First steps into a Gnome

[mole42]

Oh, it's so slow sometimes - sometimes it seems like days of work produces only a few parts! Here's some more progress:

A series of photos showing the front gear housing; first roughing out the mounting flange, then boring out the internal gear case, reducing the outer diameter and tapering for the front flange, then boring the holes for 10BA mounting screws:

A couple of days later I'm making the 1/4" nuts to fasten the tappet guides into the tappet rod housing. I made a few spares! The first picture is parting off a nut from the 1/4" hex steel bar, the old screwdriver is to catch it. I had threaded the bar before making each nut, but I found it best to run the tap through by hand after each was parted off and de-burred:

Then I started making the tappet guides from 3/8" phosphor bronze. Each guide is 5/8" long, tapped, relieved and bored for reaming with a 0.156" reamer. I've started making a few, I'm doing them in three operations, the first is to relieve the inward end and tap it, then cut it off from the stock. After that the part is screwed into a jig in the lathe chuck to have the centre hole drilled and reamed, then the outer profile turned. I think I'll use another jig to hold the part while the 0.062" slot is cut in the lower end to recieve the cam follower.

There's gong to be much excitement soon because I bought a Myford Super 7 lathe last weekend. I've been using a Drummond Roundbed for about 40 years very successfully, but this little nine-cylinder engine has started to highlight some of the shortcomings. When I was offered a Super 7 that was made in the same year as I was born I tried very hard to talk myself out of it, but failed. It's dismantled in my garage at the moment, there was about 4 pints of oil swimming around on and in the machine so a day with spanners and the parts washer has been necessary.

That's all folks!

 

[mole42]

Here's a couple of photos I forgot to include, first one is a collection of parts, I made a couple more before work this morning:

And I've established a process for the first procedure, adjust the material length in the chuck, set the DRO zero on both axes, reduce the diameter to 0.25" for a length of 0.437" in three passes, reduce the outer part to 0.21" for a length of 0.21", then retract the tool and bring in the 1/4" die to cut the thread. Then saw off the part, reset the material in the chuck, and repeat. I'll continue until I have ten or eleven parts, it's good to practise!

Richard

 

[mole42]

A couple more photos of the tappet guides:

Lots of tiddlers.....

 

[Derek62]

Hi, I have now received my casting from Andrew and intend to start the build later next year, so I am following the build logs on here with interest.

I also have the series of articles published in the ME about 20 years ago re the building of this engine.

Just a thought about this design, seeing as how the whole engine rotates during running does the fact that although the casting is machined, could there be issues with out of balance and significant vibration as the casting/crankcase itself is not a complete machined concentric component as it is on other rotary designs?

Just wondering.....

Regards

Derek

 

[mole42]

One of the comments in the ME article is that the main parts of the engine are finish machined assembled on a mandrel, to ensure concentricity. There is so little of the casting left after machining that variations in density are unlikely to make a difference. If the cylinders and valve gear are machined to reasonable accuracy, there should be no balance issues. However, I haven't tried mine for balance yet.....!

Please do report the building of yours on here.

Richard

 

[mole42]

I've just noticed that I haven't posted anything on this thread for six months. That's what happens when you buy another lathe that needs fettling before use!

 

[Peter Twissell]

Not to worry.
I started a thread on another forum 13 years ago and I haven't posted there for over a year. I still haven't finished the engine!

 

[mole42]

Thanks Pete, it's good to know there's another incomplete set of engine parts somewhere!

I have been able, while setting up the new machine, to check the truth of the Gnome crankshaft between the main bearing journal and the front journal and I'm happy with it. Making the crankshaft in two halves on a machine which would't allow me to check the truth of the assembled unit gave me some anxiety.

 

[Werkstattkrabbe]

Hello together,
if I may say so, I'm looking forward to your posts on gnome, as I probably want to start with it this year.

Maybe briefly asked: where would I get good information for building the engine?

Greetings
Eric

 

[mole42]

Hi Eric, there's a fabulous series of articles in Model Engineer from January 2002 with many tips which I have found useful.

There's also a series of pictures on the web detailing the machining of most of the parts, here: Gnome - Google Drive

There's another here: Gnome Rotary Aero Engine which looks really useful.

Hope these help to get the creation going!
Richard