And still making good progress, I continued on with the prop bolt stubs today.
First I marked out the bolts with some 18mm masking tape.
Then cut them off with the cordless angle grinder, the cutoff wheel has seen better days!
As long as I didn't cut too close to the masking tape there was plenty to finish up in the lathe.
Not shown but I drilled out the centers to 5.5mm in the lathe. I started the internal thread of each hole before removing it from the lathe...
Then set up a vice and collet holder on the CNC bed and hand tapped each hole. The high tensile steel is really hard to tap and work hardens easily. I would have preferred to have drilled the hole out to 5.7mm (75% of the thread) to make the tapping go smoother, but since I couldn't find a drill bit around, 5.5mm had to do. Eventually got them all threaded 1/4-28.
I put them on a threaded fixture in the lathe and turned them to length. I also set up a 1/4" drill in the tail stock and counterbored the front.
The bolts fit!
Aluminium is nasty, especially the lower grades because they are so gummy! I have broken a few quality taps in aluminium, mostly after using them in steel. I try to keep a set dedicated to aluminium so they stay nice and sharp.
I continued making the prop hub stubs today and almost got them finished. I made them a press fit in a hole I had reamed with a 3/8" reamer as a test. Even doing that they are bit tight in the actual parts. I think I may turn them down slightly more.
I also set up the two prop hubs and spinner mounts in the CNC and milled the holes out to 9.4mm ready for reaming.
Once I had the holes CNC'ed I shifted the whole mdf jig over to the drill press and ran the 3/8" machine reamer through all the holes,
Very happy with results.
I haven't pressed the stubs into place yet. I think they need to be reduced in size ever so slightly and I also want to alodine the hub. I might do a trial fit of the hub onto the crankshaft first, before alodining anything.
While I had the CNC running I cut a couple of bits of 10mm acrylic,
And stuck them together with superglue. some 1/8" drill bits kept everything lined up while the glue set (really fast)
And I have a jig for drilling the holes for bolting this onto the front of the crankcase.
I decided to fit the prop bolt stubs into their hubs and fitted a hub onto a crankshaft. I will have to take them out again sometime to alodine everything but checking that everything fits is important.
I also drilled and tapped the retaining bolts on the starter/ignition mounting brackets.
Stubs come through the spinner mount nicely.
And moving into the realm of 3D printing, A friend printed the ignition sensor holders on his 3D printer. Thanks Mark!
And with some hall effect sensors sitting in place, eventually they will be epoxied in place. Which reminds me, I need to check how well epoxy bonds to PLA and ABS plastics!
Three versions (so far) of the ignition sensor holders, it is taking some time to get these exactly right, and I'm still not on the final version
More slow progress...
First up, a test fitting of another updated version of the ignition sensor bracket on the engine. Looking good but the bad news is that I might have to make these from phenolic rather than PLA. The 3D printed plastic gets soft at a far to low temperature to be much practical use. I may test an engine with PLA brackets but I don't count on them lasting.
I have been thinking about this next little job for quite some time. The flapperon bearings have a 4mm internal hole but I really wanted to use aircraft hardware to hold these on. Most of the M4 metric bolts I have been able to source have been closer to 3.9mm, leaving a lot of play when inserted into the bearings. When things are clamped up tight it might not have been so much of a problem, but still..
There is also the unknown quality issue.
I made this fixture in the lathe for reaming the 4mm hole in the bearings out to 4.15-4.20mm. I started by turning up a cap (in the previous and next pictures) and then making this externally threaded holder with a counterbore for locating the bearing. I had machined the bore to 12mm to fit the bearing but when I used a milling cutter in the tailstock to flatten the bottom of the bore, things went wrong. The hole ended up 0.7mm oversize! I had the use a piece of heatshrink on the outside of bearing to center it for reaming. Turned out okay in the end.
With the cap screwed tightly in place, the ball part of the bearing was clamped from each side and I could ream the hole. The reamer is made from a broken 3/16" solid carbide router cutter that I ground the diameter down to slightly under 4.2mm. I used the diamond wheel the grind a bevel on the end to act as the cutting edge. The holes in the first few bearings came out a little bigger than I wanted at around 4.2mm, but after a few tweaks to the homemade reamer, I got the fit much closer to the bolt size. Having a few spare bearings helps.
I pressed out the previous bearings from the flap levers ready for installing the new resized bearings. I have some polishing to do first.