Glueing tapered lamination question

[Heath F]

So im still new to building bows. Ive built a couple selfbows and quite a few board bows, but have been thinking about trying an all wood laminated bow, but want to learn as much as possible before diving in head first. After combing this sight, and others ive learn alot, but one question ive found that i cant seem to get a definative answer on is riser and lamination fitup. For all intents and porposes. Lets say i wanted to build a flat laminated longbow (no deflex/reflex, to rule out and curves or anything). when glueing laminations, u'll get a hump/pyramid in the center of ur bow. Im sure im over thinking it, but is the best way to fit the riser to sand it to match the bulge, or sand out the bulge to fit the riser. Some people have also talked about adding a lam with reverse taper to allow for a flat glue up. But wouldnt that counteract the taper, So u wouldnt gain anything from tapering and may as well use parallel laminations? Sorry for the word vomit of my post, and if this has been covered previously (lots of the links ive tried clicking on dont seem to be working)

[kennym]

The reverse lam would be applied to the form and not glued in the bow.

Or you could parallel the taper lam to the end of riser .

hope that answered the question!

Welcome to the bench!
kenny

[BMorv]

I'm not sure I'm following your question.  Lams on an all wood bows are typically spliced together then sanded flat.  If you aren't bending the lams with reflex or deflex then lams will be flat and you just glue your riser to them.  
If you are talking about a power lam (some call it a riser too) then that goes between your backing and lams, and your clamps will bend the backing around it.  A power lam needs to be feathered paper thin on both sides.
Purple heart power lam (riser) under the bamboo...
  [/url] [/IMG]

[Heath F]

Sorry, i guess what i was meaning is when useing tapered laminations after splicing them together, the center will be thicker than each tip of the lamination. So should u sand the lamination parallel with the riser in the center or sand the riser to match the hump caused by the laminations. Not sure if that makes more sense or more confusing.

[BMorv]

Oh I gotcha now.  I don't think that the difference is something you have to worry about.  At most you will have 0.006" taper per inch on the entire stack, so that's .036" difference on a 12" riser from the middle to the end of the riser.  That's 1/32", and I think the clamps would close that gap.  I normally glue up deflex and I'll have 1/4" or so to accommodate, so I trace out the outline and make the riser fit lams.

[BMorv]

I guess it depends on how you do your glue up too.  If using a form like for a glass bow you could do like Kenny suggest.  If you are just using c-clamps then I would imagine that the clamps would bend the lams the 1/32" to close the gap.  Or just sand the riser a little to match the tapers if it concerns you.  It wouldn't take much.

[Heath F]

Ok, i will most likely just clamp it with wood clamps flat,till i get the hang of messing with laminations, before adding other variables. So if clamping wont take out the gap, i'll hit the riser with a little sandpaper. Ive got two osage selfbows to finish up first, so ive got plenty of time to keep researching. But thank you guys for the input.

[monterey]

No, don't try to clamp it to shape!!    

You will be glueing in huge amount of stress in the riser to lam joint.  The feathered ends of the riser will easily compress but halfway back to center where the riser is much thicker not so much.

Best case scenario is a thick glue joint.  Or worse you could end up with an open gap.

Kenny set you on the right track.  I'll expand a bit for clarity.  Let's say you want .006 taper rate and will do it with three tapered lams of .002 each.  Order or grind six pairs of tapered lams.  Put three pairs of tapers on top of your flat form with the thin tips at the center end to end.  Tape them down.  Now they are a part of the form.  When you lay the bow up with the thick ends of the taper at the center the form is now flat.

[BMorv]

Yeah that's true about the stress.  My bad!    

I wasn't thinking about the stress on that joint as I have never done it that way.  I always have a power lam and deflex so I fit the riser to the lams.