Aluminum sand casting for Chenery Gnome Rotary

[mole42]

Here's the thread about my engine: https://www.homemodelenginemachinist.com/threads/first-steps-into-a-gnome.33644/

I haven't a mill, so everything gets done on the lathe. Looking at your mill set-up, I think I'd go for the tap rather than single-point, it looks more rigid.

 

[albd5a]

Richard, thanks for all of your help. That build link is a lifesaver. Did you finish the Rotary engine? I believe the link ends short of completion. Q: that counterbored area in the cylinder boss, at top of the threads, can be done after threading the threads, correct? (For cylinder liner fuel intake).

 

[mole42]

No, I haven't finished the engine yet. I bought a Myford Super 7 that needed some work to get into shape and I rebuilt my 1972 Triumph Stag which took a lot of my time away from the engine. This year I'm making a new crankshaft because the first one was 10 thou out of true on the camshaft spindle and although I tried to true it, I decided that starting again was the best way. The crankcase and front and rear parts are done, as are a lot of the smaller parts, just now waiting for the crankshaft to be finished.

Yes, the counterbore in the cylinder boss was machined after the threading. That's when I made the dummy cylinder so that I could check each bore after completion to make sure is fitted properly.

I heartily recommend the seies of articles in Model Engineer about the building of this engine. There are several useful tools and jigs mentioned in there as well as techniques to help with some of the trickier parts. The articles start in January 2002.

 

[albd5a]

No, I haven't finished the engine yet. I bought a Myford Super 7 that needed some work to get into shape and I rebuilt my 1972 Triumph Stag which took a lot of my time away from the engine. This year I'm making a new crankshaft because the first one was 10 thou out of true on the camshaft spindle and although I tried to true it, I decided that starting again was the best way. The crankcase and front and rear parts are done, as are a lot of the smaller parts, just now waiting for the crankshaft to be finished.

Yes, the counterbore in the cylinder boss was machined after the threading. That's when I made the dummy cylinder so that I could check each bore after completion to make sure is fitted properly.

I heartily recommend the seies of articles in Model Engineer about the building of this engine. There are several useful tools and jigs mentioned in there as well as techniques to help with some of the trickier parts. The articles start in January 2002.

Yes, although I’m in the USA, I managed to track the ME’s down; I have them. I just now tried ‘Single point ‘ thread an aluminum cylinder boss: I really trued up the casting and used an Axial gauge…. Not as scary as I thought until my threads aren’t getting deeper. I’m using a 60* cutting but should perhaps be using my 55* thread cutter? Also I figured I could use my 1”-32 Tap as a tester… started threading through the entire height of the boss.

 

[albd5a]

Yes, although I’m in the USA, I managed to track the ME’s down; I have them. I just now tried ‘Single point ‘ thread an aluminum cylinder boss: I really trued up the casting and used an Axial gauge…. Not as scary as I thought until my threads aren’t getting deeper. I’m using a 60* cutting but should perhaps be using my 55* thread cutter? Also I figured I could use my 1”-32 Tap as a tester… started threading through the entire height of the boss.

 

[mole42]

You need a 55º tool - the ME thread won't be too happy with 60º and won't form properly. It's worth checking the angle of the 1" x 32 tap that you have to see if that's 55º.

In your video of the thread too going in, I feel that the tool spring is not helping you - ISTR using a very fine cutting depth when I did mine, perhaps 0.001" per pass.

This page is useful for information about the ME threads: https://britishfasteners.com/threads-me

 

[Jasonb]

If you are going to single point the cylinders then 60 or 55 won't really matter provide you use the same for both. So will depend on what form your tap is now that you have chased the thread with it.

Video looks and sounds like the bottom edge of the tool is rubbing against the work and that is what is pushing it away not spring.

I would also take a skim off the top of each boss at the same setting as the threading which will ensure the face is true to the thread