I released a video on how to make a rocket motor test stand that is resistant to motor explosions! Check it out!
Video Here: https://www.youtube.com/watch?v=C5j-w0-Lx2g
Category: Machining
I need a simple anvil to hammer against when I load rocket motors, so I grabbed the largest piece of steel scrap I had on hand and started facing it down so that it’s flat and the faces are parallel. Not exactly a complicated operation for most lathes, but my little 1HP lathe is definitely not cut out for this. For starters, it’s barely able to hold the 8″ disc in the 4-jaw chuck. I’m pretty certain that if this were half an inch larger, it would not be machinable in my shop. At any rate, perseverance paid off and I got it done. Probably would have been cheaper and easier to use a rectangular steel block and mill it flat, but I thought this would be more fun.
In order to create the clay nozzles and fuel grains, you need to hammer them into place. To do that, I’ll need to create tamps with proper shapes and clearances for the nozzle, spindles, etc. Each motor uses 4 different tamps, and they are made from nylon plastic in order to be lightweight and durable. This also makes them a hell of a lot safer than making them from steel, since in the worst possible situation (where the motor spontaneously ignites during the ramming process) the tamps will simply shoot out the top of the motor rather than exploding into metal shrapnel. These are relatively easy to make, provided you happen to have aircraft-length drill bits (18″). Also, the nylon does not make a nice chip on the lathe and turns into a mass of spaghetti, but to combat that, just stop every once in a while and don’t let it build up like I did 😛
When ramming the clay and fuel into the engine during assembly, it creates a lot of outward forces that have a tendency to damage the cardboard tubes. In order to abate this problem, you surround the cardboard tube with a casing retainer that will take up some of that force and prevent the tubes from deforming or bursting. This can be done with either plastic or steel, but steel allows you to use fewer clamping bolts due to rigidity so I went with that. The fabrication process basically starts with a schedule 40 steel pipe, which is cleaned up and slit down the middle with a slitting saw on the mill. Then a flange is machined and welded in place. The only really tricky part of this is that you need to be VERY careful not to overheat and warp the part when welding. The easiest way to accomplish this is to simply go very slowly, welding about an inch at a time and then giving the part time for the heat to equalize and cool a bit. Seems like everything went pretty smoothly, though for the large retainer the flange warped a tiny bit, which reduces it’s clamping range somewhat. Shouldn’t be too hard to account for this, and i can easily make another in the future if it becomes bothersome.
Now that the nozzle molds are finished, making the core spindles is a relatively easy task. These will be used to create the hollow inner core of the motor. Compared to the time spent machining the nozzle molds, this was a relatively quick task. Probably less than 6 hours in total. Simply start with a rod of stainless, bring it down to nominal size, then file a rounded point and tediously sand the surface with finer and finer grits to bring it to a smooth finish.
Categories
Nozzle Molds
I’ve been working hard for the past month or so machining several different nozzle molds for different sized engines. So far I’ve made 5 of them, for engines of size C, D, and E. I plan to make one more for F-size engines. Boy have these been a huge pain on my tiny lathe! Because these parts come in contact with oxidizers, they need to be made of stainless steel, and my tiny lathe is not really rigid enough to take large cuts in such a hard material. I can normally get away with 20-30 thousandths in mild steel, but stainless maxes out at about 10, so making these parts took between 30-80 facing cuts just to rough in the features. All in all I think I spent at least 24 hours of total machining time making these! Fortunately, if I don’t accidentally drop them face-down they should last me forever.
Categories
Slitting Saw Arbor
I needed a slitting saw arbor and didn’t really want to buy a crappy one from amazon that has tons of runout, so this made for a nice little lathe project. Nothing too fancy, just a bit of stainless on the lathe. If I do this again I’m going to take extra care to make this even more low profile, so that the slitting saw has more reach.
Categories
Learning to Make Threads
I wanted a simple project to learn how to make threads on the lathe, since I haven’t really done that yet. I made this knurled brass knob for the gibs on the mill. I’d say that this was definitely a fun project but a waste of $20 of brass for sure.
Small Benchtop Mills usually have an optional cast iron table, but I didn’t like the height (it was too low) and the lack of storage that these tables have. I decided to make my own, just like the lathe table. I didn’t spend quite as much time making it perfect like the previous table, but this one is certainly built like a tank and should last me forever. Like the lathe table, it has both leveling feet and wheels to move it around and keep it stable.
Categories
Milling Machine!
I purchased a PM932 Milling machine from Precision Matthews. It’s 850lb and definitely a beast to move, at least in my small shop. Honestly I’d have preferred a knee mill but I promised myself to keep the tools below 1000lb so that it’s not a complete nightmare when I move in the future.
