Tiller help Please.

[rascal]

I posted these pictures on my previous thread but now I seem to be getting some contradictory advice on the tillering.  I dont want to remove too much material and make this bow way too light for my purposes obviously so Im gonna ask for a bit more advice.  At this point the limbs bend which is good I assume.  Do I need to worry more about following the contour of the sapwood of the bow or worry more about how the limb bends?  Do I need to heat and straighten out the limbs to take out some of the natural contour in the limbs?  Currently the bow is still 74" long with a 12" rigid handle section and Im not set on the final length so I can shorten to gain some poundage back if needed.  I am trying for an American Long Bow (think Glenn St. Charles) if that helps.

Im drawing the limb down with a string that is just barely snug (not flexing the bow) to 12" and that is approximately 20# of weight.

This is unflexed

 

Unflexed right limb

 

Unflexed left limb

 

Flexed to 12"

 

Flexed right limb

 

Flexed left limb

 

If you have advice for me dont be afraid to dumb it down, I wont be offended since Im feeling pretty dumb right now anyhow.  

[Jason Jelinek]

It doesn't look like you have much thickness taper in the limbs.  The tips look as thick as the end of the dips/fades.  This is going to put most of the bend near the handle, giving you more set and a slower bow.  At 74" long you can have more bend in the outer half without it stacking.  This will also give you a faster bow.  If it was 64" long you would need to get the inner limbs working but that's a different bow.

If you do put more taper in the limb thickness you will drop weight, probably forcing you to shorten the bow slightly to gain back the weight.  You still have plenty of length though.  I made a 70" ntn (73" long with antler nocks in English style) yew bow with 12" stiff handle section and I draw it 29".

Jason

[gordonf]

Hard to say with a long string and a short draw, but the left limb looks like it is bending primarily near the fades and the right limb is bending mostly between the two wrappings.

[BamBooBender]

I agree with all the above. I went and read through the other thread.I think they're givin you good advice too.  Tillering advice over the net can be at times difficult, even confusing(to say the least). Anyway,I see your from Iowa, maybe you can get together with Shaun. Nothing like a little one on one with someone that has experience. I don't know Shaun personally, but from what I have seen of his postings here, he has made a few. just my 2 cents

[tecum-tha]

I usually start tillering my bows like that:
I grind my bows down to a recommended tillering start thickness( I use Osage,though). You`ll get some info in trad bowyers bible.

1. Draw dynamic zones on your limbs: 6-8 inches should remain stiff at the tip ends, then the main bending zone, and then the slight bending zone near the handle. None to very slight bending should occur there.

2: Use a dynamic tillering device, a pulleye where you can draw the bow and take a look at the profile at the same time and let it back down immediately.Don`t fix it for long terms (over 10 seconds). It helps to put a spring scale between the pulleye and the tillering string. If you never draw your bow further than your desired draw weight, there should be hardly any string follow.

3: calculate your required poundage at brace height: [Desired bow weight- (3pounds/inch * your desired draw length)]+ 20 pounds.
This will give you a good idea of how much wood to remove to get to brace height.

4: After removing wood pull your future bow 20-25 times in the device to allow the wood to settle for the interior forces. With hunting weight bows, this requires a lot of power without a pulley and you can`t concentrate on the bending of your future bow. Your eye will show you the stiff areas, that don`t end and there you will have to work some next.

Have fun!
Roland

[Linc]

Rascal, The area between the tapes is not hingeing it is too thick compared to the areas before and after. Use a caliper to make measurements if you need to, but the thickness of the limbs should be a steady and gradual taper from the flairs to just short of the tips.The belly will need to conform to the back.Example: on your left limb and your right limb (between the tapes)there are humps in the back but the belly lines go straight. They will be stiff and make tillering much harder.

Take a rope or a hose and lay it down perfectly straight and jiggle one end a little. It will now be snakey. Observe how the underside follows the shape of the topside. This is how your limbs will need to look.

[gordonf]

I don't know Linc, something is bending on the right limb and it does not seem to be the fads or any of the areas outside of the taped area. I agree that, in general, the belly should follow the back, but something is going on in that spot.

[rascal]

The right limb between the tapes has a natural hump in the sap wood that is somewhat deceiving to the eye.  Ive questioned whether it is a hinge but I really dont have much experience to go by.  

