Can String Follow be Fixed?

[John Scifres]

Here is a page where I think I salvaged a bow that was destined for the wall of shame or the burn pile.

  Fixit

[George Tsoukalas]

Nice job. John. Jawge

[Bob Barnes]

good one John.
Bob

[John Scifres]

I hear this question a lot?  Most of the time the anser is "No"... But sometimes it is "Maybe".  

String follow is caused by one or more of several factors.

Natural Deflex is one.  Belly cells being crushed due to too wet of wood, bad design, bad tillering or any combination of these are some others.  Crushed bellies can also be caused by leaving a wooden bow strung too long or in really hot/humid conditions.  Also natural wear and tear can break a bow down.  The end result is a sluggish bow that generally gets assigned to a wall or pile of first bows.

But, all hope is not lost.  I have found that sometimes we can correct these things.  

Natural deflex is the easiest since it isn't really caused by damaged cells.  Simple heat bending can correct or at least mitigate this, even after tillering.

Crushed belly fibers can sometimes be fixed with heat also.  Wood that is too wet and bent will deform but not totally crush the belly cells.  Even roughly tillered or poorly designed bows can be made better.  Removing some of the crushed wood and then toasting the belly will reform the cells somewhat.  Don't expect miracles with this or any fix but it can save a bow from the wall of shame.  The first step is analyzing what went wrong and correcting it.   If you don't correct the disease, expect the symptoms to recur or probably get worse.

Here's an example of a possibly fixable bow.
 

This bow was a gift to me in a White Elephant exchange several years ago.  It has about 6" of string follow and has a horrible hinge in one side.  The bow was a very aggressive design.  Made from what looks like maple with a maple veneer backing, it is way too short for a full draw bow.  It is marked as 45# at 28".  It is 58" NTN and 1-3/4" wide with a pyramid design.  If I were making a 28" draw bow of maple, the minimum length would be a full 10" longer and I would have started with 2" in width.

 So I am going to toast the belly and make it a 30# or so at 24" draw.  I will have to retiller and hope for the best.
 

Here's the heatgun and the first caul or form I thought about using.  But then I recalled an article several years ago about toasting a belly.  The author (forgive my misremembering his name) recommends using a narrow form so that the back of the bow is not burnt by heat reflected off the caul.  I decided to cut a new caul out of a stout 2x4 I had handy.

 

Toasting a belly isn't like adding reflex to a stave before tillering.  I do that with a gentle touch trying not to scorch the wood.  With toasting, I am trying to change the wood (for the better I hope) by basically heating it to the melting point, or somewhere close, and deforming it back to a state that will more effectively resist compression.

Here you see I got it really hot.  I decided that since this was basically a salvage job that I would not remove the finish.  I assumed it would melt off but it held up to the heat and only the wood was toasted.

 

[John Scifres]

This is what it looked like afterwards.
 
 
 

It looks like the follow is corrected but this is before retillering.  After I work the bow, some of the follow will return.  I just hope it won't be 6" and tiller will be better.

 

The first look on the tree is not promising.  The left (lower) limb is bending way more than the right.  Both limbs are really stiff at the handle.  I am going to rasp it about 20 times at the handle on the right and 10 times on the left.

 
Here's the result.  Better but still bad.  Ten more on the left and 20 more on the right.

 
Better on the right but that left limb is really stiff at the handle.   The right (upper) limb is now bending more than the left which is what I want.

[John Scifres]

After a few more passes at the handle, the tiller is close enough for me.  It is slightly positive.  In other words, the upper limb bends more than the lower limb.

It finished at 32# at 24".  I like it.

 
I drew it about 200 times and ended up with about 2" of follow.  I will probably see 1" or so more after a 1000 or so draws but at least it shoots hard.
 

Here's the first shot.  Shoot your TV  

[Bob Barnes]

great job John...do you think it would benefit from a 2nd heat treatment now that the wood is bending correctly?  I've never done this but just curious...
Bob

[AkDan]

good stuff as usual John, cant wait to see you're new improved website when you get it going again!

[Bill Sagues]

Very cool - thanks for posting!

