Pushing the limits a bit

[Kirkll]

I'm curious why your DFC graph starts at zero @ 8" when your brace is just over 6" ?   just curious...   Kirk

[Longcruise]

I'm curious why your DFC graph starts at zero @ 8" when your brace is just over 6" ?   just curious...   Kirk

Heh heh, I knew that would come up!    I adjust my rule (yardstick) to compensate for the "AMO" surface of the riser.  I don't have a typical tillering tree so I clamp a block on top of the yardstick so the riser sits up against the block with the bow laying flat on the table and then draw the bow down the yardstick inch by inch with a scale in my hand.

It's a very stout table!

[Longcruise]

Not a very clear description.

BH

Addjusted

[Kirkll]

I get it…. Thanks.   

You would be wise to build a tiller tree so your riser is about head height, and use a small boat winch with pulleys. You can see the way your limbs are bending much better stepping back and looking at them.

I think a hand pulled rope on a tiller tree works better for exercising a self bow. That hand crank holds it too long in one position me thinks….  But it’s great for glass bows.

Food for thought… Kirk

[Shredd]

  Did you make another bow prior to this one, with all the same lams but wider at the fades??  I am curious what the arrow speed was on that bow... You need to compare the two to see what direction you are headed and what changes are needed to get you in the direction that you want to go...

[Kirkll]

Width at the fades can be mitigated by wedge thickness , length , and taper rate to the fade tips too. It’s a bit trickier working with a one piece, but it can be done easy enough milling power lams to push the fade tips out further. I prefer double ended power lams on the back of the riser vs having them slip around on the belly ramps.

Once you get the perfect combo going extending your fade tips out further, it’s a thing of beauty watching the string angle flatten out, and those wedges, or extended fades start working like over load springs.  This is a huge part of a limb design that is often overlooked by the masses.     Another .02 cents.    Kirk

[Shredd]

  Exactly... Was leading up to that... If the wider bow was faster and built the same exact way as this one then this one either needs more taper rate in the lams and / or beefed up or extended wedges...

  I would like to see a side profile drawn to 28" without a cluttered background... By the looks of bow now and the dfc it appears that the bow is bending too much at the base of the limbs... Which will be very smooth drawing but lack performance...

[Longcruise]

Thanks guys for the great feedback. 

Kirk, that tillering tree is something I need to put together.  I have all the materials needed but have been held back by a place to put it for use and to store it.  I did see one of our members photo of their tree strapped to an actual tree.  That is going to be my solution.

I don't have a shop per se.  Just a very small 5 X 8 alcove in the corner of the garage.  All the power tool action is done on the driveway with the tools pulled out and set up for each session.  I also use the covered patio in the back.  Pretty much a fair weather operation.  Recently I managed to set up a work table in the basement that allows me to do glue ups indoors which is a big help.

Nuff of my tribulations!

Shredd, I've built quite a few off this form but those have been at 1.4" width.  They were all good shooters and had pretty good chrono numbers but I had a drive crash and it wrecked my data during a lengthy period of time.  Shoulda kept paper copies!  I'm ready to glue up another of the same design which I plan to keep at 1.4" so I'll do some comparisons.

So, this morning I did some further experimenting with string length and the chrono. 

Increasing the BH a mere 1/4" to 6 3/8" made a noticeable difference in vertical stability. 

Shooting over the chrono with the same arrows as posted above resulted in only minor variations in speed.  with a sample of five it's not enough to conclude anything.

Switching to a FF at the same 6 3/8" BH and once again the same arrows showed about a 4 fps increase for the 445 grain arrow, but the surprise was an 11 fps increase for the 538 grain arrow.  Still only a sample of five.

I'll see if I can get a photo at full draw.

[Kirkll]

Another option is a tiller tree / shooting machine combo.  You could build a saw horse of sorts to mount it on.
I built one years ago before i bought a hooter shooter. I used a stout piece of oak 4/4 X 4" X 5' long  and mounted a small boat winch on one end and mounted it on a stand that was about 40" off the floor so i had good clearance.   I just used 1/4" braided nylon rope and rigged up a trigger release aid to hook on the string and just clamped a yard stick on the board with spring clamps. I just used bungi cords to hold the bow in place for awhile until i fashioned a rubber strap that worked better.

Something like this can be used for DFC charts, tiller tree, and an accurate way to measure your speed. Doing DFC charts shooting by hand is not accurate enough for measuring the true performance differences in your bow while tweaking limb design. 3 different guys shooting the same bow will get different numbers, and your numbers will change from one day to the next.  A shooting machine with very accurate arrow weights, draw weights, and draw length is the only way you can really see small differences of gain or loss.

another .02.....  At this rate you will have a bucks worth in no time,,,      Kirk