Any advantages to the Holmegaard design?

[habs]

Not to ask a silly question, but is there any advantage to the Holmegaard style bow?  Is ther any reason to make one other than history?

Just curious.

[Jeremy]

When made correctly the tips are stiff, narrow, deep and light compared to other bows.  Stiff light tips = better performance.

[John Scifres]

Jeremy has it right.  The holmegaard design is intended to reduce mass at the tips.  Mass out on the ends does a lot of harm to efficiency.  

In general, tips are stiff to help keep string angle low to reduce stack.  They are kept stiff by either leaving them wider or thicker.  Wood that is twice as wide is twice as stiff.  Wood that is twice as thick is 4-8 times as stiff.  It follows that you can reduce mass (weight) at the tips by making them thicker rather than wider.

[BLACK WOLF]

You can also use the needle tips as weapons when you run out of arrows    I put trocar tips I mine for that very reason  

Seriously though...it's just as Jeremy and John explained.

Ray  

[habs]

OK, that makes sense.  The Holmegaard design just looks odd because of the unsual tiller. Since the limbs do not bend in a continuous curve, I was wondering how it could be an efficient design.

Thanks.

[Springbuck]

Actually, the part of the limb that bends, which is the inner, of course, does best when it does bend in a continuous curve.  Thus, the inner limb bends to a perfect arc of a circle, though the outer limbs remain stiff.

  I think there is more to this than a lot of others seem to.  let me see if i can make sense.

  Circular bending supposedly stores the most energy, because wood along the limb is doing its share wherever it is, BUT....

  A perfectly pyramid limb (which bends to a circular arc) quickly stacks once drawn a certain amount, depending on length of bow and length of draw, SO....

  Stiffer tips will prevent this by keeping favorable limb tip/ string angles, BUT...

  This can overwork the inner limb on most bow designs because the tiller becomes too round in/near the handle....HOWEVER...

  If the stiff tips are long and stiff enough to act not just as stiff tips, but as levers, the inner section can be made parallel both side to side and back to front, so more wood is bending, total, and the levers will bend it evenly in a circlular arc...THUS..

  The inner limb is now very stiff, stores a lot of energy and is evenly strained, AND...

  Because it is very stiff, but not actually being bent a great deal, it can take high draw weight and stiffness, but not take much set, because the distance travelled is small, AND....

  The attached levers let us pull this very stiff middle limb, due to , well, leverage... OF COURSE....

  The energy storage is now high, but the efficiency will be low if these levers are not very light in weight, so we must make the tips light, AND...

  As posted above, making the outer limbs stiffer is easier if we increase their thickness, so we increase thickness until they are perfectly stiff, and then narrow as much as we can get away with to save weight.  AND SINCE...

  The outer limbs hardly bend at all, they take no set.

  So you have a very stiff, high draw weight middle, that does not bend far enough to endanger its elasticity, but stores high energy, attached to long stiff tips that keep leverages favorable throughout a fairly long draw, and are physically very light..

   So the bow is well suited for shooting heavy arrows at decent speeds with little hand shock, stores good energy for its draw weight, and is likely to be durable and long lived weapon that takes little set even when made from marginal materials.

[RayMO]

Thanks John and Springbuck. What I find so amazing is that this design is so old.

[Springbuck]

Me, too.  I am a born tinkerer, and I have made a couple of these, but I keep planning crazy bows based on this design, stuff like a really wide sinew backed juniper Holmegaard with bamboo outer limbs and a little setback in the handle.....  The original bowyers had a fine grasp on some very complicated principles and tricky trade-offs..

[shamus]

The Holmegaard to me seems pretty much a modified pyramid design..witht the outer limbs talking on a more sever taper and stiffness.

The holmegaard is currently in vogue right now, but I'd opt for a pyramid bow because it's easier to make and follows similar principles of less mass in the outer limbs and circular tiller.

[Pat B]

Shamus, I would venture to say the pyramid bow is a modified Holmegaard being that the Holmegaard is one of the oldest bows to be found to date...about 8000 years ago. The design so ingenious, even a cave man could do it!      Pat

[shamus]

Pat, good point. Either way, the pyramid and the holmegaard share the same design principles.

[Springbuck]

Yeah, they do share some design.  When I think Holmegaard, I think about the original 64" elm version, myself.  That is the artifact where the limb is essentially half wide, bending inner limb / half narrow, stiff outer limb.

   I see a lot of bows that are essentially a modified pyramid limb, with shortened, but very narrow Holmegaard tips.  Also a true Holmegaard,  but a slight variant on the theme.  If the bending limbs are more than half the length, or if they taper side to side, you have this type.  In some ways this acts more like a pyramid bow, but the stiff tips and even bend give most of the same advantages.

  The main difference as far as principles go is that the pyramid style bends basically through the entire limb and ends up with less mechanical advantage later in the draw.  It will stack if not made correct length for the draw.  The Holmegaard's stiff outer limb gives you a bow with smoother draw and less stack.   At the same time, because the outer limbs store essentially no energy, the Pyramid might be a tiny bit less efficient at storing energy, but is likely MORE efficient getting it to the arrow.

  Comparing just the few I've made, the  half/half Holmegaard draws smoother and feels like the draw weight is lower than it is.  A true pyramid @ same length is a TINY bit less smooth, but has a better feel at release.

  Once again, like it often does, it is a lot like two paths to the same destination, though...

[Blaine]

Perhaps another comparison would be to the asian composite bow, or horn bow.  One could argue that the stiff tips on the holmgaard act in the same manner as the siyahs on a horn bow, with the working limb being concentrated to a shorter section in the middle.  

Add sinew to the back and horn to the belly to the holmgaard and what do you have?

Is the horn bow an evolution of the holmgaard or is it a case of convergent evolution?

[Springbuck]

I have never said it, but I kinda agree here Blaine..  The mental leap from Holmegaard stiff, straight tips to long stiff reflexed tips, then maybe another step to a more severe recurve is an easy one to make..

 I think convergent evolution, probably...  But if you get messing around with it, say with a more elastic wood, and you maybe you set the handle back on a Holmegaard, then deflex them back to the starting point, then have a retroflexed outer limb, what does that look like in your mind?

  Also, interestingly, I did some testing in the shop.  If I take a slat with parallel width/ parallel thickness, like I was describing, clamp one end in a vise, and add a stiff piece to act like the Holmegaard outer limb (just a notched stick stuck on the end) the slat will bend to a circular tiller if the two parts of the limb are about the same length.  

  If I recurve the stiff end, or attach it at an angle, the leverages are applied later in the "draw", and the recurved end must be shorter, say 1/3 of total limb length.  The more severe the recurve angle, the shorter the outer section must be to achieve that circular tiller.