Ill get a pulley put on that tiller tree, Ive got one handy anyhow, and Ill rig it with the scale for starters.  I can take some measurements to see what the thinest/thickest spots are on the limbs as well.  That should be a pretty good start.

[rascal]

Well I got the pulley mounted on the tiller tree and managed to get some measurements on the thickness of the limbs which I think are still plenty thick from what Ive heard here so far.

I grabbed a quick picture to show where the thinnest portion of each limb was on the bow right now and marked that with blue tape (I gotta get some other tape color).  The thinnest portion on each limb was 3/4" but I havent tried to re-establish a line that contours the back of the bow yet.  I dont want to take anymore off until I get some feed back so if you need more pictures or more measurements or anything else just lemme know.  

 

Sorry about the lawn tractors in the picture there guys, momma wants short grass or its my... err ummm... butt, so had to do a bit of work on them as well.

[gordonf]

Is there a knot that goes through the belly between the two tape wrappings?

[rascal]

No gordonf there are no knots on the right limb at all there is a bump in the sapwood (twist maybe a better word here) that makes it seem to hinge at this point.  There is only one knot in the limb and that is in the left limb between the fade and the solid line of tape.  The two lines of tape were put on earlier to indicate a hinge and where I should not take any more material off.  The tape that goes along the length of the limbs is to indicate the thin spots in the limbs.

[gordonf]

Okay must be the picture then. I definitely see the thin spot you marked on the right limb, but I'm a little perplexed why it isn't bending more there.

[rascal]

Well that makes two of us that are perplexed then gordonf.

[rascal]

Now will the tillering gizmo posted in the "How To" section here work on a self bow like this?  Seems like the answer is no to me since you have to follow the contour of the sap wood but again I have very little experience to go by.  Here is the link to the exact How-To I am speaking of.

 http://tradgang.com/noncgi/ultimatebb.php?ubb=get_topic;f=2;t=000075

[Linc]

I don't see how it could but I never tried it on anything that had any character.Might be better off asking Eric,it's his gizmo and he has much more experience with it.

[rascal]

OK it sounds like popular theory is to re-establish a contour from back to belly on each limb for starters and then gradually taper the limbs out from fade to tip.  That would give me 3/4" thickness from fade to tip to start with.  Ill leave the taper business till I can take some more pics.

Sound like a reasonable start?

[rascal]

Well for lack of any more input Ill put some work into the contour issue tomorrow as it seems to be a recurring point of concern.  Thanks for the advice so far Ill check back when I make some more progress.

[Linc]

Following the contour of the back now is a good idea. Cause you will have to do it sooner or later, so it's better to get it over to begin with. It shouldn't be too much problem with your stave.

[rascal]

Well took some time to re-establish the contour from belly to back tonight.  I set the calipers to 3/4" and removed material until I could slide them across the limb at any given point, its probably not perfect but very close to 3/4" from fade to tip on each limb.  Ill see how it looks pulling it down a bit tomorrow perhaps and work on tapering the limbs after I take care of any problems areas.

[rascal]

OK Ive been quite busy as of late and havent worked on the stave at all.  The bug bit me again tonight since I couldnt sleep, too many years of working 3rd shift I guess, so I did a little more on the stave.  Mostly measurements and such but I did bend it a little.  I put some marks back on the stave for reference since the old ones were getting a bit worn and while I was at it divided each limb into 3 equal portions to make working them a bit easier for me.  Now I have lines approximately 10" from each end and 20" from each end and then at the fades which are about 31" from each end.  I measured across each of those lines to make sure they were even from limb to limb and put new center marks on them as well.  Did centers on the handle too and laid a weighted string across, its not exactly on and that worries me.  I know I can heat and bend this but wanted to show the pics here and get some input.

Here are some pics showing the extent of the offset as best as I could get them.

   

Here are 2 of the right side as it laid on the bench.

   

   

Two of the left side as it laid on the bench.

   

   

Here we are back on the tiller tree with a new longer string.

   

Here we are I pulled it down to 23# weight, maybe 6" not sure on that.  I didnt see anything that shocked me but again I am no expert.

   

Lemme know what you think I need to do now, I think its bending OK from what I see but didnt want to bend it any farther without a little input.  Its definetly tweaked to one side as you can see, I would say its 1/8 to 3/16 inch off at the center of the handle.  The pictures probably show it better than I can explain.  Im guessing I need to take care of this next.