Made some "tillering blocks'

[rodlonq]

At least that is what the recurve makers on Pirates of Archery are calling them. The use them to find the "dynamic" centre of take down recurves to determine the location of the limb tip centreline to undo any inherent twist in their take down limbs.

Anyways, I really wanted to find out which end of my latest D/R blank has the "weaker" top limb because when I cut out the riser there was a nasty gum vein against the belly lam well up the ramp . I knew if I could force the weaker limb to that particular end of the riser I should be able to cut out the gum vein when shaping the window (for a RH bow that is).

I set about making some tillering blocks from 50 mm aluminium bar so I could see if I was successful. They are 13 mm wide so when they are on the limb tips at roughly brace height I can check for twist in the limbs and use the recurver's philosophy of moving the centre of the tip toward the stronger side of the limb to counteract any twist that occurs due to material non-uniformity in the lams. When it is all "just right" put a mark either side of the block and you have your limb tip roughly marked out.

I think the tillering blocks were very successful and I reckon I will use them on every blank even if it is just to see if there are any surprises to learn of before cutting the limbs to width. Here's an as-built drawing of the basic shape for anyone that is interested. I just laid it out of the top of my head when I made them but it these dimensions should work.

TillerBlock.png (28.9 KiB) Viewed 2383 times

It turns out the full width 1.5" x 72" long blank showed neutral tiller so I can cut the offending gum vein out with the window and hopefully finish up with 1/8" positive tiller by the time I finish the bow.

TillerBlocks1.JPG (108.82 KiB) Viewed 2383 times

TillerBlocks2.JPG (134.3 KiB) Viewed 2383 times

Oops.... my drawing is upside down

I also used them on another partially finished D/R bow that I have cut the limbs to width and sanded the sides. This enable me to find the weaker limb without having to cut in the string grooves. I will still cut in string grooves before I shape the riser however, because that blank has fairly hefty purple heart veneers and it is the first time I have used veneers in a bow. I am unsure if it will be a bit heavy at 68" NTN so I am going to cut string grooves in at 70" NTN and weigh it.

Thanks for looking.

Cheers.... Rod

[GrahameA]

Morning Rod.

[quote="rodlonq"I set about making some tillering blocks from 50 mm aluminium bar ...[/quote]
Great choice. Fan of Aluminium.

Excellent little 'tool' - they will serve you well.

[Flatliner]

Great idea Rod might make a set my self. Being able to find true center dynamically has to be an advantage.

Rob.

[Gringa Bows]

top job ,Rod

[greybeard]

Hi Rod,

The tillering discs look very well made but I would be reluctant to use them on a recurve. It is not so much the design of the discs but the nature of the recurve.

Being able to find true center dynamically has to be an advantage.

Hi Rob,

I may be missing something in the translation, can you elaborate on the above?

Daryl.

[bigbob]

Have to look into making something similar Rod, as they would take out a long of concern about possible limb twist.

[Flatliner]

Hi Rob,I may be missing something in the translation, can you elaborate on the above? Daryl.

What I mean Daryl is at the moment I am using a string-line to find the center line with the bow unstrung, using the tillering blocks allows you to find true center while the bow is at brace which I feel could possibly be more accurate because you are accounting for at least some of the residual tensions in the limb blanks. I could be wrong but worth trying out.

Rob.

[greybeard]

Thanks Rob, I was visualizing your statement with the braced bow on the profile and not the plan view.

Daryl.

[rodlonq]

G'day Daryl and Rob,

There is a very detailed build along on Pirates of Archery forum where the fella explains how he uses them to find the "dynamic centre" of blank take down recurve limbs (about 3/4 of the way down the first page).

http://piratesofarchery.net/bb/viewtopi ... =20&t=1788

Obviously this idea is not mine but one from a bloke who seems to take his bowyering very seriously, not necessarily old school but seriously all the same. I was intrigued at the level of sophistication he put into his bows.

Cheers........ Rod