Tillering R/D Tri-Lam

jvermast · October 13, 2011, 04:44:00 PM

I've just cracked a second Tri-Lam with the belly lam going over the fades right at the tip of the power fade - the crack is in the backing - both bows are 1/8" hickory backed, 1/4" cherry core (tapered) - 1/16" maple belly

It almost seems like I'm getting way too much bend at the fade and not enough at the tips but I thought the whole point of the R/D was to leave the tips somewhat stiff and get most of your bend from the fades to mid-limbs.

Any posts detailing the tillering of an R/D Trilam would be great.

okie64 · October 13, 2011, 05:01:00 PM

Be easier to give you an opinion with some pics of the break. Are they breaking on the back or is the belly giving you problems? When I build an all wood r/d bow I try to get most of the bending at midlimb and a little bit of the bending in the inner limb.

jvermast · October 13, 2011, 05:12:00 PM

Sorry, I'm gluing up the small crack right now so can't grab a picture, but definitely will.

The crack is at the end of the powerlam on the backing, I thought hickory was fairly crack proof - maybe my backing is too thick at 1/8"?

It's maybe 1/4" in towards the middle of the bow and 1" down toward the tips.

okie64 · October 13, 2011, 05:53:00 PM

1/8" should be right for your backing. Thats the most common place to get air gaps. Did you get it clamped good at that spot with no gaps? Sounds like you might have too much bend at that area though and its causing a hinge there.

jvermast · October 13, 2011, 07:34:00 PM

The left limb looks stiff in these pictures and I was working on that, but the amount of bend in the hickory can't be enough to crack like that...

soopernate · October 13, 2011, 07:58:00 PM

Too steep of a riser and too short fades are concentrating the entire bending force on that one little area that let go on you. Try longer fades tapering to a very very fine point. Try to be no thicker than 3/16 og sn inch or so two inches in from the tip and a smooth curve to the top of the handle

jvermast · October 13, 2011, 08:19:00 PM

That makes sense, I guess it has become more of a corner and less of a smooth curve?

I wonder if there's any way I can salvage it by recutting the fades....

eflanders · October 13, 2011, 09:10:00 PM

+1 Soopernate. Unfortunately I don't think you are going to be able to salvage this one.

jvermast · October 13, 2011, 09:12:00 PM

If I recut the fades to this and grind/hand plane off the belly lam - I should be able to redo to this shape and put a new belly lam on...

jvermast · October 13, 2011, 09:38:00 PM

Sigh...broke.

I think I'm done with R/D lam bows for now - first three X backed Y bows I've made I had absolutely no issues with and they are shooting fine and I have now ruined two laminates in a row...

Just as a take-away from this - the Buck Buckley BuildAlong I've been using as a guide says 14" powerlam/12"x2"x2" with the fades 3.5" in from each for a 64" bow - both bows I made seemed that the fade was way too steep with those measurements.

Anyone happen to have any insight? Powerlam/Riser should be longer perhaps?

soopernate · October 14, 2011, 11:03:00 AM

Most of the D/R bows that I have seen have longer risers and correspondingly LONGER fades. Risers I usually see in this style are 18 to 22 inches in length with fadeouts that are 7 inches long or longer. I think even the redrawn riser you have will be too steep and not gradual enough to the ends of the fade. Fade it in VERY slooooooowly and you will get a winner. The overall shape is TOTALLY doable.

jvermast · October 17, 2011, 11:14:00 AM

I went off this post from Buck Buckley:

QuoteThe riser on this bow is going to be 12" so my power-strip will be 16". Bows from 58" to 62" will have 12" riser and a 14" power strip. Bows from 64" to 68" will have a 14"riser and a 18" power strip

His block was 2x2 - so I made my riser 2x2x12" with a 14" power Lam but looking at his pictures, I can't see how that is at all possible when compared to mine.

Argh.

Anyone have some advice on a 64" NTN Power Lam and Riser sizing?

soopernate · October 17, 2011, 12:37:00 PM

I never even noticed the power lam until today. Sorry about that. I usually make my power lams on trilams four inches longer than the riser so that the fades on it go at least two inches past the handle on each side.

jvermast · October 17, 2011, 03:46:00 PM

Do you think I would have been able to use this handle design with a longer power lam? That makes much more sense to me.

soopernate · October 17, 2011, 04:19:00 PM

Probably. I dont think the abruptness of the handle would have had as much affect on the spot where it failed if the power lam was pushing the bend further out in the limbs. I would follow bucks buildalong you referenced...its a good one. I am hunting for some osage boards currently so that I can build a similar one for the next trade.