Laminated bow

[ivory marten]

Hi guys. I'm currently working on a crossbow, but I'm having some difficulties. I can make the stock and the trigger mechanisim, but making a proper bow for it is where I hit the wall.

Since I work in a woodworking factory there are a lot of thin strips of wood that I can use to make a laminated bow, but when I tried to do it previously it failed so I'm curious if anyone has any experience with this who can help me out with some advice.

Strips are about 55 cm long (technically they go up to 2 meters but since they are joined at 55 cm increments that's what I'm using to avoid any weakpoints) and I'm not sure exactly what type of wood they use but judging by the resin it's probably pine or something similar. Thickness of those strips varies, but the ones I'm looking at are about 3-4 mm thick.

Previously I covered 3-4 pieces in glue and stuck them together with some weights on top. After a day of drying I tried to test the bend but either it didn't want to bend at all or it would bend slightly but crack after pulling it back for like 10-15 cm.

So my question is: what am I doing wrong? Should I change the process in some way or is the issue with the wood, or am I using too thick/thin strips or is something else the issue here? Any help is appreciated.

[drifting whale]

A couple things come to mind. If it is pine, it may not be strong enough. Check the direction of the grain, you want it running the full length. You should be able to glue it up with the start of the curve in it. Different glues have different applications your glue may not be correct for that use. The glue may need to dry for longer.

[ivory marten]

Thanks for the info. I didn't mention it, but I did make sure that the grain is going along the entire length of the pieces, so that shouldn't be the issue.

I'm using standard woodworking glue and drying time on it was noted to be 24 hours so that's what I did. I'm not an expert on glues so I don't know what is the difference between different wood glues and how would they impact the end result.
I'll try to glue the next one with a curve to see how it goes and will eliminate the possible issues as I go along

[drifting whale]

The difference would be flexibility. Standard wood glue may not allow it to flex when pulled back.

[ivory marten]

Is there a specific glue that you can recommend? At least as far as ingredients and intended use are concerned since I doubt that same brands are available here

[drifting whale]

I cannot. Do some research, Google is your friend. You want something specific for bows

[tough vector]

You might find this interesting: https://youtu.be/ZoaTZY5cSQE

Especially for the back you want to use wood with as little 'run-off' as possible. Grains that end halfway your piece (run off) are quicker to separate. With a backing this issue can be reduced.
Similarly a layer between the wood could also help.
For fabrics you could use think of things like canvas, carbon fibre, fiberglass or rawhide.

[normal cobalt]

Hey op, did you succeed at the end ?
My 2cts, since I did make bows out of pine (as no one should ever try, like it is written everywhere on the internet) : glue is probably not the issue, grain along your strip is

Also I'm not sure pine would do for a crossbow, considering you'll have a higher lb than a bow, and it is already not good for a 18lb bow

[ivory marten]

Nah, it didn't work. I was careful with the wood grain and stuff, but it seems that that the wood type is the issue. I'll probably come back to this when I find a proper piece of wood to make a single-piece bow or just order a fiberglass limb and make it look like something more authentic, but I'm not in a rush

[rough rampart]

In an old book about making stuff for boys from like the 1950s or something, I saw a setup: the bow was made from just putting 3 strips one behind the other, and each was like 5 cm shorter from the ends than the one before. So outer is 55, 45, 35, and they are stacked longest to shortest from the front. No glue is used in that design, just a sstring loop that ties inner against outer bow.

For a crossbow, the bow usually would be laminated in a curved fashion anyway - cutting the string of a crossbow resultes in the bow still being bent, which prevents damage from more bending