Hickory Heat treating, balancing weight and tiller

[Azmdted]

Hi all,

I built a pignut hickory flatbow, 68" total, 66" NTN, steamed in 3" reflex and more reflexed tips.  This is my first time trying heat treating and I'm having a heck of a challenge balancing heat treating with the need to retiller and eventually scraping through the effects of heat treated wood.  Here's what I've done so far:

1.  First heat treating was done at floor tiller stage.  Heated it in the caul I used to reflex it.

2.  Tillered it to 50#, but scraped through the darkened wood and the bow lost it's reflex.

3.  Heat treated again after tillering and weight went from 50 to 58#.  I want it at 50.  Used a 1200W heat gun, in stand holding nozzle 4" from belly.  Took an hour to heat treat both limbs.  I'm thinking I should probably cut that down to 3" to make up for the 1200 v 1500W gun.

4.  Tillered again with removal from both the belly and sides.  During this phase one limb became very weak compared to the other.  I assume I heat treated it less than the other and scraped through the goodness.  Continued tillerring till it was even and back at 50#.

5.  I still have reflex in the tips, but the limbs themselves are maintaining about 2" of string follow.  I've put about 200 arrows through it now.

My thinking is that heat treating at floor tiller probably wasn't necessary, is that right?
I'm also thinking that I didn't heat treat it well enough after I tillered it and that's why further scraping caused me to work through the tempered wood.  Sound about right?

How do you deal with the increase draw weight from tempering?  Do you tiller to desired weight, treat it thoroughly, and then retiller to weight?  Or tiller it to under weight by 10% or so knowing that tempering will bring it back up and then touch up from there? 

This is a learning bow so if I temper it again, no problem.  If I screw it up completely, I'd be disappointed but I'd learn from it.   I'd just like to break the cycle of tempering/tillering before I'm left with neither

Thank you,

Ted

 

[PatM]

I'm not sure steaming and heat treating is the best idea for the wood.  No need to steam the reflex in first.

[Del the cat]

Sounds to me like there is too much reflex and it's just pulling out. I think you are asking too much of the wood, though, TBF you don't give the draw length.
An hour to heat treat the whole bow isn't actually that long. 45
mins per limb isn't excessive.
The longer and slower the heat treating the deeper it goes. I also advocate clamping side cheeks to the limb during the heat as it directs the hot air along the belly and keeps it off the back... it gives a more even heating.
https://www.youtube.com/watch?v=kM1_A2A0_TI

Your suggestions at the end of the post will all work, but it depends how critical of draw weight etc you are being.
Working out when to heat treat is down to experience and target weight etc. I recently made some flight bows... I made 4 to so I could pic the best.
The first one had the same problems that you describe. Subsequent ones were made closer to final dimension before hear treating. (I was heat treating the Yew belly before gluing the boo backing.
Del

[Azmdted]

I'm not sure steaming and heat treating is the best idea for the wood.  No need to steam the reflex in first.

Thanks Pat,

I will try it without steam next time.  I've read about as much that says that steam drives moisture in as it drives moisture out.  I thought it would be more gentle on the fibers so I gave it a try and then let it dry for 4 or 5 days before heating it.  The dry heat did drive a dozen or so small droplets of water out but I don't know if that was in the wood to begin with or induced by the steam.

[Azmdted]

Thanks Del,

The DL is 28".  That's a good point about asking too much of the wood, I'll be less ambitious next time.  I like the idea about side cheeks.  I believe that I lost a lot of heat off the sides so in addition to protecting the back that seems like it would channel the heat more productively.  I hadn't thought about that.  Thank you for the video link, that's quite the set up.  It's always nice to see how others do it.

I appreciate your reply and suggestions, thank you.

Ted

[bownarra]

Yes best to limit yourself to 1 - 2 inches max reflex to begin with.
Whne you had it finish tillered to 50# and you heat treated it again you could've reduced just the width to get you back down to 50#. This keeps the strain the same and is more effiecent than removing just the thickness.
I personally heat treat once around 20 inches of draw or when the first set starts to show itself. I then access where I am at with strain levels/set eg. am I wide enough for the drawlength/weight I want. Continue tillering both side and thickness until about 25/26 inches then heat treat again to even everything out. Then tiller to finished drawlength (side tillering).

[IrishJay]

I haven't built nearly as many bows as the others who've responded so you may want to take my advice with a grain of salt. But, what I generally do is tiller for my target draw weight, then when I heat treat the weight does go up a few pounds, but then after 500 or so arrows the weight drops a few pounds, putting me right where I wanted to be.

Tiller--> 50lbs --> Heat Treat +4 lbs --> 54lbs --> 500 arrows -3lbs --> 51lbs Final Draw Weight.

[Deerhunter21]

wouldnt the heat treat throw the tiller off a little irish, making you need to re tiller it and then lose a little of weight?

[IrishJay]

Again I'm not as experienced as many others here, but so far I've found that if I have a good even tiller, and I apply a good even heat treat it doesn't effect the curve of the tiller, just the weight. I think if heat treat is affecting your full draw curvature then either the tiller wasn't quite even to start with or the heat treat isn't even. If you have light spots and dark spots in your heat treat the dark spots are going to stiffen more than the light spots and that will throw off your FD curvature. If your heat treat is uniform then the stiffness added to the limb should be uniform and FD curvature won't be affected only weight.

[DC]

If you start out with a less than perfect stave and have to do a little heat correction just to get you in the ballpark then there is a real good chance that subsequent heating will move the bow around as it tries to go back to where it was originally. This can affect tiller, string alignment, your mood.

[IrishJay]

Good point there DC, I wasn't taking that into account. I generally try to clamp the bow to something to hold any heat shaping/corrections in place while I do the heat treat.

[DC]

Even if you clamp it to a caul sometimes they will move just enough to throw out your string alignment and possibly tiller. I guess the stresses that you locked in the bow with the first heat treat move around a bit with the next treat.

[Azmdted]

Thank you all for the added information and discussion, very useful.

[IrishJay]

Azmdted, you definitely want to listen to DC over me. He builds some of the best RD's on here and has exponentially mpre experience than I do. I've learned a lot from him in my time on this site.

[DC]

Well thanks IJ but I've just been copying the guys that came before me. If you want to make an RD just hang a couple of pictures of Marc St Louis' bows on your tillering tree and make your bow look like that. That's what I did.