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

 

[KellisRJ]

I know next to nothing, but what depth of cut are you using? Former aviator, cool engine to be building!

Ron

 

[albd5a]

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

Richard, I am learning a lot here. Which is great but, I do not want it to be at the expense of one of my precious castings.…! Yes, I chased the single point threading with a 1/32 tap. I’ve discovered that even though the tap feels like it’s going in square and straight When rotated and supported by hand; it’s probably not. I finally had the sense to mount the tap at one end with a live center, and then it negotiated straight as an arrow. I’ve also learned how aggressive a new large quality tap can be where did all these giant chips come from? I thought I just single point threaded it! Yes, the spring phenomenon with my cutter was actually visible and as the other person mentioned, I think maybe the back or bottom of the cutter is rubbing against the side of the work. Something continuously is making my leave crash. It’s rubbing it putting the brakes on… I’ve spent way too much time trying to do the single point threading on only one cylinder boss . I probably need to reposition the cutter go to the 55° and use a compound angle for the internal threading… When you look on a tap chart for the drill to be used for tapping 1–32 it says to use a 15/16 drill , is that size the same as the minor diameter? I don’t think it is. And yes, I do have the engineers handbook… also, I believe my depth of cut will be the difference between my major diameter and minor diameters. Also, I am still confused of where these threads are to be placed within the casting (crankcase casting bosses ) Chenery shows that the threads are 0.187 inches deep… Not sure if that means starting at the top going in or after going in 0.187 inches? Also, I believe I do understand the holes configuration, which serves as an intake valve for each cylinder…

 

[albd5a]

Richard, I am learning a lot here. Which is great but, I do not want it to be at the expense of one of my precious castings.…! Yes, I chased the single point threading with a 1/32 tap. I’ve discovered that even though the tap feels like it’s going in square and straight When rotated and supported by hand; it’s probably not. I finally had the sense to mount the tap at one end with a live center, and then it negotiated straight as an arrow. I’ve also learned how aggressive a new large quality tap can be where did all these giant chips come from? I thought I just single point threaded it! Yes, the spring phenomenon with my cutter was actually visible and as the other person mentioned, I think maybe the back or bottom of the cutter is rubbing against the side of the work. Something continuously is making my leave crash. It’s rubbing it putting the brakes on… I’ve spent way too much time trying to do the single point threading on only one cylinder boss . I probably need to reposition the cutter go to the 55° and use a compound angle for the internal threading… When you look on a tap chart for the drill to be used for tapping 1–32 it says to use a 15/16 drill , is that size the same as the minor diameter? I don’t think it is. And yes, I do have the engineers handbook… also, I believe my depth of cut will be the difference between my major diameter and minor diameters. Also, I am still confused of where these threads are to be placed within the casting (crankcase casting bosses ) Chenery shows that the threads are 0.187 inches deep… Not sure if that means starting at the top going in or after going in 0.187 inches? Also, I believe I do understand the holes configuration, which serves as an intake valve for each cylinder…

…chased the single point threading with a 1”-32 Tap…

 

[Jasonb]

Your tap is 1" x 32NS from the photo so that is a 60deg thread form so stick with that and don't change to 55deg

Typical tapping size for a 32tpi 60deg thread is 1/32" less than the nominal so you would start with a 31/32" hole.

Your depth of cut will depend slightly on the grind of your tool and any tip radius but approx 1/64" or 0.016". Should be able to do that in two passes of 5thou, one of 3 thou, one of 2 thou and then a spring pass at the same last setting.

For such a shallow thread and in ali I would not worry about setting the topslide at an angle.

 

[Jasonb]

Looking at the drawing in the mag I read it as thread 1x 32" and then open up the top to 1" dia x 0.187 deep.

Thread will need to go in at least 1/2" from top of boss as you need to be able to screw the liner in until the flange seats on teh crankcas boss.

 

[albd5a]

Looking at the drawing in the mag I read it as thread 1x 32" and then open up the top to 1" dia x 0.187 deep.

Thread will need to go in at least 1/2" from top of boss as you need to be able to screw the liner in until the flange seats on teh crankcas boss.

Thank you. You’ve saved me hours of work.

 

[albd5a]

Thank you. You’ve saved me hours of work.

Only two more cylinder boss threads to do on this aluminum casting. I am not ‘single point’ threading at all now; just using the 1”-32 tap. The threads look more perfect and consistent. A lot of cutting fluid, live center at tailstock, backing off every couple of turns and using a wrench (spanner). Still gets real tight toward the end but nice threads. I will turn the steel cylinder sleeves in a few days- guessing but will probably use a round Die for those threads….

 

[albd5a]

Thank you. You’ve saved me hours of work.

Only two more cylinder boss threads to do on this aluminum casting. I am not ‘single point’ threading at all now; just using the 1”-32 tap. The threads look more perfect and consistent. A lot of cutting fluid, live center at tailstock, backing off every couple of turns and using a wrench (spanner). Still gets real tight toward the end but nice threads. I will turn the steel cylinder sleeves in a few days- guessing but will probably use a round Die for those threads….

 

[albd5a]

Only two more cylinder boss threads to do on this aluminum casting. I am not ‘single point’ threading at all now; just using the 1”-32 tap. The threads look more perfect and consistent. A lot of cutting fluid, live center at tailstock, backing off every couple of turns and using a wrench (spanner). Still gets real tight toward the end but nice threads. I will turn the steel cylinder sleeves in a few days- guessing but will probably use a round Die for those threads….

Oh, I have round bar steel, 1.25” O.D., #4130 steel alloy on the way.

 

[albd5a]

Oh, I have round bar steel, 1.25” O.D., #4130 steel alloy on the way.

After thinking about the steel sleeve fabrications, I’ve realized that the threads located at the top of the sleeve structure are not really 1”-32 where I could use a round Die conventionally. Or could I make those threads the same 1”-32 via my Die procedure? That is the .920-32 tpi changed to 1”-32 ? (Or Single Point procedure to specs as drawn by Chenery).

 

[albd5a]

Have my first mistake (that I know of). On my second to last threading, I was more concerned about regaining concentricity, that I probably distorted the round hole that I had. If I had just left the hole alone and tapped it, the threads would’ve been perfect. Here, you can see that part of the wall is unthreaded!… There’s probably a name for this. Re-tapped it with a Chinese tap thinking maybe the spec. would be a little bit larger but still there’s an area which is not threaded; although it would probably still be tight. What do you think?

 

[GreenTwin]

Did you drop the hot casting in cold water?
That makes it a bit harder, and easier to cut.
You can go the full temper method to approximate T-6 if you want full hardness.
.

 

[albd5a]

Did you drop the hot casting in cold water?
That makes it a bit harder, and easier to cut.
You can go the full temper method to approximate T-6 if you want full hardness.
.

No, I did not drop it in any water at any time. I let it cool on its own completely, which took just over two hours. The aluminum is machining, so far, perfectly there are no porosities or voids anywhere. But that information is good to know; thanks. Did you see the photo where I am showing that I do not have thread penetration into part of the wall of the casting because I did not thread the hole that I had rather, I tried to make it concentric with everything else and it backfired… Again, this was the second to last one. I’m doing the last one right now.