Explosive failure of air hose!

[kiltedcelt]

Woo hoo! So, I'm in the process of gluing up limbs for a take down longbow from Bingham plans and materials. For starters, I already had some firehose so I only bought the plug ends for the hose. To begin with I could never get the supplied clamps on tight enough that the hose ends wouldn't leak. So, I wrapped inner tube around the plugs stuck 'em back in and tried again. Was able to get the clamps tighter but then they began deforming. So, I went to a plumbing supply place and found a tougher all stainless steel set of clamps. I was able to get the ends much tighter then. Still, the other end was a bit loose still so I ended up going back out and found an even better set of clamps included as part of one of those rubber plumbing connector pieces.

These clamps appeared to have reinforcement built into them and were much better design than regular clamps. So, I put them on the tail end of the hose (the non-Schrader fitting end), and checked it all again. No leaks. So, after I get the limb glued up, put in the form, clamp the hose down I start filling it up. Of course the lams start moving from side to side so I have to deflate the hose about half a dozen times before it seems like I’ve got everything straight. So, I pump it up to 60 psi as per the instructions and pop into the 150F heat box. About an hour later - BLAM!!!

I knew something had gone wrong with that hose, either it had ruptured outright or one of the ends had blown off. Incidentally, one of my cats had perched on one end of the box, no doubt to suck up some warmth. Needless to say, he shot straight up into the air and went tear-assing off along with another freaked out cat. The cats seemed fine so I checked the oven. Indeed one end had blown off - the end utilizing the stainless clamps, not the end with the reinforced clamps. So, at this point I was at a loss as to what to do so I disassembled parts of the form so that I could drill holes and insert dowels for rubber band clamping (using inner tubes).

Now, I’ve used inner tubes before and been satisfied with the clamping pressure I get and I’ve never seen bad glue lines except where my fades were crap to begin with. What looks to have been in my favor was that the limb had been cooking long enough for the epoxy to have begun to set up to the point that the lams were not coming out of shape while I was doing all of this. I’d say it probably took me about 15 minutes to get it re-rigged and clamped back with inner tubes. At this point, do you guys think this limb is going to be trashed? I’ll go ahead and cook it for the rest of it’s time but I wonder if this brief episode will have affected my glue lines or the overall integrity of the limb.

Finally, the hose - there was a nice big dent in the foam insulation on the end of the heat box where the plug end shot out. Man, it’s a good thing my take down heat box has CDX plywood ends. If it had been all foam like the sides I probably would have been hit by that plug end since the heat box was pointed right at where I was sitting on my laptop. Now, Bingham says ABSOLUTELY NOTHING in their instructions about the simple physics fact that the air in the hose is going to increase in pressure as the air heats up by being in the heat box. No where does it tell you to open the box and continue to check the pressure, lowering it so that it doesn’t exceed 60 psi. Unless, the air pressure is supposed to be allowed to increase to 70 psi or 80 or whatever it gets up to. The next limb I glue up tomorrow will be done the rubber bands regardless. As for the air hose method, I know lots of guys use it but as of now I’m less than impressed.

[Trux Turning]

I'll bet your cat won't hang out there again-- your limb sounds like it will be ok- I have some "homemade" ends on my hose and wondered the first few times if they would hold- so far no shots going off in the hotbox (5-6 years and counting).

[SourOwl]

Kiltedcelt - It's been about ten years, but I'm sure that the hose I used was purchased from Binghams already assembled;  and, if memory serves, the directions said to pump it up to 40 p.s.i.  The whole set-up belonged to my friend, and we both built a couple of long bows with it with no mishaps.  the hose and hot-box has been stored under a lean-to behind my shop since then, and just two days ago my friend and I got it into my shop, laid up a bow, pumped the ten-year-old hose up to 40p.s.i. and got a good glue-up; no leaks even after ten years - - -Sourowl

[GREG IN MALAD]

The hose that binghams sells is the right size for their plugs, the plugs fit tight enough that I use a rubber mallet to drive them in. If you had to wrap the plugs with inner tube,your fire hose was too big. You don't have to open the oven and lower the pressure in the hose, I have heard of people using 180 psi. Most people use 60 to 75 psi.

