Limb design philosophy and ideas

[Appalachian Hillbilly]

Being a new guy,  3 piece  designs seem to be the easiest as far as mold changes and r and d go because it is easier to build a limb mold for that than a one piece.

I love the look and design of Kirk's limbs and some of the others that have what appears to be a stiffer section in the area of the fades and this leads to a shorter working section, and less string angles than bows that start bending immediately from  the riser with short fades. I think the first design leads to better performance as well.

Looking at the pics some people have posted of their lam layups you will see a long wedge, maybe a power lam, cores and a tip wedge, and glass.

My questions are about taper rates with these designs. If you are using  a power lam, what is the taper rate of the power lam? Then are your cores tapered as well? Tip wedges.  Same question about rates?

Tapered power lams, parallel cores,  and tapered tip wedge? Or
Tapered  everything?

With the price of glass, it is going to be pricey to  try everything in my head.  Just want to eliminate the "hey, I could have told you that idea want work" ideas!

These are hybrid long bows by the way.

Thoughts, pointers ?

[Mad Max]

EDIT This is not the only way to do it
Some of the other guy's use a long butt wedge
First thing is I build Recurves.
I use a .005/.002 taper, 1 lam
2nd lam is parallel for my recurve


Example on how to make a .005/.002 taper SLED 40" long, or .007/.003, what ever
If you make a .005 taper and a .002 taper, cut the .005 18" long. cut the .002 22" long, butt them together on a 3/4" thick parallel sled and glue them to the sled.
(1) they have to be the same thickness where they butt together
(2) The sled profile has to be opposite of the lam that will be sanded on it (the .005 will be thinner on the left and thicker at the intersection of the .002, and the .002 will be thicker at the far right.

So the .005 taper will be thicker coming off the fades/butt wedge, and get thinner (bend more at the .002 taper.)
Now with a 40" lam, you can cut 2" off the butt end, or 4/6" off the butt end to get the bend you want.
The .005 area is going to bend, not as much as the .002
Your bow design is different that other design.

My 2 cent's

[Mad Max]

Again Recurve
Tip wedge
With the bow on a tiller tree (horizontal) Braced
A tip wedge will push up on the last 3rd/4th of limb from the wedge.
A 4" radius on the recurve will be stiffer than a 8" radius and a tip wedge may not be needed on the 4".
a 2-1/2" radius will be static without a tip wedge.

My 2 cent's

[Appalachian Hillbilly]

Max, had to think about that for a minute, but with that sled you end up with a lam that is progressive.  Starts out at 5 thou taper rate and then at 18" , switches to 2 thou taper rate.

Thanks for explaining  that ! That helps!

[Mad Max]

 

[Kirkll]

Looking at the pics some people have posted of their lam layups you will see a long wedge, maybe a power lam, cores and a tip wedge, and glass.

My questions are about taper rates with these designs. If you are using  a power lam, what is the taper rate of the power lam? Then are your cores tapered as well? Tip wedges.  Same question about rates?

Tapered power lams, parallel cores,  and tapered tip wedge? Or
Tapered  everything?

I'm afraid Max might have complicated things for you a bit going into details a bit heavy. Its obvious he's been doing this stuff awhile.

How bout we start with basic taper theory and a few facts first...

If we are talking D shaped long bows. These are typically very narrow width profile compared to RC limbs. A faster taper rate of .004 is very common on long bows. Typically 2 .002 tapers are used. The same long lean fades used on TD limbs to push the working limb portion out further towards the tips is still very desirable, but is harder to do shaping a riser block on a one piece bows, and that is where power lams come into play.  You can use 16"-18" riser block material and push the fade tips out to 22-26" placing the power wedge 4" past your riser fades.

Power lams can be used on TD limbs too to extend the fades of a shorter wedge assembly, but most guys just mill longer lean wedges. In some cases like TD Bear aftermarket limbs, or wild curved wedges on some designs, its easier to use a power wedge in combination with your  milled wedges like an ILF toggle wedge for example.

