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Making a Rotary Table

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NormanV:
 I have started on my Rotary Table. Here is the worm and wheel that I shall be using. It is a single start worm and the wheel has 30 teeth. This will give me 12 degrees for each turn of the worm.

NormanV:
Here are the drawings showing the main details of what I plan to do. The main body is 160 x x150 x 50mm.

NormanV:
I will be making the main body of the table as aluminium castings. These are the patterns. Although the main body of the table will end up open topped I made the pattern with a thin plywood top to make the moulding easier.

NormanV:
I've had two days of problems trying to produce the two simple castings. On my first attempt the flask opened and the molten metal leaked out all over the ground. The main casting was ruined but the flat top plate was OK.
This is the second time that this has happened with this flask, I am guessing that it is too light, it will become firewood.
I started to remelt the faulty casting casting and ran out of gas! I haven't got any transport at the moment so am unable to go to get any more so I decided to use charcoal.
I started today with the charcoal and could just not get enough heat, if I had the air blast too high I was showering the surrounding area with cinders and on a low setting the charcoal was burning too slowly. It was rubbishy charcoal, tiny pieces and lots of dust. After 3 hours the metal melted and I was able to pour the casting. It did not turn out perfectly but it is usable. The metal cooled and did not fill the top where I had used the thin ply. I had expected this and planned to cut it away anyway. There are also two quite large shrink cavities in the top but they are of no consequence as I have left quite a large machining allowance.

vtsteam:
You're forging ahead Norman! :thumbup: :thumbup: :clap:

I like your pattens with very heavy sections. Nice and solid.

3 hours to melt!!! That's painful. Must be very different to the charcoal briquettes we get here. Generally takes about 20-30 minutes from a cold furnace to melt 5 pounds of aluminum.

If I use the charcoal I make from wood (real charcoal) it does shower if the blast is too high, as you say, and it burns up faster, being less much dense. But the furnace temp can go much hotter than the commercial BBQ briquettes will take it. It will actually melt a steel rebar, and certainly melt bronze or brass. The downside is you have to add it a few times during an aluminum melt. Briquettes will usually complete an aluminum melt without any additional fuel top-up  for me. They are really different fuels.

Anyway, I'm glad you finally got your parts cast -- that was a Herculean effort in a 3 hour melt -- and a second one, as well. Great work!  :clap: :clap: :beer:

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