Form making for Bent Laminations

[Doug Mason]

Making some bent laminations (26 radius over a lenght of 20 inches) and was debating if I should use a router (with template) and glue up blocks of plywood, or just take a 4x4 of Doug Fir and cut it on the bandsaw; after consulting my Tage Fried book, I built a jig he describes as per below. It worked very well.

I cut the Form at a 26 radius upon which I'll laminate to a 1/2 width. You'll notice the middle cutout, which is 3/4 in width--1/2 for the lamination plus an 1/8 of cork for each side of the form. So for those of you who do this often, what do you think? Is there a simpler way, i.e, just cutting freehand on the bandsaw, not using cork as a liner--or using something other than cork? Or is this pretty much the best way of doing this?

[Lawrence Smith]

I have made several bent laminations succesfully using two by six pieces of construction lumber which were screwed together to give me enough height to bend three inch strips of walnut.

I was bending to a radius of twenty three inches. I also wanted my final piece to be about twenty inches long so I made each strip that comprised the lamination about twenty four inchs long. I found the ends of the lamination are not always usable after glue up. I used West System epoxy glue and wax paper between the jig and the lamination. I used six bar clamps and started clamping on one end of the the lamination and worked to the other end so as not to create a void. I did experience some "spring back" when the clamps were removed. Keep that in mind if you have to maintain an exact radius. I was using walnut and I experimented with the thickness of the laminations to achieve a bend that was uniform. I ended up using four one eighth pieces to give me a finish thickness of one half inch. If you are using a different wood you may have to cut different thickness pieces to determine what is the best combination for the radius and thickness. I did not use cork at all on the jig.

Hope this helps. My$.02

[Mike Henderson]

I use MDF for bending forms - glue several pieces together for thickness. I cut it on the bandsaw, then adjust the shape with a spokeshave and sandpaper. I don't use cork on the forms, but I do put something like packing tape on the surface to keep the bent lamination from getting glued to the form. If you're going to use the form a whole lot, you can put plastic laminate on the bending surfaces. [Side note: Sam Maloof has plastic laminate on the forms he uses for gluing up his rockers.]

As Doug commented, you get some springback so if the radius is critical, you'll need to do some trials and adjust the radius of the form to take the springback into account. Using more laminates will reduce the springback.

The ends of the glued up piece will generally not be usable so make the pieces longer than needed and cut to length. Also watch the alignment as you glue. One thing you can do is screw some metal (maybe aluminum) on one side of the form and push the pieces against the metal as you clamp.

I put clamps on from the center to the ends.

You can bend with a single piece form or with a two part form. If you go with a single piece form, make it convex so the clamps point "outward". Otherwise, the clamps can interfere.

Mike

[There's some pictures of a one-part form in a paper I wrote here. Note that the form is concave - that's how I learned you should make it convex :-).]

[Larry Edgerton]

Many of mine are large, as long as twenty feet so solid forms are not an option, and I consider it a waste of material. Tage probably wrote that before Doug Fir/solid wood costs what it costs today.

I use whatever scrap is aroung the shop, and cut all the pieces with a router/compass. I make my height by turning two curves into a ladder, screwing blocks perpendicular between two plywood/melamine/whatever curves. I screw this to the bench and laminate away. If the lamination is too large I screw the form to the floor. The center of your form does not need to be solid, but the edges do need to be continuously supported. Space your blocks close, moreso as the curve gets tighter and put them in perpendicular to the curve.

Ditto on making it extra long, the ends are always junk.

If they are large, either use something besides phenolic resin, or spray them down with water do extend clamping time. Sucks when the glue holds and you are only half clamped.

Clamp up dry. If you can't clamp it dry you are not going to make it work with glue. Have a plan. I start in the middle as well.

Make your laminations extra wide, and trim to size. You can run curved laminations across the jointer and then threw the tablesaw, or if they are large get out a hand plane. They will not always cooperate as grain variations will steer the wood up and down as it bends.

Sometimes I will steam and prebend over a form, but usually I just use thinner plys. Steam does all kinds of things to wood and it is usually too hard to clamp out all of the voids.

[Doug Shepard]

So far all mine have been MDF done with a router on a trammel arm, and covered in plastic laminate. Mine have all been male/female but the one thing I would do different if making any more is to add some guide runners. Just some hardwood strips on the bottom edge of both forms so that they slide together straight. Until you get a few clamps on, the 2 halves want to slide side to side without something to keep them aligned. Also if you use plastic laminate, make sure to include the thickness when yu cut the wood or MDF forms.

[Doug Mason]

thx for all your replies--very helpfull. I have to make a couple more Forms--so I'll use glued up MDF. I am making a country rocker--albeit much simpler than Mikes per below. And Mike--I plan on doing some chip carving on the slats as well! Larry--I am currently experimenting with steam bending right now as well--where I can steam pieces with a tight radius before transfering them to a form (for either lamination or non-lamination).

Using a spokeshave on MDF? Never occurred to me--I'll see what happens.

One other related question; I have a vacume pressing system and I was debating how I could do this bend in the bag? Correct me if I'm wrong:
1) Building a Form with ribs for the vacume bag would be too much work for this one-off project--simpler just to make an MDF two-part form and do it manually
2)Or could I just put the two-part MDF form in the vacume bag and forget all the clamps? And in this case I could forget about the top form--all I would need is the bottom form.

thx for your thoughts.

[Rob Diz]

I made a form out of MDF for my bent lam project. I went to the BORG, asked if they had any damaged MDF they wanted gone cheap, and sure enough, 50-90% off, depending on damage and what I could talk 'em into.

I made one template, then screwed a sheet of mdf on top, and off with my router bit, screwed on the next sheet, same thing. Screws are more expensive, but you don't need to wait for anything to dry.

I used cork on both sides, although some will say you only need it on the show face. I used Saran wrap to keep the glue from sticking to my form. Ineligant, but handy.

DAP Weldwood and Unibond will have the least amount of springback. You may want to get a brayer (roller) to apply the glue - I got mine from Dicks Art Supply. Well worth the money

And don't forget to "go long" on your cuts. Things move around a bit as you clamp them up