Sizing a Bow Back

[GaryL]

Hello.  I am fairly new on here and only completed two successful bows so far, both of which were self bows.  I am working on my second osage and the rings were pretty thin on this one.  I chased a ring and I believe its pretty good but I think I will try my hand at some rawhide backing for the first time just as a little insurance.  I have seen a few posts regarding this topic but the one question I have is after sizing the back with glue.  When sizing what steps should I take? 

Should I just rough up the back with sandpaper and apply a layer of glue, then after it dries do I use a hacksaw blade to score the back before the rawhide?

Or,  do I just score before the sizing and not after it dries? 

I guess the biggest part of this question is do I score the back before and after the bow is sized or just before the sizing and leave the sized back smooth before the rawhide? 

Hope this makes sense?

[Don W]

I've only done 2 with rawhide. I just let the first layer of titebond sit for about 20 minutes the applied a second coat. Both have stayed on so far.

I actually had one of them I wanted to rework. I heat treated a recurve in and the rawhide stayed on. Unfortunately I had to do it a second time and burnt it at the very tip. I still fixed the bow, but bottom line, it is the way I'll glue the next ones I do with rawhide.

[JW_Halverson]

I like to use 80 grit sandpaper on the back of a bow before sizing. I clamp the grip area to the bench or vise and then take long strokes from the grip area to the tip. 80 grit is pretty coarse, and it doesn't take a lot of strokes to put roughened surface on the wood.

If the bow has been handled a lot in the tillering process, I will go even further with the sanding of the back with 80 grit to take up whatever oil from my hands may have been in contact with the wood, too.

If there was any oil used in heat treating (and I tend to avoid using oil in heat treat), then you will want to wash the wood with Dawn dishwashing detergent and hot water, or even degrease using oven cleaner if it has penetrated very deep into the wood, then a wash with water and baking soda to neutralize the caustic compounds in the oven cleaner. (Now do you see why I avoid using oil in heat treating?)

Remember that wetting the wood will also raise the grain and open the pores so that it will soak in the glue even better and improve the mechanical bond.

Then for sizing, I thin hide glue down with warm water and brush it on, allowing to set up and even dry a little between coats. Two or three coats are sufficient. Lightly sand with 220 grit if you wait more than 12 hours before applying the full strength hide glue and rawhide. This makes sure that you have a fresh hide glue to hide glue contact so that they bond properly to each other.

If using Titebond, I go through pretty much the same process.

[mmattockx]

Should I just rough up the back with sandpaper and apply a layer of glue, then after it dries do I use a hacksaw blade to score the back before the rawhide?

Well, my first question is what kind of glue are you using? My understanding of sizing (as I do it) is that you put a light coat of glue on the wood and let it soak in for a couple of minutes, then add more glue to ensure a fully wetted out gluing surface and put the two pieces together. The sizing coat is not allowed to dry, just soak in some.

I know some swear by scoring the wood surfaces for EA40 but that is not the manufacturer's recommendation and I would make a less rough surface using coarse sandpaper such as 60 or 80 grit sandpaper.


Mark

[GaryL]

I like to use 80 grit sandpaper on the back of a bow before sizing. I clamp the grip area to the bench or vise and then take long strokes from the grip area to the tip. 80 grit is pretty coarse, and it doesn't take a lot of strokes to put roughened surface on the wood.

If the bow has been handled a lot in the tillering process, I will go even further with the sanding of the back with 80 grit to take up whatever oil from my hands may have been in contact with the wood, too.

If there was any oil used in heat treating (and I tend to avoid using oil in heat treat), then you will want to wash the wood with Dawn dishwashing detergent and hot water, or even degrease using oven cleaner if it has penetrated very deep into the wood, then a wash with water and baking soda to neutralize the caustic compounds in the oven cleaner. (Now do you see why I avoid using oil in heat treating?)

Remember that wetting the wood will also raise the grain and open the pores so that it will soak in the glue even better and improve the mechanical bond.

Then for sizing, I thin hide glue down with warm water and brush it on, allowing to set up and even dry a little between coats. Two or three coats are sufficient. Lightly sand with 220 grit if you wait more than 12 hours before applying the full strength hide glue and rawhide. This makes sure that you have a fresh hide glue to hide glue contact so that they bond properly to each other.

If using Titebond, I go through pretty much the same process.

Thanks JW, this helps!  I have not had to use oil when heat treating so far and have had pretty good results.  Think I will definitely avoid it if possible.

[GaryL]

Should I just rough up the back with sandpaper and apply a layer of glue, then after it dries do I use a hacksaw blade to score the back before the rawhide?

Well, my first question is what kind of glue are you using? My understanding of sizing (as I do it) is that you put a light coat of glue on the wood and let it soak in for a couple of minutes, then add more glue to ensure a fully wetted out gluing surface and put the two pieces together. The sizing coat is not allowed to dry, just soak in some.

I know some swear by scoring the wood surfaces for EA40 but that is not the manufacturer's recommendation and I would make a less rough surface using coarse sandpaper such as 60 or 80 grit sandpaper.

Hey Mark.  I plan on using TBIII.  I thought I read somewhere that you were supposed to let your sizing dry for 24hours before applying the rawhide but maybe thats not accurate?  I guess the point of sizing is to allow the bow to absorb the glue so I dont see the harm of applying the rawhide before the sizing is dry as long as the bow has absorbed as much as its going to?

Mark

[Pat B]

For rawhide or skin backing using TBII, TBIII or hide glue I clean the back well with Dawn dish soap, rinse with boiling water. While doing this I have the rawhide soaking in warm water then wash it with Dawn and rinse well. I then size the back of the bow with the glue, let it set for a few minutes, size the rawhide and lay it down. I like 2 pieces of rawhide, one for each limb with an overlap at the handle. Once the rawhide is down I work out any air bubbles or glue pockets with my thumbs. If the rawhide is thin enough there is no need to wrap but with thicker stuff I use strips of old bed sheets for the wrap. Be sure the rawhide stays centered if you wrap it.
 After an hour or so I remove the wrap if used and while the rawhide is still damp I use a razor to trim the excess rawhide. Now I let it all dry completely then sand the edges with a sanding block or a flat file.
 Once the back is well cleaned there is no need to score the back anymore that your final sanding.

[mmattockx]

Hey Mark.  I plan on using TBIII.  I thought I read somewhere that you were supposed to let your sizing dry for 24hours before applying the rawhide but maybe thats not accurate?  I guess the point of sizing is to allow the bow to absorb the glue so I dont see the harm of applying the rawhide before the sizing is dry as long as the bow has absorbed as much as its going to?

You could let hide glue dry like that but once TBIII is set you aren't reactivating it like you can with the hide glue. Yes, sizing is to allow the material to soak up however much glue it wants before the main glue application to prevent a dry joint.


Mark

[GaryL]

I appreciate everybodys response!  Now I just have to wait for my rawhide to arrive. 

[Hamish]

100% agreement with Mark on TB.

I can't see any benefit sizing a bow's back with hide glue  for applying rawhide either. Just coat both surfaces, apply, adjust and wrap.

[bownarra]

Don't score anything! Use hide glue and make it smooth! Scraper smooth for best adhesion.
If using colagen based glues definately size the back first. Warm the wood and use 5% glue for the first couple of coats then one coat at 10%. Let these dry in a warm place between coats. Do the actual glue up with 30% glue and everything nice and warm.
Follow those steps and it will never lift.

[Pat B]

Just be sure to remove any finger prints from the glue surfaces.