Little histlory behind the mass theory

[Barrage]

With regards to heat treating, since this has seem to become the hangup of choice now...

Correct me if I'm wrong Steve, but the mass principle isn't really concerned with the mass of the bow; it's concerned with the strength of the bow.  Not to say mass isn't important (ie big fat tips vs skinny tips, etc).  

Wood, almost all wood, demonstrates an absolutely amazing correlation between strength and density, like the black line on the graph below.  Generally, as density in a wood goes up, the strength goes up.  Remember, this is a correlation.  If you measured strength and density and plotted them, there would be a scattering of dots, but they would follow a trend.  You would have variations between species, within species, and within the same tree, but overall a good trend.  

Now, I mentioned we are interested in the strength, not the mass.  We can't go around doing destructive testing on all our wood or bows to determine this strength.  This is what you would need to do to know the exact strength of your exact piece of wood.  Because the next piece from the same tree would be slightly different, and so on.

This is why Steve's mass priniciple is so handy.  His method realizes the relationship between mass and strength, allowing for a good practical application to work our craft and attempt to optimize our bows.  It isn't intended to tell you where to place the mass, bending does that.  That said, if you so desired to could get out a million lines of formulas and design a bow on paper which would either break on the tree, or be grossly overbuilt due to: the VARABILITY OF OUR MATERIAL!

Now, on to heat treating...  The heat treatment process again varies with the wood type, so sorry, you'll never see a formula.  At best you'll need thousands of experimental data points to again come up with a species specific correlation post-heat treatment.  Without going to all that trouble, I can tell you that what you'll see is that the data points won't fall on the old (black) density/strength line, they'll move over to say the blue line.  You essentially altered the material so it no longer behaves like wood.  That doesn't make the mass priniciple wrong.  It is like using a different material with different strength/density relationship.  But, as Steve has mentioned, heat treated bows can knock ~10% off the weight as a rule of thumb.  That is simply accounting for the shift from the black to the blue line.  

I don't know, but this all holds up to me, and seems to have the flexibility to account for a wide variety of styles, woods, and wood treatments.   It's not intended as a auto tiller guide.  If you want that, write the million lines of formulas and build your bow.  You'll still need to adjust for material strength differences though, so what's the point?

Again, sorry Steve if I've misrepresented anything you've said here.  Please feel free to correct...

[Badger]

  Barrage, I think you are pretty close, you definitely have the right idea. The bowyer designs his own bow always, the mass formula assumes a logic to specific designs based on stressing the wood equally. Something I often do and I imagine other bowyers do it as well is simply scrape the bottom to get the tiller right. This goes against my own principle but once I am close I don't concern myself with it. As you said, it treats all wood the same even though we know it's not the same. It averages thigs out. Different tecniques and wood will affect the mass here and there such as heat treating, refining tips, lighter than normal wood affects handle weight, etc, as we become familiar with our own woods we can adapt a factor to multiply the projected mass out by, maybe X.85 or evn .80 if the bow is tricked out with real skinny tips and heat treated. The main thing it does is try to encourage the bowyer to put the mass where the bow is working.
    As far as design goes it will do some interesting things, if a design is way off base you won't be able to get anywhere near projected mass and once you learn how to use it can make little adjustments in the design. It becomes very apparent when working with elbs, especially lighter draw weight elbs that are very long. Simply moving the tiller out away from the handle will bring the mass projection right up and usually will be reflected in good performance as well. I amke my biggest mass adjustment once the bow is roughed out and starting to bend, I like to be 4 oz over at that point, I often wont go back and check again till I am up to about 22" pull. For sure not a cure all, just another tool in the bag if we choose to use it. Sometimes working with a new piece of wood much different density that we are used to for instance it might come in handy. Steve

[Jesse]

Badger I like the idea of attempting the zero set tiller with you method. I think it would be great in conjunction with using a chronograph to keep checking that it was also not decreasing in speed with the tiller adjustments. Might be helpful in the final stages to use the crono to shed extra mass untill performance stops increasing and set is about to occur.  Just an Idea

[sulphur]

adb thanks for setting me straight.  i like good (i said good) discussions of almost any subject.  don't like to see trouble makers though.  thats why i dont visit the LW much anymore.

[Badger]

Jesse, If I am really tweaking on one I do use the chrono along with the scale, I test it every 1 inch then go abck and test it at the benchmark measure to see if it changed, I would have said that but didn't want to push my luck LOL> Steve

[Jesse]

Jesse, If I am really tweaking on one I do use the chrono along with the scale, I test it every 1 inch then go abck and test it at the benchmark measure to see if it changed, I would have said that but didn't want to push my luck LOL> Steve

Most people "including me " dont have a crono anyways.  I would like to get one though. I always take my bows to the archery shop to test but doing that while tillering would be a pain

[Badger]

