Questions on Tempering

[matts2]

I have read many posts on tempering either different parts of the bow or the whole bow.  What does tempering really do?  I read that some woods are good candidates and most aren't.  What woods do you normally temper or is it a case by case.  And finally, how hot does it take to temper.  I have a large oven mounted on a trailer that I could easily lay a bow in and bake it.  What kind of temps does it need to get to?

Thanks

[b.glass]

Good question. I'm thinking about tempering some pecan which very similar to hickory and wondered if it is a good candidate. I've tried some hickory baking and the bow ended up failing. I don't know if it was me or the hickory that was more at fault.

[John Scifres]

I highly recommend the Trad Bowyer's Bible Vol. 4.  There is a Chapter in there with all your answers.

[k-hat]

I second John's suggestion.  From what i've read, heat treating/tempering is thought to change the cellular structure in the belly, some have equated it to "melting" the cells together, increasing the strength (sometimes significantly).  Heat treating/tempering should only be done to the belly, not the back.  I heat treated the belly of my red oak flat bow over the stove to remove excessive set (3+ inches).  Found out after the fact i should have scraped off the old compressed cells first, but still wound up with very good results.  Got 2+ inches of reflex treated in, then after re-tillering, scraping, and sanding, she stands at about 1/2 -1 inch of string follow just after shooting, and returns to almost a flat profile after sitting unstrung for awhile.  BTW, tempering initially added some draw weight, but i tillered it back to previous wt.  Definitely get a little more educated on it, then dive in!

[k-hat]

Forgot to address your last question on temperature.  I didn't monitor temp, but heated about 5 inches over a red hot burner, moving back and forth constantly, moved on when it got toasty on belly and began smoking lightly, and the back became almost too hot to touch.  You want the heat to penetrate the belly pretty good but not burn the back.  The Natives did it over hot coals in a similar way if i understand correctly.

[b.glass]

K-hat, did you bend that bow at all while treating with heat, or was the reflex achieved by heat only?

[matts2]

String follow is the main reason that brought this question up for me.  I think I am understanding that string follow is caused more by the belly.  So tempering the belly is a possible way to "help" prevent this?

[k-hat]

Glass -- Sho did!  I rigged up a jig similar to what the guy (forgot his name) in TBB4 did.  Basically reverse strung the bow with a long string, then a stick in the middle between the handle and string to hold it in about 5 inches of reflex.  Probably pushed it, i was waitn on it to pull a splinter or something, but it never did.  I actually treated it twice.  The first time, i heated then bent the limbs and let it cool like that.  Helped, but one limb didn't take at all.  So the second time i did as i mentioned above and heated with it bent.  Worked much better.  This is the only bow i've done this too, so may not be a good idea?  But it worked!
Just to be safe, i backed with linen afterwards.  Shooting nicely now.

I will add this:  This was an exceptional board i used for this bow.  Very straight grain, and very dense.  I tested a piece and it came in at above .8SG, which i believe is high for red oak. That made this bow very forgiving of my learning errors!

Matt-- I've heard of people treating before tiller, and others treating after.  TBB mentions that many bowyers of the past used this to correct excessive set.  Some guys here will say it's useless after already crushing the belly cells by bending, but I think the key here is to remove that outer layer of cells before treating.   Seems to me that it also helps to have it tillered properly b4 treating so you don't end up scraping off the treated cells.  

I'm still learning so take it for what it's worth!

[matts2]

I might have to give it shot.  I am working on an experimental bow right now.  Trying different things on this one just to learn.  It has some decent string follow.  If I ruin it, no biggy.  Only have a couple bucks into it.

[Pat B]

