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PM Research Dynamo

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EricB:
I decided my little engines needed something to do, so I bought a PMR Dynamo kit thinking it could be an easy build. I started making chips about a month ago. My first step of course was to search youtube to see what others had done. Among others I found mrpete222 has 3 videos for his dynamo build. I learned a couple of things from him, the most important being he used a Bridgeport (because he has one) and an Atlas lathe. The other builders used larger machines too. I have Sherline machines so I could not use many of their holding techniques.

I studied the diagrams and measured the castings to decide where to start and figure out how to hold them. For me the logical choice for alignment of the frame casting's features are the two mounting lugs that would secure the dynamo to a platform. I wanted the tops of the lugs about the same height and parallel to the bottom surface. Once machined the bottom would become the master surface. To accomplish this I set the casting on a pair of 123 blocks as shown and gently filed the high spots from the top sides until it did not rock, then clamped it to the mill table again using the blocks. It's at an angle because the casting was 1 5/8" end to end and the t-slots on the table are only 1 1/2" between centers. It worked ok. The only problem I had with the setup was the back block came in contact with the mill column. A better setup would have been on a tooling plate, which I had at the time in a box.

For the ends I faced the boss for the lifting ring, found the center of that and marked it with a punch. Then I measured and marked half the finshed length to each end from that mark. After that it was secured in the vise. I used the straightest edge of the casting against a square to find the first end. Then it was just flipped over for the other end.

This seemed like a good place to check and measure, and it became apparent that I needed to correct for the built in table error in my 5400 mill. The immediate solution was replace it with a 2000 mill I picked up last summer (because it was local and inexpensive). It came with it's own set of quirks but it's a higher quality machine than what Sherline made in the 90s.

More later.

Eric

propforward:
Excellent project - I will enjoy seeing this progress. Seems like you are off to a good start.

crueby:
Following along here too, very interested to see how it goes.


 :popcorn: :popcorn: :popcorn:

EricB:
Part 2.

The next operation was boring the frame casting to fit the magnets. In addition to the mill I needed a longer boring tool than I had on hand. While waiting for that to arrive I investigated the problems with the other machine. That's still on going but I've already replaced the table and repaired some damage to the base which I thought was only cosmetic. It's better now but not quite where I want it yet.

One of the reasons I had not switched to using the 2000 mill is my work bench (a small child's former desk) is shorter front to back than the machine. I had to cut out spaces in my chip guard for the base board and the column ram to pass through, and the machine hangs over the back of the bench. It's still stable enough for most things. Boring might not be one of them.

Back to work. The casting was held in the vise, lifted to give clearance at the bottom of the bore, and indicated square. I centered it roughly using the tool and took out the crust and about half material needing removal before crashing the tool into the vise. OOPS!

Time to stop, remove the part, clear the chips, dress up the damage on the vise, examine the tool, and start again. The bore was looking good at this point and the tool was ok so I put the part back in the vise with more space at the bottom, indicated it square, located the center and continued. All was going well until those last few light passes, then vibration vent up and the finish went away. The bore is to size and a cylinder but it looks like hell. I later found that the motor bracket had worked loose and was bouncing around with the off balance boring head. I also found the tool had chipped.

Next up, the end bell castings.

Eric

propforward:
Well looking at the pictures that seems to have gone very well.

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