[Tommy Leach]

John, do you think adding a couple of coarses of sinew would help "hold" the repair? I've got one I've been thinking of trying this on, just curious if you think it might work.
Tommy

[John Scifres]

Bob, I doubt another heat treatment would do much as far as making it a better bow.  Think about the torture we have already put these poor little wood cells through.

Tommy, Sinew is fantastic in the right design.  But sinew is way too much work to use as a bandaid for a bow.  Think about the problem that caused this sub-par bow.  It was primarily a failure to design a bow correctly for the wood.  I simply worked backwards and "designed" a tolerable application for an existing design.  In other words, I came down in draw length and weight to something that more closely approximated a proper design.  Adding sinew is basically a design change after the fact.  But the bow is not worth it.  As it sits, the fix will work and the bow will be fine for what it is.  A wood bowyer has to accept the limitations a wood has and design appropriately.

[DCM]

Can string follow be fixed?

No, not if it's from crushed wood.  Natural deflex sure, but that's not the question rather more of semantic gyration.

Remember the chemist from WI (Cooter) way back in the 'wall days.  Had a hickory bow that took a bunch of set.  He soaked it in a tub of water for weeks, reshaped it and then started the process again.  Seems like there was something to it, although most likely the same scenario as this, just different technique to change the profile.   ... 'member "cooter skin."  I think I still have some.

Can a underbuild "bow" be reclaimed?

Sure.

I've reworked a number of bows I built early in my learning.  Dang convenient source for bow wood in some cases.  ;-)

Same thing with any less the optimal (overbuilt) bow.  I've tweaked a number of older bows and while I may have sacrificed a pound or so of draw weight, increased the cast more than enough to compensate, glass production bows for example.

[John Scifres]

Hi David,

Agreed on the semantics point.  The semantic gyration is probably applicable to the word "fix" too.  I am pretty sure I could not build a rigid-handle maple bow that is 58" and drawn to 30# at 24" that has less string follow than this one after I reworked it.  So, in effect, I have "fixed" this bow.

I think Cooter was experimenting with reforming the cells via rehydration.  He was hoping that the cells would swell and reform somehow.  It didn't work.  Plus Cooter's crazy ya know.  

Heat tempering/treating seems to reform the cells by "melting" them and sort of stretching them back to some other more compression resistant shape.  Rehydration doesn't accomplish the same thing it seems.  

I don't know if the science is valid but the observations sure are.  Maybe some microsopic analysis is in order.  Wood cells are big and viewable under even the cheapest student microscope.  My daughter has one I believe.  Perhaps I should don the lab coat.

[John Scifres]

Nah  

[DCM]

Cooter was a hoot fer sure.  Microscopes is fer sissies.  ;-)

[John Scifres]

He popped his head in late last year  http://tradgang.com/cgi-bin/ultimatebb.cgi?ubb=get_topic;f=1;t=081708;p=1   Case ya' missed it.

[Roy Steele]

Once wood cells a crushed there crushed.99 out of 100 you may reshape it[heat or water]to a form and cut the weight way down you may not have as much string follow but if you shoot it a lot you will liky end up with the same results.Unless you want to change it to a kids bow or sinew it its stuck with the string follow.It's not worth the time and affert.It's only wood build another.Right design and good tillering.But there's aways that 1%.

[John Scifres]

Here are my observations after doing this a bunch over the past few years.

If a bow has excessive string follow from bad design, you will lose weight or draw length approximately equal to the bow that would have fit into the bad design in the first place.  In other words, as in this bow, you have to go backwards and accept that you screwed up.

If a bow has excessive string follow from rough tillering techniques but has otherwise good design, you can fix it a little but you will lose a percentage of your weight and probably have more follow than a gently tillered bow.

If a bow has excessive string follow from wet wood but has otherwise good design, you can bring it back pretty much to what it could have been if you would have waited for the wood to be dry.  You'll lose some of it but it won't be bad.

I haven't done one that follows the string too much due to being strung too long or one that is just worn out.  I suspect they are beyond repair though.  But that's what I suspected about the other ones before I actually tried to fix them.