New Bamboo backed Ipe bow

[macbow]

With using Roy and junkie's tillering method everything works out.
I would ask the question when shifting the center.
From what I got from watching Dean Torges video the main thing stressed was the bow carried and balanced better in the hand.
I never found that to be a big deal. Is there another reason?

[Bowjunkie]

Shortening the bottom limb makes it balance better in the bow hand, and I prefer it that way because it's not only better balanced to carry, it's also better balanced to swing, point, and hold on target the way I shoot.

And yes, there are other reasons. Shortening the bottom limb moves the bow's longitudinal center upwards, closing the spread between static balance, string hand fulcrum, and dynamic balance at full draw. This makes the bow limb/balanced better throughout the entire draw cycle, easier to synchronize the limbs, less handshock, treats the arrow better upon release, etc... all imho of course.

I hope I said all that right... I'm in a hurry.

[Roy from Pa]

Mac I can't see how it would make that much of a difference either in hand balance. It's just how Jeff taught me and how I've been doing it. Think my next bow, I will make equal length limbs and limb time it for craps and giggles..

[mikkekeswick]

They work both ways but shorter lower limb is the best in my eyes. Definitely carry better.

[macbow]

Thanks guys.
Couldn't hurt to have that little bit of extra clearence when you hunt,fromthe ground like I do.

[Ismail]

Here is a mock set up before glue up. Put toothpicks in to keep the bamboo aligned.




One thing im concerned about, is the clamping to the mid limb post will need a great amount of pressure. The clamp im using cannot seem to provide that pressure.

Should I switch to the metal clamps?

Will the wood be able to handle the pressure?

[Ismail]

I switched to the metal clamps, the blue ones in the above picture. Much more leverage.

The only thing is i came to the end of the screwing capacity and there was still an inch of space left to go.

Will have to find a way to lower the clamp more before using the srew on it.

[Buemaker]

To me the end posts looks very tall compared to the other posts. Since it is your first try how about making them a bit lower? You will still have a nice DR bow.  

[Roy from Pa]

Yes they do, Bue. How high are they from the form?

[Ismail]

They are just like Roys: 2 3/4", 3 3/4" and 6", including the form bases.

[Ismail]

Did the glue up today:

 



As I was tightening the last inch on the mid limb post, heard some creaking. Quickly relased it a little and left it at that height. Then tightened the other side to the same height.

Thats why the limbs are not touching both the mid limb posts.

[macbow]

If some of the belly wood cracked, hopefully not enough to cause a problem. That is the area that I remove wood first when floor tillering.

[Ismail]

Also hoping it wont cause a problem later on.

Are all the clamps placed right?

Think the creaking was from the bamboo, not the ipe. When i did the mock clamping to the form, did it with the ipe only. Clamped down nicely.

[macbow]

With the rubber bands and clamps I think it looks ok.
Usually when I get to where you are I add all the spring clamps I have spaced throughout.

It would be unusual if the bamboo was doing the creaking.

[mikkekeswick]

Remember what I said earlier about ipe being stiffv stuff and not going for too much reflex?!?  
Bamboo won't make noises as it was being compressed as you tightened the clamps but the ipe with square edges was feeling tension (being on the outside of the curve).
Also notice how the outer limbs are almost straight after your big clamps. This will make it harder to tiller down the road.
Anyway it's all good learning  

[Bowjunkie]

To further clarify, it's straight after the midlimb clamps because you didn't taper(or didn't taper enough) the limb thickness prior to glue-up.

At first glance it doesn't seem like a big deal, but pretapering causes it to not only take on a more even reflex during glue up and save you work when you get to tillering, it helps thwart a phenomenon that can occur if you have to remove too much material afterwards to get the outer limbs flexing. Under these circumstances, a limb can tend to gain reflex as you remove belly wood... you remove more belly wood to try to get it to come around, it gains more reflex... and on and on until, wham, it finally comes around and you're under weight.

There's not much you can do now. So when you do get to tillering, go slow and exercise it a LOT each time you remove material from the belly.

[Ismail]

Took the bow off the form and unwrapped it. At first it looked quite good...until I saw the crack. Tragedy.

 

 




 

Here is another picture of the glue up.

 


The crack was on the shorter lower limb (right). Just after the mid limb post.

Any ideas what went wrong?

Few thoughts came to mind:

1. The end posts were too high (6") - Like Bue warned before.

2. The mid post was too far away from the end posts.

3. The Ipe was too thick (13mm)

[Ismail]

Ah, pre-tapering limb thickness. Didnt know I had to do that. How much should it have been tapered?

[Roy from Pa]

#3.. The ipe was way too thick and not tapered. I'd have made it 1/2" at the riser, tapered to 1/4" at the tips. Also there is bad grain run out where it broke.

[macbow]

Agree, it is slightly over 1/2 inch in thickness and IPE is tough to bend.  The run out definetly added to the failure.

I don't remember what the target weight was. A 3/8 inch thick tapered slat at .004 per inch will easily make a 50 plus pound bow at 28 " of draw.