Sizing horn

[davidjw]

Hey folks, I had a question about sizing horn.  I noticed some grey streaks in the grooves after about the 10th coat of 2% glue, they are only visible for a couple of minutes after a fresh coat of sizing goes on.  I was wondering if this is a sign that I should wash the glue off and start over?  Thanks!

[mikekeswick]

How deep are your grooves? They should be about 2mm and the tips of the triangle should be points.
Yes any grey lines/areas indicate a void.
The horn should be placed on its side when drying the glue, then flip on the next coat and repeat until it is glossy. I normally do about 20 coats to get it glossy with 2 - 3 % glue.

[davidjw]

The grooves are between 1 and 2 mm, and were dried on alternate sides for each coat.  At this point all the parts have 20 coats, only one of the horns shows this problem in the grooves.  I suppose I could glue up one side while re-sizing the other to avoid oxidation.  But, definitely wash of the horn pictured above, ya?  thanks

[Tc]

I think it is good enough.

[davidjw]

thanks, I think subconsciously that's what I wanted to hear.  It will be a lightweight bow, 50lbs or so, so I will hope for the best as is.  I'm pretty sure this has happened on previous bows, but only one is tillered and shooting at the moment, so I don't have much experience to draw on.  Perhaps I need to heat the parts more before each sizing, but I've been nervous to blister the glue from overheating without a full day of drying between coats, as I've had that happen before.

[mikekeswick]

Each to his own but I don't see the point in taking any risks with poor bonding. How much work have you put in so far? How much to go? Then the waiting All that with a possible weak glueline? Not for me!
Any grey areas are voids. The whole surface should be glossy black. The hotter the glue (upto max 60 degs) the more 'flow' it has and therefore better wetting of the surface. Warm horn and hot glue are the keys in my opinion. I keep the horns/core in a small hotbox kept at about 25 degs during drying and warm each part further before applying each sizing coat.
As long as you are using thin glue during sizing and you leave enough time inbetween coats you can get the parts to 30 degs or so in safety.

[DC]

Would it help to heat it up a bit and run a sliver up each groove to dislodge the air?

[davidjw]

Appreciate the input folks, after mulling it over last night and fighting with myself, I decided I would rather be safe than sorry.  Indeed, as you said Mike, all the work that would go into the bow after a faulty glue up, only to find out much much later, would make me kick myself a little too hard.  I ended up running both horns under warm water and running a knife tip along the grooves to clear them.  DC, I actually hoped to just pop the air bubbles while leaving some of the sizing on, but I ended up just pushing out the re-liquefied glue.  I suppose I will add a coat of sizing to the core every now and again to keep it from oxidizing while I re-size the horns.

If I remember correctly, glue weakens from gelling then being re-heated repeatedly, though this glue is to dilute to gel, but it also weakens from too much heat.  Since the sizing process takes a few days, I was wondering if it is ok to keep the glue hot at 60 degs (but covered to not lose water) the entire time, or should I be letting the glue pot cool between coats? 

Thanks again y'all

[bubby]

I don't think good enough is the answer. Do it right or not at all especially with a horn bow the amount of work that goes into one you want to be doing it correctly. Do or so not there is no try😝

[mikekeswick]

Would it help to heat it up a bit and run a sliver up each groove to dislodge the air?

No the sizing coats are dry. The problem is that the grooves are triangles and if you simply brush glue on the surface tension of the glue will cause it to not reach the bottom of the groove.

David the key is to not heat anything too much. I used to keep a digital thermometer handy and regularly check on the glue but now I just use my fingers and feel. If the glue becomes damaged it won't gel or at least take longer than normal to gel. I generally take about one day to do the sizing coats then let them dry for one/two days. I let the glue pot cool between coats.

[Tc]

Those grey streaks are probably burn signs of the grooving tool, and not air bubbles. They appear when you do grooving too fast and the surface of the horn slightly burns (you can smell it as well). In this case the color of the affected areas of the horn change to grey or brawn but it has no effect on bonding. Air bubbles would be a problem. So again, it was good enough....

[davidjw]

Mike, thanks for the info, and woo-wee, all the sizing in one day, good on you!  Perhaps letting my horns dry at room temp could contribute to the glue not wetting enough by gelling too soon, as well as longer drying times, up to a couple hours on the later coats.  I've taken your idea of using a heat box and am using the closet with my water heater to size in.  It's about 20-25 deg in there at any given point and the glue seems to dry a bit quicker, and no sign of air bubbles...yet.  I've been using a candy thermometer to check the glue temp.

Tc, thanks for letting me know about the burning, I had not even considered this.  Probably didn't notice a smell because, well, the horns seem to smell a bit in general.  I will definitely keep an eye out for this in the future, and check to see if the grey streaks appear in the same place this time, which could indicate that this is the case.  Glad to hear it doesn't affect the bond though.