Aluminum sand casting for Chenery Gnome Rotary

[albd5a]

Rainbowtronics in Germany can make an Electronic Ignition based on a Hall Effect and there’s a guy in UK who can do a coil system for the spark…. What did you use?
Back to the above: the break terminology was confusing to me. And what makes the Magneto itself spark at the correct time?

With respect to Tap and Die: for External threads is steel, max and min, what diameter to start with, Major Diameter or Pitch Diameter for say, 1”-32 UN ? Thanks.

 

[albd5a]

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

Jason or Richard, when cutting threads by way of single point threading, do you first start by cutting a groove at the starting point? Without a groove, it seems that the cutting tool will not get a proper bite, especially with steel… Without starting in a groove, also, it is taking a really long time for me to drill or cut holes through the steel for the steel cylinder liners. It’s taking hours to cut a 0.900… hole. Do you guys ever use drillbits in consecutive sizes or sharp for fluted End cutters?

 

[mole42]

No groove at the start, I usually relieve the end point of a thread if it’s up against a shoulder. With a suitable tool, the thread should start from the open end without trouble. I use a light cut to get going - maybe a 10 thou cut for starters - and finish with a couple of passes at the same setting. I’ve just made a special chuck to fit the Chenery cylinders onto the nose of my Myford S7 so that I can complete the transfer ports more easily. I’ll photograph it in a day or so so you can see what it does but the thread and register for the Myford spindle are all cut from a bored hole in the blank.

 

[mole42]

For the cylinders, I used a ¼” twist drill, followed by a ½” twist drill followed by a TCT boring bar to get close to the bore size. I then used a ¾” reamer to finish the bores. I know it’s not sized according to drawing, but I’m making the pistons to fit the bores so no matter.

 

[albd5a]

No groove at the start, I usually relieve the end point of a thread if it’s up against a shoulder. With a suitable tool, the thread should start from the open end without trouble. I use a light cut to get going - maybe a 10 thou cut for starters - and finish with a couple of passes at the same setting. I’ve just made a special chuck to fit the Chenery cylinders onto the nose of my Myford S7 so that I can complete the transfer ports more easily. I’ll photograph it in a day or so so you can see what it does but the thread and register for the Myford spindle are all cut from a bored hole in the blank.

I’m still a bit confused if you start at the open end, wouldn’t that mean you were going right to left as normal rather than the reverse threading? Or is the open end at the relief that you are mentioning? Thanks, Norman.

 

[albd5a]

For the cylinders, I used a ¼” twist drill, followed by a ½” twist drill followed by a TCT boring bar to get close to the bore size. I then used a ¾” reamer to finish the bores. I know it’s not sized according to drawing, but I’m making the pistons to fit the bores so no matter.

This is pretty much the order that I am going in also. Actually, I may have an additional drillbit size in between there. I am not using a reamer though; at least not yet. Turns out I will probably be making my pistons to fit these sleeves also. Still taking me a lot of time to drill/bore these holes in the steel. Maybe my steel is harder and I know that is one click above a toy. it’s a harbor freight 7 x 12” mini. Has no balls at all.

 

[albd5a]

I’m still a bit confused if you start at the open end, wouldn’t that mean you were going right to left as normal rather than the reverse threading? Or is the open end at the relief that you are mentioning? Thanks, Norman.

(Also, a tapered or straight Reamer?)

 

[Jasonb]

If doing the external thread towards the chuck just leave the end facing the tailstock untouched, but a runout groove before the shoulder. Same if cutting away from the chuck.

I'd drill to 20mm working up the sizes say 6, 12, 16 & 20 but your lathe may not be upto it

I don't ream bores but if I did then use a straight machine or chucking reamer not a tapered hand reamer.

 

[albd5a]

If doing the external thread towards the chuck just leave the end facing the tailstock untouched, but a runout groove before the shoulder. Same if cutting away from the chuck.

I'd drill to 20mm working up the sizes say 6, 12, 16 & 20 but your lathe may not be upto it

I don't ream bores but if I did then use a straight machine or chucking reamer not a tapered hand reamer.

I am thinking about an expanding reamer…. I am just over 0.75” bore now ( by mistake). How deep for runout groove? THANKS for your valuable help.