This morning started cutting the steam chest bases for the Erie engine, same procedure as for the Marion already shown. Got the blanks bolted together with the jig plates, this time a narrower gap between the blanks since the dimensions from the cylinder are different:
Here is the sketch for figuring out the gap - varies with diameters of the center section and the end flanges and thickness of the base. Drew it out full size to help figure things out before cutting the blanks. As with the first set, the blanks are extra long to let the jig bolt to them and have room to trim off the screw holes.
Turned in the center section to fit the plug gauge made the other day,
Then turned in the end to fit the end flanges on the cylinders, past the screw holes:
Now, here is where things diverged from the first set. On that one, I did lots of measuring of the length of the blanks, the length of the flange counterbore, length of the center section on the cylinder, and did some easy math to determine how deep to counterbore in the second end. All well and good, but there was no way while cutting the second end to get a really good measurement of the center section left - the distance figured out was good, but I like to get actual measurements to get the best fit possible. Last night had the idea of rigging up a depth gauge block on the calipers.
Many of the manufacturers of dial calipers make a depth gauge accessory block that screws onto the side of the caliper to span holes when using the tail bar in the calipers. I don't happen to have one, but they are easy to make, simply a bar with a groove in it thats a close fit on the outside of the calipers, and a screw or clamp bar. That would get me halfway there - all the way if it was a blind hole or there was an easy way to put a plate at the inside end. So, next best thing - made another little clamp bar that goes on the end of the sliding bar on the calipers! Here is a view from the back side, showing the grooves in the blocks:
and from the front, showing the little clamp bars holding them in place. All is removeable, no changes made to the calipers
To calibrate the dial, I used a 1" wide machinists parallel, and set the bars so the dial read about 1", and tightened them down
That got it close - with the 1" piece still in place, then rotated the dial on the caliper back to zero.
and its ready for use. Since the new crosspiece on the sliding bar keeps the jaws from closing all the way, the minimum distance it will read is less than an inch, but for this use thats fine - all the cylinders are longer than that.
Next step was to turn the jig around in the four jaw and center it up to cut the counterbore on that end. Here is how the new dial caliper rig works - ran in the lower end so the new crossbar hooks over the counterbore, and the jaws closed until the crossbar on the main caliper body is against the part:
The dial now reads the length of the center section directly. This should save lots of time when counterboring the second end, now I can check the distances as I go to get a good fit on the cylinders.