Getting back to taper rates...  You can go with faster taper rates like a pair of .002 for depp core long bows, but going with RC limbs, or RD long bows (Limbs with a lot of deflex / reflex) or even hybrid long bows like mine, you need to come down on your over all forward taper rate to maintain limb stability.   For example:  i use .004 FT on my Flatliner design.  .003 on my hybrid long bow, and i go with .001 on my RC limb design. I even drop down to using just parallel lams in my low poundage RC limbs to keep the limbs from going sideways.

There are a lot of guys that go up to .002 forward taper on their  RC limb designs with fairly good results. But it depends on the actual limb shape how stable the results will be. There are a lot of guys that used to use .002 and tried an .0015  then a .001 on RC limbs and figure out they get better overall stability in lighter weight bows using less forward taper, and often times better performance.

that should give you some basics to chew on...

 As far limb design itself goes there are some basics too. But if you built one limb form with no stops set, and sent it to 10 different bowyers, you'll most likely end up with 10 different bows completely. one form can produce 50 different limb configurations shifting the stops, limb lengths, and taper rates.... Its never ending....     Kirk

[Kirkll]

First thing you need to do is create a boyers log. I just built a spread sheet in Excel that i can keep adding to.   here is an example of my entries.

 

[Appalachian Hillbilly]

I have a notebook I keep in the shop with all my measurements from each limb, wedge length and taper etc. I need to put it into a spreadsheet.

My current set of limbs from my mold are 27" from butt to tip. I just pulled them out and have not cut them to profile yet. I am shooting for mid 40's draw weight. Think I will be light.
I am using 2 forward  .001 tapers with a 9" wedge and a .001 reverse taper center core.

Same basic design as my first set of ILF limbs that came in at 42-3 lbs but with shorter wedge and a profile that started tapering width  at the ILF lever pad area to about .650 at the tips.

They shoot well, but not as fast as I want.

I love the look of your hybrid bow you sent in the other reply.

My thoughts on this set of limbs was to extend the wedges and start the width profile a little later, about 1.5 inches or so past the fades.

[Kirkll]

How are you going about mounting your limbs to the riser and getting them reasonably straight before limb profile? 

one or two location pins?

[Appalachian Hillbilly]

I glued a .075 wood pad to the bottom of each limb in the pad area. Set each limb in my mill and face milled the pads parallel with the limb best as I can measure.  Then set them on a flat surface side by side on the pads and compare them. I had to remove a few thou on the leading edge of one butt to get the tips even.  Once the tips are even and they are as parallel as I can get  them, I scribed a center line on each pad using a laser on my table. Laying the limb on its side,  the laser runs the whole length of the limb and I can get the center line to run true through the curved sections as well.


On the riser block, I scribe a center line as well and work from one side in the mill.

This limb I only have 1 pin, but thinking about 2 locating pins. I was amazed at how much with even fairly tight pin hole and takedown bolt holt hole, how much you can move a tip 20+ inches away.

[Kirkll]

Well if you have a mill, you are in good shape. Takes all the fight out of it with a machinist vise and a vertical mill.

I use an over sized bolt hole in my limbs, two pins in the riser, and when i drill my limbs i do a slot rather than a hole on the outside pins. Those limbs bolt on first time every time doing that, and never make noise. I've also found that 1/4" carbide tipped router bits work better than end mills for some reason.   Kirk

[kennym]

Kirk, I've thought about that slot thing but no mill . Guess I could set up a router table...

[Appalachian Hillbilly]

Got a picture of how you do the pin slot by any chance? Not quite sure I follow  exactly.

I have used carbide router bits in the mill for years! They have less rake than carbide endmills and when I do aluminum,  they don't gum up like some endmills.

They are generally  easy easier to find  as well.

[Mad Max]

I'm afraid Max might have complicated things for you a bit going into details a bit heavy. Its obvious he's been doing this stuff awhile.

