Offset Turning

As discussed in the last post, I need the beam engine cylinder head partially complete as part of my plan for drilling the various matching holes in the cylinder. This is a fairly straightforward turning of a 1/4″ projection on one end of a 5/8″ round bar. The fun part is that the projection is offset from the center of the bar by 3/32″. I thought it would be fun to show how I get the part set up in the lathe to achieve that.

Firstly, I blue and mark up the end of the length of 3/4″ brass bar. (It was actually .748″) Knowing the diameter of the bar, I measure the height of the bar sitting in a vee block on the surface plate. Subtracting half the diameter from that gives me the height of center.

I use the scriber on the end of the height gauge probe to scratch a line on the bar. I then rotate the bar and scratch a line twice more. If I haven’t messed up anything, all three lines should cross in the same place and that is the bar center. I then scratch a line 3/32 below center as perpendicular to one of the center lines as I can manage and center punch that point.

Now comes the magic part. I put the bar in the four jaw chuck and I set up my wiggler in the tail stock with the point in the center punched mark. I then adjust the chuck jaws until the pointer stops moving when I manually rotate the chuck. (Some people can just put an indicator on the bar and move the bar via chuck adjustment. I one try at that was an unqualified failure. This method works for me.)

Lastly, I set a dial indicator against the pointer and and refine things until it shows no movement.

Visually, success is demonstrated when I power up the lathe. The center mark should not be moving even as the actual bar gallops around. This is the ML7 going flat out at about 1100 RPM. It really is in focus! 🙂

Lastly, here is the finished product. Brass is like aluminum in that is comes out nice and shiny and looks really good.

I just need to drill the appropriate hole through the projection, and then I can re-chuck the bar in the 3-jaw chuck, turn it down to 5/8″ and part it off.

Starting the Beam Engine Cylinder

I have been having a really hard time getting off my duff and down to the shop so I actually started the beam engine cylinder block about a week ago, got called away and took this long to get back to it. But back to it I got where I finished turning the bit on the bottom that goes into a hole on the base and got set up in the mill to put in the holes for the piston aka the cylinder proper and, in this design, a parallel hole for the valve as well as a couple of screw holes to hole on the cylinder head.

This is the first real use of the lathe DRO and I am getting the hang of it. It is also my first real use of high speed steel lathe tooling. I had been getting by on carbide insert tools but the ML7’s top speed is only about 1100 RPM and that is low for brass and HSS, nevermind carbide. Also of note is my fancy aluminum shim stock(aka Coke can) protecting the brass hex bar from the chuck jaws.

Here is a dry fit shot of the progress to date.

I put the vise back on the mill table, got it squared up and the cylinder set up in the vise. I left it there because I am thinking that doing the head first would be better since I could use the holes in the head to place the valve and screw holes. A bit of thought prior may save me some aggravation later. I have learned that it is possible to machine a part into a state where you have no good way to do the next operation.

Beam Engine Progress or Go With What You Got

I have gotten out of the habit of regular posting as my current machining focus is a bit off the beam from what this blog started out as. I have finally admitted to myself that it will be a while before significant model railway activity takes place and also have reminded myself why I chose the blog name I did. So, I shall report on what I am doing in hopes that it will be of some interest albeit perhaps not to exactly the same audience.

To recap, I have been developing my machining skills by working on a model beam engine based on plans by Elmer Verburg. This engine is commonly referred to as #24 (Elmer created many plans and made them freely available, may he rest in peace). I have done the base, flywheel bearing, flywheel, eccentric hub, and column. Here is a dry fit of those pieces.

The part in progress is the beam. This is attempt the second as the first effort is now part of the scrap pile with the end of a #55 drill firmly embedded in it. Trying to drill that size of hole with the lathe going at 1100-ish RPM was not a success. The mill going at 4300 and a less ambition depth did the trick.

There are three 1/16th inch reamed holes in that piece. Photographing shiny aluminum close up is still something I need to work on.

Next step will be to flip the part over and mill it down to final thickness and take off the edges at an angle to produce an elongated lozenge shape. I have a plan but it may not work out. On the other hand, the only crucial dimensions on this part are the holes and the thickness of the hub. All else could be done with a saw and a file.