Thanks Tim. We have enjoyed overcoming the sticking points and problems and working on the solutions to the perennial question, "Why won't it work NOW?" Those things and the unexpected ones, like a 12" drill bit breaking off at 5.4" in a 7.4" bore. Sometimes no matter what you do, the only way to fix it is by starting all over again. C'est la vie! The second time around you try for optimum deep hole drilling technique and then hope for the best. The second time to get to the same point it only took two hours, not three. That brought smiles back, because time is money. The pictures tell the story; the tube is done except for bluing.
Mike and Tracy
Preparing to machine the guide groove in the Breech Block. Alignment of the rotary table and 3-jaw chuck is ongoing here prior to machining.
The .125" 4 flute end mill is delicate so we team up to do this type of job. While Mike rotates the -x- and -y- axis cranks, I create a "waterfall cut" to the full depth of .020" per pass to ease the end mill into the work to make a deeper groove. Full depth was .125", so five passes were necessary on each of the 3 legs of the groove path.
Here is a little gunsmith's trick on how to find the center of a round pin or shaft or journal. Place a 6" steel scale on top of the pin with roughly half the scale on either side. Press your centerdrill down on the scale, roughly centered on the pin. Move the pin side to side until the scale is level. You are now within .004" of the pin's top-dead-center. In this case we were drilling a hole for the Breech Block end handle.
Our set-up for drilling and boring the 1.000" dia. Trunnion/Rimbase holes to .700" depth. The test indicator centers the tube in the mill vise while the indexer holds the muzzle in it's 3-jaw chuck. The indexer and the work are both shimmed for height so their central axes are coincident. After getting the Breech Block hole parallel to the mill table, the indexer is set to zero deg., then it is rotated 90 deg. for the first Trunnion hole. We use a center drill, .25",.50",.75",.875"drill bits, then we rotate 180 deg. and do it all again, then switch to the Criterion Boring Head and bore out the remaining metal in 3 steps, the last being only .006" for a nice finish. Then rotate 180 deg and complete the boring on the other trunnion hole.
The .750' dia. drill bit sends out a big steel pig's tail chip. Since these big drill bits have a large drill point, the boring bar is used to flatten the hole right at .700" deep.
Here we are using the 20 ton press to push the Trunnion/Rimbase into the hole. No pics of turning these. Mike is way too fast and I handle the compressed air cooling and measuring. The holes are 1.0020", so the rimbase is turned to 1.0035. .0015 interference is plenty for a very tight fit. Two secrets here are put a 5 deg. bevel about .25" long on a one inch press-fit pin and use a very small pinch (about the size of a small ladybug) of lithium grease on that inserted bevel end. We use a 15 second dwell-time, at max pressure, to get the hdw. to the hole's bottom.
I don't think he want's to sell it! We both had loads of fun building this Krupp blaster!
I was trying for a "Machine Age" or "Industrial Revolution" theme for this photo. It's complete except for bluing. Carriage build on Friday.
