Build Along ( building by mass)

[Badger]

   I wanted to see how the formula would work on a small kids bow. 51" long, stiff handle and fade, 20#@24". Shoots a 300 grain arrow at 152 and a 211 grain arrow at 167 fps. Calculator projected 7.75 oz bow came in at 8 oz but is not cleaned up yet. I had originaly set the calculation up to start at 54" but it seems to work in reverse as well. Steve

[Justin Snyder]

OK Steve as promised.  69 NTN 3/4" string follow. 65# at 29" I got it bending in the middle so I entered no handle, but maybe your inturpretation of that is different. But hey that is why Im posting it.  Justin

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[Badger]

Justin, that came out great, I would use a figure for the handle of maybe 4" maybe 2", but I would be looking for about 20 oz on that bow. How much did it come in at? Steve

[Justin Snyder]

I wondered if you would.  I left it a little heavy for figuring 0 but I might still be a little light at 18.5. I figured at 2 it would be 18.5 so I called it good. So now tell me how you get 4 since that was the point of this exercise.  Not bending quite as much in the handle and a little stiff in the tips?  Asking not telling.  Justin

[Badger]

      The handle area is pretty much subjective, Yours is bending pretty good but slightly less than the rest of the bow. From experience we both allready know that ipe is a heavy wood and we also know that there is not much penalty if any for a little extra wood in the middle of the bow. I figured my base weight at about 19 oz for that bow and just gave myself another 1 oz to play with in the center of the bow. Exact figures are not important as long as the bowyer understands where the mass is going and has a good idea why he can distribute it
        Your bow is a real good example of sometning else, you did a very good job of keeping the bow stable. At 3/4" wide this is not always easy. I give myself a minimum width of just about 1" for a bow 69" long, I would have left the center stiffer and probably finished the bow around 23 oz but in your case it worked at well just as you did it. I really appreciate you working with me on this. Real life tests are what will make it, break it or change it. Dave Woodbear, will make changes to the calculator as I see it needs. He added a yes or no for backed or unbacked for a 10% deduction. I think I will add a bendy handle choice of slight , moderate, full arc of the circle. This would be close enough. Steve

[Justin Snyder]

Thanks Steve, Justin

[DanaM]

Steve please be sure to post the new excel spreadsheet when its ready, I know I'm learning from this discussion.

[Badger]

Here is one I am working on right now, I didn't intend to do a build along with it but ran into some problems so thought it might be a good example. As I noramly would I estimated the demensions for this 50#@28" holmie. After roughing the bow out and getting it to floor tiller it became apparent that the wood was not s dense as I had anticapated and I don't have enough mass in the bow to complete the bow as I originaly planned. This is where I play with the numbers and change my design based on the amount of mass available

Original plan. length n to n-66"= 6oz    modified- 64"=5oz
         nock position         +1"=  .5oz                  0  =0
  stiff handle and fade-     10"=   5 oz                 8" =4
  draw length                  30"=1 oz                   28"=0
   draw weight                50#= 10                    50#=10
total                                     22.5 oz                      19 oz

At present the bow is 20 oz, it will likely finish at 18 oz, still a tad light but closer than the original plan. I will tiller the bow to bend closer to the handle to shorten the handle and fade #, I will also get the stiff outer limb bending a little further out to reduce the figure for draw length and lastly I will pike the bow about 2". This is a baord bow and may end up breaking nayway but at the original plan I feel it would have taken too much set if it didn't just break all together, Well back to the workbench.

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[Justin Snyder]

Steve, what is the actual draw on that one? I'm sure with the holmie style you must have added some to the draw length to adjust. 
BTW I was shooting for a little heavier on my bow, but after weighing and checking I just didn't have enough mass according to your calculator so I adjusted the weight down before I even got to brace.  Justin

[Badger]

Justin, actual draw length is 28", I have it bending more in the upper limb near the fades now and working a bit through the narrow outer limbs. I checked the loisture of ther wood because of all the rain we have been having and it is a tad high at 9.5% so i finished the bow at 47# and will heat treat a bit, mass is sitting at 18.5 oz before rounding off the belly corners and such, shooting a little over 10 grains at 165 but that will go up a bit as it dries out, It took 3/4" set when first unbraced. I put about 50 arrows through it and the weight and the set haent changed so i will proceed to heat treat slightly reflex and then hopefully not expode the bow. Heat treating will get you a lower mass figure as well. This was an edge grained board so I wasn't too worried about cutting the nocks through the back of the bow at the tips. As I finish the bow I will make some adjustments to the tiller also. This is just a quickie belt sander special board bow that I do a lot for my morning entertainment. This one shows a little promise so I will slow down now and try to tweak some good stuff out of it. Steve
For some reasons my pictures didnt work???  Steve

[George Tsoukalas]

Badger, I try to get a feel for the density and quality  before I start. Also, I look at the rings, etc particularly with osage. Then I decide on a wood width accordingly. What do you do when you are coming in underweight? Looks like you shortened the handle and the bow length which is fine. I guess my question is how did you determine your initial, lay out width?  Jawge

[mullet]

      Justin, That bow is bending nice. Dang I'm really starting to like Ipe. That dark wood looks kinda like a stave in my shop. Is it backed/

[George Tsoukalas]

Excellent bow, Justin. Jawge

[Badger]

      Jawge, for an initial lay out width I don't want to be too narrow so I tend to make an educated guess on the wider side. This particular bow my educated guess was a bit too narrow. For a mid length bow form a medium dense wood such as maple or red oak I usually start arounf 2" for a stiff handled bow and then narrow it down as I reduce mass. The longer the bow the more I might make it narrow from the start. The formula is actually pretty conservative. A good example, I gave Ibex a yew bow yesterday, I tillered it to 71#@ 29". Steve has a 31" draw and asked if I thought it could handle it. I said lets give it a shot. At 29" the bow onlyhad a hint of set about 1/4" when first unstrung, at 31" draw it took about 1" set, still not bad. The other thing I want to really stress is that being exact is not a critical thing, the mass formula will steer you into a pretty well designed bow if you are pretty close.
Steve

[George Tsoukalas]

Thanks, Badger. LOL. Even after all the bows I've made I'll miss weight now and then too. I think his formula could really come into play for me when working with a new wood. Jawge