What exactly does it mean Tillered 3under?

[SERGIO VENNERI]

What james said.

[twotimer]

what sergio said both times.      

[bigcountry]

Ok, I measured the tiller on my martin savannah and my martin dreamcatcher.  Both are dead even at the fades and both, I nock the top of the nock of the arrow 1/2" over center shooting 3under.  

On my zipper, I measure more than a 1/4" difference with the top being 8 1/4" from limb butt to string and bottom being 7 7/8" from limb butt to string.  So that means my zipper is tillered for split finger?  But strange thing is my zipper likes the nock point to be only 3/8" over center shooting 3 under!!

Sorry for these stupid questions.  But seriously, you guys are really helping me.

[bowdude]

Where is the center of the pivot point??!!
  Sorry man but it is relative.  So is length of working limb, is one fade farther from center or equal, etc.  You can't focus on 1 feature and say ok this is right wrong or whatever.

[bigcountry]

But to add even more to the complexity, the top limb unbraced is 25" long and the bottom limb is 24.5".  Unbraced, the zipper is 58" long from nock to nock point but shelf is 28 1/2" from top of top limb and pivot point on handle is 29 1/2" from top of top limb.  

I am trying in my head to figure out how this thing is balanced.  Ah shoot, lets just it and be happy.

[bigcountry]

On my Martin Dreamcatcher that was tillered even at the fades I measure 56" total length from tip to tip, with pivot point right at 28".  This bow likes its nocking point (top of the arrow nock)to be 1/2" over center (pretty high).

Reason I am asking all these qeustions is I am taking a bow making class and would like to understand the basics before I start cuttin.  I am also reading thru the bowyers trad bible vol 1 and 2.

[3Under]

I don't know no "Tillered 3under". I just know me, "3under"!

[Hoytman]

Dang,
I thought you guys shot these bows because they were simple.
For years guys have been telling me to get rid of those complicated training wheel bows and go simple.
I'm not sure I'm smart enough for this.
My head is going to explode.

[bigcountry]

Well, hoyt it is simple if just buyin them and shootin em.  But I plan on building them.  Or attempting

[Hoytman]

Originally posted by bigcountry:
Well, hoyt it is simple if just buyin them and shootin em.  But I plan on building them.  Or attempting

Who knows Big Country. I may be buying one of your bows someday.    
Good Luck.

[warden415]

Let me ask a question or give my thoughts on this. If a bow is tillered so the bottom limb measures say 1/8 less than the top. Seems like most would agree it is tilled for split. I think it is done like this because most of your fingers are placed below the true center and you are pulling closer or more on the the bottom limb. Therefore you need the bottom limb "stiffer" hence the 1/8 less measurement,
Now if you shoot this same bow 3under, your fingers are even closer to the bottom limb because you have now moved your hand down the string by one more finger width and therefore pulling even more on the bottom limb. So why wouldn't this bow need to be tillered say 3/16 or 1/4 less on the bottom limb therefore makeing it even stiffer to equal out the hand moving closer to the bottom? Seems logical to me from a physics standpoint? This is how I have been doing the bows I have made and it seems to work better for me.
Granted, My bow building experience is limited but it seems logical to me? Just thought I would see what some others had to say? Steve

[DCM]

http://www.goarchers.org.uk/mechanics/  

Click the menu [Bow Mechanics], then [Tiller].

Positive tiller compensates for drawing the bow string, necessarily as has been stated, above the fulcrum of the bow hand.  In the most general terms three under tends to mitigate this effect and consequently requires less positive tiller to compensate.

[bigcountry]

DCM, I can't seem to find that webpage.  But I appreciate it.

[DCM]

Sorry, I think the server is down right now.  I'd try it again later.

I google "tapley tiller" and get "Tapley, Joe - Topics on Bow Mechanics -" as the title when I want to find it and don't have the url handy.  It was working this morning.  This is a topic which can melt one's brain.  Tapley's explanation has helped me to understand the underlying dynamics enormously.

[Chris Wilson]

David....That's a good site.  I'll have to book mark that one for future reference.  

Are ya'll going to be at Twin Oaks in May?

[DCM]

I hope so Chris.  Fighting chemo/radiation treatments for colon cancer which finish on that Friday.  Probably, even if I'm draggin' arse and for no other reason than to see folks.  Probably take the Monday off and stay over versus our traditional take the Friday and leave early Sunday.  Hopefully will have opportunity to catch up with you Sunday morning that way.  Hope all is well with ya'll.

[Chris Wilson]

Dang brother, first I've heard about you being sick.  I'll keep you in prayers.
 
We've got plans to be up on Saturday this year.  We're planning to pitch the tent and hang out through Sunday.  Hope to see you there.

[DCM]

No worries dawg.  90% survival rate.  I don't go parading my stuff around, but by now it's just old hat.  Had colon re-section 6 wks ago, diagnosed in Jan.  Large hassle factor, wearing a portable chemo iv around my neck (through a porta-cath) 24/7 for 5 weeks w/ radiation doses every weekday, then 2 days on the "bag" every two weeks for another 24 weeks.  But I'll be done with the treatments and have it all behind me by archery season, well mid October.  Life comes at you fast.  LOL

[Badlands]

Warden415
Almost, but remember that the center of the bow is not the arrow shelf, it is probably an inch or more lower depending upon the type of bow, therefore just the opposite is true. you pulling above the fulcrum and are bending the top limb a little more than the bottom limb at any given drawlength. The difference in tiller is to compensate for this.  It seems to me that the further your string nock is above the center of the bow, the more you would have to compensate. Some bows have there selves an inch and a half or more above center and the string nock may be another 1/2 or 3/4 inch above that.  Even if you shoot 3 under you would still be pulling well above the center of the bow.

I had never thought about tillering a bow by shorting the length of the lower limb.  This would effectively move the fulcrum up.  Hmmm.


Brad

[DCM]

"tillering a bow by shorting the length of the lower limb"

The beauty of this alternative in a wooden bow, in paricular one where you want to minimize the overal lenght, is you help relieve the strain on the upper thru the geometry, bringing the string angles more into parity by virtue of nock point nearer to dimensional center of the string.  In the so called "even" limb design, where the arrow pass is 2" above center on a 4" handle, the upper limb is actually 4" shorter than the lower from the string's perspective AND is required to bend farther.  

Notable bowyers have tried to advocate this alternative, and it is well practiced in antiquity, but for some reason there seems to be much resistance to the idea and much confusion circulating about it in more recent times.  Evidently folks value the ability to "flip" a selfbow upper for lower limb at some point during it's construction over the theoretical benefit of arrow pass nearer dimensional center.  

In a glass bow paradigm there's so much extra work capacity at hand in the material I'm not sure it matters, beyond the obvious need to give the bow enough tiller to be tunable to the intended archer's style.