Primitive Archer
Main Discussion Area => Bows => Topic started by: Eric Krewson on May 11, 2010, 11:44:34 am
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Thought I would add this to to this board as I often make reference to it.
Since I made my initial tillering gizmo there has been an input of ideas to make it work better from other bow makers. Consequently it has evolved into a differently made tool than my original design.
Here is how to make the latest version. I use a drill press, bandsaw and belt sander because I have them. This tool can be made out of any scrap wood, holes drilled by hand, out of square and work just fine.
I cut a large downed cedar looking for a bow stave. I may or may not have found a stave but I definitely found a bunch of beautifully grained gizmo material.
I start by cutting a piece of wood 1" square and 6" long. You can make the gizmo longer if you want to, length is not a critical issue
(http://img.photobucket.com/albums/v181/ekrewson/dead%20cedar/gizmo1.jpg)
A little sanding to get rid of the saw marks.
(http://img.photobucket.com/albums/v181/ekrewson/dead%20cedar/gizmo2.jpg)
Mark the center of the block length wise and center.
(http://img.photobucket.com/albums/v181/ekrewson/dead%20cedar/gizmo3.jpg)
Drill a 5/16" hole on the center mark.
(http://img.photobucket.com/albums/v181/ekrewson/dead%20cedar/gizmo4.jpg)
I use a 1/2" forstner bit to cut A 1/2' deep hole over the 5/16' hole I just cut. The forstner bit cuts a clean hole but any 1/2" bit will work just fine.
(http://img.photobucket.com/albums/v181/ekrewson/dead%20cedar/gizmo5.jpg)
Next I mark the ends of the block with a 45 degree angle to shorten side opposite the pencil of the gizmo. This allows one to run the gizmo closer to the tips while tillering.
(http://img.photobucket.com/albums/v181/ekrewson/dead%20cedar/45marked.jpg)
I cut on my lines
(http://img.photobucket.com/albums/v181/ekrewson/dead%20cedar/45scut.jpg)
I tap a 5/16" nut into the 1/2" hole and seat it all the way down with a piece of dowel.
(http://img.photobucket.com/albums/v181/ekrewson/dead%20cedar/gizmo8.jpg)
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Too many pictures for one post so here is the rest of the story.
Screw a pencil into the nut(I put the pencil in a vise and screw the gizmo on it) and you are ready to tiller. I sand the pencil a little after I cut thread on it so it will screw in and out easily. It only took me 10 minutes to make this tool, start to finish.
With a little Tru-Oil this will be a beautiful little tool, it has a wonderful grain pattern.
(http://img.photobucket.com/albums/v181/ekrewson/dead%20cedar/finishedgizmo.jpg)
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USING THE TILLERING GIZMO
After floor tillering your bow, bend the bow slightly on your tillering tree or tillering stick using the long string. Retract the pencil in the Gizmo and run the wood block up the bow’s belly and find the widest gap. Screw the pencil in the block to a point it is almost touching the bow’s belly at the point where you found the widest gap. I change the angle the pencil has been sharpened to a very short angle and sand the tip of the pencil flat for the best results in marking the limb. This lets you work very slight bends.
(http://img.photobucket.com/albums/v181/ekrewson/bow%20making/adjustinggizmo.jpg)
Initially I set my gizmo pencil about 1/8” off the limb for the first few corrections. This course setting will mark only the stiffest spots. If you set the pencil too closely for your first few passes it will mark the whole limb.
Run the Gizmo up the belly making sure it is centered on the limb. The
pencil will mark non bending areas that need wood removed. Always check the entire limb with the gizmo every time you use it and scrape wood from all the stiff spots at the same time, not one stiff spot at a time. Start on the long string, continue at brace and up to about 20” of draw. You do need to have a way to hold your bow string while you mark the limbs with the Gizmo.
I often set my gizmo for one limb and use this setting on the opposite limb as well. This way you will end up with two closely matched limbs.
I have holes in my tillering tree and insert a 3” piece of dowel in one of the holes to hold the string with the limbs slightly bent while I mark the limbs with the gizmo.
