the mass principle in one sentence

[Badger]

     Good point about the sapling, glad you brought that up. After the paper was turned in I checked out some bows with higher crowns and found it is similar to trapping, most woods are stronger in tension than compression and the crown compensates for that a bit lowering the mass some. I was going to discuss that with one of the gentleman here who has a sapling he wants to do a buildalong with. Steve

[Gordon]

Steve, the belly was tempered during the floor tillering stage and then tempered lightly again after the first bracing. The handle is 1.5" in depth, but hazelnut is quite light relative to most of the woods I use (with the exception of yew) so the handle is probably somewhat lighter than most.

A very interesting post. Thank you.

[scp]

IMHO heat tempering would not change the mass much. I'm just guessing here, but it might temporarily make the bow lighter by drying it out too much.

[Badger]

  Not much you can really do with a sapling bow besides get them as wide as you can and see what you can get out of them. If you go to wide the outside wood is so thin it really isn't doing any work, just adding mass.
SCP, heat treating hardens up the belly and will allow you to go with less mass than a non heat treated bow. It doesn't really change the mass of the wood than much but it does change how much wood you need. Steve

[Gordon]

Not much you can really do with a sapling bow besides get them as wide as you can and see what you can get out of them.

Agreed. I used to make my sapling bows wider, but after a while I began to question whether such width yielded much benefit given a high crown. Now I make the limbs narrower and temper the belly in an attempt to compensate for the loss of compression area. It seems to work okay.

[scp]

SCP, heat treating hardens up the belly and will allow you to go with less mass than a non heat treated bow. It doesn't really change the mass of the wood than much but it does change how much wood you need. Steve

Fascinating. Does that mean heat treatment defeats the mass principle?

[mullet]

 Steve, I always thought that heat treating really did nothing more than shrinking and sealing the wood cells. Like when you see skin that has been burned, drawing it in creating really, scar tissue, that makes the belly tighter and dense. Also cutting down on moisture absorbing ducts to the inner wood?

[Badger]

No, SCP, it means a bowyer has to know what he is doing and allow for various things. Lots of things change projected bow mass, trapping, backing a bow, heat treating a bow, excessive dryness in a bow. It is not designed for idiots, more for advanced bowyers. Steve

[scp]

No, SCP, it means a bowyer has to know what he is doing and allow for various things. Lots of things change projected bow mass, trapping, backing a bow, heat treating a bow, excessive dryness in a bow. It is not designed for idiots, more for advanced bowyers. Steve

I'm afraid you are not thinking clearly here. If you can reduce the mass required by the WOOD mass principle through heat treatment, that means the principle is no longer applicable.

Let's look at the nature of heat treatment. If it somehow changes light wood into heavy wood, the WOOD mass principle should hold even after the heat treatment. That is, still same mass is required.

If it somehow changes wood into something other than wood, say fiberglass, we don't expect the WOOD mass principle to be valid anymore. You appear to be thinking this is the case. That means we cannot use the same mass principle for the heat treated wood bows, just as we cannot do so with fiberglass bows. Of course, each different materials will have their own mass principles, so long as they are cohesive enough.

Now, what is the nature of heat treatment? Does it change light wood into heavy wood? Or, does it change wood into something else?

[Badger]

   None of the above, it changes the typical ratios of compression to tension strength, allowing for a lower mass bow. Please read the chapter you questions are all answered there. I don't think you have enough knowledge here to carry on a conversation on the topic. Steve

[scp]

None of the above, it changes the typical ratios of compression to tension strength, allowing for a lower mass bow.

I don't think you understood what I said. If heat treatment "changes the typical ratios of compression to tension strength, allowing for a lower mass bow" does that mean heat treatment renders the mass principle useless?

[Gordon]

scp,

I'm not sure why, but heat treating (when proprely done) makes the belly wood more resistant to compression. I even use it to tweak a tiller when I don't want to remove wood. For instance, I will sometimes lightly temper the outer limbs when I want them to bend slightly less. You have to be careful, however, because too much can throw the whole tiller out of wack.

I'm no expert on Steve's mass theory, but I expect that you have to account for this effect like you would with any other model.

[Badger]

I answered that, You make an adjustment for that the same way you make adjustments for many other factors. Thats where experience come in. If you are too lazy t read a chapter I don't really want to deal with you anymore, it is getting rediculous here. Steve

[scp]

scp, I'm not sure why, but heat treating (when proprely done) makes the belly wood more resistant to compression. I even use it to tweak a tiller when I don't want to remove wood. For instance, I will sometimes lightly temper the outer limbs when I want them to bend slightly less. You have to be careful, however, because too much can throw the whole tiller out of wack.

You can think of it as scraping out a certain amount of wood and replacing it with the same mass of OTHER MATERIAL, say bamboo, horn or even fiberglass. For the belly, that other material better be something that has more resistance to compression. You are basically turning your bow wood into something better than it was. It is possible that, as Badger says, heat treatment "changes the typical ratios of compression to tension strength."

Whether it can do so enough to become an exception to the WOOD mass principle is another story.

[mullet]

 Steve, Am I in the ball park with my question above, or mistaken? I've never used your theory till I'm about 98% finished with a bow. If it is a high performer, just for the hell of it I have weighed it. Most of the time it is close or a little over. And then I have removed some wood after taking a closer look.