Some Hill Style Dimensions for General Info

[canopyboy]

There's been a lot of questions on Hill dimensions lately.  I don't really know that much, but will share what I have.  I've carefully measured three by Howard Hill Archery in the last year, and made three myself.  The stacks, etc are below for you to use as you see fit.  Note that the thicker stack for the yew bow ended up with a lower poundage bow.  For bows of this style with a thick core, core material matters more than I thought.  The only way you're going to nail a weight is a lot more data and good handle on the materials you're using.  I also contend that working limb length is more important to your stack calculation than bow length.

 
**UPDATED for typo and added nock widths.**

Would be great if others have had the opportunity to carefully measure Hill bows from other bowyers or their own and post.  We could have a little library here.  The more data, the better one's chances of hitting the right stack.

[fujimo]

thank you!!
i also noticed that about the yew- i have only built two glass bows now with yew,on kennys form, and they came out lighter for his stack heights for other woods- i saw about a 10%, roughly, variance in the yew vs other woods

so do you have any bow "recipes" to go with these figures- ie; thickness of the stack at the butts, taper rates etc.

many thanks
wayne

[canopyboy]

Total taper is in there, if you take that times the distance from the fade to the center of the bow and add to the stack at the fade you'll get total taper at the butt ends.  I can give you what I used for individual lams:

For the swap bow, core lams were as follows:  (2) 0.043 clear ULS glass, (2) 0.080 x 0.001 cherry veneers, (2) 0.135 x 0.002 black locust core lams.  For the swap sister bow (in case I missed weight), it's the same except for 0.145 x 0.002 black locust core lams.  All wood was local and air dried before sending to Kenny for grinding.  Both have one cherry lam up the belly of the riser.

For the yew bow, I used: (2) 0.040 black ULS glass, (2) 0.150 x 0.002 yew and (1) 0.170 x 0.002 yew for the core.  Only the glass goes up the belly of the riser.  Yew came from Kenny, not sure where he got it.

Using the HHA bows as a dataset, I hit my cherry/bl bows within a pound or two of target.  But definitely missed on the yew bow by about 8 lbs, or 15%.  My understanding is that dense, tight-ringed, old-growth yew would probably have been at or above my target weight.

[LittleBen]

You also used a different thickness of glass. If you kept the same stack and used the .0043 glass I wonder how much that would have changed weight ... 3#? 5#? if yew can lower the weight over bamboo or something, then glass should certainly raise it.


I also would speculate that the closer to the neutral plane the lam is, the less effect it has on the draw weight.

[fujimo]

sorry, i missed the taper rates in the chart.
thanks.
how far out from center did you start your side tapers?
i was using some pretty reasonable yew- and noticed the differences.
guess i will build some more- and post data here as i go.
many thanks
wayne

[canopyboy]

Ben - Agreed that the glass thickness could have played a role as well.  I definitely don't think it's all glass though.  While I couldn't get exact thickness on the glass in the finished HHA bows, it was not all the same thickness.  Yet the other 5 bows all have the same relationship between section modulus, working length, and draw weight.  As for the lam(s) at the neutral plane, they carry very little strain from tension/compression, but are under the maximum shear strain.  I also speculate that makes less of a difference on draw weight and more on longevity, but I'm not 100% sure of that.

Wayne - I start the tapers nominally at the fades, but by the time I'm done sanding they kind of fair in farther up the riser.  Similar with the HHA bows it looks like.

[monterey]

Originally posted by canopyboy:
There's been a lot of questions on Hill dimensions lately.  I don't really know that much, but will share what I have.  I've carefully measured three by Howard Hill Archery in the last year, and made three myself.  The stacks, etc are below for you to use as you see fit.  Note that the thicker stack for the yew bow ended up with a lower poundage bow.  For bows of this style with a thick core, core material matters more than I thought.  The only way you're going to nail a weight is a lot more data and good handle on the materials you're using.  I also contend that working limb length is more important to your stack calculation than bow length.

     

Would be great if others have had the opportunity to carefully measure Hill bows from other bowyers or their own and post.  We could have a little library here.  The more data, the better one's chances of hitting the right stack.

