curving half inch plywood

[muttman]

I have some cabinet grade 1/2 inch plywood leftover from a project that I'm hopefull to get some shields out of. I plan on maybe keeping one for myself but I'm hoping to donate about six blanks to my barony in different configurations to people can try different types out. At least the heater and kite I'm going to want to curve and I'm not sure how to go about it. I tried running it through the tablesaw making a 1/8inch groove every 1/4 inch for the length of the blank with the intention to bondo the grooves in after I got the desired depth of curve. I used six ratchet straps and maybe got overzealous because I had a catastrophic failure and ruined the blank. I wasn't wild about bondo-ing the grooves anyway.
So, barring that failed plan, and keeping in mind that I don't have any money to throw at this but I do have a pretty full compliment of carpentry tools, does anyone have any suggestions? Thanks in advance!
Drefan

[Sigurd]

How deep did you make the cuts? You'd need to go through all but the face layer, and fill with bondo/glue+sawdust before curving it. Individually each layer will bend, but 2 layers laminated will fail before curving.

[wcallen]

Every time we have curved 1/2" ply it was by putting 2 layers of 1/4" ply on top of each other with glue and curving them to form 1/2" ply. I don't know of a good way to curve 1/2" ply from scratch other than just leaving it out in the weather and hoping that it stays flat - so of course it won't. Not a good way to do things that you want to control.

Maybe make some flat shields with bosses for center grips?

Wade

[Paladin74]

What you need is a shield press; here's a guy who built one and tells you how to make your own, as well as tips on shield-building.

http://yeoldegaffers.com/project_shieldpress.asp

Good stuff there; good luck.

[Blackoak]

I have had some luck using ratchet straps and pouring pots of boiling water on it. I did not get a deep curve, but I did curve some. The problem I ran into was that it did not keep the curve very long, especially outside for a humid weekend event.

I did not seal with polyurethane afterwards, so that may help some.

Uric

[losthelm]

1/2" cabnet grade is expencive stuff you might consider tradeing for regular 1/4" and useing the shield press tieebon III method.
Two layers will get you a much more stable curve with a lot less work.

[WendallVonDerEisenstein]

I come up with 3 options I'd be willing to try.

1) steam the wood until it is soft and bendable. Strap to a form and let cool and dry. May not work, I'm pulling this from a woodworking technique used with wood that is not laminated like plywood.

2) Saw cut the 1/2 plywood into two 1/4 thick pieces (well not really 1/4 once you subtract your blade thickness), then re-glue 2 pieces together over your curved form.

3) flat shields for your group!!!!!

[Sean Powell]

I have heard that laying 2 rows of bricks in a bathtub, laying down the shield blank, piling a bunch more bricks on the center and then soaking for 24 hours is productiove but I've never tried it. I've always laminated 2 pieces of 1/4 inch

Sean

[Thomas MacFinn]

I've always laminated 2 pieces of 1/4 inch

Me too. A single sheet of 1/4" would give you enough material for two curved shields 24" x 48" (or one 24" x 48" and two 24" x 24" or ...), more than enough for a curved heater and a kite shield.

[Ehryk]

1/2" is pretty beefy. I did 3 crossgrained layers of 1/8 (luan IIRC) covored all around with heavy linnen and edged with 3/8 climbing rope covored with rawhide. Very durable and quite light.

[muttman]

I do have some luan leftover from the same project that I do know I can curve. I'm saving that for myself. The half inch is whats left over from a project, most already cut into shield size rectangles. I thought about doing something like Seans idea but had concerns over delamination. The shield press while slick, is more than I'm looking to do. I'm really not looking for a deep curve either. So far, unless some silver bullet comes along, I think I'll try the bathtub idea. I'll let folks know how it goes!
Thanks everybody!
Drefan

[Lazarith]

One problem you might have soaking interior plywood is de-lamination on the edge and can also ripple the inside curve. I tried this method with mixed results. The 3 layers of 1/8" plywood is what i like plus it is somewhat lighter than 1/2". Cover it with cloth and you'll have a very durable shield.

Good luck.
Lazarith