First, thanks to all that are watching this build log and making comments. They are always appreciated, and of course I appreciate any good tips or techniques!
So, on to the next part on this build, the front frame.
In one of the previous posts, I'd already squared up and brought to size a chuck of Al for this part, plus on the lathe, I'd bored the hole thru the entire block and put the counter bore on the back side, all as per JE Howell's drawings. The next step in my planned OoO (order of operations) was to create the profile(s) as viewed from the side. I do all the work using my DRO for positioning, but because this was a fairly complicated series of operations, I blued up one side of the part and marked it out just as a reference. That way I could double check myself to make sure I wasn't about to make a tragic mistake.
Here's the part marked out and ready to go into the mill.
That arc on the upper right surface doesn't actually go all the way to the back of the part, so i first milled away that straight portio with the result as show in this pix.
Then back in the mill vise to chew away most the material that needed to be removed in the upper right area. I stayed well short of the marking lines at this stage. That's a 1/2" roughing end mill and it does chew away Al fast!
Next I positioned the mill spindle over the center of the arc which is actually not on the surface of the part. Then I took repeated passes advancing the boring head between each pass.
And in not much time at all, I ended up with what you see in the pix. I kept progressing the boring operation until I just met the layout line at the front and the previously milled away horizontal surface at the rear. A bit of measurement also confirmed that the radius achieved was as per the drawing. How can also see how this feature intersects the previously bored hole and counter bore to create a good portion of the rear of the part.
Then back into the mill vise. I didn't show the operation but i put the mill spindle over the center of the arc that forms the front radius. Then I drilled thru in steps and ended with a 1" drill. Then i switched to the boring head and progressed the cut until that arc being cut met the front and bottom layout lines. I also confirmed the dimensions by measuring.
Next I reoriented the part in the mill vise and started chewing away everything that didn't look like the front frame. That roughing end mill works fast so this didn't take long at all. You can see how this operations is intersecting the previously bored hole.
Then after I got most of the material removed I switched to a convention 1/2" end mill and brought the piece to dimension.
There was also a bit more material to remove on the base of the part so i did that with the same end mill, being careful to try to blend this cut and the previous cut as closely as possible to the arc.
And here's a couple of pix of what the part looks like at this stage of the operations.
and
Back into the mill vise in yet another orientation. This time I milled away the material in order to form the feature that will become the joint between the this front frame and the rear frame.
Next the rest of the material that needed to be removed was done. Again I started with the 1/2" roughing end mill as shown.
Then i finished it with a conventional 4 flute end mill.
And here's the part laid on the drawing. I've shown it as compared with the drawing's isometric view. So far so good!
Back into the mill vise yet again, this time oriented to drill/tap for the drip oiler. That's a PM Research oiler that's threaded 3/16-40 in what they call their 'UST' thread. I ended threading the hole 3/16-40 METP, but I've also noted that you thread it 10-40 and that will also work. I always do use some thread compound prior to final assembly and I've not any problems with leaking either way.
Orienting in the mill vise again and checking to make sure that the part is straight in the vise.
Then centering the spindle over the cylinder hole and setting the DRO to 0/0.
Next drill and tapping 3 holes for 6-32 and drilling a 4th hole to provide a passage for oil from the drip oiler eventually thru to the cylinder liner.
Next tragedy struck. I was overconfident and entirely too aggressive trying to tap the 4 2-56 holes in the side of the part. Of course I managed to snap off the tap on the right off on the very last hole!
And here's the remaining bit of the tap buried in the Al.
After some weeping and gnashing of teeth, I decided that there's no way that I was going to remake this entire part, so I was determined to at least attempt a repair. I was pretty convinced that there was no way any sort of removal process was going to work given that there was nothing above the surface, I decided to attempt to mill it out. So I went after it with a 4 flute 1/8" carbide end mill and slowly progressed it and in fairly short order, I had a clean 1/8" hole through the part.
Then I enlarged the hole to .1875" with a larger end mill as shown.
I cut off a short plug of 3/16" Al rod and put a very slight chamfer on the leading edge of it just so it would start into the hole. I applied some Loctite 638 and pressed it into place using a 1/4" pin in the drill chuck, using the quill downfeed lever.
And here's what it looked like after pressing into place and letting it cure overnight.
This time, being quite careful, I drilled and tapped the repaired hole. This time successfully! I used a spring loaded tap follower and a very small tap wrench handle this time.
And here's the part with all the holes drilled and tapped, with the exception of the holes that will be added where the front and rear frames will be joined at, but those come later. You can see the repaired hole with the plug, but that will be hidden after painting and assembly.
Next I rounded the top using the same setup with the rotary table as I did for the water hopper. I think that this worked better as i could more easily tell where to begin and end the rotation.
And here's the part on the drawing after the operation to round the top was completed.
And the very last operation was to round the front corners of the base off using a rounding over end mill. This was a pretty simple thing, but I think it adds to the appearance.
And this part is now entirely done! This part really turned out to be much easier than I originally though it might be. There are a a LOT of different operations and setups, but none of them turn out to be that difficult.
I hope this was entertaining and at least a bit helpful!
Enjoy!
Mike
