Heavy recurve bow (glass)

[IanBB]

I must have last posted here months ago and I meant to keep more active but things have been so busy recently. I've been working on a recurve form for heavy glass bows. Something I've seen once from Sky Archery back in the day and a few others have tried it. I like heavy bows and the challenges they present.

Questions welcome, I will ask for plenty of advice so I am happy to offered it where I can.

The absolute bane of my life has been making the bow forms flat and consistent. I have had most of the bow come out needing some alterations. And the limb twist in some has been beyond manageable. Getting two 18mm ply woods glued together perfectly has been an issue. Adding to that my router which didn't cut a 90 degree angle, I have had to take long breaks in between the different bow forms.
104lb @ 30"

Just wanted to share the final successes. I still haven't totally worked out why they sometimes twist at the tip. And what I am trying to work out is if a narrower nocks helps the limb stay good. So far the narrower string groove has worked better and the wider string groove is more prone to twisting.

[Crooked Stic]

I would think a bow of that weight would not have twist issues if your form is right and you work off a center line.

[Flem]

Thats a beast!

Plan for tendonitis and arthritis when you get older.

[Bvas]

Cool build.
But I would want no part of a bow that heavy

My semi educated mind would say that narrower nock grooves are not correcting your problem, they are concealing it. Either something is off with your form, or you are not getting an exact center on your limbs to cause the twist.

A small difference at the center of limb is a big difference on the edges of the limb

[Mad Max]

what is the stack high and glass thickness ?

[IanBB]

Cool build.
But I would want no part of a bow that heavy

My semi educated mind would say that narrower nock grooves are not correcting your problem, they are concealing it. Either something is off with your form, or you are not getting an exact center on your limbs to cause the twist.

A small difference at the center of limb is a big difference on the edges of the limb

You're right about the groove size I think. It's my form to blame. I couldn't get it perfectly flat and with such big recurves there was a lot of room for error.

[IanBB]

what is the stack high and glass thickness ?

Forgive the mm. 12mm total stack depth including the 2.8mm of glass. Width I tend to keep 1.5" full glass width minus anything I need to sand off.

The biggest I made was 154lb that was 15mm deep total made from Cherry limbs.

[avcase]

I like it!  You must be doing something right to keep these heavy bows in one piece.

I also enjoy building heavy bows for flight archery. They certainly do have unique challenges.

Alan

[IanBB]

Alan that's exactly what I will be planning to do this winter. I use the 'warbow' spec arrow as some kind of benchmark. Matching arrows to these bows is a little tricky, given the limb weight they really don't appreciate arrows under 9gpp which would be heavy for a flight arrow in my eyes.

Your thoughts are always welcome, I know this isn't a flight forum per se.

[avcase]

Ian,
Unfortunately, I am not aware of any flight-specific forums for bows made with modern materials.  It seems like this forum should be okay for this since we are still talking about building single-string bows. I am looking forward to follow your progress through the winter.  Building bows like this for flight shooting never becomes routine!  I feel I am constantly learning something new that I can use to benefit bows I build for more standard applications.

Over the last three years, I built two takedown recurve limb sets and one single piece longbow for a fellow flight archer that were around 120# @ 31”.  These were the most challenging bows I ever built!  I also struggled with keeping the tips aligned for the recurve designs, which is why I dialed it back this year with the mild deflex-reflex longbow design which was used at this year’s flight competitions.  So I know firsthand what it is like to deal with limb twist issues.  What does your bow look like unstrung?

Matching arrows to the bow is another challenge. The archer, Jim Martin, was shooting 300-320 grain X10 arrows out of these bows this year for regular flight, and around 600-650 grain arrows for the Broadhead flight competition.  The effect of small changes are greatly amplified with light arrows. For example, a small change in brace height or string material may be almost hard to detect with a 10ggp test arrow, but with a 3ggp arrow it can register a 5-10 fps change.

You learn some interesting things when testing bows at these arrow weights. First, you learn that it is possible to build bows that do not experience large efficiency drops with lighter arrows. Second, you learn that it is possible to build bows that are extremely durable.  Third, you learn a lot about bow-arrow tuning. Finally, you learn a lot about safety!

Alan

[IanBB]

"I also struggled with keeping the tips aligned for the recurve designs"

I think I've cracked it now. I used to make the core taper go into the recurve, now I find it works best if the fade has all the taper and ends at the recurve (not into it) and the core woods are parallel to the tip. These bows are totally straight back, full length of glass and 5" recurves. Kept as wide as any lam slip will allow. My next step is to add mass to the tip and do a horsebow hybrid, almost like a syiah but made with a lamination wedge thickening to the tip.

I have a few of these recurves now, one 108 @ 30" which I don't mind risking with flight arrows. I'll report back with results but I'm writing this before I drive off to the field.

I don't know if you tried but I have put all the taper on one side (like a warbow) to get the arrow shooting straight off one side and not having to bend. I think this will help a lot and will mean I can work more with weight than spine. I know very little about compound bows but I will try out a metal or carbon arrow to see what I can achieve with it. Like you said Safety First!

[avcase]

A reverse taper through the recurve is a good next step. Most flight bows have this feature. This helps reduce limb vibration efficiency losses, especially when shooting lighter arrows. Stiffening they tips with reverse tapers does not have to add mass to the limb tips, but it does require them to be narrower to achieve this.

I haven’t built a bow with the taper to one side. Are you referring the side taper profile of the limb?  This seems like it would make it difficult to do this without inducing a twist to the bow!
Alan