Primitive Archer
Main Discussion Area => Bows => Topic started by: simk on October 21, 2020, 06:00:24 am
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Hi
I'm on the trilam route for the first time and have a q:
Does it make any difference wheather I'm gleueing all 3 strips at once or if I do the glueup in two steps: first belly and midlam and then backing later?
I'm using a well curved caul for the glueeup.
Thanx for advice! (-S
cheers
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I believe there are advantages to gluing up one at a time with different degrees of reflex with each glue up. The disadvantage to gluing it all up together is keeping everything lined up and in place as you clamp it.
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Glue-up everything at once to begin with. Once you have some stack figures you can start experimenting. The simplest way to pre-stress or perry refelx is to glue your belly lams (spliced at handle) in deflex then 'force' it onto the form and into reflex.
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Thanks very much guys, that all makes sense and helps for decision making - I will glue everything at once. My caul is rigid and the lams are full length...once I will have to splice them I will play that trick. (-S
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My caul is rigid and the lams are full length...once I will have to splice them I will play that trick. (-S
It doesn't matter if they are full length or not, you can always glue in deflex on the belly lams, then pull it into reflex on the form while gluing on the backing.
Mark
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thanx Mark,
sadly I will not be able to force a doubled lam into my caul :-\
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Simk,
I have done it both ways. I have done many by gluing all at once. Lately I have been gluing up the core and then adding the backing. I feel that I potentially get better limb alignments when I do it in two steps, but If done correcting gluing all at once certainly works just fine. You will have have to try for yourself and see what works best for you.
Cheers,
Taylor
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My caul is rigid and the lams are full length...once I will have to splice them I will play that trick. (-S
It doesn't matter if they are full length or not, you can always glue in deflex on the belly lams, then pull it into reflex on the form while gluing on the backing.
Mark
Unless you use thin lams you will be struggling :) You will also need some good pressure strips.
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thanks Taylor! very helpful information! doing all at once anyway seems more economic ;)
:)
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If you do it all at once wrap masking tape around the bundle in a couple of places.It gets pretty slippery. Something else I've done is to add an alignment pin at the handle area to hold the bundle together while you add the clamps. I drilled a 1/8" hole down through the center of the bundle at the handle into the riser and added a bamboo skewer or dowel as the pin. Do a dry run first. You can cut the pin flush after the glue dries.
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Yes PatB, it gets slippery - not easy to control that middle lam. I too was thinking about that pin idea...this really could work well :OK This time I just started clamping in the middle and continously aligned everything while clamping more towards the tips. Got acceptable accurracy and have enough wood for last little adjustments.
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One pin works well, 2 pins side by side, even better. :OK
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Just tape it down with parcel tape. A wrap every foot or so. You can use spring clamps on the sides of your lams to hold them still and in line intially. Then wrap the full thing in what we call clingfilm and I think you call it saran wrap :) Nothing moves after you get the tape on and the saranwrap stops glue getting on everything.
Once you get your method sorted it is easy enough.
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Clamping like you have done isn't ideal without using a pressure strip. Aluminium strips or thin stainless strips work well. You risk poor gluelines when using a few too few clamps. There is a lot going for using innertubes on these sort of glue-ups.
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you are probably right bownarra ;D I usually use the innertubing bad was too lazy this time to cut new rubber bands...just went with the clamps I had. glued two bows, not so bad, quite happy with the results. one limb shows little gaps on one side, but wont fail ;D will probably buy a few more of the liitle cheap clamps... clamps allow good control. rubber bands sometimes seem to tend to tighten somehow assymmetric if not applied very careful.
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If you want to stick with the clamps definately make/buy a pressure strip it will stop those fat gluelines. Good luck :) Lam bows can be fun.
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I like your monitoring bownarra ;) would a 0.75mm steel sheet be appropriate as a pressure strip?
other trilam question: does the perry glueup relieve stress from the belly and instead put it midlimb towards the gluelines?
thanx!
(-P
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other trilam question: does the perry glueup relieve stress from the belly and instead put it midlimb towards the gluelines?
Yes, a bit. The effect is not as dramatic as Dan Perry seems to think, but you can reduce the stresses on the belly surface by 2-5% with enough Perry reflex added in. Keep in mind this also increases the stresses on the back but that is not usually a problem for most woods.
EDIT - I went back and looked at Perry reflex in more detail. Dan Perry recommended that single wood bows (all lams are the same material) have the back be 1/3 of the stack and the belly 2/3. This results in the 2-5% reduction in belly stresses I stated above. For bows where the backing is much stiffer than the belly wood Dan suggests the back be 20-25% of the stack and the belly the rest. With this arrangement it is possible to achieve reductions in the belly stresses of 15-20%, which is very significant and explains why lam bows with bamboo or hickory backs often perform so well.
Mark
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hello again ;D
after screwing up and got underweight with no1 I did some more careful tillering today with no2
still needs a few finishing touches, currently drawing 46# @ 26", already shooting nicely
took a pic after every tillering step and put the frames together on my mobile phone
next time I'll taper the middle lam to mostly skip tillering ;D
;D
https://www.youtube.com/watch?v=CYKJmW0AhOI&feature=youtu.be (https://www.youtube.com/watch?v=CYKJmW0AhOI&feature=youtu.be)
;D
cheers
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Looks pretty good to me. :OK
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Looks real nice. What kind of wood? Chrono? It looks fast.
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DC, it's ash-ash-yew. this pic is not the actual situation anmymore. Still fiddeling that top limb ;D not finished yet. Also remarked a little handshock shooting it today. this one is quite long and is supposed to be a target bow, probably not the fastest. also made a shorter version but it came underweight - rushed the tillering :-(
thanx for inspiration (-S how the heck do you keep so much reflex on yours???? i really tried to do very careful tillering with this one but saved only 2,5 of 4,5". it might be the boo backing.... (?) Anyway planning some some little design changes again on the next one. will check the chrono sometime then...
cheers
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How thick/wide is the Yew? I'm pretty sure set is wood compressing/collapsing so what else could it be? I have tighter recurves on mine so I started out with more reflex. Some of mine had 6-8" of reflex off the caul and some of them gained reflex while tillering(Perry). You have more patience than me. First shot is through the chono ;D ;D
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DC, set is miracle, nobody has seen it under the microscope. but it happens and its a fact.
in this case its not classical set i think, its lost of artificial reflex, which i think is someting different. it's a matter of design. i will work on that 🙃 bow is 1 3/4" wide at the fades and close to pyramid. yew tapers from 5mm to around 2,5mm. i hardly observe any set with d/r's in the deflexed part where most work is done. cheers