Woodbear's Spreadsheet as a tillering aid
I have built two bows with the assistance of Woodbear's spreadsheet. Both bows were made from the same hickory board, and came out very close to the predicted set for the particular design. The first...
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Bob, The sheet can easily be used in a manner similar to "no set tillering", Especially the later versions. Originally I had the strain at each station (row 12 in the earlier versions) explicitly...
View ArticleRe: Woodbear's Spreadsheet as a tillering aid
DaveI have tried to look at the underlying formulas to determine which value you refer to as """design" strain for the whole bow in the specifications block"". I am using selfbow-10arc-rev081114.xls...
View ArticleRe: Woodbear's Spreadsheet as a tillering aid
Bob, Apologies for the confusion. The version you have does not use the "Design strain" specification. The versions are the date I updated the file on in yymmdd format. I think the first to have it...
View ArticleRe: Woodbear's Spreadsheet as a tillering aid
BadgerIt amazes me that you can take a stave and tiller by eye to brace height, and be essentially finished.I appreciate your generosity for passing along so many tillering tips to the forum.DaveIf I...
View ArticleRe: Woodbear's Spreadsheet as a tillering aid
I suppose it might work to adjust the brace height. The program takes the specified strain and thickness distribution and derives an exact shape at full draw. It also derives the shape unbraced from...
View ArticleRe: Woodbear's Spreadsheet as a tillering aid
Adjusting brace height exerts a different leverage on the limbs as compared to drawing the bow. Though the stresses will be different, you might have more success 'seeing the bow drawn' by adjusting...
View ArticleRe: Woodbear's Spreadsheet as a tillering aid
Regarding getting the EXACT tiller shape from the program, I think you are right about changing the center thickness rather than the working strain. However in both cases the brace % needs to be...
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I'm aware of the calculation of bending moment for a drawn bow. In fact I drew this illustration demonstrating the difference between Hickman's and Nagler's description of bending moment some time...
View ArticleRe: Woodbear's Spreadsheet as a tillering aid
OK,............ now I see that you were talking about the bend test, not the bow. Sorry for the confusion. In the simple beam bend test with supports at a fixed distance, and the load hung in the...
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Hi Dave, regarding the graphs in the second post at the top, what is the nock-to-nock length of the 47# bow?
View ArticleRe: Woodbear's Spreadsheet as a tillering aid
Dave- thanks for your explanation of the operation of your program. I can now make the adjustments I need when tillering. Aussie- seeing intermediate shapes helps me with tillering, as I can get...
View ArticleRe: Woodbear's Spreadsheet as a tillering aid
Eric, I am not absolutely sure about the 47# bow, I think it is somewhere between 66" and 70". Perhaps Badger will se the post and may remember. (That is, assuming he was really involved with Tim at...
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Interesting concept with regard to the pyramid shaped sample for bend tests. A 1/2 wide sample cut to a pyramid shape wouldn't be all that easy. A 1.5" wide sample would possibly too stiff for...
View ArticleRe: Woodbear's Spreadsheet as a tillering aid
Aussie- I agree that it would not be hard to construct and test pyramidal samples. That is basically what I did with one of the "bows" mentioned in the opening post. If your pyramid test sample...
View ArticleRe: Woodbear's Spreadsheet as a tillering aid
Theoretically, as long as your method of calculation and mine were the same, the dimensions would not matter, as we would both be calculating strain, stress and stiffness. I do have a spreadsheet that...
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I have both a simple beam, and traditional bowyers bible 1 (Tim Baker's chapter) bend tests as sheets in my design workbook (program). In both cases the math is specific to the sample geometry. You...
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All the same, I'll look forward to that. To truly have consistent stress along the length, without having an infinitely narrow tip, it would have to change in thickness, but also not taper in...
View ArticleRe: Woodbear's Spreadsheet as a tillering aid
I think it is too difficult to get uniform stress along the entire length of the sample, and suggest something less ambitious. In the case of the TBB test, the sample is 18" long, the fulcrum is...
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