[kiltedcelt]

Greg - I had a feeling the hose I was using was not correct. I thought about getting some hose from Bingham but when I talked to them on the phone they felt that pretty much all fire hose was the same interior diameter and that it shouldn't matter. If I end up trying to use the air hose again, I'll get some hose directly from Bingham. For now though, I'm going to use inner tubes for gluing up the second limb and the recurve limbs I'll be gluing up in a couple weeks. I'm just way more familiar with inner tubes and have always gotten good results with them and the air hose is just one more new variable.

[GREG IN MALAD]

At least nobody was hurt. I heard of a fella who made his own plugs, had one blow out of the hose and almost hit his head. That would have left a mark!
Don't give up on the hose method yet, it really works good.

[Robertfishes]

sounds like you had 2 inch hose and 1 1/2 inch plugs??

[kiltedcelt]

Robert - I think you're right. If I use the hose again, I'll buy some from Bingham but for now I'm going to glue up the limbs with inner tubes.

[kiltedcelt]

Well, the limb is trashed. The glass on one side shifted a whole 1/8" over and underneath most of the glass there are bubble-like squiggly marks which indicate either not enough glue or that maybe too much was squeezed out. So, I think I'm just going to skip gluing up the second limb and maybe go for a whole new set of lams. Might also go for lighter colored wood next time around as well. The original riser was going to be walnut and the limbs walnut under clear glass. Any suggestions on a good wood for the limbs to complement the walnut? I'd prefer to stick with a domestic species of wood versus all the exotics.

[GREG IN MALAD]

red elm, cherry, any of the maples, hickory, or any white wood dyed brown. I think curly maple dyed light brown would look great.

[Bob Tebeau]

I would not give up on the air hose yet, it’s the best way to do it. I’ve never had a problem. There are a few little tricks to make it easier. Use pin holes and tooth picks or small finish nails to keep lams from sliding and washers on the sides to keep it all lined up. I also use zip ties or some of my forms have pigs for lacing thin tubing to hold every thing down before I set the air hose I don’t like using tape. Take your time and change your gloves, have some rubbing alcohol on hand to clean your hands. Use plastic sheeting on the form and wrap your stack before you put it in the form.. I make a lot of horse bows  for those I only use inter tubes because the forms are very simple and thin. Anyway keep building.

[mater]

They also make 1 3/4" air hose. It looks almost the same as 1 1/2" but the plugs dont fit right.
 I wouldnt be scared of it if it was the proper size though. Im a fireman and we test 1 1/2" hose to 300lbs. of pressure yearly. So 60-80 shouldnt be even close to hurting it.  Mark

[kiltedcelt]

mater - this hose was clearly larger than what Bingham sells and the fact that I couldn't get the clamps tight enough without first wrapping inner tube around the plugs is a dead giveaway. I think what happened is that the plugs were tight enough to prevent air leaks but not tight enough to hold the plug in place when that pressure started to build inside the hose. If I do the air hose method again I'll buy the correct hose from Bingham, but for now I'm going to stick with inner tubes for my next couple glue-ups. I know what to expect with inner tubes and have had no problems getting good clamping pressure and I won't have to mess around modifying my forms to prevent the lams sliding around and such. At some point I probably will give it a try using the hose but for now I want to get my limbs glued up and the easiest way to do that without further screw ups is doing it the way I know best which is inner tubes.

[ChristopherO]

My first attempt had a hose blow off, too.  Good thing it was in the oven long enough not to matter.  I've since built up my plug with plumber's epoxy, glued the hose on with black polyeurathane caulk and reclamped it.  Hopefully, this will not happen again!