Easiest Arrow Making Jig you'll ever make (Pic HEAVY)

[Wooden Spring]

"The denser woods would be proportionaly narrower to make the same weight."
----------------------
Amen to that... I can make a hickory backed red oak bow at 2 inches wide, and it comes out to 40 pounds.
The same dimensions, but using jatoba instead of red oak, and the bow is now 60 pounds!

[willie]

wooden spring
I hope you don't think that I was advocating you employ excel into your
bowmaking, quite the contrary as I also find the computer/math thing an antithesis to the pleasure of working in the shop. The suggestion to monitor densities  was offered as a way to incorporate a simple measuring procedure into your work flow, as a way to increase the certainty and reduce the variation you experience. Contrary to what is often repeated, i have found clear wood to be very consistent in properties.

willie

[willie]

badger

The more elastic a wood is the lighter mass you can potentialy build a bow most of the time.

thanks for this insight, it is just the kind of knowlege that can only come from long experience and observation.

willie

[Wooden Spring]

wooden spring
I hope you don't think that I was advocating you employ excel into your
bowmaking, quite the contrary as I also find the computer/math thing an antithesis to the pleasure of working in the shop. The suggestion to monitor densities  was offered as a way to incorporate a simple measuring procedure into your work flow, as a way to increase the certainty and reduce the variation you experience. Contrary to what is often repeated, i have found clear wood to be very consistent in properties.

willie

No problem. Actually, the only way that I have of consistently measuring wood density is to hide out by my wife's bird feeders and whack squirrels with it until it breaks. Red oak is generally 5 squirrels, while jatoba tends to be about 15.

[willie]

there's easier ways than that. any ripping with a even cross section that can be floated vertically in water will work. the sinking length divided by the total length is the specific gravity. I have often dunked samples the size of pencils  into pop bottles  My pup would be your best friend forever if you brought your jatoba here to help him with the tree rats

[Wooden Spring]

there's easier ways than that. any ripping with a even cross section that can be floated vertically in water will work. the sinking length divided by the total length is the specific gravity. I have often dunked samples the size of pencils  into pop bottles  My pup would be your best friend forever if you brought your jatoba here to help him with the tree rats

OK, that's awesome! As soon as I get the metal version of my jig from the machine shop, I'm going to HAVE to try that!

So would this be a reasonable way to go about determining draw weight based on SG?

Get the SG of wood used in a standard bow. Say, 2" wide at the fades, and 40 pound draw weight.
Next, get the SG of a test sample, and compare that to the SG of the known sample. Let's say the test sample is 5% more dense than the known sample.
Does that mean that the test bow will be 5% heavier draw weight???

[willie]

woodenspring

Does that mean that the test bow will be 5% heavier draw weight???

S.G. and width are pretty much directly proportional, and the width and weight are also directly proportional, so yes to that. As Badger posted earlier, this relationship holds true within an identical design. Hence the reason I thought you might be interested, as you seem to prefer making a lot of bows with the same design. There is a caveat although, and that is moisture content has to be considered when testing the samples. I would simply write the specs of the bow on the sample, and keep the samples for future reference and inspection. One of the regrets I have about the various bows I have made and attempted to make, was that I did not keep very good notes and samples of materiel. Also the changing of designs at a whim made it harder for me to grasp the principles of the craft, as I would not know which effect was caused by what change.

 Badger, by the way, was instrumental in bringing these density correlations into the view of the present community. He is the author of The Mass Principle, a chapter in tbb4, and he has developed criteria for using mass to fine tune performance, and extrapolate known qualities into different designs. Perhaps he will weigh in with another nugget of experience.

willie

[Wooden Spring]

Willie,
That's awesome if a simple density comparison could be used to predict the outcome of a bow... I've never thought of it before.

OK, so MAYBE there's the possibility for extrapolation in bow predictions...

Example:

You have a known sample bow of given dimensions and given density.

You have another wood that tests 5% more dense than the known sample. So, to make a bow out of the test wood that is the same draw weight of the sample, we should reduce the width of the fades by 5%...

Is that an over simplification? I realize there may be many other factors, but will this get us into the ball park?

[paoliguy]

Seems like it loses all the romance once formulas and spreadsheets come into play to me. I prefer to just make chips and go by sight and feel. Guess there's a lot of ways to skin this cat though. I must admit I'm right there with you on those Tab Benoit CD's though. Tab, Albert Cummings and I have shared quite a few projects over the years!

Like your arrow jig by the way!

[willie]

wooden spring,

Is that an over simplification?

not at all,

but will this get us into the ball park?

probably get you on base, at least better than comparing by species
5% accuracy seems doable, 1% might be asking too much

check out badgers thread, down about the middle of the page.

http://www.primitivearcher.com/smf/index.php/board,29.0.html

willie

[Badger]

  I think the whole thing behind density is that bowyers are working with different kinds of woods, it is not critical that they might get a bow too wide but it is critical that they don't get it too narrow. The denisty range of bow woods is not all that great they average from about 60 to 85. Knowing about how much a specific type of bow should weigh when finished is just a guideline for safety and not over working the wood. Some people assume that the mass principle is about building as low mass bow as possible. Just the opposite it is about having sufficent mass in the right places, My average 66" long osage bow has gone from about 17 oz to closer to 20 oz now and they perform better. ( still look like crap)

[TimBo]

I am going to make one of these arrow jigs, and am wondering about the function of the top holes.  Are they necessary?  Do they make it easier to adjust the router depth?  Or, (most likely choice), am I missing something?

[willie]

Timbo-
do you mean "top" when looking at the holes facing the viewer in 1966.jpg?, those holes are extra large to provide chip clearance around the cutter.


 

[TimBo]

I get it now...I failed to notice that after you connect the jig to the longer wood for clamping, you flip it sideways...duh.  I was seeing the side with the diameters marked as the top.  Thanks!  I figured it must be me...

[Jim Davis]

toomanyknots,
Nah, don't let anyone bring ya' down. I'm one of those folks who buck trends on a regular basis just to find out for myself WHY things happen the way they do.

The biggest way that I buck trends these days is that I build backed board bows to exacting dimensions - exacting to the point that they hold tolerances to within the thickness of a pen line. And they produce outstanding, predictable, and repeatable results... I was an architect, so I guess I come by it honestly.

The name of the game is trial and error, and the only WRONG way to do anything is just not to do anything at all!

but....... what if the wood is different densities and bending strengths along the length of the bow?

Very  unlikely.  We make "pyramid" bows all the time that are uniform thickness throughout the limb and have straight  taper sides. Any  small amount of variation in material can be corrected by slight scraping.

Back  on topic, when you guys run your square stock through the router setup and get the stock in as far as you can with  the drill, just  unchuck your adapter parts and chuck the drill on the far end of the finished part of the shaft and pull it on through. No need to back your shaft out because the drill can't reach any closer.

Also, there is no need to make your square stock half  inch. That just wastes wood. Make the square stock  3/8" and your entrance hole  33/64".  You will have a 25% saving in wood.

Your placement of the cutter directly under the shaft avoids having to make an adjustment arrangement, but your cut is cross  grain. Putting the router bit  at the side of the shaft puts the cut in line with the grain,  resulting in a smoother cut. That also allows the use of a dial indicator, making adjustments visible in thousandths of an inch.

Jim Davis