He's Rookie of the year in my book and only been here 4 months or so.
He needs to be pushed

[Appalachian Hillbilly]

This is one heck of a rabbit hole. I love it. After being in numerous shooting sports and off road racing, this stuff feeds the inner mad scientist  urge. I love the idea of a progressive taper. That might actually speed the process up by being able to make the pretty wood lambs parallel pieces.

I am here to stay. May have to slow down some over the summer to work on our house, but having a healthy local club of about all trad enthusiasts helps.

[Kirkll]

I can do a short video when i mill my next set of limbs if you want. But basically i always dill and mill all my limbs  and risers the same with one 1/4" pin 1/2" above center of my bolt hole  (11/32") and the other pin 2" below center.....  The over sized bolt hole gives room for tap drift when you put your inserts in the riser. That and there are plus and minus tolerances of .005 in the inserts themselves. Worst case if you get an insert off is, you need to take a round rasp to the bolt hole. It has no effect on limb alignment.

Milling the slot with a 1/4" shank router bit can drift on you just using your machinist table. That bit can and will flex a bit cutting .265 deep. What i do is instead of drilling 2" to center, i drill one hole at .180 and then another at .220 then move the slide the table to make the slot. Then i knock the edges off with a counter sink bit.

For guys that just have drill presses i would strongly recommend buying a machinist 2 axis cross / slide bench to mount on it. This thing takes all the fight out of precise drilling and milling for TD bows.    Check this out...   Of course you'll need a good vise to mount on it too.

https://www.vevor.com/rotary-table-c_10128/compound-milling-machine-work-table-2-axis-cross-slide-bench-drill-vise-fixture-p_010230619047?utm_source=bing&utm_medium=cpc&utm_term=&utm_campaign=PLA-All%E9%AB%98-US-All%E9%9B%86%E5%90%88-2%E6%9C%88%E4%B8%ADTest3-eCPC-20220218-mxy-zzp&msclkid=cdeec995a72a1b567ef4aba72aeb85fe&utm_content=Ad%20group%20%231

I run a power feed on mine for just the X axis and have slide micrometers attached for X,Y, & Z.
It would be nice to have an electronic DRO set up, but it was expensive, so i used slide micrometers.     Kirk

[Appalachian Hillbilly]

I would be lost without a cross slide and machinist vise!

All the router bits I use in my mill are large shank. That helps with deflection.

A tip for using a tap and keeping it straight. The square end of the tap has a divot in the end. It is for a live center to keep the tap straight.  Leave the work in the exact same position,  and use the bit you just drilled the hole with to keep the tap centered.

A little light pressure down with one hand on the drill press while you turn the tap with the other. Or you can chuck up a center etc.

Most of yall probably know that, but maybe it will help someone  get the tap started straight.

[Shredd]

  Good tip, Thanks...

[Kirkll]

There are a lot of beginners that use all sorts of self centering drill guides to get their limbs mounted and struggle with accuracy drilling by hand. I was one of them years ago. The best ones I’ve seen were made by machinists, but it’s still tough to be accurate with both riser and limb drilling.

The best system I found that was truly accurate was not using a drill guide at all.
I laid out the limb pads, got the bolt inserts installed, then bolted the limbs on with no location pins. Then I straightened the limbs with a straight edge and drilled clear through the limb butts into the riser for the location pins, and finished up by doing limb butt overlays.

This system was very accurate, but good luck putting a second set of limbs on the same riser. It wasn’t happening… lol

[Mad Max]

I would be lost without a cross slide and machinist vise!


A tip for using a tap and keeping it straight. The square end of the tap has a divot in the end. It is for a live center to keep the tap straight.  Leave the work in the exact same position,  and use the bit you just drilled the hole with to keep the tap centered.

A little light pressure down with one hand on the drill press while you turn the tap with the other. Or you can chuck up a center etc.

Most of yall probably know that, but maybe it will help someone  get the tap started straight.

I did this a lot back in the day when tapping big threads (3/4" 1") because the tap would slip in the chuck, it's not good for the chuck either, and always used 2 people.