First steps into a Gnome

[mole42]

Today brings some very satisfying work. The keyway has been let into the camshaft bush, the small gear for the camshaft drive was machined and fitted to the bush and then screwed together. I started truing up the rear crankcase bearing housing, at over 3" diameter it really does test the drivetrain of my lathe. I can only take small cuts, and the blank is 90mm diameter, to be reduced to 3¼" as a first operation. Perhaps it is time to invest in a new flat drivebelt!

Here's the cam bush in my Drummond shaper with the ¹⁄₁₆" keyway cutter. The cutter is centered on the workpiece using a DTI to find the largest diameter position:

And here's the finished keyway. A slight pickup on the thread, but I only caught it once. There's a small amount of flash in the keyway at the end furthest from the screw thread, I'll grind the key steel a little to clear that:

I made a small fixture to help machine the gear. It's an offcut of hex bar bored to be a tight fit on the gear which is Loctited in while the boss is cut away and the hole bored for the 32tpi thread. Heating the whole with a blowtorch helps the Loctite to let go afterwards:

This is the gear after it's been machined, ready to fit to the cam bushing:

And here's it's fitted to the bushing and the bush end trued to match the gear:

Next was to mount the 4kg steel bar into the lathe to allow me to start machining the crankcase front and rear housings. The bar was held in a four-jaw self-centering chuck and the ends centre-drilled. After that it was time to start cutting down to size, but as I bought a piece of steel long enough to make both the front and rear housings, at some point I'll have to part the two pieces. I'm not looking forward to that, but maybe I'll find a pal with a power hacksaw.

I machined the bar end to fit the cast crankcase, and had to take a picture of the trial fit of the crankcase on the bar end:

A lovely snug fit, now there's just several hours work to do on the bearing housing....

Richard

 

[stevehuckss396]

Nice work.

 

[mole42]

I've been working on the main bearing housing at the rear of the crankcase. I bought a 90mm diameter piece of EN1 weighing over 4kg to make the front and rear and has taken a couple of days so far to reduce it to somewhat near the finished size. This is the first part, the flange is close to size and I'm reducing the rest of the diameter:

A pal helped parting off the two pieces although we couldn't part to full depth so I ended up using a hacksaw - 15 minutes of arm-ache! The front part was set up in the 4-jaw to centre the register and ensure the flange was running true, then the bore was made to a little under 0.75".

I have a reamer that is slightly less than ¾" that was used to size the centre hole, and my master chuck has a ¾" bore so a piece of silver steel was turned to a tight fit into the main bearing housing bore:

The mandrel was firmly fixed into the workpiece with some Loctite which works well - except that at one point the work got hot enough for the Loctite to break down and the part stopped turning! Note to self: take lighter cuts and go slowly. This picture shows the awesome size of the blank:

Several hours later the part is beginning to look something like the drawing. Here you can see it resting on the crankcase, the mounting flange is finished to size but there's still a long way to go to bring the outer diameter to the working dimesnions:

And this is the state of play today, almost to size but I'll leave that until after the bore is done for the bearings. There's also a fearsome 32 tpi internal thread to cut in that front boss:

Lessons for the next part are to machine the main body before working on the mounting flange since that flange is 3¼" diameter and I can't get the saddle of my lathe under it. I need to be able to machine the bulk of the work, then turn it around and machine the flange last so that it doesn't get in the way!

 

[methuselah1]

That's lovely work, Richard! Those little hand shapers are great for keyway cutting up to a flange, aren't they? I sometimes wish I'd kept the little fella.

I had been away from home for about three years, and I'd forgotten how much I'd actually done on the Gnome. I found a bag of gears yesterday, and thought my luck was in- turned out they were ones I'd cut for my Anzani "Y" instead... Oh well!

 

[methuselah1]

I also found the conrods and the pistons, also (different design) enough tiny cylinders to build not just a Whittle V8, but also a four of the same pattern!!

 

[mole42]

I'm glad you didn't keep the shaper, Andrew, it's done some great work over the years. I still haven't finished the feed bar though, never needed it!

I chickened out and bought the gears for the Gnome but that was quite a shock to the bank balance. I figured it's going to take long enough without learning how to hob gears on a Roundbed lathe.....

 

[methuselah1]

I'm glad you've enjoyed the "J" type, Richard! I bought it from Ted Hartwell, an early M.E.W contributor, in Poole. Dunno what it is with people and Hammerite, but when I got it, it looked like it had been dunked in a bucket of sky blue... (Gags on vomit...)

Sky blue?! On a machine tool? Seriously?

I don't hob my gears, I cut tooth by tooth. I knew a dealer called Michael Watson who had bought several cutter sets, ex MOD, and sold many to me over the years, for £50 per eight cutters.

Last time I looked, they were £50 each, new, so there's no shame in buying gears- Les always did, genius as he was! Life's too short. His final project was a model Manx Norton engine, and he keyed the head design around the bevel gears HPCs could supply. He was a lovely man, and I was lucky to have met him.

 

[mole42]

Here is the rear bearing housing, finished but for the keyway and fitted to the crankcase which has been drilled and tapped 8BA for the fixings. I borrowed a Myford chuck to fit my dividing head and used the collet chuck in the Drummond lathe to bore each of the 18 holes:

Here's the part with the drillings finished. Notice the locations were marked using the dividing head before starting to drill - I've been bitten before! All the holes were first drilled 1.6mm tapping size for the 8BA thread, then transferred to the crankcase on the pillar drill. I then opened up the bearing housing holes to clear the 8BA studs. Seen here is also the 1.415" 32tpi internal thread which was cut with a single-point tool using the variable speed inverter drive on my lathe. It wasn't anywhere near as scary as I feared:

The work above took me about two-and-a-half days all together. I'm quite slow sometimes and that 2kg piece of steel did create 1.7kg of chips in the process. Of course I had to try the bolts for a fit! Only managed two though:

I really must start to machine that crankcase casting and make some cylinders....

Richard

 

[mole42]

This day I decided upon making a piece that could pretty much be finished in one day, so the commutator ring was planned but Murphy got in the way and slowed the process..... The piece of Tufnol was available but square, so that had to be cut out, the corners sawn off and then turned to the correct diameter and shape, after which the centre was carefully bored to fit on the crancase spigot. The Tufnol is slightly thinner than the drawing size, so a small shim will need to be made to pack it out. The Myford dividing head was employed once again to bore the holes for the nine copper contacts but for some reason I forgot to photograph that part of the process.

Here's another item that slowed the job today. The drawing calls for some ¼" copper round bar to make the nine contacts for the commutator, but the materials box offered only a piece of ¼" copper busbar about 1¼" wide. A session with the hacksaw produced a piece of square bar, which was rounded off using the four-jaw chuck, a tail centre and a travelling steady. Then it's time to start reducing the spigot to fit in to the Tufnol:

Here's the commutator ring part furnished with some copper contacts and another one waiting to be inserted. They are pressed in (I used the bench vice, that's why they are so nicely deformed on the top) and the next job is to bore and tap 8BA from the outer periphery to insert brass screws which both hold the contacts in position and provide a means of termination for the spark plug leads.

This is where the job got to today. As mentioned earlier, Murphy was very active, the copper was flat, not round, half of the contacts ended up hiding on the floor when I'd sawn them off in the lathe and the 8BA brass screws hadn't arrived so fitting those will be another day....after which I'll face the contacts so that they are all flush with the Tufnol mounting ring.

Richard

 

[mole42]

A quick note about thread sizes. I hadn't previously heard of the "Model Engineer" thread specification but having found a chart covering ¹⁄₈" to ½" diameter threads of Whitworth form in both 32tpi and 40tpi, the thread sizes that Les Chenery uses make more sense.

Richard

 

[mole42]

Some more photos from today, first making a master cylinder with correct dimensions to use as a gauge for the crankcase machining. The light chatter is due to using the 'wrong' edge of the tool...:

And here's it's bored to something like the correct size. Les specified a bore of 0.745"but I think I'm going for 0.750" since I have a couple of reamers that size. So long as the piston and rings are sized accordingly I can't see a problem. I have decided to make the cylinders in pairs but with the bottoms joined together. It will be easier to machine like that.

The commutator ring has been drilled and tapped 8BA for the connection studs:

The studs are just an 8BA brass screw with a nut run all the way to the top and the top machined round.

Here's the collection of parts on the bench today:

 

[mole42]

Some more work to show, it's the turn of the crankcase today - setting out and starting to bore, screwcut and fit the master cylinder. Here's the setting out, using the Myford dividing head and a scriber:

Then it's onto marking the cylinder centres - I managed to mark them all slightly off-centre from the casting, but each is the same and it'll not be too obvious when the engine is built:

Each bore is then centre drilled, faced and a ½" drill put through to start the bore:

Then follows a boring bar to bring the bore to just shy of 1" prior to cutting the 32dpi thread for the cylinder:

I didn't photograph the single-point tool pushing the thread into the internal diameter but it's pretty much the same as every other internal threading job! So here's the final stage before fitting the cylinder, counterboring the outer part - the transfer ports rely on this annular groove because the monosoupape engine has only an exhaust valve in the cylinder head, relying on the piston opening a transfer port to inlet the fuel mix:

And here we're checking that the cylinder fits the crankcase. This is a "master" cylinder, the purpose of which is to make sure that all the crankcase bores are correct, so now I have to make nine operational cylinders exactly the same...:

That's all for today,

Richard

 

[mole42]

A little bit of progress, it's been a busy month and I've really only finished the crankcase, the rear bearing housing, made a small chuck for the cylinders so I can machine the cylinder heads, almost finished the commutator ring, that sort of thing. I was in the workshop one day and decided that there were too many parts that needed one little job to finish, so that's what I did.

Here's fitting the big end onto the crankpin, it's a critical piece of work so I blued the pin and pushed the big end onto it, using a very fine file to relieve those places where it touched. I've probably got an hour of work to do:

Here's the 'master' cylinder and the special chuck that screws onto the spindle nose of my Drummond lathe. I made a master cylinder to the correct outer dimensions so that i could finish the crankcase and make sure that the cylinder screws correctly into each of the nine positions.

This was quite fun. The tufnol commutator ring has nine pieces of copper pressed into it, then the contact screws are threaded into the periphery. After that, the part is faced so that when the high tension brush runs around and makes contact with each cylinder in turn, the polished copper offers no resistance.

That's all for now!
Richard

 

[D and D]

Lovely job and best of luck mate.

 

[mole42]

It's time I made an update, after several weeks of nothing but a little bit of machining here and there, a 12,000 mile round trip to visit family and sorting out another project that had a deadline.....

I've been working on the front tappet rod housing which keeps the cam followers aligned with the camshaft and has the camshaft reduction drive gears and the propeller drive on the front. Quite a hard-working bit of the engine. It starts as a 3.5" diameter piece of steel (90mm for metric readers!) and most of that is machined away bit by bit. Here's a picture of the start of the process:

As you can see, there's a lot of chips to make! The next part seems to have been so exciting I forgot to photograph the process, but the blank is bored out 2" diameter for a depth of 1 inch, a 0.500" hole is reamed in the rear face to accept a phosphor bronze bush, and a flange is formed on the front to accept the front gear housing. Having done this work, it's required to turn the work around to machine the main flange at 3.25" diameter, so a workholder is needed which I made from a piece of aluminium bar. Here it is in progress:

Once the inside diameter is turned to the correct size, the fixture was parted off and cut with a hacksaw to make the jig which is seen here holding the housing in the chuck while I size the outer flange:

Once the flange has been machined - 3.25" diameter and 0.05" thick, the inside face is machined to clear the crankshaft web and the boss tidied up for the phosphor bronze bush:

Then the piece is removed from the chuck and, still using the aluminium workholder, fastened into the Myford chuck on the dividing head. I marked out the nine first pass holes, then drilled them in the steel flange. Next pass is to reset the work so that I can drill the next pass of nine holes - the tappet rod housing is fastened to the crankcase with 18 8BA screws:

This is the end of the day today. I had left the 8BA tap in the other workshop so I didn't finish making the fastening holes in the crankcase. To ensure alignment I drill two holes first, fit the screws, and then drill and tap all the others. I spent the journey home scheming in my mind how to make the nine cam follower holes in this part (you can see them on the drawing to the left of the parts) - I think I've got it, but so far the idea involves the Drummond lathe, a vertical slide and the dividing head.

 

[creast]

Very impressive work!
I feel your pain on all the swarf generated
Would love to make a rotary/radial but not sure I have the patience yet!
Rich

 

[stevehuckss396]

Must feel good to be back at it after a long break.

 

[oldCB]

Here is the rear bearing housing, finished but for the keyway and fitted to the crankcase which has been drilled and tapped 8BA for the fixings. I borrowed a Myford chuck to fit my dividing head and used the collet chuck in the Drummond lathe to bore each of the 18 holes:

View attachment 137015

Here's the part with the drillings finished. Notice the locations were marked using the dividing head before starting to drill - I've been bitten before! All the holes were first drilled 1.6mm tapping size for the 8BA thread, then transferred to the crankcase on the pillar drill. I then opened up the bearing housing holes to clear the 8BA studs. Seen here is also the 1.415" 32tpi internal thread which was cut with a single-point tool using the variable speed inverter drive on my lathe. It wasn't anywhere near as scary as I feared:

View attachment 137017

The work above took me about two-and-a-half days all together. I'm quite slow sometimes and that 2kg piece of steel did create 1.7kg of chips in the process. Of course I had to try the bolts for a fit! Only managed two though:

View attachment 137018

I really must start to machine that crankcase casting and make some cylinders....

Richard

Richard, Your rockin mann...............I could only aspire to your level, but it shows me "it can be done" Outstanding work.

 

[oldCB]

I have a foundry I need to get going always wanted to produce a 4 valve Norton head. I'll need to learn 3D printing IMHO, but you got my wheels turning.

 

[oldCB]

I have a foundry I need to get going always wanted to produce a 4 valve Norton head. I'll need to learn 3D printing IMHO, but you got my wheels turning.

Like everyman on here sometimes life gits in the way of our projects.....I am looking forward to maybe racing at Mid-Ohio in 2023.........if the world is still here. Like many, I have many must do's AND Honey-do's in front of that.

I'm juggling putting together my 1/2 VW engine for MoJo Ryder, that's my Airbike AND putting together a new engine for my little racebike. I raced with AHRMA in Vintage SuperBike Lightweight for several years, it satisfied my adrenaline needs but after getting the #1 plate and becoming the "Bunny" it kinda went from fun to kinda serious so I built a GP200 bike and it was a BLAST!. Larger grids with bar to bar racing and did I mention I enjoyed the challenge of racing against those evil 2 strokes who had a significant edge in power?

Dont get me started on 2 smokes

So I'm gonna focus on those 2 projects whilst doing what all us Dads do, putting beans on the table while maintaining a fleet of 6 cars and keeping up the house!

In the meantime I'll be lurking here soaking up what I can to improve my half-arse maching skills and explore metal casting till I fire up that foundry.