Bow draw weight down and up

[Don W]

I've been playing around with draw weights, arrow speeds etc. For the last couple days I will take a bow and check the draw weight. Then shoot 12 arrows through. The arrows are around 640gr. Each shot is through the chronograph and the hi, low and Ave recorded. I then check the draw weight again, shoot the 12 arrows, check the weight.

Each set I loose a little draw weight. The first time might be right around a pound. Maybe a little less for lighter bows. Each set looses a little less each time. After about 4 or 5 sets the weight loss stops. Cast drops slightly as would be expected. Total loss is never 4#, can come close for a 55# bow, and may only be a pound or 2 on a 40# bow. My osage board bow actually gained 4# the first time before going into the loss routine.

The next day I start over, all weight has been regained and a very similar routine starts. The end weight is close to yesterdays end weight but usually not the same (although this could be inconsistencies in weighing and my scale)

I've searched but could not find any references as to the draw weight going down, so if it normal that seems odd I couldn't find anyone noting it or asking, if it's not normal how did I manage it on absolutely every bow I've made.

Edit to add images:


Day 2


 Day 3 added

[airkah]

Sounds to me like soft set and then the bow returns to its initial profile overnight and the cycle repeats.

[Stixnstones]

What Airkah said...

[Don W]

Sounds to me like soft set and then the bow returns to its initial profile overnight and the cycle repeats.

I agree it's soft set, but is it typical? Is it a problem? Is it bad tillering?

[Eric Krewson]

Very typical, every selfbow I ever made did the same and that is 158 of them so far. My first 5 or 6 arrows out of a bow are noticeably faster, then it settles into a consistent speed.

My current bow steps down one more time about the middle of a 25 target 3D round and I start shooting a little left as my arrows become a slightly overspined. I have already shot a few dozen warm up shots on the practice butts before I hit the course so my last stepdown is at about 50 shots. My last bow, which became to stout for me to shoot as I got older, had only a very slight loss after the first few shots and settled in to be stable for as long as I kept it strung, even if that was 8 hours. All my bows are osage.

I have also had bows that seemed out of tiller for those first 5 or 6 shots then settled in to be a tack driver for the rest of the day. When I hunted with one such bow I would fire off a half dozen arrows at my archery target before I headed to the woods to settle it in. I won a lot of tournaments with that bow but knew it had to warm up a little before I got into any serious shooting.

I have been making selfbows for 28 years so this is not a selfbow trait I just pulled out of the air, I noticed it long ago.

[Don W]

Thank you Eric. It seems like a somewhat important aspect of a self bow that nobody seems to ever mention. I've built up quit a library over the last year or so and I've heard and read about set, soft set and string follow (still a little fuzzy on that) but nothing about draw weigh changing like this.  I know in a hunting situation it's not as much of a concern, but practice all day would be.

I've been concerned about using hickory which I have easy access to because I hear a lot of folks talk about how their hickory bow will loose weight even in a day of humid shooting. It didn't make sense to me. Others say that as long as a bow is kept indoors a day or two of hunting in the rain will not matter if the bow is well protected, which makes perfect sense.

Now I believe what those folk who see the weight drop have is this "soft set" condition (which should have it's own name I think) and has nothing to do with moisture content.

[Don W]

I've added the HHB log to the original post

[RyanY]

It’s possible most bowyers have an intuitive sense of this and exercise their bow a bit before measuring draw weight. Unless I was flight shooting I wouldn’t consider the fresh/right after stringing draw weight to be representative of performance over time.

[Don W]

It’s possible most bowyers have an intuitive sense of this and exercise their bow a bit before measuring draw weight. Unless I was flight shooting I wouldn’t consider the fresh/right after stringing draw weight to be representative of performance over time.

But for a hunting bow, it's that first arrow that counts most of the time. For a target bow it's required to know the bows change over time. It's not as simple as a single draw weight. Based on Eric's response, a few warm up shots isn't close to sufficient and my test show a need for up to 60 arrows to get to a flat line.

It's certainly good information to know, and at my age, if it takes me 10 years to make "bowyer" status, it'll probably be to late.

[RyanY]

60 arrows seems like a lot. I could be wrong but that seems abnormal if conditions aren’t extreme like humidity or hold time at full draw. What is the behavior of the set of these bows after unbracing and when allowed to return fully?

[Don W]

The behavior is different. Some of the bows I tested I made before I started researching"how" to make a self bow, and the have excessive set and string follow. The last few show almost no set. The last reflex deflect has no noticable set, so it's small.

I would assume wood type and design will have some effect.

I have an white oak, backed with ash and a bloodwood power lam and handle. Its 43#@28 (@1st draw) 56" ntn. It only takes about 36 arrows to level out. It's also been hanging in my shop forever so MC is likely high. It's also one of my first, so set is higher than others.

A maple bow takes about 36 arrows.

I also assume arrow weight would play a role. I would think a lighter arrow would take longer, but that's just me using logic, which seems to bite me sometimes.

[RyanY]

What I’m wondering is how much set does the bow have immediately after unbracing versus over several hours. For example, a bow may have 1.5” of set right after shooting but may relax to 1” over several hours. I would guess even bows with no set might lose a small amount of weight but bows that have more unbraced set and lose some over time lose more weight. I wonder if the poundage loss is proportional to the change in set during that relaxation period.

[Don W]

What I’m wondering is how much set does the bow have immediately after unbracing versus over several hours. For example, a bow may have 1.5” of set right after shooting but may relax to 1” over several hours. I would guess even bows with no set might lose a small amount of weight but bows that have more unbraced set and lose some over time lose more weight. I wonder if the poundage loss is proportional to the change in set during that relaxation period.

I'll add that to the log

[Don W]

Day 3 added for the HHB bow

[StickMark]

seeing similar.

My sinew bows pull back out of set after some arrows or lots of pulling on string.

I see as much as 3# loss after a lot of arrows, but I can not recall exactly because these are wood bows and arrows and I am tired of using decimal points.

I like to shoot a stumper or two before getting into the hunt properly.