Author Topic: How to measure set  (Read 4977 times)

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Offline willie

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Re: How to measure set
« Reply #30 on: June 28, 2020, 01:12:08 pm »
Quote
If I lay out the last ten  or so bows in order of speed the one thing that sticks out is the increase in reflex. It's not a lot of increase, maybe a foot or so per bow.

just curious how much the reflex has ranged in those 10 bows for that 10 FPS or so?

Offline DC

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Re: How to measure set
« Reply #31 on: June 28, 2020, 07:30:07 pm »
Probably from 1" to 3" maybe 4". I don't keep records, I might be past 200 if I did. :-\ :-\

Offline Azmdted

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Re: How to measure set
« Reply #32 on: June 29, 2020, 11:33:23 am »
Thanks to all for your replies, a lot of information to digest.  I've picked up a new hickory stave that is two months from cutting.  Yesterday it had 3/4" natural reflex and then I cut it down to rough bow dimensions plus about 3/8" to help it dry.  By the evening the reflex was gone and one limb is perfectly flat and the other has about 3/4" deflex from about mid limb out.  I'm thinking that moisture loss and strength from the belly side of the stave was holding the reflex and with the loss of wood and some moisture loss it changed.

I'll be building a new caul for heat treating.  Consensus seems to be that my current 5" reflect caul is way too much.  BTW, it's a gentle curve from handle to near tips of about 2" and then 3" more in the tips getting me to 5" overall.  My goal is to end up with a 50#, 29" DL, 67" NTN bow with little set and good efficiency.  Based on all I've heard, what should I do?

Straight flatbow?
Flat out to the tips and then 2-3" reflex tips?
Gentle curve for an inch or so and then 2" reflexed tips?

Also, since I never knowingly exceeded my desired draw weight on my last bow and the wood was a year from cutting, did my set come from me being too aggressive in flexing it during floor tilling, attempting to short string it before it was ready and exceeding my design weight there, breaking fibers during too aggressive bending on the caul?  On the last bow I steamed it before putting it on the caul, let it rest for 3 days and then put it over the coals.  I didn't want to try to bend a not even floor tilled stave without steam first thinking that I would be too aggressive. 

Any ideas and suggestions are helpful and appreciated.  Thanks.

bownarra

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Re: How to measure set
« Reply #33 on: June 29, 2020, 12:04:35 pm »
Your stave has moved because it was growing on an angle. Wood can 'store' the forces it felt whilst growing. As you remove wood these hidden forces reveal themselves. It can be quite surprising how much wood can move once you cut a bit off, even stuff that has been drying for years. Of course it could also be from regular moisture loss but my guess is the former.
Don't worry too muc about it. The problems start when your stave goes sideways :)
Personally I would get it to a nice limber floor tiller to speed drying. Strap it to a board to stop any further warping as it dries.
Once nice and dry. I would heat it into a gentle 2 " reflex. Least (none!) near the handle, gradually increasing as you progress along the limb.
Then gently tiller to 20" or as soon as you see any set. You can trace your pre-bending profile on a wall or something to use as a reference as you continue.
Then do the fire hardening process. Keeping the 2" reflex as a max.
Tiller out using Badgers no set method.
Then let us know how it turned out :)
Good luck :)

Offline willie

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Re: How to measure set
« Reply #34 on: June 29, 2020, 12:17:48 pm »
........ I think in this case I followed the thin clues in the Shannon video too literally.  They said to fire it when it 'was barely bending', so that's what I did.  Which I think caused some over stressing as I tested the floor bend after that.  Next time I'll wait till it's about done with floor tiller and be more gentle on stressing the bends........

thin clues are not too helpful sometimes. I have never seen the video, but I understand it is an involved process, and would hope the the video shows more about the tillering required before the heat treating session is begun. It suppose it is possible to cook the stave too hard, and conversely, to get the proper amount of treatment on the belly, only to remove the treated wood if the stave is not close enough to dimension after cooking. Steaming the stave to get it on the caul before the heat treat seems to suggest you are being too cautious or still had it too thick.

Bracing too early is an easy enough way to over stress a bow. I think every bowyer can remember one like that.

Learning floor tillering can be a bit of a subjective exercise as it's an acquired skill. The long string and a tillertree can help with developing the feel for how much and where when it comes judging bends.

Without seeing some pics of your stave, its hard to tell. If you are going to build a caul and do another heat treat? why not draw up your new proposed shape on another 2x6 and post some pics also? There are some new guys here recently that I think would also be interested in a thread seeing some simple deflex reflex curves.

Bowmarra's suggestion to get the bow built before fire hardening has merit, so maybe propose a curve, then build to it as close as feasable, then cut your caul, possibly adding some final recurve?


« Last Edit: June 29, 2020, 01:03:20 pm by willie »

Offline Badger

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Re: How to measure set
« Reply #35 on: June 29, 2020, 02:50:29 pm »
  I just put an osage bow on the cawl, the cawl was 3 1/2" came out of the caul at 2 1/4"  Just unstrung profile is 1 1/2" reflex and goes to 2" after sitting for an hour.

Offline Azmdted

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Re: How to measure set
« Reply #36 on: July 01, 2020, 09:06:04 am »
I've started my next Pignut Hickory bow.  This started as a stave with 3/4" natural reflex.  I've floor tillered it being very gentle in my bending.  It's bending nicely, but it's already at 1.5" backset on the upper limb (left) and 1.25" on the lower limb.  It started bending this way as soon as I took off some wood, well before I ever got around to bending it myself. I clamp it on the edge of a 2x4 when not I'm not working it. I've only flexed it about 4-5 times and backed off before the pressure got to be more than where it should be for a 50# bow.

The weight is stable so I think it's most of it's drying.  Length is 68.5 TTP.  My goal is a finished bow at 50#, 29 DL, 67" NTN that will keep most of that weight as I shoot it.  I've left the last 6" on the ends near 1/2" thick because I'm still looking to get 2" or so reflex fire hardened in and thought I'd need the extra support to hold the flex in.

Thoughts?


Offline Badger

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Re: How to measure set
« Reply #37 on: July 01, 2020, 10:33:36 am »
  Depending on how humid it is where you live hickory can take a long time to drop those last few points of moisture. About 8% is the minimum I like to work hickory at. I would put it in a drying box unless you have a very dry climate.

Offline Azmdted

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Re: How to measure set
« Reply #38 on: July 01, 2020, 10:37:16 am »
Thanks Badger, I'll get one made up.  Maryland is not known for it's dryness.

Offline mmattockx

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Re: How to measure set
« Reply #39 on: July 01, 2020, 01:10:22 pm »
I would put it in a drying box unless you have a very dry climate.

Can you define 'very dry'? It's been a stupid wet June here, with the outside RH into the 90's many days. Indoor seldom gets more than 45-50%, even in a wet month like this one has been. Is 45-50% dry enough to keep hickory workable?


Mark