Marc St Louis wrote the chapter in TBBIV with info he came up with over years of testing. Marc didn't invent the method he just developed his way of doing it to increase the performance of his high performance wood bows(some in the upper 190fps).
  I have been tempering bows for a few years now. I don't do it as extensively as Marc does but we are after two different results.
  Ideally you should temper a bows belly to prevent string follow and not as a cure for it.Once wood cells are crushed(set) it is too late to fix them. You can minimise the set with tempering. I believe this is temporary but I can't prove it.
  When I'm ready to temper a bow it is anywhere from floor tiller stage to after tillering is complete and sometimes two or three times between the two.
  First I clamp the bow to a caul, belly up, with one clamp at the handle and one on each tip. I use a heat gun set on high and hold it about 1" above the wood surface. I move the gun back and forth over about a 6" area until the wood begins to darken. Ideally you want the wood wo turn a chocolate brown color. As I get the color I like I move out and get the next 6" but keep coming back over the last area so I get an even toasting down the whole working portion of the limb. I keep moving out in 6" incriments until that limb is done and move over to the next limb.
  Tempering is only for the belly of the bow. Be careful not to scorch the sides or the back. Tempering hardens the wood(fire hardening) and increases compression strength. Some woods react better than others and whitewoods get the best results. I have had good luck with osage and locust too.
  When I say whitewood I refer to all wooda that are not osage, locust, mulberry, etc. I consider hickory, ash, elm, red oak, white oak, hackberry and others whitewoods(as far as wood bow building).
  After tempering it is imparitive that you allow the wood to rehydrate before stressing it. If you don't it will fail. Depending on the R/H of your area at the time this waiting period could be a week or two. I also add reflex while tempering.
I use two different heating methods for two different reasons. For bending, straightening and untwisting wood I oil the wood first as to not scorch it. I also think the oil helps the heat penetrate the wood better and holds the heat longer. When tempering a bow's belly I use dry heat with no oil. I want to purposly scorch the wood to harden it and increase the compression properties of the wood.

[matts2]

Thanks Pat, that was some great info.  I just have the first Bibles and will be getting the other two as soon as I can.

[Pat B]

Marc did an article in PA Magazine a ferw years ago too plus talked about tempering in a more recent issue. He also did a post on PA about tempering not long ago.

[k-hat]

Thanks Pat for filling in the gaps!  Don't have TBB4, but read excerpts that contain the info you gave before tried it on my bow.

While we're on it, is there a difference between heat-treating and tempering (using the same heat source, ie. dry)?  I've seen and used the terms interchangeably, but does the trad community consider these same or dif?

[Lee Slikkers]

This is interesting...I'm not sure where ERC fits into the white wood vs osage, etc but I know it is weak in tension and good in compression.  Based on the results of heat treating improving the compression aspect of a bow would an assumption that a heat treatment on the belly of ERC would be wasted effort?

Thanks~

[b.glass]

I get the impression that different woods take heat treating differently. That's why I asked about the hickory. I don't know if ERC would be a good one for heat treating or not. As I recall Marc St.Louis heat treated ironwood and elm maybe, and some other woods,(I'd have to get my copy of TBBIV out to check). It seems not all reacted well. I need to read Pat's post, it may say.

[Pat B]

I'm not sure about ERC. I know yew reacts well to tempering from what I've heard. Bona, hickory is one of the better choices for heat treating as is elm(which Marc uses most) and ash. I think the oiler the wood the less the effect but I have had good success with it on osage and locust.
  On the Trade Bow I made last year(that Joe Weed got) I didn't exactly heat treat it per se but with all the heat straightening sessions I went through I think it was an accidental benefit.
  Kevin, I interchange heat treating and tempering, both meaning the same thing. For heat straightening I use oil. For heat treating and tempering I use only dry heat.
 Lee, try an ERC test strip. Give it a few days to rehydrate before stressing it though.

[Lee Slikkers]

Thanks Pat, a test strip is a good idea (sometimes the simple ones elude me, grin)

[Stiks-n-Strings]

I know you don't want to haet any kind of tropical bow wood. I tried to heat jatoba last year and it was a fatal mistake. it made the belly crush and fold under compression.

 I have been using heat since I started making bows and love using it to straighten and add reflex. Never tempered per say gut I get it good and hot. I have heated and straightened my yew bow that I am building about 5 times to straighten and adjust.

 Stiks

[eflanders]

You can temper the wood in several different ways, torch, heating element, heat gun.  I honestly can't say what the key temperature is but I can say that you do want the wood to heat quickly, change color, cool and then rehydrate.  I judge the amount of heat to use by the amount of time it takes for the wood to change color to a nice chocolate brown but not black.  I recently did a multi-laminated all-wood bow that had a black cherry belly with a torch.  It took me about 10 minutes for the whole bow to temper and I did it after tillering it.  I then lightly scraped the bow and let it sit for 24 hours.  I then re-checked the tiller and draw weight.  The bow gained 6 lbs. of draw weight and it really brought out the reddish hue of the cherry wood.