Limb Design Discussions

[OldRawhide42]

I dont

[Kirkll]

Old compoumd

Well you should get some kind of award for redneck engineering on that set up...

But.... I think i'd be concerned with lateral limb alignment issues using two different limb bolts like that. Once that limb bolt is adjusted out that far, your plus / minus tolerance on the threaded inserts alone in the riser is going to be all over the place. Then you have your location pin alignment too.  

Jay... i sent you a PM.

[OldRawhide42]

Kirk   the compound limb rocker keeps the lateral alignment pretty good. And ya the locator pins were a pain to do. I have shot it but it is not a fun bow to shoot. But it does help with the feel of the limbs . I mostly use it as a tool.   
     Jim

[Watsonjay]

Alright guys, I am perplexed. I built another riser making it with 14 degree limb pads instead of 17. I put the limbs from the 17 onto the 14 and it bumped poundage up 4 lbs no surprise. The surprise is that after short drawing it to 28 to match the 51 from the other riser it shot the EXACT same speec 145 with 486gn arrow. I guess this means i need more reflex in my limbs?  The unstrung pic is limbs on 17degree. The strung pic is on 14degree. And 2 risers side by side.

[Kirkll]

Did you measure the in line string tension on this one at brace? What draw weight @ 28" is it?  Another question: how long is your string vs bow length tip notch to tip notch following the curve of the limb belly and measuring straight through the riser?

Something sounds off here. Those are very low numbers. You should be easily getting into the 170's or low 180's with that rig.

How have you got your chrono set up? Are you using a light kit indoors with a shooting machine? Or shooting by hand outdoors?

[Watsonjay]

Did you measure the in line string tension on this one at brace? What draw weight @ 28" is it?  Another question: how long is your string vs bow length tip notch to tip notch following the curve of the limb belly and measuring straight through the riser?

Something sounds off here. Those are very low numbers. You should be easily getting into the 170's or low 180's with that rig.

How have you got your chrono set up? Are you using a light kit indoors with a shooting machine? Or shooting by hand outdoors?

I don't have a way to measure the tension. It is 51@28" 486gn arrow 51" n2n. My string is 48" brace 7.25".

I ran it through my chrono with a new battery outside in the sun and got 144,145,145,144. I ran a compound through the chrono that always shoots 274 and it came up 274

Since it went up 5 lbs I could narrow the limbs or trap the back for lighter limbs. It just seems that changing it to 14 would have done something other than just add lbs

[Kirkll]

I would experiment with a longer string and lower brace ht. Believe it or not, that will increase the pre load weight first. Do this before narrowing the width profile and putting it on the shooting machine again.

If you want an accurate comparison, do a DFC chart on it going to 30" draw.

[Watsonjay]

I will do the dfc for sure. On the first I am going to order a cheap small digital scale and rig up a couple short strings and a turnbuckle to measure tension. What should the tension be for good performance?

[Watsonjay]

I would experiment with a longer string and lower brace ht. Believe it or not, that will increase the pre load weight first. Do this before narrowing the width profile and putting it on the shooting machine again.

If you want an accurate comparison, do a DFC chart on it going to 30" draw.

Not a lot of difference other than starting heavier and finishing heavier. Im guessing that means more tension on the string

Blue us 14 degree, Red is 17 Degree

[Kirkll]

That is a strange DFC chart and its hard to determine the draw length vs weight differences.

here is the industry stander form.

F:\2020 regroup\Bigfoot Order back up\DFC Charts\Copy of FD tables_blank template_new.xls

[Kirkll]

Here are a couple of my old DFC charts i did. these are on my hybrid long bow limbs.

John Paul Kelly Sas.xls

Thoms Sas.xls 

[Kirkll]

Now look at the difference between this recurve DFC shape to my hybrid DFC charts. You'll notive the heavy weight on the first few inches of the draw, then it tapers off or lets off mid draw, then climbs again. This is a high preload bow that is about twice the string tension weigh as draw weight.   About 100# on the in line scale at brace.

[Watsonjay]

That is a strange DFC chart and its hard to determine the draw length vs weight differences.

here is the industry stander form.

F:\2020 regroup\Bigfoot Order back up\DFC Charts\Copy of FD tables_blank template_new.xls

My bad. I was doing it in excel and didn't notice it changing the top row from inches to lbs. I'll redo it but I started at 11" and ended at 29"

[Kirkll]

Well it looks like I screwed up my attachment for the DFC chart template. I'll try again later today. I also have a quick video showing the contraption I built for my tiller tree that has a light panel spaced in one inch increments that makes your readings very accurate.

Kirk

[Kirkll]

Lets try this again.  You put in your own info in the yellow boxes and the sheet is set up to calculate the data and give you a graph.


Copy of FD tables_blank template_new.xls

[Longcruise]

Lets try this again.  You put in your own info in the yellow boxes and the sheet is set up to calculate the data and give you a graph.


Copy of FD tables_blank template_new.xls

Shows up in Libre Office viewer on my phone should download and work on any device that has excel or Libre Office loaded.

[Kirkll]

Lets try this again.  You put in your own info in the yellow boxes and the sheet is set up to calculate the data and give you a graph.


Copy of FD tables_blank template_new.xls

Shows up in Libre Office viewer on my phone should download and work on any device that has excel or Libre Office loaded.

i had a tough time pulling it out of my hard drive back up files, and finding the right format to save it in before it would post on the forum.  ".xls" seemed to work ok. I Just wanted to make sure others could open it.  I haven't played with DFC charts in a long time, and don't do a lot of testing anymore.   Thanks for letting me know. This universal DFC blank template should be placed in the sticky files at the top of this sub forum.

[Watsonjay]

Here is a better chart should make more sense. I also glued up some different limbs with parallel cores, no tip wedges, and more reflex. In the pic I have them mounted on the 17degree riser and the old limbs on the 14. We will see how they do after profiling and tip overlay. Maybe too handle forward for the 14 degree riser. We will see if thus gets me more speed.

[Watsonjay]

I also extended the limb wedges 1". I know a lot of changes at one but I don't have unlimited supplies.

[dbeaver]

Parallel core on a r/d longbow would have a lot of limb bending, possibly way too much at your wedge depends on geometry.  Limb tips would also travel farther with the whole limb bending more and no tip wedge so the limb eats up some of the energy returning to brace.  But try