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CriCri MC-15 in NZ

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MadRocketScientist

Well-Known Member
Joined
May 16, 2009
Messages
1,642
Location
Canterbury, New Zealand, Earth, Milky Way Galaxy.
And still making good progress, I continued on with the prop bolt stubs today.
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First I marked out the bolts with some 18mm masking tape.
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Then cut them off with the cordless angle grinder, the cutoff wheel has seen better days!
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As long as I didn't cut too close to the masking tape there was plenty to finish up in the lathe.
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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...
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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.
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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.
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The bolts fit!
 

MadRocketScientist

Well-Known Member
Joined
May 16, 2009
Messages
1,642
Location
Canterbury, New Zealand, Earth, Milky Way Galaxy.
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.

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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.
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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,
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Very happy with results.
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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.
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While I had the CNC running I cut a couple of bits of 10mm acrylic,
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And stuck them together with superglue. some 1/8" drill bits kept everything lined up while the glue set (really fast)
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And I have a jig for drilling the holes for bolting this onto the front of the crankcase.
 

MadRocketScientist

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Joined
May 16, 2009
Messages
1,642
Location
Canterbury, New Zealand, Earth, Milky Way Galaxy.
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.
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Looking good
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I also drilled and tapped the retaining bolts on the starter/ignition mounting brackets.
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Stubs come through the spinner mount nicely.
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And moving into the realm of 3D printing, A friend printed the ignition sensor holders on his 3D printer. Thanks Mark!
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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!
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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 :eek::D
 

MadRocketScientist

Well-Known Member
Joined
May 16, 2009
Messages
1,642
Location
Canterbury, New Zealand, Earth, Milky Way Galaxy.
More slow progress...
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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.
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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.
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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!:confused::confused: I had the use a piece of heatshrink on the outside of bearing to center it for reaming. Turned out okay in the end.
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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.
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I pressed out the previous bearings from the flap levers ready for installing the new resized bearings. I have some polishing to do first.
 

BJC

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HBA Supporter
Joined
Oct 7, 2013
Messages
11,774
Location
97FL, Florida, USA
Mad:

When you complete your airplane, please do not fly it; it deserves to be in a museum devoted to individual craftsmanship.


BJC
 
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