Giving it a shot... My First Laminated Glass Bow Build

[Major Boothroyd]

"The best laid plans of mice and men..."

I was hoping to get more done today, but things always seem to take longer than expected.

The good news is, I completed the heat box.  It's wired up with a thermostat, and 4 sockets, and I have four 200W bulbs in it.  I stapled in some insulation, and it works!  I'm planning to test it tomorrow for a couple of hours, to see if it reaches 160 - 180 F.  If not, I'll have to find some higher wattage bulbs.

I didn't have time to work on the form after finishing up the box.  I hope to get some work done on the form tomorrow.

       

It's Alive!
     

[mikkekeswick]

Looking good  
It should get hot enough but if not add more bulbs.

[monterey]

That's pretty much the identical layout of my box.  I had a bad experience with my hose losing pressure during the bake and not knowing it until the bow was cooked.  So, I cut a round hole in the end of the form that allows the hose to protrude.  Then I attach a pressure gauge to the hose so it can be monitored.  Some rags stuffed around it keeps it airtight.

It never happened again, but. . . .!

[Major Boothroyd]

monterey, man that's a drag.  Was that bow basically toast?  I plan on pressure testing my hose overnight to make sure it keeps pressure, before I use it for the first time.

So I'm at the point where I have a couple of questions regarding my form...

I ordered a basic laminating press kit from Binghams and I've generally been following their instructions, with the exception that my bow shape/pattern differs from their designs.  The kit came with a pressure strip as well as what was supposed to be a "formica" strip, but instead appears to be a fiberglass strip that's pretty much identical to the ones I will be using for my bow build, although those came from a different supplier.

I'm guessing using glass instead of formica should be fine, as I plan to wax the glass strip after it's laminated onto my form, and I'm also planning to use kitchen plastic wrap over the form when I glue up the bow.

I'm wondering what kind of glue I should use to laminate the glass strip to my form?  Is Titebond III suitable, or would I be better off using an epoxy of some sort?

[BrushWolf]

I used 3m spray adhesive on my forms and it has served me well.

[chackworth3]

I use contact cement on mine and it works well

[Roy from Pa]

Monterey,  that's too bad your hose won't stay up..  

[monterey]

I knew as I typed it that I'd get a "rise" out of you, Roy.    

Major, I had no idea how long it had held and it had been in the oven for eight hours.  So, I went ahead on the supposition that it was ok and it's still shooting.

[Major Boothroyd]

monterey, that's good to hear that the bow worked out.

I worked for several hours today on the form.  I drilled the holes for the clamps, and fabricated and drilled  the 1/2" ply offset pieces for the clamp hardware.  I just need to fasten the 1/2" ply offsets, and cement the fiberglass strip on the lower half of the form.

I'll post pics tomorrow.

I also have my riser section cut out of my Zebrawood stock.

The next step is to cut the riser shape, and sand the fades, and then do a dry fit test run.

[Major Boothroyd]

Well, I'm not impressed with the performance of the thermostat I purchased from Bingham.  I put a probe thermometer in the box (in the middle of the box and at the approximate height the bow would be while in the press) and turned on the bulbs, and let the box run for an hour.

I wired it in as per the instructions:  not closer than 3" from the edge of the box, and not closer than 14" from the closest lightbulb.

Initially, the temp rose quite quickly to 182 F, before the thermostat cut the circuit.  The temperature in the box dropped down to 128 F before cycling back on again.  

After leaving the box on for a while, and having the thermostat cycle on and off, the thermostat started cutting the circuit when the temperature in the box reached 155 F, and then didn't start up again until the temperature dropped to 124 F.  The temperature drop takes a few minutes, and the temperature ramp up takes slightly less time.

The high temp reading just as the thermostat cuts the circuit:
 

The low temperature before the thermostat cycles back on:
     


I think I'm going to rip that thermostat out and just play around with bulb wattage combinations to get a steady temp between 160 F - 180F.  I think that's going to be better than having the temperature constantly ramp up and down, and actually never really staying in the desired range for Smooth On.

[Major Boothroyd]

My (almost) completed form.  I still have to glue the glass strip to the bottom half of the form with contact cement.  

