Heat Treating Hackberry

[brianvanh]

I have some questions about heat treating hackberry.  A friend gave me half of a hackberry log (enough for 2 staves).  I've split it in half and I just pencilled the layout this morning.

The wood is well seasoned (several years for sure) and is just beautiful.  However, the back has some built in reflex and also has some minor propeller twist.

As I understand it, I need to do 2 things...

1.  Get the propeller twist out of it.  I've read that for seasoned hackberry, I would need to use dry heat.  Some have even said to use grease (crisco) to keep the bow from overheating.  Can someone explain this process for me?  Is it as simple as heating up the twisted areas and then clamping them down flat?

2.  Second question - Once tillered, I've also read that hackberry responds best when heat treated.  Helps to strengthen the wood and helps it to take less set.  Question - what is the process for doing this?  I've seen where some people say to heat it until it starts to turn brown.  Is that it?  Do I do it to the whole bow (belly, back and handle)?

Sorry for the long drawn out question, but I'm very interested in how this works.  Thanks!

Brian

[Dan Landis]

Brian, I use crisco or olive oil when heating  wood to remove twist or to make alignment adjustments.  I never apply heat to the back, only belly side.  To remove twist, clamp the bow in a vise and place a bar clamp or pipe wrench beyond the area to be heated so that it is angled up past level.  Heat the area to be straightened gradually, when it is hot enough you should see the end of the clamp or wrench start moving slowly toward the floor, You may have to add weight to the end of the clamp depending on how much twist you need to remove.  I usually go a little past where it is straight to allow for spring back.  
To heat treat I follow the method described in Vol, 4 of the Bowyers Bible.  I've had good results with this method.

[Dan Landis]

Brian, forgot to mention, leave the clamp or wrench on until wood is completely cool to the touch.  Sometimes takes more than one session to remove all the twist, just go slowly and be sure not to get the heat too close to the wood and scorch it, don't ask how I know this.

[SportHunter]

I've used steam to get prop twist out of hackberry so both will probably work. If you look at last years bow swap thread I included quite a few pictures of the construction if you're interested. The bow turned out excellent. I would steam for about 40 minutes and have the bow rough sized at the very least.

Here is the link to the page I started posting the hackberry bow project. You'll see the stave is prop twisted and deflexed. I took the twist out and recurved the tips with steam.

  http://tradgang.com/noncgi/ultimatebb.php?ubb=get_topic;f=125;t=007554;p=12

[Pat B]

A little prop twist won't hurt anything. You don't have to rewmove it.

[brianvanh]

Great stuff guys.  Really appreciate the input.  Dan, do you prefer olive oil over the crisco?  Also, how much do you put on?  I assume you don't want to over do it?  Also, what do you use to clean the grease off when done?  

Pat - I haven't cut the bow out yet.  I'll see how much twist is in it when I make the cut.  I may not worry about it if it's not too bad.

[Dan Landis]

Brian, Prefer olive oil and I use a light coating and re apply as needed to keep it moist.  I usually don't worry with cleaning it off as most of it dries up, any excess is wiped off with a rag.  I will use denatured alcohol to clean up any areas where I plan to glue anything, like tip overlays, etc.

[brianvanh]

Perfect...thanks Dan.

[Pat B]

The type of oil doesn't matter. I prefer veg oil and usually use olive oil because thats what we have available.
 The oil will help prevent scorching, concentrate the heat where needed and hold the heat longer from what I can tell. I always use oil when bending or straightening wood with dry heat. For tempering I use no oil because I want the wood to scorch(belly side only).

[brianvanh]

Thanks again guys.  I've read (and re-read) the chapter on heat treating in BB4.  Thanks again!  I'm almost ready to try this out!

[brianvanh]

I'm finally getting around to being ready to do this and have one more question.  In TBB4, the author says to make sure that the bow is dry and that heat should be applied when dry.  He then applies varnish to the various sections of the bow once it has been treated.

For you guys who use oil, do you apply the oil BEFORE heat treating?  Or do you brush it on after as described in TBB4?  It seems like you all are saying to brush it on before heat treating, but that doesn't seem to jive with the directions in TBB4.  Maybe I'm misunderstanding?

