Shaping 'Glass Lams?

[KenH]

Anyone ever use heat to 'mould' back and belly glass lams to accommodate extreme curves such as this:
 

On another site it was mentioned that if one had a steel form say 3/8" thick, fastened the back and belly glass rough sides to the faces of the form, then put that in a hot box at around 275F to 300F, that the glass would relax and take the shape.  Yet when cooled back to 'normal' temps, the glass would retain all its usual bow-friendly properties.

Comments?

[KenH]

Bumping this up in hopes someone will see, know and answer...

[Jon in North Idaho]

Simple answer - I wouldn't try it!  The fiberglass is not constructed like PVC or an Uponor pex which is basically an extruded cylinder that holds shape when cool.  The fiberglass is a layered fabric and resin composite - the composition stays the same through and through until you get it hot enough to cause the glue to relax, in which case it loses it's strength.

There are some bowyers who have tapered their glass to get extreme recurve tips, but tips like you show would require tapering it to almost nothing...

As is, the glass would follow the contours of most of the "form" you posted.  I think the biggest problem in the inside curve at the very tips.  At first glance, this appears more like a horse bow to me - I think it would be best treated like one with siyahs glued on for the tip and could be shaped to achieve the extreme curve.

There's some other issues with this, though... with the tips curved that much, your nocks would have to be set in quite a bit from the ends,  otherwise you'd have a brace height around 12 to 15" -- if you could ever get the thing strung, that is.  Also, with nocks being several inches from the end, you would risk blowing the tips off the first time you shot it.

Just curious - is this actually a bow idea, or something else such as a part of product?

[KenH]

The bow pictured in my first post is an actual 2500 year old bow from a gravesite in Western China.  It really is 44" long and was approximately 1" in diameter and had a draw weight estimated in the 80# range.  The originals were made up from 25-30 individual pieces glued together, the spiral wrapped  in raw silk embedded in layers of lacquer.

My Mark II Prototype features a two Red Elm lam core totaling .12 (.24 over the 8" of handle) with the outer extreme curves formed from 8 lams of .02 White Ash scarfed into the rest of the core.

I can actually get .030 glass to follow the smallest inside curve.  But trying to hold together the glue-slathered back glass, wood core assembly and belly glass on the form while "lashing' it in place is a job for "three men and a boy" as we used to say -- but there's room for only one or two around the form.  This I discovered during construction of the Mark I Prototype,  which with its .26" core was far too heavy of draw (over 75# at 26") for this feeble old man    :eek:    

With my Mark II prototype I'll be adding the glass in two operations -- first the belly glass, then the back glass.  I am just looking for a way not to have to fight both glass strips and the core onto the form...  If the glass could be even partially shaped it would help things tremendously...

[fujimo]

maybe check out this thread
 http://tradgang.com/cgi-bin/ultimatebb.cgi?ubb=get_topic;f=125;t=010914
and chat to him, he might give you some insight into how he did his, not as convoluted as yours- but i am sure his experiences might offer up something.

what if the extreme curves on the ends( in the non bending areas) were glued on siyah's- done after the fact!!??
good luck, keep us posted

[KenH]

Thanx Fujimo.  I've checked out Trux's builds.  They're certainly lovely.  He did mention that the fit few he made were a major pain  to assemble...

If I did the recurves siyah style they'd have to be very large (relative to the rest of things) and just not very "artistically pleasing".  It's one solution, true, but I'm still looking for other possibilities.

Recently I heard about "fiberglass prepreg".  Which is glass cloth 'pre-impregnated' with epoxy and taken to a partial cure state.  This can then be molded to shapes.  I've got some info requests out to prepreg manufacturers..

The prepregs I've seen are much thinner than our thinnest Bow-tuff(tm) lams, and are woven cloth rather than unidirectional fibers.  So I might need two or three thicknesses, and then a fill layer of epoxy to smooth of the outer surface.

Does anyone know if ordinary woven glass cloth and epoxy resin will work with bows?  It certainly should

[fujimo]

yea..i have heard of it working, but usually the way these things are made- is the glass is under some tension- to pre stress the glass, and to keep it all aligned-the glass to resin mix needs to be correct- one doesnt want the glass strands swimming around loosly in the resin, then they are ground to the required thickness- precisely.

you might consider trying something kenny did recently- by grinding the last bit of the glass with a taper- he did it for different reasons, however it might facilitate easier bending for you- then you might have to put in some tip wedges  to retain the stifness in the tips- to compensate for the loss of thickness from the glass grinding.
i am sure that is something kenny could help you with- contact him...hes a bit gruff and abrasive- and dont part easy with info- but he might help you   :D      .....
pre preg might work very well- but remember the cross fibers will just be excess weight- see if you can find some unidirectional with a scrim, and any thickness variations would just have to be tillered out as you finish the bow- if there are any that is!!

good luck.

[KenH]

Thanx Fujimo.  I've checked out Trux's builds.  They're certainly lovely.  He did mention that the fit few he made were a major pain  to assemble...

If I did the recurves siyah style they'd have to be very large (relative to the rest of things) and just not very "artistically pleasing".  It's one solution, true, but I'm still looking for other possibilities.

Recently I heard about "fiberglass prepreg".  Which is glass cloth 'pre-impregnated' with epoxy and taken to a partial cure state.  This can then be molded to shapes.  I've got some info requests out to prepreg manufacturers..

The prepregs I've seen are much thinner than our thinnest Bow-tuff(tm) lams, and are woven cloth rather than unidirectional fibers.  So I might need two or three thicknesses, and then a fill layer of epoxy to smooth of the outer surface.