Experimental Limbs...

[TradBowyer]

yeah man that's the trouble with loading up the preload with that degree of pad....it makes the limbs a little unstable. I don't really know if it affects shootability though. I would think horizontal stability has a greater impact on shooting than the vertical stability does. Once the arrow is gone, what the limbs do doesn't matter. However, the bow is super easy to torque, that is a problem

[Shredd]

  Very True, TB...  I put the limbs on the 7* riser and the stability was fine... 

   I have a lot of work cut out for me but man am I gonna learn so much from this...  Here are some pics at 5*, 7* and 9* pad angles...   They are all drawn to about 27" in reference to the limbs and not the riser...  I went from 32# on the 5* riser to 28# when I put the limbs on the 9* riser...

[Shredd]

I also filed the nock grooves in a little closer to accommodate a 59" string...  Now I need to make a nice string to fit this bow to do speed tests and some DFC's...  Plus I still have to finish up the 7* and 9* risers so I can shoot out of them...

      I will try to comment or or discuss all of your advice and comments so please keep them coming...   

[Mad Max]

I like the 7* and string angle

What is the angle on you normal bows?

 

[Shredd]

Max...  One design is about 10* and the other about 7.5*...   

   Well I shot it through the chrony as is with a 6 1/8" brace height, weight at 28" is 33.3#, 334gr. arrow drawn to 28" - 184fps...
Shot a 305gr. arrow at 189fps...

   As a one piece and at 6 3/4" brace height I am guessing she will be shooting in the mid to high 170's...  I could be wrong...  All this translating from a 3 piece to a one piece is beginning to confuse me...

[Mad Max]

  Nice speeds

I would make my 1P riser as long as the TD riser + 2" or so each side
same angle for the fades as the butt wedges are.

[Crooked Stic]

If you want to draw then 27 and under I would go with the 7 degree. Still got good string angle but closer to the wall than 9 degrees. Those numbers pretty good for the weight.

[Shredd]

  I am kinda agreeing with both of you guys...

  I did some math and I think I am pretty close to what the speeds would be as a one piece bow...  The speeds may be pretty close no matter what angle riser I use...  Probably because of the very thin limbs...  With the change of each 2* angle the draw weight changes 2#...  So to do a true test you would need 3 sets of limbs measuring all the same draw weight at different angles... Here are some speeds all at 5* and 7* at 6 3/4" brace and 9* at 6 7/8" brace... (was a little short on the string to get 6 3/4")

5* riser  32#     string tension 52.4# / 81.8%

                     26"           27"          28"
303gr.           166           174         182fps
334               160           169         177
410               147           154         162


7* riser   30#     string tension  51.5# / 85.8% 

                    26"            27"           28"
303              162           170           178
334              157           165           172
410              144           150           157


9* riser   27.9#    string tension  50# / 89.6%

                    26"            27"           28"
303              156            165          172
334              151            159          167
410              138            145          153


   As you can see  the string tension is greatest with the 9* riser and it also had the best numbers on the DFC charts...  When I am comparing two bows of one set design the bow with the better DFC and higher string tension usually results in better performance...  Being that I am dealing with three different angles (designs) who knows what will give the optimum performance...  DFC's and string tension may not be comparable from one design to the next in this case...

[OkKeith]

Hey Shredd...

Very cool data you are collecting! I have a quick question about your construction methodology (unless it is Super Secret Squirrel Stuff).

Are you using a jig on your table saw to run the angles on those risers? I figure I have a year or so to build a few bows so that I can up my build game before next years bow swap. I like the idea of making a take down but don't see myself adding any major power tools to my cramped home shop. I have a bandsaw at my folks place as well.

My thought was to make a tablesaw sled with hold downs for the risers. Since I am thinking about a D/R longbow I am considering a 6-6.5 degree angle on the risers.

Also, do you have two forms and run both limbs at the same time or one form and run one limb and then the other?

Thanks for the help!

OkKeith

[Mad Max]

I'am going to highjack this a little
If you table saw blade is not perfectly  square your limbs will be twisted.

[OkKeith]

Hey Mark...

I figure EVERYTHING will have to be as square as possible! The blade to the tabletop, the sled to the blade and the material will have to be dead square. I will do my best but I doubt it will be anywhere near perfect.

What is your suggestion on how to cut the angles on the riser?

OkKeith

[Mad Max]

I would buy the best square I could find and make a test cut using the sled.
 hold the test piece up so you can see light between the square and wood.
Keep moving your blade a little until you get it where you want it.

Google  Machinist Square
Good luck

[Shredd]

Sorry OKK...  I just saw your post last night... 

   I use a bandsaw and free handed these since they were one-offs...  I would make a jig if I was making a certain riser all the time... But yes, you can use a table saw and a jig and pretty much do what Max said...  You can touch it up on a disc sander set accurately at 90* if you have one...

  I only have one form as for now, these are experimental limbs...  One form should be fine for most people unless you were gonna go into business and mass produce them... I which case you might want to have 10 forms...   

   Being that you are going to make a 3pc...   I would do as I am...  Make a couple of risers with cheap or defected wood and test your limbs at different angles to get the best performance, stability and shootability out of them...  You can always shim the limbs a degree or two to finely tweak it to what you want...  I would do this method before you spend time and money on a pretty riser that makes for a sub-par bow...

[Crooked Stic]

What I have done is made a profile jig to do the riser pads. put the riser in it and profile the whole riser. this puts both pads on the same plane with each other. They are square with the side of the riser but would not have to be perfect. The trouble with the saw jigs is you are flipping the riser to do the other end and things need to be dam near perfect.

[OkKeith]

Mike-

When you say "profile jig"... are you doing this process on a milling machine?

Thanks,

OkKeith