Finishing the Bottom plate

Now that all the round features are finished, I brought it back to the mill. Because we are drilling through the plate, mounting in the vice is not an option because we would drill into the vice. So, I mounted it directly to the table on top of parallels. I snugged the clamps down ran a dial indicator back and forth along the edge. Watching the indicator, I tapped the corners with a dead-blow hammer until the indicator did not move when swept across the edge.



To properly locate the holes, I used the dial indicator to find the center of the large hole. Placing the indicator against the inner surface of the hole, I rotated the quill and noted the how much the readings varried both in the X and Y axes. I then moved the table so that when the indicator was rotated within the hole, the reading was the same all around. The quill was now perfectly assigned with the center of the hole so I zeroed the X and Y axes on the digital read out (DRO).



The print gave polar (radius from center/angle) locations for the holes. I could have used a rotary table to place the holes but our rotary table is HEAVY so I avoid using it when I can. Instead I simply used the magic of trigonometry to find the X,Y coordinates of the holes from the center of the plate.



I realized that I had mounted the plate to close to the edge of the table so I wasn't able to drill the far corners. Also, one of the holes called for a tapered pipe thread and that had to be done from the other side of the plate. So I flipped the plate over, squared it and indicated the center.

I decided to tap the large center hole by hand but since it was already mounted, I used the machine to help me out. With the quill centered on the hole, I placed a spring center in the chuck and lowered it onto the tap before running my threads.



I started the pipe thread with the mill but I didn't tap deep enough. It would have been easy to destroy the threads, especially in the soft aluminum so I finished it off by hand. I used a brass plug to check my depth and stopped when there were about three threads still visible.





I finished my last two corner holes and cleaned it up. Our first part is done! Only 30 more to go!

Bottom plate in the lathe

After squaring up the bottom plate at the mill, I put a rough layout on the top surface to act as a rough guide at the lathe. I made an “X” across the piece with layout fluid and scribed a line from the corners to find the center. I punched the center and then scribed the ID and OD for the grove and the corner radiuses.



I placed it in a 4 jaw chuck using ¼ inch dowels to bank off of. After squaring it in the chuck I center drilled, drilled and bored the center hole. I did not tap the hole because I need a smooth surface to indicate when I take it back to the mill.



Here at my school, we have boxes of old high speed steel tools from students past. I didn’t want to have to grind my own tool so I dug until I found one that would make a good trepan. It took a little fussing to get the speed and rake right because it kept wanting to chatter but once we got it straight, it was a quick and simple job to cut the groove.



The finished groove:



Finally I cut half of the corner radius, flipped and squared the piece and cut the remaining radius.



I'm a little behind schedule as I get into the swing of things. I've ordered more stock so will be picking up the pace in the next couple of weeks. Next I will move back to the mill where I will drill and tap the remaining holes.

The project begins!

I have just started building a Tesla Turbine. I could go into great detail about how it works but I'll just let you click the above link. It explains it much better than I can. I am using a design from Phoenix Navigation. Their design is simple yet elegant and well within my capacity and ability to build. Plus, their complete plans only cost $90. An incredible deal considering all the effort they put into design and testing.

For those that don't know me: I am a student at Pima Community College in their Machine Tool Technology Program. I am building it in their manual machine lab. Of course I'd love to use the 4 and 5 axis CNC machines in the same room but independent study is only offered on the manual side. Giving students free reign can be risky and crashing a $10,000 manual mill is better than a $60,000 CNC mill!

I started with the bottom plate as it will be subject to the least stress. I want to get more comfortable with my abilities before I start cutting the critical parts. So far I've faced and squared the plate on the mill. This coming week I will be putting it onto the lathe to radius the corners, cut the grove that will seal to the case and cut the center hole. It will then go back to the mill on a rotary table to drill the remaining holes.

Here is the plate getting faced to thickness:


And here it is getting squared and milled to size: