First steps into a Gnome

[mole42]

Here's a photo of progress so far on my build of Les Chenery's 'Gnome Monosoupape' engine. I've been mostly making jigs & fixtures but I've started on the crankshaft.

Richard

 

[mole42]

Some more progress. This is my solution to the fixed steady on the Roundbed lathe.

Yes, the steady travels with the saddle but since it is mostly used when using the tailstock, and for those instances where I need a slide, I can turn the cross slide through 90º. Not a perfect solution but it isn't easy to fix something to a Roundbed!

 

[mole42]

A little more work on the crankshaft today. Not all sweetness and light but another day should have it complete.....

Marking out the web:

Shaping the web, all done with a hacksaw and a 2nd cut flat file:

Finish shaping, blued so I can see what I'm filing....

This last photo shows the state of play at about 3pm today. The two parts are not screwed together and the slightly eccentric machining of the front part shows what happened when I thought the parts were firmly screwed together but they weren't.

The front journal ended up about 0.050" out of true and so I've removed the old centre drill at the front and, making sure that the two parts were firmly fastened together, drilled a new centre. The part is turned almost to size now, next it'll be fitted to the master chuck to complete the turning work.

 

[mole42]

Here's some photos of more work, mostly parts and moving the crank onwards, plus starting the crankcase:

Starting to set up the big end on the rotary table:

Truing up the crankcase casting:

Starting the crankcase boring:

Fitting into the jig:

 

[mole42]

Here's some photos from today. The big end is actually a write-off since I dialled the rotary table wrong, but it's a good exercise! First photo is centering up the rotary table on the lathe with the table fitted to a vertical slide:

Next drill the 3mm tapping hole for the 4BA thread:

Then open out the facing side for the reamer:

And then we ream that hole to size for the wrist pin:

Then use an end mill to sink the wrist pin head:

And this is how I measured the depth for the end milling:

 

[davidyat]

Are you using the Rotary Table on the lathe because you don't have a mill?

 

[mole42]

That's right. I have a Drummond Roundbed lathe, a US-built WW2 pillar drill and a Drummond hand shaper.

 

[davidyat]

You're a better man than I am, Gunga Din

 

[Joe]

You're a better man than I am, Gunga Din

Ditto that, all hail Mole42.

 

[Peter Twissell]

Good show sir!
I bought a milling machine a few years ago, but before that I did everything on my Drummond roundbed.
The roundbed is a wonderfully versatile machine. I tell people I can do anything on it... Eventually!

 

[Peter Twissell]

I note your steady in one of the earlier photos.
I have two steadys for my Roundbed.

The first is a travelling steady made by my grandfather. It fixes to one of the T slots in the saddle and has the conventional adjustable fingers to bear on the workpiece.

The second I mad myself to support the crankshaft for my big radial (which incidentally is made in two pieces, very much like yours, but mine has a keyed taper interface with a screw passing through it to pull the two parts together). The steady consists of two 3/8" steel plates, each with a semi-circular bore so that they clamp together around the bed. To these is bolted an aluminium plate which carries a ballrace (actually one of the main bearings for the engine for one operation and one of the big end bearings for another).

 

[mole42]

I was thinking about making a fixed steady out of a spare saddle that I have but I haven't needed to yet.

The steady I have made allows me to support either end of the crankshaft using different brass bushes - essentially I think I need to support it at one end or the other for drilling counterbores, or at the main bearing position to check for true running. My crank is probably a similar design to yours, the crankpin has a taper which is pulled into the tapered front web by a small screw. There's a 1/16" dowel to key the two together. The real fun has been drilling the oil passages!

 

[mole42]

Here's an update, not a lot of progress on the Monosoupape, but a bit more improvement to the machinery.....

This is the big-end, second attempt with the nine holes at the correct locations, the counterbore is done and the 4BA threads. It still needs finishing to size and boring the oil holes:

Next is an example of what happens when you read the instructions, but the instructions are wrong. I this case it's the blanks for the con-rods which the magazine article suggests should be cut from ³⁄₈" x ¼" mild steel, 1¾" long. So I cut ten of them, only to realise that the 0.156" diameter wrist pin and gudgeon pin holes are 1.687" apart which is slightly difficult to fit into a 1.750" blank. New material has been sourced and the blanks will be cut a little longer:

Then a pal suggested that a 4-jaw self-centering chuck might be a useful addition to my lathe. So I went and bought one - a nice 4"example from HBM - the same company that made the 3-jaw that I have been using for about 10 years. Of course, it needed a backplate, so I got a lovely cast-iron blank and machined it all over to fit the 4-jaw to my Drummond lathe. I was very pleased to achive only 0.0005" run-out on first checking. Hopefully I can improve that but it may be the best that this chuck can do. Anyway, it's pretty good.

 

[Figor]

Very creative fixtures. Nice work.

 

[mole42]

Some more work today, made the gudgeon pins and the aluminium end slippers as well as starting to machine the conrods.

Reducing the 4mm aluminium bar to ¹⁄₁₆" - all done in one cut:

Then the gudgeon pins are tapped onto the end:

Before being sawn off for final finishing:

I only made 20 of these:

But they are all fitted to the silver steel gudgeon pins:

Then some work on the conrods, EN3 which has been normalised (and will be case-hardened before use):

Then the holes were reamed to ⁵⁄₃₂" to match the gudgeon pins and wrist pins:

There's a scrapper in there, but I'll probably finish it to test the jig setup...

 

[methuselah1]

Richard, your progress is astonishing! You will very soon have caught me up!

However, a question... I have long suspected that Les had a friend with a cyanide bath, as many of his designs use case hardening in (seemingly) unnecessary places. Given the laws of roots and squares, never mind the possibility of distortion, doing it with a blowtorch and kasenit, do you suppose the conrods need doing? Surely if the gudgeon pins were hardened, that would do the trick?

What do you think?

-Andrew

 

[mole42]

Hmmmm. I don't think I'll be catching you up anytime soon Andrew! You are at least nine cylinders in front of me....and I do seem to spend some of my time scrapping bits of the job. And currently a lot more trying to fit a DRO to my Roundbed!

I'm not sure about the case hardening. If Les hadn't specified it, I'd have oil hardened the wrist & gudgeon pins as you suggest and left the conrod as machined. As it stands, I have a friend with a small oven in which I can do the case hardening evenly (four hours at 650ºC) so I'll probably go with the hardening as Les suggests. Watch this space!

Richard

 

[methuselah1]

Well, do keep me posted, mate! I did win a muffle from the University (it's lagged with white asbestos) but I don't want to fire it up 'cos of my employment situation, and the 'leccy cost.

Those cylinders will drive you mad. You'll need a jig, and lots of patience. Some music, prozac and a comfy seat. Make spare cylinders- you won't shift a busted drill...

Andrew

 

[mole42]

Patience I have. This project is primarily to improve my machining skills and it seems to be improving my machine as well. I plan to make some spares, not just spare cylinders, and I’ve yet to dare fully machine the casting I bought from you. I’ve been joking that this is a 5-year project but that might be a little ambitious!

Richard

 

[mole42]

After a brief pause to install the DRO on my lathe (seperate thread) I was back to making parts for the Gnome today. Not much, but I found that because the specified threads are all 32 tpi but on larger diameters, I was having to calculate the sizes.....

Here's the crank bearing retaining nut (smaller one) and the main shaft retaining nut.

And then, because i was in the mood for more single-point thread cutting, I put the thread on the end of the cam bushing:

Onwards!