Other than that, I have a little adjustment I want to make to the riser section of the top half of the form, and I plan to fabricate and install some edge alignment washers to keep the limb laminations lined up nicely during glue up and curing.

     

[Mad Max]

You need to have something large in the box  to heat up.
I had a BBQ smoker, I put a gallon of water (or meat) in there and it smooth out.

What did you do to the bottom form to get it smooth and square to the sides.

You are making good progress, but slow down a little.

[Major Boothroyd]

Originally posted by Mark Daniel:
You need to have something large in the box  to heat up.
I had a BBQ smoker, I put a gallon of water (or meat) in there and it smooth out.

What did you do to the bottom form to get it smooth and square to the sides.

You are making good progress, but slow down a little.

Mark Daniel, are you suggesting that the thermostat may work better if there is something with mass in the box?  As in, it may not ramp up and down so much?  If so, I still don't know why it seems to be shutting off the circuit when the highest the  temperature gets is below 160 F.

As for the bottom of the form, I cut it on my buddy's Laguna bandsaw, and the cut came out perfectly perpendicular/square to the sides.  I sanded it with a combination of a spindle sander and a belt sander (the kind where the belt is perpendicular to the work table) to smooth it out.  It still checks out square to the sides.

As for slowing down, I don't think I'm rushing at all.  If anything, I feel like I'm spending more time on many of the individual steps than most people probably do, because I haven't built a bow before, and I'm trying to minimize my mistakes.  I have a little block of time off before work starts up again, so I'm trying to make hay while the sun shines, and I'm having fun working on this project.    

[Mad Max]

yes on the mass
 How close is(Binghams) thermostat to the  probe thermometer?
Just checking on what you are doing.

You are doing a fine job.

Put the form in there and run it again.
My box takes 1 hour to come up to tem. with a form like that. smaller pieces take less time.

Any recent movies you worked on, I might know?

[kennym]

Be sure to do a dry run ,no glue but all other parts , before you start the actual glue up. Bad time to find out something don't fit.

Once started a glue up on an actionwood bow, and discovered the riser was still a 2x2x18 pc.

Fastest riser I ever prepped!! LOL

But made it before glue set!

[monterey]

Actually, unless you are going to be overly perfectionist, your temperature range will be fine.

Did you put a small fan inside to keep the temperature evened out?  One of those little battery operated fans sold for RV refrigerators would probably be adequate.  But I have not tried it so this is just speculating.

[Major Boothroyd]

Mark Daniel, the probe was not close to the thermostat, but rather about where the center of the bow would be.  I will give it a try with the press inside, and see how that does.  I'll also let it run for a couple of hours to see how it does over time.

As for movies, I tend to shoot more TV shows than movies.  I shot "Entourage" for a couple of seasons, "Last Man On Earth" last season, and a bunch of others.  Movie wise, I shot the "Borat" and "Bruno" movies, and a documentary film called "Religulous," with Bill Maher.  I also shot a movie last year with Nic Cage, but I don't know if or when that will be released.

kennym, I definitely intend to do a dry run prior to gluing up.  That sounds like a close call on that riser prep!

monterey, I have seen a few posts by folks saying they installed a fan like that.  I may do that, but as of now, I don't have a fan installed.  Good to know about the temperature range being ok.  I just found that the manufacturer's tech sheet recommends a stepped temperature ramp up over the course of the use for bows:

2 hrs at 120 F
2 hrs at 150 F
2 hrs at 185 F

Man thats specific, and there's no easy way to get that kind of precision with this style heat box, so I'm glad to hear there's some wiggle room.

Thanks for the great tips!

[peanut39350]

I had the same problem with the bingham themostat the issue is without fans circulating most of the heat stays at the top of the box so when the t-stat reaches temp the middle of the box is several degrees lower i just took the thermostat out and i will screw in enough bulbs to get up to temp. I have a thermometer stuck through the side of the box right next to the form so that i can monitor temp while it cooks

[Mad Max]

cool

[Robertfishes]

Thats funny Kenny..I keep an extra ready for glue up riser in my shop for every bow form.. just in case.