Above is a picture of the motor made with no machine tools.
My quest for an all steel motor had one big obstacle. I needed a metal lathe. Ironically, my father gave away two
large lathes many years ago. I really thought I could pick one up for a reasonable price at an auction. No such
luck. I went to a number of auctions, and the lathes all went for over $1,500. I had set my limit at $1,000.
In pure frustration, I decided to go to work in my shop and come up with a motor, any way I could. I had purchased one each, 10' lengths of 1", 1.25" and 1.5" EMT tubing. So what I needed was a nozzle and an end closure.
I found an old rusty chunk of 1.25" steel bar, a little oversize for a 1" and too small for a 1.25" case. So it had to be a 1" motor. I used my 14" chop saw to cut off about 2" of the bar. I then center punched the bar and drilled and tapped a 1/4" hole in the center. The reason for threading the inside was I wanted a handle on the bar stock. I then ground the bar down to fit snugly into the 1" EMT on my 8" bench grinder. After the bar was ground to size, I cut off 1/2" to use as an end closure. The remaining bar was just under 1.5". I then went to my drill press and started drilling out the nozzle. First I drilled completely through the bar with a 1/4" bit, then enlarged the hole to the desired .32" final throat diameter. I then used progressively larger bits, cutting to a shallower depth with each larger bit. I tried to form a 60 degree convergent angle and a 30 degree divergent angle as best I could. They really didn't get close to those angles, but I figured anything was better than nothing. I tried to grind the angles to a better shape with small grinding stones, but the effort was more or less futile. In the end I did manage to smooth the surface, but that was all.
With the nozzle and closure made, I decided on a casing length of 10.5", leaving room for a 9" grain. I debated the attachment method for the nozzle. I finally decided to just weld it to the case. I really didn't see myself using the motor for any length of time.The top end closure was secured by means of 4) 10-32 x 3/8" screws. I just drilled through the case with the end closure in the case, and tapped the threads as an assembly. I also drilled a short hole in the closure, and tapped it for a 1/4" bolt. I could then screw in a bolt as a handle to make removing the closure easier.
I cast two 4.5" grains, using a paper inhibitor on the outside of the grain, no spacer was used between the grains. The top closure was inserted after applying a thin layer of RTV silicone to the inside of the motor case. The idea here, was to form an o-ring inside the case as the top closure was inserted. The 4) #10 screws were then inserted in the top closure, and the completed motor was put in my desiccant box to cure overnight.
The following day I prepared the motor for a test firing. My primitive test stand was set up and my video camera was set to record the thrust. The motor fired perfectly. The video recorded a thrust time of .673 seconds with a maximum thrust of about 130 pounds. Total thrust was inconclusive, as the test stand oscillated about midway through the burn. Post firing inspection revealed no blow by at either end of the motor, no throat erosion was noted, the exterior of the casing showed no signs of heat as the zinc plating was still intact, with the nozzle heat discolored but intact.
The motor was launch tested inLaunch Test 13 . This is more than likely the last firing of this motor, as I now have a metal lathe and am able to make better components. It does prove however, that an effective motor can be made with very simple tools.