    Jesse, I worked on a 57" sapling bow today that would have been a great one to put on the chrono and test every shot. It was raining like hell and I didn't care too much for stave anyway so was just playing around. I braced the bow at first brace and the tiller looked good so I went ahead and started pulling it. It was very tight at brace, reading 28# at 18". I decided to see if it would go all the way to 28". I worked it up to 28" and checked the draw weight at only 36#. Went back and rechecked it at 18" and was now down to about 16#. I took the string off to check the set the bow took figuring it must have taken a lot and it was about 1" set is all. Bow shoots decent but would havebeen a lot better had I started removing belly wood the minute it started to show signs of weakening on it's own. More dramatic than I had expected. Steve

[George Tsoukalas]

Saplings are fun to make into bows, Badger.  A 57 in sapling drawn to 28 in. is a strong sapling and a tribute to good tillering. I leave them longer than my reg. stave bows. Jawge

[Traxx]

Ill Tell you what now!!!!!!!
This "No Set" tillering approach is kina exciteing to me.Its somethin that even a guy like me can grasp.I cant wait to give er a try.Its rekindled my desire to build some bows now.
Thanxx Steve.

[Keenan]

 Steve, excellent descriptions and If anyone would know what they are talking about I would bank on the knowledge that you've learned from pushing the extreams. The knowledge that you share is priceless.

[Swamp Bow]

WOW!  I stumbled across this last night, and was so cross eyed before I even started reading it that proverbially everything went in one ear and right back out the other.  I could however tell that this was interesting stuff.  I just reread it and I can't wait to play once I find some time.  Things are clicking that I did not even realize were out of place.  I hate it when I don't even know what questions I should be asking.  Reading what some of you have to say make me feel very small indeed some days.  Thank you all for sharing.  For those of you that are trying some of this out for the first time, how about posting some results/impressions here?

Swamp

[DCM4]

I haven't found irregularities in the wood like knots or whoop-d-do or twist or snake to have any consquence in the zero tiller method, but absolutely effect the finished mass.  I think all bowyers who strive to improve cast eventually come to the same realization, this premise stated by Steve.  If it's wide enough, you can stay within the elastic limits (or near) of the material.  If it's too wide, you aren't close enough to the limits to make the most efficiency.  Similarly, if you are slingin' around knots and otherwise corrupted wood mass (which can't store energy efficiently) then you won't have as fast a bow.   But using zero set rules (being extremely attuned to the set a bow takes) you can get the most that specimen has to offer.  This is why I've always held the view all wood is NOT the same.  Rather, some speicimens, species, grain orientation (ie. boards) have inherently different elastic limits and conquently can yield bows (assuming optimized design and construction) with different capacity for efficiency (cast).  As an aside, I've also been surprised at how well some knarly looking wood can store energy efficiently.

Steve didn't mention it, and I know it's a contentious topic, but "working" a bow on the tiller tree before the tillering process is completed (which is to say while it's still not bending perfectly) does more harm than good imho.  This is the idea one should draw a bow some arbitrary (20 or 50 or whatever) number of times after each adjustment to "work it in".  Yes, it helps one be certain to make an arbitrary draw weight, but since frequently at the expense of cast I don't see that as a particularly valuable trade off.  All you are doing is making sure what wood is bending is thoroughly set, then what wood you start bending it thoroughly set, before even move along to the next adjustment.  I'd rather not set the wood at all, or as little as possible.  One can over design (using too much wood) then remove width or lenght (again as Steve alludes to) in the final stages of tillering and crafting to achieve the desired draw weight, AND preserve the potential for cast in whatever specimen.  As I understand it the process from antiquity of "piking" a bow and "bringing it 'round full compass"  after it's tiller is basically finished and the bow shooting (from Toxohphlie) alludes to this principal.

[Badger]

   DCM, excellent points you made. I know you and I have discussed this over the years. Working a bow in, (and yes I sometimes still do it) basicaly just breaks down the wood unless it has a perfect tiller at that point. Idealy a bow has no recolection of ever being bent, we never attain that perfectly but as close as we can get to this is a good thing. I often hear training a bow to bend, nearly all bow makers use this term, in reality if a bow were somehow perfectly tillered without ever flexing it you could take it right to full draw with no problem at all.
   DCM was one of the first guys I latched on to when I came on line, I appointed him one of my mentors. I always admired his logical approach to bow making and willingness to look at new ideas. Steve

[George Tsoukalas]

DCM, I guess we have some different views of tillering but you get there  better than I do but I'm stubborn and set in my ways and I guess I need more verification for a pell mell rush to full draw. . If you note in Steve's description, in a previous post above, he had the limbs bending well and in sync early on. Easier to do with a board. Difficult to do with a log stave. Much more difficult to do with a character stave. Setting up my tiller at brace and then hoping you'll get a good tiller hasn't worked for me much with difficult staves. Boards are another matter. Nice to see you back you on you irascible curmudgeon. Jawge

[DCM4]

That's a nice thing to say Steve.  Thanks.  But as I'm sure you agree, we all stand upon the shoulders of those who went before us.  I personally found Jim Fetrow's insights in this regard to be helpful. for example.  I realize you'd been building a lot longer than I had, we just happened to be thinking about this aspect at about the same time.