Further on in TBB4, the author says "When heat-treating, the wood needs to be very dry or checks and splits can develop in the belly."  Seems to me that brushing oil on before you heat try would contradict that statement.  But again, maybe I'm misunderstanding.

Can anyone clarify?  Thanks!

Brian

[vanillabear?]

[scars]

For you guys who use oil, do you apply the oil BEFORE heat treating? Or do you brush it on after as described in TBB4? It seems like you all are saying to brush it on before heat treating, but that doesn't seem to jive with the directions in TBB4. Maybe I'm misunderstanding?

Maybe I'm misunderstanding? Correct,,,


Heat treating and heat tempering the belly "IS" not the same as heat correction of the stave.

Heat correction or heating to desired shape- Use oil/Crisco. Dry heat-dry wood, Wet wood-wet heat, boiling the wood is to be considered also can be used on dry wood or wet wood,,,

There are exceptions even in same wood same tree instances. The simplest thing to do is to use the cut offs from the bow wood you are using as test subjects.
1- shows what heat is best for that wood you have on hand.
2- shows the fracture point at the temperature of heat applied.
3-and when to apply oil or grease, before or after

Heat treating/tempering- No oil or Crisco needed use heat gun or hot plate. Look and observe the belly while applying heat. Loose fibers will dry out and burn off, then annual growth rings will slowly darken, as the rings start to darken touch back of bow to gauge heat transfer. While growth rings start to get darker early growth will sort of get clearer, once you notice that touch back of bow once more to gauge heat transfer should feel more heat on the back of bow. Now the early growth will start to darken (keep heat gun in movement at all times slow but moving) Keep a close eye on the color of the early growth as it darkens, you are looking for the color of toasted bread. When the toasted color is seen for the first time, once more feel the back of the bow. The active bending part of the bow should never get hotter then the heat on the back of the bow from that point on. Continue toasting the limb.

As vanillabear says pitch or resin can be used but most oil sealers or oil base stains will do the same job.
Good luck

scars

[Black Mockingbird]

You can remove most of the twist and heat treat it all in one shot over a form...no oil needed.

[John Scifres]

Stop reading, start heating  

Oil, no oil?  Correction, no correction?  It is all for naught if you ain't making bows.  Paralysis by analysis.

[Pat B]

When making corrections to a wood bow(bending or straightening) I use oil. When tempering a belly I do not use oil. These are two different things. However, you can add reflex to a stave while tempering.
 I have used pitch/terpentine mixture on tempered bellys but I have also done it without. Whether heating for bending/straightening or tempering be sure to give the bow plenty of time to cool and/or rehydrate. I leave it alone at least over night when bending and straightening. After tempering I leave a bow alone for 4 days or more to rehydrate before stressing it.

[LittleBen]

haha paralysis by analysis ... thats funny

[brianvanh]

As someone who is new to this game, it's painful to spend months working on a bow only to have to blow up on you because you didn't do your homework.  I've blown up a few so far, and it's been because of my own lack of patience and/or my immense ignorance.  I know that experience is the best teacher, but I won't apologize for supplementing my experience by asking questions.  Guess I thought that's what this forum was for??

In any case...thanks for the feedback.  It's clear as mud now.

[John Scifres]

Just razzin' ya'.  There are many paths.  Choose yours.  Your'e not clearing up the mud reading this forum for months.  Get to work  

[eflanders]

Bending, shaping, straightening of wood requires that the core of the wood needs to reach 212' f which is also waters boiling point.  This can be done with dry or moist heat (steam).  The key to success is in the temperature reached at the core.

Heat tempering otherwise called heat treating wood can only be done with dry heat.  This is accomplished by the intense heat creating a chemical change within the wood cells.  Color change is one of the easiest indicators if the chemical change has occurred.  You want to see a consistent darkened hue without charring / burning the wood.  This takes patience, practice and an understanding of which wood species respond favorably to this.  

Adding oil when either heat treating or straightening wood is sometimes used with certain wood species using dry heat only.  The use of oil is very subjective to the woodworkers own preferences.  It is not required, but some find it quite beneficial with certain wood species commonly used by bowyers.