#3 - Maple Pyramid Bow

[mmattockx]

65" NTN, 38lb@28". Hard maple board with mystery wood from a bin of offcuts for the overlays and bits in the grip area. Looks like white oak, but I am not certain of that. Finish is Helmsman spar varnish.

This bow was designed using David Dewey's spreadsheet and then worked down close to finished dimensions without ever putting it on a tillering tree. I left a bit of wood to allow for weight adjustments but ended up right where the spreadsheet said I should be. Aside from weight adjustment the only tillering was one very light scraping mid limb on the top limb to get it closer to circular tiller. The spreadsheet got amazingly close to perfect, especially considering the inconsistent nature of wood as a structural material.

It had a fraught creation. I started with it backed with fabric using TBIII, but scorched the edges of the backing when applying heat to add some reflex, so I sanded the backing off and applied a patch over a pin knot that I was worried about. That worked out well. After several hundred shots a hinge began developing on the bottom limb at a knot that was revealed as I was cutting the board down to size. I rasped into the soft area on the belly and put a patch of maple over it. That has survived several hundred more shots but you can still see the kink where the hinge had started. Next time I do something like this I will clamp the bow back straight when I glue the patch in.






















Mark

[DC]

Good job. It will be interesting to follow your progress with this method. I've had to patch up a lot of bows that I messed up tillering and although they shoot fine the finished bow doesn't give me that warm fuzzy feeling that an unpatched bow does.

[willie]

Looks very nice all finished out.
Leaves are falling and you have your camo on. hmmm, seen any of those big whitetails around?

I have used woodbears spreadsheet before, but never cut that close to the line. Your experience has given me some second thoughts about wood designed in such a precise fashion.  Did the set come in as predicted with the calculation?

[mmattockx]

Good job. It will be interesting to follow your progress with this method.

Thanks. Next up will be some lam bows using Perry reflex and designed using the spreadsheet as well. I found a really nice straight grained red oak board the last time through home depot that I am going to cut into lams and glue into deflex and then reflex on forms.

One thing to note is that you have to do a bend test to get the MOE for the piece of wood you are using in order for the calculations to be accurate. Now that I have done one this way I will be a bit smarter the next time up. The way this one went I cut a sample piece from the board and did the test, which got me a good estimate for MOE (+/- 5% or so). Then I measured the draw weight at 20" and compared that to the predicted weight and adjusted the MOE in the spreadsheet until the two matched and I finished working the bow down to size with the updated MOE in the calculations. Next time I will start looking at the draw weight earlier and use that to adjust the inputs to the sheet before I have pulled it so far on the tree.

I've had to patch up a lot of bows that I messed up tillering and although they shoot fine the finished bow doesn't give me that warm fuzzy feeling that an unpatched bow does.

Considering how many things tried to go wrong on this one I figure it is a small miracle it survived at all. I think I went a bit thin on the patch and am concerned the hinge will eventually cause a failure there. So far it has survived 400+ shots with no sign of failure, but I still don't trust it. Next time I do a patch I will use the belt sander and remove more wood before patching it.

Did the set come in as predicted with the calculation?

To be honest, I screwed around with it so much in removing the backing and heating in reflex (that promptly pulled out...) and the hinge that I can't say. The board had a bit of deflex that warped in while it sat in my shop and then I reflexed it a bit and didn't keep really good track of where the tips were throughout, so I don't know where to start measuring from. Currently it has about 7/8" of permanent set on the upper limb (measured from straight) and a bit less on the lower limb. After unbracing it shows about 3/8" more set on each limb that goes away overnight.


Mark

[DC]

Something to remember is that any deflex/reflex in a limb will still be there even after you bend them over the same form and glue them up. I've often wondered why limbs would come off the caul with a different bend. This last time I marked the lam that had a little deflex, glued them up the same way and the one that was deflexed was still deflexed. The reflex in the lam was minor, maybe 3/8" in 32 inches in a 1/2" thick lam but it was still there.

[HH~]

Now that a rest. Very well done.

I do like the color of those woods!

v/r

Hedge~

[MM2]

Greetings, Mark!

I think this is a great bow.

Congrats and thank's for sharing!

Michael

(A few months ago I built a hard maple bow too. And I had almost the same troubles like you with this - knots, hinge, etc. Nowadays its name is: Problem Guy.  )

[simk]

intetesting 😁 a calculated bow 😁 congrats - nice work and good result 👍 is there any thickness taper or is the bend the result of the pyramid alone? if it was mine i'd like to have a tad more bend towards the handle and a tad less towards the tips. keep up the good work! cheers from here

[mmattockx]

is there any thickness taper or is the bend the result of the pyramid alone? if it was mine i'd like to have a tad more bend towards the handle and a tad less towards the tips.

The limbs do taper for the last 11" or so to compensate for the extra width that having a real nock causes (the nocks are 5/16" wide). I agree that it looks a bit stiff out of the fades and a bit weak at the tips. It didn't look as much so on the tree, but I will be leaving the tips a bit stiffer on the next one. The bottom limb also bends a bit more when hand drawn than on the tree. I will be leaving it a bit stiffer on the next one as well to compensate for that. It is certainly all a work in progress getting these fine details sorted out.

This picture shows the tiller as it initially was with the backing on. It got a bit worse after removing the backing and the tips got a bit weaker, which is where I ended up. Next time I leave the tips a bit stiffer and the bottom limb will have closer to 1" difference from the top on the tree to balance out in the hand.




Thanks to all for the kind comments.


Mark