Where were we? Ah yes, all the bearings had been fitted to their square holes, but still needed their tapers and respective wedges.
And to fit the wedges on the conrods, I had to make some square holes. I opened up the existing 3/16" hole with a 1/8" end mill followed by a 3/32" end mill, to reduce the amount of filing required:
watching a couple of digital indicators to keep the holes to size. Then I decided to use the traditional approach, filing! To help keep things square, I milled up a couple of filing guides from some gauge plate (O-1 hardening):
then heated to cherry red, and quenched in water (for some reason I have better luck hardening in water than oil; maybe I just need a bigger oil pot). What I didn't expect was the distortion; the slots pinched in by about 0.005", which required some tedious stoning to make these fit to the conrods. I should have left a bridge piece at the top.
So now I could fit these to the conrods, using a machinists clamp to hold them in place while getting things set up in the vise:
I had to stock up on some files:
You'd think that Nicholson would have a catolog that tells you the dimensions of each file, right? So you can get a file that fits into a 3/16" x 5/16" hole? Not so!
The catalogue that I managed to find (with some trouble: Nicholoson don't appear to have a web site) only gives length, not width or thickness. So I took my business to Grobet who have a better cataglogue, and found some of their nice pillar files on eBay.
I found that wine (actually beer
) corks make good small file handles:
and after some tedious filing, marking up and holding up the light, we get far enough to insert what will become a wedge:
The wedges started life as some bits of 3/16" 1018 bar, with each end mill down, then turned and threaded:
by holding in the 4-jaw chuck, centering on a punch mark on the end:
These wedges have a 4° taper, so we need a wedge to get matching angles. With the help of some trig I use the "two parallels separated by a known distance" technique and use it to mill a bit of scrap Ally:
which is then stamped with the angle for posterity. Here are the bits, with some marks to make sure I cut the angles in the right directions:
The two wedges are easily done in one go, sitting on the 4° wedge:
Feeling please with myself, I then proceeded to mill one of the bearings undersized
and the other with only barely enough on the angled face. At assembly, the bearings should be snug with plenty of travel left in the wedge for later wear adjustment, but the wedge on my better bearing is at mid-travel already, and on the bad bearing it runs out of travel
I'll rescue the bad one by silver-soldering on a bit of material and re-milling the angle, but I can't do that now because it'll melt the soft solder.
So now it was time to drill the hole in the conrod bearings. They were marked up in situ, measuring from the crosshead hole to get the right throw. The hole center is pretty close to the solder joint, which is good. After a bit of thought I decided to drill the bearings in situ, holding the conrods in the vise, hoping that this would lead to better alignment. With things set up I checked for alignment in two axes; the first:
looks OK, but the second not so good, probably because I'm clamping down on imprecise faces on the conrod big end:
A bit of shimming of the vise fixed that:
and now I could drill in stages:
leaving a bit to be taken off by boring to make sure the hole is straight:
before reaming at low speed:
Both done!
After some trimming of the flanges, I rounded the corners:
and we're left with this little lot:
I plan to mount the bearings on an expanding mandrel to skim off the surface and leave a bit of a raised ring in the middle to avoid the main bearing surfaces from contacting the crank throws, so I haven't yet cleaned up the surfaces.
While mucking around with bearings, I also finished off the crosshead bearings. They take a wedge too, so that required another angle, 14° this time, again cut with the help of some trig. It was used to mill down some bits of 1018 steel:
and to cut the angle in the crosshead bearings, so we can have another fun fitting session:
That wedge could have a little more leeway, but it's close:
Both done:
These bearings will also get a skim to take them to final width. I presume they should stick out a tiny bit from the sides of the crosshead, to keep the forks from marring the crosshead sides?
Once I've skimmed the bearing faces, they can be separated by melting the solder, any required remediation done, and then the mating faces milled a tiny bit to create a gap.
And when the bearings are complete, I can get back to the crankshaft and actually put some moving parts together
Simon