Some Pictures and Notes on Making My Bow Oven


There's nothing especially technical or difficult about making a bow oven, or hot box, nor is there a lack of good guidance. Probably the most common plan and information source is the box covered in the Bingham Projects company's dvd. I watched it several times before building my oven, and even had the opportunity to borrow and use a Bingham plan box from my friend Boyd. I did make some small changes, however... and a mistake or two. Below I'll share some pictures and comments that may be of some help to anyone undertaking this project.

 

Dimensions: Bingham's box is designed to be 88" x 22" x 12", and constructed from 1/2" plywood. I had a couple of problems with this. First, Boyd's box was very heavy. I decided I wanted to make mine a bit lighter, as I have some strength problems and knew that I would have to manhandle this thing around in order to store it out of the way when not in use. I decided on 3/8" plywood instead of 1/2". I also decided to reduce the length. At 88", it would not be possible to stand the box on end for storage in my garage... lying down, it simply takes up too much footprint. I did some measuring and found that I could have a box 78" long and still be able to tip it up on end for vertical storage.

It also happens that I have a double bow form... a Hill style on the bottom and my flatbow design on the top. In using Boyd's box, we found that the clamps on the form had to be carefully positioned in order to avoid the light bulbs in the box. I raised the box slightly, using a height of 24" instead of Bingham's 22". This should solve that problem, but I still plan to cut this double form into two separate forms, but that's another project.

 

 

Okay, here we go... If you use lighter 3/8" ply in cuts this long, you need to back up the edges with 3/4 x 3/4 square pieces. Here you can see the interior construction of the box, with the square stock running along each seam, andon the lips. I used 1x2" stock for the back lip, both in the lid and the box, so that there would be good purchase for the hinges. I used a 1x4 down the center of the lid to mount the light fixtures on.

 

Note another change here. Bingham uses four 200 watt bulbs. I knew my box was shorter by 10". hence would have less volume. Also,Bingham's plan calls for insulating with aluminum foil, which has much more loss than the insulation I actually used. For these reasons, and because in my small home shop I have only standard home circuit breakers, I tend to favor the least amp draw for most applications. I decided on using three bulbs intead of four.

You may note the junction box on the end... this eventually got moved to the lid and flush mounted.

 

A couple of construction features... I used some scrap 2x2 for handles. You can see the center lid handle and three pieces on the end. The middle of these end pieces is the actual carrying or moving handle. The purpose of the other two pieces is that this is the end the box will stand on. The corners of these pieces are sanded over into a "soft" corner. The box can be tilted over onto the wide side, then simple tilted up to stand on end on these three pieces. The other end has only the middle piece to help handle the box.

You'll note that there seem to be a lot of screws visible... I used a lot. They are more visible than they might be because I used 3/4" self-washer lath screws. These have a flat wide head and are just a joy to use with a drill driver. They also happened to be the perfect length to use to go through the 3/8" plywood and fasten to the square edge pieces inside. Note: nothing is just screwed... everything joined is both Titebond II glued as well as screwed. When I die, they can bury me in this thing!

 

 

As an old forest fire safety officer, I'm always on the alert for accidents looking to happen. I spotted one immediately when I first opened the assembled box... the lid overpowers the base. This is obviously an invitation to an eventual upset with a hot bow inside. The easy solution is a couple of hinged braces. I tried braces that were triangular, pointed at the floor end, but they weren't adequate. It took these full sized rectangles that spread the load all the way to the floor. Now you can open the lid safely without having to worry about a tip over.

 

 

Here you can see how well I think ahead (after all, I may need one...). I hinged the brace pieces so that the both fold in the same direction, toward the stand up end... that way, their natural fall will be down, in keeping wih using minimum space.

Note the use of four hinges on the lid...

 

And here the braces are in use. I don't know why Bingham never mentions this problem. You may think I made a bit too much of it here, but I'm serious... these boxes are heavy, and end up containing heated metal clamps and hot light bulbs.

Also, note that if you look carefully you can see that I put two 1x2 runners under the length of the box. I did this for two reasons. The runners make moving a heavy box easier. I'd have used them in any event, but the lath screws I used stand proud from the wood, so they would tend to scratch anything the box was set on. The runners eliminate this problem.

 

 

 

Okay.. .next step was insulation. I used the double foil sided bubble center insulation. This stuff is good, and expensive! The key to easy installation of this insulation is to cut the pieces in panels and pre-fold them. Then you can staple them in quite easily. 5/16" staples work well and don't go through the 3/8" plywood. I did the two ends first, then the bottom, then each side. In the lid, I did one strip that did both ends and the middle, then stapled on two panels for the sides.

Note that I'm folding the insulation over the lip. My thinking was that it was squishy enough that the lid would still close and make a good seal. That was a mistake... It was much too thick to get the lide well closed. I had to go around after I had finished the installation, lift all the lip staples and trim the insulation even with the lip.

 

Here's a good picture of what I mean by forming the panels. This is the panel for the bottom. The bottom is 10" between the square edge pieces. This piece of insulation is 16" wide, and I've folded up the edges to leave a bottom of 10" ...

 

Here the panel has been set into the bottom, ready to be kind of formed over the square edge pieces and stapled in.

 

 

Here I'm ready to start working on the lid. I cross cut the centers of the light fixtures in an X pattern and then opened up the X's into circles. You want to be very careful here in the lid. Remember, foil is metal and will conduct electricity!!! Make sure your wiring is covered and protected.

Something else to note here is that I have moved the junction box/on-off switch to the end of the lid, and fed the line cord directly to it from INSIDE the box. There is a small groove, same size as the cable, rasped into the cornef of the lip. My thinking here, as compared to having the junction box on the outside and the cord coming into it from outside, is that when the box is not in use, but stored on end, the cord can be coiled up and kept inside, with the lid fully closed. If the cord was fastened from the outside, you'd either have to keep the cord outside or not be able to fully close the lid.

 

 

All insulated and trimmed...

 

 

Good view of this end. You can see the power cord going in, the flush mounted on-off switch, and the lifting handle. Also note under the handle, a small thermometer dial. This is a $10 "quick reading" meat thermometer. It is not left in place... just inserted through a hole that goes through the 2x2 corner post and insulation... left in position long enough to get a reading, then pulled out. The positioning of this feature takes a tiny bit of thought... note that it's at middle height, so you're not taking a reading on the floor or at the ceiling, and also close to an edge, so that it isn't directly under a light bulb.

 

 

So, how well does it work? Very well! I've started running tests as follows: With three 200 watt bulbs, it holds a temperature of just under 190 degrees. With three 150 watt bulbs, just under 170 degrees. Tomorrow I'll test it with three 100 watt bulbs. I also have a 135/155 thermostat I can try in it. I'm thinking that running the three 150's with that thermostat should be just about perfect.

There you are... I hope there's an idea or two there that will help you.

Dick in Seattle