Made some "tillering blocks'
Posted: Fri Feb 14, 2014 7:33 pm
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. 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. 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
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. 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. 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