The headstock spider for my south bend 9a lathe made some great progress with the help of the Lewis Mill and decent vise. Up until now, I have only built one thing with my Lewis Horizontal Mill, which was a T-nut for my lathe. This project is all about me learning to use and then trust my mill to produce something a bit more technical. For those of you who know what you are doing, hopefully, you can appreciate the farse that is my current skillset.
For this enterprise, I simply grabbed some steel bar I had laying around and faced it off with the lathe. The material I used previously had a 3/8 inch hole bored down the centerline. My goal is to create four holes and them 1/4 x 28. This will allow the use some Allen bolts to help center material within the headstock. My goal on this project was oddly enough not to complete the project, but rather, force myself to understand the geometry and techniques of milling.
I have done a lot of Youtube video watching to understand the process a bit, but hands on is the way my mind turns information into knowledge. I used a piece of bar stock as a parallel and secured the bar within the vice. My original idea was to use some V-blocks, but my V-blocks where not the correct size for my material. The main criteria that I was not willing to move on, was to move the object once I started. Once I moved anything within the vice, I would loose the ability to use the protractor to rotate 90 degrees. So far so good, I’ve got this… or so I thought.
The first issue I ran into was the placement. My original thinking was that I would place the material at one end of the vice, drill, rotate 90 degrees using the protractor on the vice, and repeat. After setting up the material at one end of the vice, I was able to determine that there would not be enough drill available to drill a hold when oriented across the length of the vice. Oh well, “Rookie mistake”. To be expected. So, I move the steel into the center of the vice.
After a rethink, I then went through a “mock” drilling process to ensure I have access at all four hole locations. Originally, I had the orientation of the vice handle down the length of my table. On my vice, this is 0 degrees on the protractor. This orientation works great for 0, 90 and 180 degrees of rotation. However… at 270 degrees of rotation the vice handle will not allow the drill anywhere near the piece.
This is no good, and I did not want to reposition the piece in the vice, as this process would introduce error. Again, this is about me learning the mill and not about producing the spider at this point in time. I decided to take a break and talk about things with my dad who is also learning. During my break, I had a moment of clarity. I would oriented the vice at 45 degrees! With this setup, I could have access to all four hole locations and the vice handle would be located out of the way. Progress…
A Pivotal Change
Finally, after all of this, I was ready for drilling. Yet… I verified my procedures and clearances. I tough off the material and moved the table the radius of the material plus the radius of the drill. Everything looked good. I rotate the vice at 180 degrees and… Nope. Not even close, the drill is visibly off-center. I had a bit of the think, again.
After a bit of pondering, ciphering, and “tangent calculations based upon the phase of the moon”, I was able figure out my error and update my way of thinking. My conclusion was the the radius of the material is different from the radius of the vice. Therefor, when you rotate the vice, you need to retouch the edge and then move back towards center the amount of the radius of the material plus the radius of the drill.
Finally, I was confident that I was ready to go. I drilled the first hole. Rotated the vice, touched the edge and recentered. After drilling two holes, I realize that I was moving on all three axis. I figured out, I could complete the transition from hole to hole by only moving two axis. The scale on the mill allowed for repeatability, but the fewer movements, the better. Once all four holes are drilled, I was able to easily use a drill to visual confirm that I was very close to center.
Basking in my new found confidence where I complete this step in the project by taping the holes 1/4 x 28 threads per inch.
I am very please with this step in this project. I learned a lot and this project is about me learning how to do things on the mill and not actually producing anything. I was proud of being able to figure the solution with looking “everything” up online. I am happy with my progress and feel like I have started down a path of milling. There are a few changes to the mill which I want to do, however, that is a story for another day. The headstock spider for my South Bend 9a Lathe is well in hand.