainly easier than $1000/bend implies. I've done it several times for a boat. I was bending modest pieces (1 sq inch oak), but the technology certainly works for larger stuff. It was always a minor adventure, what with the flame and steam and all, but in the end, it just worked out like you hope, with no great drama.

I might lay out the pattern on the floor and use a block & tackle with a compression strap to help the bend along.

Preston

blackcreek · Post by **blackcreek** » Wed Dec 09, 2009 10:18 am

I should have been more specific. Yes, a vacuum bag press. I have a variety of bags depending on what I am pressing as well as a variety of platens. One bag and platen is dedicated to flat work. The others are of various size depending on the bent lamination. Bags are easy to make with the clear vinyl and a swimming pool liner repair kit (special quick dry contact adhesive for vinyl, it even works under water!) I also use this stuff to repair my bags if they are punctured.

The obvious concern is making sure that when the bag is deflated during pressing that it cannot be sucked in to voids in the form causing a lot of stress on the bag. Thus you would want to fill the voids in the center of your existing form at either end where it lands on the ground/ platen.

I agree with Preston steam bending can be fun and an adventure. Steam boxes are easy to build. I used to use an old 3 gallon coffee urn to generate steam with tube connected to the box but there are surely better and quicker ways.

preston · Post by **preston** » Wed Dec 09, 2009 1:22 pm

Here's my steam generator.

My aunt won't let my uncle work on the boat directly, so he built me the generator. The entire steel box is heated and water is added from a hose. It's supposed to be a flash boiler. Water drips onto the bottom (a thick steel plate) from holes drilled in the two water pipes and flashes immediately to steam. In practice, there's a puddle of water boiling away.

I built the steam box. This is from a trial fit; there's another diagonal brace to keep it stable.

Fired up.

It gets hot.

We bent the wood around the molds (quickly) and clamped it briefly while it cooled. A few ribs broke while we were bending them, and a couple more cracked later.

If you decide to go this way, there's lots more info around, on the web and in books.

And once you've got the technology in hand, you can use it to build toboggans, steam tamales, and cook plum puddings.

Preston

nektai · Post by **nektai** » Wed Dec 09, 2009 7:39 pm

Thanks for the pictures and the suggestions. I am not sure about the vacuum bag technique for this project. That said I am very intrigued with Toms method of building custom bags. I suspect I would use my set up more often if I had a custom bag or two lying around. I built my pump from parts and the money I saved I put into a very expensive bag. It just sits there all nice and clean because I am afraid to mess it up.

Prestons steam bending set up is also inspiring. I have steam bent before and have a solid understanding of the process. I have recently started buying curves from companies that specialize in steam bending. For certain species I can get a pre bent part for about the cost of the materials. I am not set up for it now so I am content to stick with the bent lamination when I need something special.

Here is my revised plan.

I pulled apart the sample and was blown away by the amount of force I had generated. I am the kind of guy who likes to tighten the heck out of clamps so i was pleased

I drilled the bottom piece so I can screw it to the bottom of the form and I used two nuts to capture the threaded rod without the need for a weld.,

I think I will replace the top piece of 1 x 1 with a 2 x 2. I may even get a thicker wall tube. The real reason is to spread out the clamping force and allow me to ditch one of the loose cauls i use during the glue-up.