Canopyboy, This is good info!  Can you provide any further measurements on limb width at nocks and overall limb profile?  Kinda wondering how those measurements would align with the taper rate, which seems to vary quite a bit from bow to bow.  Also, did any of the three hill bows have tip wedges?

[canopyboy]

All six had tip wedges, but they have very little to do with draw weight as they are at the end of the beam.

Width at nocks was between 7/16 and 1/2 for all six.  All were straight side tapers from the fade.  The three I made had a slight trapezoidal cross section with the back being slightly thinner than 1-1/8 and 7/16 as a result.  The HHA bows had a slightly semi-circular edge.

As far as taper rates, there is some variance, not sure how Craig and company decide what to use.  Those are measured (multiple points and best fit), whereas mine are what I ordered (I honestly never measured to confirm.)  I did notice all are much steeper tapers than what you see in flatter bow designs.  People who go to 0.002 tapers seem to have very little work being done in the outer half of the limb based on pictures.  So I settled on a round number of 0.006 as a rough average from the three HHA bows.

[jsweka]

Great idea Dave!

I'll add a list of the bows I've made.  All of these came off a straight form, but took on a little string follow after first stringing and tillering.  None are trapped and all have a rectangular cross section with the corners of the limbs rounded off.  My bows maintain their width at the fades to about 18" out from center and then taper to 1/2" nocks.

Dave visited me a little while ago and we were comparing his bow from the "HHA Owl Blank" to my bows.  The "HHA Owl Blank" used a lot more taper than my bows and you could definitely notice more bending in the outer half of the its limbs compared to my bows.  So, it you are going to go with narrower limbs, you'll need more taper in your stack and I wouldn't go much narrower than 1.25" width with only a 0.002 taper in the limbs.  Now I will narrow some over the entire length of the limb to bring the weight down a couple lbs. if needed, but not much.

So how do these design differences compare when shooting?  I'm not really sure.  Dave and I weren't doing any real quantitative comparisons when he was at my place.  I really liked is HHA Owl Blank and it seemed a little smoother drawing than my bows, but maybe it just seemed that way since it was lighter weight than the bows I normally shoot.  Both designs still had that familiar thump of these style bows at the shot (the dreaded handshock some people hate and folks like me get use to).  Maybe next time Dave and I get together we could do some more formal comparisons.  I am going to go with a narrower limb and use more taper in the next bow I build for myself, so I'll see how that compares to my typical design.


 

[canopyboy]

Originally posted by jsweka:
but maybe it just seemed that way since it was lighter weight than the bows I normally shoot.

Ouch, I feel so weak now only shooting a 56# bow.

The table above had an error, the Tembo was 51# and the Owl was 56#.  Updating now.  Sorry 'bout that.

[jsweka]

Originally posted by canopyboy:
 

Originally posted by jsweka:
but maybe it just seemed that way since it was lighter weight than the bows I normally shoot.

Ouch, I feel so weak now only shooting a 56# bow.

The table above had an error, the Tembo was 51# and the Owl was 56#.  Updating now.  Sorry 'bout that. [/b]

Well dang Dave...It is smother.  I was thinking it was only 51#.  Sure seemed less than 56# and I usually shoot 53 - 58#.

[monterey]

Bringing this to the top.  I'm wondering if anyone has anything new to add to this?

[canopyboy]

Wow, blast from the past!! I've got a few more I can probably add now when I get some free time. To be honest, this is the first time I've logged onto the bench in quite some time though, so don't hold your breath.  

[monterey]

Nice to see you here and looking forward to your info.

[passion for knowledge]

Not claiming to be in any way an expert on bowmaking, but, just a thought.

If you think about what's happening in terms of forces in a bow, the back is in tension, the belly is in compression - back is being lengthened and belly shortened.

The main force in the middle must, then, be shear forces.

Should be probably be a consideration in choosing wood for a trilam.

Don't know where you'd find the info on shear strength, but for most other info, the wood database could be a good page to bookmark, if you haven't already.

 http://www.wood-database.com