Workshop time is getting a bit more scarce now that work is getting busy, and the weeds are growing in the garden, but I made some progress over the past couple of weekends.
When we left off last time, I had milled down a couple of bits of Al on the cross-slide table to set the base at the correct height. Just to make sure, I check will a drill bit that fits the bearing hole:
and it goes in nicely, so we're good
Note how little clearance I have at the back of the lathe with the base mounted this way; about 1/4"!
I have to bore each bearing out individually before I have enough clearance for the boring bar, and I wanted to do this with the bearings in situ, so the 1" boring head goes into the lathe spindle, and I bore to about 15/32":
then flip the base around, indicate it in using a parallel in the bearing slots, then open up the other bearing:
Now we're ready for line boring.
This didn't go as smoothly as I hoped
I was getting a lot of chatter on the left bearing but not the right one (which I don't understand; the behavior of the boring bar shouldn't really be affected by the position of the carriage), so I opened up the right one to about 0.494" (leaving enough for reaming), then flipped the boring bar around to try it the other way. Chatter was still terrible:
but then I wised up and reduced the RPMs, and things settled down. I wish at this point that I'd been brave enough to just take the bearings to final size by line boring; accurate adjustments of the boring bit were pretty easy with an indicator in place:
but no, I chickened out and got out the reamer:
which reamed slightly oversize, and left a poor finish
but neither problem is a showstopper, given that these bearings are adjustable, and will bed in during use. At least a bit of test bar fits nicely:
Now I could finish the bearing faces in the 4-jaw, leaving a nice boss in the middle:
but at this point (it was getting late) I made another mistake, and proceeded to put a radius on the outside face of one of the bearings (I guess I was all eager to use the form tool just like the conrod bearings). That face shouldn't have a big radius
Luckily it's the one behind the flywheel, so will be mostly hidden. Don't tell anyone.
So now that I had bearings, I pulled out my test crankshaft hoping to get some parts running. The journal needed cleaning up, so I made some fixtures to hold the crankshaft to rotate around the journal axis:
The bandsaw is a quick way to cut the slot, provided you're careful to set the part at the right angle, and stop it when it breaks though to the appropriate hole:
So we have these, which are mirror images of each other:
I took care to align the journal. That indicator and Starrett base were $5 at an estate sale this weekend; I just had to clean off the sawdust
Well, after setting this up between centers on the lathe and putting and indicator on the journal, things were all over the place; I was getting runout of about 0.006", which changed when I tightened up the live center, or even put a bit of pressure on the part
so I tried some spacers between the fixtures and the throws, and that helped a bit:
but I wasn't able to get the runout below a few thou. One idea I had to improve these fixtures was to actually drill and ream holes through where the dead center and live center sit, say 3/8", and make two bits of bar center-drilled in one end, and long enough to reach the throws; that would ensure that the tailstock pressure bears on the journal, to avoid distortion of the part. However, it would make turning the outsides of the throws impossible.
I did manage to clean up the insides of the throws with a tool ground for the purpose, and clean up the journal of solder bits reasonably well:
at least well enough to do a test fit with a conrod:
But it was bad news here as well; when rotating the crankshaft, the other end of the conrod wobbles around by about 0.03", so the journal is obviously misaligned. Good thing this is just a test crankshaft
After all these trials with a silver-soldered crankshaft, I'm considering the Loctite and pins method. But I I'll try doing the second journal on this shaft with silver solder for practice, and to see if I can improve on the alignment.
Simon