Aluminum sand casting for Chenery Gnome Rotary

[GreenTwin]

I don't have an expertise in threading holes like that, but I can say that 356 aluminum that has gone through the 2-step T-6 tempering process is much harder and easier to drill/tap without loading up the bit.
Hopefully you can work out a solution.
.

 

[albd5a]

I don't have an expertise in threading holes like that, but I can say that 356 aluminum that has gone through the 2-step T-6 tempering process is much harder and easier to drill/tap without loading up the bit.
Hopefully you can work out a solution.
.

Thank you Twin

 

[albd5a]

Thank you Twin

Can you describe your 2-step T6 tempering process for Aluminum? Thanks.

 

[GreenTwin]

I put the aluminum heat treating info that I use here:

https://www.homemodelenginemachinist.com/threads/heat-treating-aluminum-alloy.36697/

.

 

[Jasonb]

If you can sort out your rubbing threading tool then I would cut that one oversize, not really critical what the diameter is as the mating cylinder sleeve will have to be single poinyt cut to match, just thread until you have a full depth form. If the thread has cut out of line with the hole then it will also not be true to the top face of the boss so you are not going to get a good fixing as it is.

Regarding the liner threads, using a die is not going to get you close to the shoulder ( no big undercut like the crankcase end) so it would be better to single point them to the sizes given on the drawings as going larger will affect the fin depth on the cylinder and will probably need the lower part of the cylinder increasing in diameter to accommodate the larger thread if you use that. Again a tap won't get you close enough to the shoulder inside the cylinder so it needs single pointing.

When it comes to the bottom end of the liner I would still suggest you single point it to say 80% thread depth and then run your die down it to get the final profile. This will ensure the thread is concentric and square to the liner. A thread that size in a tailstock die holder or worse a handheld diestock is unlikely to cut 100% true.

This is a cylinder that has been turned, bored and threaded all at one setting so everything is true and concentric and is the best way to get an accurate part which should lead to a running engine.

 

[albd5a]

If you can sort out your rubbing threading tool then I would cut that one oversize, not really critical what the diameter is as the mating cylinder sleeve will have to be single poinyt cut to match, just thread until you have a full depth form. If the thread has cut out of line with the hole then it will also not be true to the top face of the boss so you are not going to get a good fixing as it is.

Regarding the liner threads, using a die is not going to get you close to the shoulder ( no big undercut like the crankcase end) so it would be better to single point them to the sizes given on the drawings as going larger will affect the fin depth on the cylinder and will probably need the lower part of the cylinder increasing in diameter to accommodate the larger thread if you use that. Again a tap won't get you close enough to the shoulder inside the cylinder so it needs single pointing.

When it comes to the bottom end of the liner I would still suggest you single point it to say 80% thread depth and then run your die down it to get the final profile. This will ensure the thread is concentric and square to the liner. A thread that size in a tailstock die holder or worse a handheld diestock is unlikely to cut 100% true.

This is a cylinder that has been turned, bored and threaded all at one setting so everything is true and concentric and is the best way to get an accurate part which should lead to a running engine.

Thank you Jason. This is what I needed to know. Curious: in your photo, did you ‘single point’ thread here in Reverse? How many tpi is this? Looks extremely clean!

 

[Jasonb]

Yes I run the lathe in reverse which means you can go at several 100rpm and not have to react quickly to stop the feed. Best with a bolt on chuck rather than a screw on.

Pitch is 0.75mm x 21mm diameter so not far off your 32tpi. in free cutting steel.

It's one of two engines Glow & diesel scaled up from 3.5cc drawings to 5cc, crankcases and front ends cut from solid, saves all that mucking about with castings

 

[albd5a]

Jason, beautiful engines.

 

[albd5a]

I finished machining the threaded cylinder bosses on my 1/5 scale Chenery, Gnome Mono Rotary engine, cast Aluminum crankcase. The threads are good and everything is true and concentric. This was accomplished using my second, back up casting. The first casting is a near perfect aluminum (shiny, no porosities), but not 100% true and two threaded bosses are deficient ( but can / will be re-threaded with a 1-1/16”- 28 Die). I am glad this is done as the casting has a limited availability.
Next I will start the steel cylinder liners need to somehow make these fit into these finished aluminum bosses…. Merry Christmas to everyone.