Drawing the perfect tiller profile

[Freeflynick]

Hello!
I have just set up a new tillering rig, mounted against the full-wall mirror we have in the garage (from previous owner!). I was wondering if anyone draws out the "perfect tiller" profile on a backboard etc. prior to tillering to give them a target for the perfect shape, and if so, any tips on how to come up what the right shape would be, and how would you draw it accurately?
FYI - current now is hickory-backed ipe pyramid bow - if anyone has suggestions on the profile I should be aiming for here, that would be great.
Cheers!
Nick

[DC]

Yes with a big but. The perfect arc doesn't really exist, at least for all bows. It depends on bow length, draw length etc. Also it only works for bows that are perfectly straight or at least have the same bend in both limbs to start with. That said, I found that most of my bows are roughly the same length and the same DL so I have a line there that I can look at. Use an erasable marker. It can be very helpful to trace the bow you're working on so you can see where the changes are taking place.

[PatM]

You can always draw two large perfect circles for reference and then sketch in degrees of variance from that which will best match the particular tiller your stave shape requires.

 Just like the pictures people post with circles overlaying the drawn bow.

[mmattockx]

FYI - current now is hickory-backed ipe pyramid bow - if anyone has suggestions on the profile I should be aiming for here, that would be great.

If it's a straight up pyramid profile the tiller is very close to a circular arc. Depending on what you do at the fades and tips it may be slightly stiffer at each end of the limb, but the vast majority of the limb bend should be circular.


Mark

[Del the cat]

Arc of a circle can be handy... but's tricky to work out the actual radius... you'd think at first glance that it would be half the string length... but that wouldn't reach from the full draw point to the back of the grip (due to brace height)... unless you make the centre of your circle a6" above the full draw point... errr then it all starts getting confusing  ... trial and error prob works best!
Or its easiest to chalk round the limbs of a few of your favourite bows . 
Del

[willie]

Del. I have used a factor to multiply the NTN distance by when doing bendy handles, (arc of circle or ellipse).

As Mark points out, with a Pyramid, two adjacent circles separated by a distance according to handle width is best.

I hang my back board from the upper corners with twine so that I can easily move the board around behind the tiller tree.

[bownarra]

First couple of inches out from the fades should be a wee bit stiff and the last 6 inches going into the tips but the rest of the limb should be bending the same amount along its length. Perfect to use a tillering gizmo on.
There is a great chapter in TBB about what limb width profile relates to which tiller profile and why. I highly recommend getting your head around it then any bow is easy to asses tiller shape on. Its all logical stuff

[mmattockx]

Arc of a circle can be handy... but's tricky to work out the actual radius...

That it is. I find it far simpler to take a picture and then impose a circle onto the picture on the computer. You could probably get quite close with Hickman's mathematical bow model description and drawing the bow up in a CAD program but that is a lot of work compared to putting circles on pictures. The actual radius isn't really important, so long as the limb bends along a constant radius away from the fades and tips.


Mark

[Freeflynick]

First couple of inches out from the fades should be a wee bit stiff and the last 6 inches going into the tips but the rest of the limb should be bending the same amount along its length. Perfect to use a tillering gizmo on.
There is a great chapter in TBB about what limb width profile relates to which tiller profile and why. I highly recommend getting your head around it then any bow is easy to asses tiller shape on. Its all logical stuff

Sounds like I may have to open the wallet and get a copy of TBB....I went with Clay Hayes Handbook since I used his online videos for a lot of my learning, I felt obliged!
This is very useful stuff guys - thank you! This is my first non Home Depot bow, so I'm keen not to screw it up! And since I am still very much in the "I don't know what I don't know" stage, there is so much opportunity for screw ups!
Cheers!
Nick