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CNC conversion – The mill base

My first thoughts were that the base  of the mill would have ground flat surfaces. That may be true but it’s not relevant. This all unfolded as a mystery, but in hind sight I  can simply the story.

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When I unbolted the mill base from the stand, the two pieces were strangely joined. There was a separation between the two pieces and they were bolted together, but once separated the base didn’t have 4 even legs, but 4 legs of different heights. First plan, bolt is upside down and machine the legs flat. Tried that but it didn’t work.

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In the picture is my helper John. He’s working with me on this project to learn about machining. I also have another friend Eddy helping with the electronic side of the project while I handle the mechanical side.  The 3 of us are a pretty good team.

When unbolting the mill base from the stand, it un twisted. It must have been assembled and when the bolts were tightened, twisted. So when I unbolted it, it got a twist. Not a small one either, at least 1mm. when I bolted it to the mill, it wasn’t really flat and machining the legs left we with a base that wobbled. This confused me quite a bit. It is a new to me manual mill so I thought about the mill being the problem. I did have to move the head to reach all the legs. Shouldn’t cause a big wobble, but could account for a few thou. Anyway. I put an indicator on the dovetails and they were not flat.

So I shimmed the base upside down on the mill to split the difference of the warp evenly. Then machined the legs flat (thus eliminating the wobble), bolted it to two flat plates (so I had something nice to clamp to and for it to stand on) and machined all the surfaces in one operation on the top side of the base.

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Update 01/17/2017

Now everything is flat (to the precision of my mill (.05mm)  and I can mount rails etc. We drilled holes underneath for mounting limit switches.

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Y-Limit switch mounting holes.

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The bottom of the base is a really rough casting so we needed to make a flat place to mount the limit switches.

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This was the last setup for drilling the holes for the limit switches.

It was a huge job with lots of setups and head scratching. I’m happy with how it turned out and I have a great sense of accomplishment by coming out of it with a fairly sturdy base with flat surfaces and machined surfaces to index off of and mount to.

Next up the milling table.

About Brian Barrett

Brian Barrett is a Canadian Engineer living in China.

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