(http://img.photobucket.com/albums/v181/ekrewson/bow%20making/tilleringtotheshortstring5.jpg)
Go slowly, no more than ten scrapes on the marked areas of the limb, flex the limb 30 times and recheck. I have found it usually takes 5 or more check, scrape and check sessions to get a stiff spot moving so be patient. You can get the limb bending perfectly this way. You will still have to eyeball bending in the fades but the rest of the limb will be perfectly tillered. Hinges will be a thing of the past.
(http://img.photobucket.com/albums/v181/ekrewson/newgizmopic2.jpg)
Make a few passes with the gizmo on your limb and the areas that need attention will be perfectly obvious. You can fine tune the tillering by closing the gap between the pencil and limb to almost nothing. At this point I like to use a cheap orbital sander to remove both wood and any tool marks that are left. With course sand paper, the sander will leave tiny swirls in the wood so I like 220 grit for my final tillering work with the sander and follow with a light hand sanding.
The gizmo doesn’t work in the fade out area of the riser so you will have to eyeball the bend in this area or put a flat board across the back of the bow in your tillering tree and watch the gap between the back of the bow and the board to see where the limb is bending.
Tillering that once took me hours to get close takes me about 45 minutes with the Gizmo and the end result is close to perfect.
Remember the key thing to remember for proper tillering is using a scraper or sand paper and work slowly, only scrape off your pencil marks, flex the bow and recheck. I often make a zig-zag pencil mark from one side of the limb to the other over the gizmo’s pencil mark to make sure I remove equally from one edge of the limb to the other.
If you ever get the urge to grab a course rasp or use a belt sander to speed things up even more, take a coffee break and come back when these thoughts have passed.
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Thanks! This is going to give me an excuse to steal one of those little pencils next time I go golfing :D
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Im sure a lot of guys will find this very helpful. Thanks for posting. I tried one a few years ago and it worked good. The reason I dont use one alot is that I seem to like building r/d bows where you wouldn't want the whole limb bending the same. Also do you think character staves might present the same problem ?
Great instructions and great pictures. Thanks :)
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No problem with snakey bows but this tool won't work well with a roller coaster limb. It does work well on board bows, round belly bows and flat belly bows.
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Thanks for that instruction. :)
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Eric, I have thought your gizmo was a great idea from the start.
A decade or so ago, I read in "Archery the Technical Side," about a device to do the same thing, called with tongue in cheek, a "bend-o-meter" if I remember Correctly. It used a dial indicator and was far too complicated in use. One had to record the readings at different stations on the limbs and scrape accordingly.
Your gizmo is much more practical! I made one of the dial indicator versions and only used it a couple of times before I realized it was just too involved.
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Ive used this method before and it works! Thanks for posting it it will give others a good idea on "gizmos" to help perfect their craft. Have a good day!
Russ
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Great tutorial and advice on using it!
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Thought this needed to be backon the 1st page for anyone that might have missed it. Very nice Eric ;)
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has this been archived?
would'nt be a bad idea to do so
Ron
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I can move it to the "How To" section. Just let me know.
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Eric,
I was reading another post where this was mentioned and thought I would look it up. seems like a great little tool and I have decided I am gonna make one. Gotta question though....
- If you don't want the wood to bend in the last 10" or whatever on the levers, say like on a molly or something like Blackhawk makes like a modern holmgard, do you stop the marking when you reach the areas you want to bend?
Thanks in advance Danny
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A tillering Gizmo only tells you where the working portion of the limb is not bending enough. In non-working areas it is not necessary. Every wood bowyer should have a tillering gizmo in his tool kit.
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I started using a gizmo a couple of years ago. Great tool. I make mine 4" long. I might try 6" and see if I like it better. I like a bit more of an elyptical tiller instead of circular so I have to play with it a bit. I start off getting it bending equal then use it to increase the bending radius mid limb by comparing the two limb marks. I was trying to figure out a way I could modify it to change the width of the mark as the depth changed but didn't come up with anything uncomplicated. It would be possible to make an air brush type set up where the pencil was replaced with a needle in the tip of an air brush that changed the spray pattern as the needle changed depths. But a little too complicated.
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Wouldn't build a bow without it. Dean
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A tillering Gizmo only tells you where the working portion of the limb is not bending enough. In non-working areas it is not necessary. Every wood bowyer should have a tillering gizmo in his tool kit.
Great thread with invaluabe advice..