Question about using a tillering gizmo

[ajbruggink]

Heh guys,

I started using a tillering gizmo about two years ago and I can say that it has helped me find stiff spots better but I have been making a lot of bows way too light lately and its making me think that I am using it wrong. I have been using it to find stiff spots by starting out so I can barely feel the tip of the screw poking through the block of wood and then I slide the gizmo down the limb. If the screw scratches a spot, I remove wood at the stiff spot, exercise the stave, check the tiller, then run the gizmo down the limb again and I repeat this process until the stiff spot is gone. As I pull the bow further, I bring the screw out further because the limb is bending more and the gizmo can travel further down the limb, at least I thought that was how it was supposed to be used. Is this how it is supposed to used? I have been making a lot of bows way too light lately and I think its because I'm removing too much wood during tillering, I don't think its a design mistake. For the past year the bow I have been trying to make is a 72" long, 55#@28" D-bow out of red oak, 1 3/8" or 1 1/2" wide at the grip and it maintains that length up to half of the bow's limb, where it then tapers to 1/2" nocks but my bows lately haven't been able to pull 20 lbs. A week or two ago, I shortened a stave down to 64" and it finally pulled 22 lbs but I thought the tiller needed to be adjusted and after that adjustment it no longer pulled 22 lbs. Based on the experience of other bowyers, at least 50 lbs should be doable at those dimensions and I've heard of bowyers getting more weight at even narrower widths with whitewoods. I thought there was a thread somewhere that gave details on how to use the tillering gizmo on here but I couldn't find it. My explanation of my problem might be hard to follow, I'm having a hard time putting it to words, so I'll just sum it up with one question: How do you use the tillering gizmo? Any advice and critiques you can give is greatly appreciated.

Thank you,

Aaron

[JWMALONE]

Try this link. Its in the build along section.
http://www.primitivearcher.com/smf/index.php/topic,61422.msg862049.html#msg862049

[Badger]

   Aaron, if you are coming in light it is because you are not pulling the bow to 50# early in the process. Try to get your bow bending nice and even when it is still way too strong and then start working the bow down using your gizmo, in between scraping on the tiller tree pull the bow to 50#. If it won't take it you didn't have enough to start with. I assume you are making a bendy handle bow. 3/4" thick in the middle should be enough for that at 72" long but you are pretty close. If it looks like it is bending too much in the handle with 50# on it you might consider cutting it down to about 66".

[Eric Krewson]

Are you using the Dean Torges walkie talkie type gizmo, it has a screw.

My gizmo has a pencil to mark the limb.

[ajbruggink]

Are you using the Dean Torges walkie talkie type gizmo, it has a screw.

My gizmo has a pencil to mark the limb.

I actually got my idea from a Rudderbows build-along pamphlet, he called it a 'cheater tool' and it seemed to serve the same purpose as your tool and it looked a lot easier to build, drill a hole in a piece of scrap wood about 3" or 4" long and find a screw that will fit inside the hole without it falling through easily.

[ajbruggink]

   Aaron, if you are coming in light it is because you are not pulling the bow to 50# early in the process. Try to get your bow bending nice and even when it is still way too strong and then start working the bow down using your gizmo, in between scraping on the tiller tree pull the bow to 50#. If it won't take it you didn't have enough to start with. I assume you are making a bendy handle bow. 3/4" thick in the middle should be enough for that at 72" long but you are pretty close. If it looks like it is bending too much in the handle with 50# on it you might consider cutting it down to about 66".

Thanks, Badger, I will try that next time, right now I'm working on a hickory stave that is currently pulling 26#@18". The last bow that I made which didn't come under weight too much was a hickory bendy handle bow, it was 1 1/4" wide at the grip and tapered from the grip to 7/8" tips and that bow pulled 54#@29". The bow I'm making now is basically like making that bow again, but in both cases I have tried to get rid of stiff spots and hinges before hitting target weight, so I'll try as you suggested next time.

[Springbuck]

  Badger gave you the key.  You are not using the gizmo wrong.  You just aren't checking the draw weight enough.

Lots of guys have tillering tree setups with a spring scale and a pully so they can watch the wood bend and pull with an exact amount of force.  My ghetto setup has some old barbell weights threaded on a piece of pipe, with an "S" hook on the end.  I can hang the bow on the tree, then hang the weights on the string by the hook.

  If I want a 50 lb bow, I put 50 lbs on the pipe.  Then I look at the bend.  If 50 lbs of weight pulls that bow 3", I DON"T pull it any farther. Just carefully make adjustments ONLY to any stiff spots (basically with the screw BARELY out).  After a couple times scraping the stiff spots the bend will improve and the limb tips will bend maybe to 5" when I hang the weight on the string.  Great, go over it again and adjust any flat spots.  Now it may bend 8".  Just never pull harder than the final draw weight, and never move on until you have fixed everything you can see at that stage of bend.

You are basically doing the opposite, which is what I did a lot early on, by working and working toward perfect tiller, finally getting there and realizing you made a kid's bow.  Since I have been doing as above, I finish almost every one close to weight, and usually ruin them early on if I'm going to.