DDK - Die Deutschen Klassiker

Having run out of room in the garage and sheds for cars and bikes, the next DIY project will be smaller.

Testing to see if there is any appetite for a slow thread on making a 5 cc model aero engine from bar stock and one casting on my 1921 Drummond lathe?

Yup. Interested in mechanical stuff

Will it work ?

Looking forward to watching this thread

Oh yes

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Will be tricky on several fronts, but that is the challenge. Nice simple diesel, but sometimes simple is hard.
Have a very good friend with a thread cutting lathe to cut the back plate thread (about 42mm dia) but what I have should be enough.
The lathe is a real darling, just need a few tools more, ie a rigid boring bar.

Hardest bit is getting the centre lines for everything.

Are you going to twin spark the head?

Any parts coming from the USA?

All home made, so what can possibly go wrong?
Ha!

Eager to start this task, but the decorating of the HUGE landing and staircase and hallway was on the top of the list and after 5 recent days it is almost done.

Painting 57 spindles white is mind numbing, acres of wall too in a light grey and 10 doors worth of handles to fit tomorrow.

DIY in the home is not my best skill base, but the Boss is happy.

Happy wife, happy life.

Not quite sure where to store the Brownie Points, but i know how to spend them...

The decorating is all but done, awaiting some glass for the dining room doors, but have done some prep and even thinking about how to do this project.

I have limited facilliites, but fond memories of machining at school in metalwork and my early years of my apprenticeship back when I was 16, which was a very long time ago.

Thus, preparation was needed to get ready for the machining, build, and hopefully running of this 'big' diesel, big at least in model aero plane terms though I only fly electric.

My lathe is a fabulous 1922 or so Drummond round bed lathe which eventually was given to Myford just at the end of the WW2 era. The history of the lathe design is as facinating to me as doing anything on it.
It has been a god-send when building the Lola hillclimb car and various old motorcycles etc over the years. x 10

It came via ebay and a sale from the very back of a village garage deep in the Lake District when i retired from boring work. I built a floor stand for it and it has been great, will skim a thou or two easy esp since fitting it with a new Chinese 3 jaw chuck, and recently a 4 jaw.
The Myford cross slide pictured above makes this lathe into a versatile milling machine for this scale of work and was cheap and is new.

To make the parts to this engine I need to expand the lathe's capabilities to cut threads. That sounds easy which is is on a more modern higher-end lathe than this Drummond which would have been treadle powered(!)

The steel cylinder and the aluminium crankcase are screwed together firmly using a 24 tpi thread on around 3/4" diameters, yes, this engine is all in Imperial and the Drummond has NO indexing on any movement, so you machine and iterate to the size.
Digital calipers are my best friend.

To get threads cut you need to gear the head stock spindle to give 1 thread in a 24th of an inch.
Thus you have a chain of spur cut gears that come off the headstock spindle to the lead screw that dog clutches together to give this movement/turn.

The lathe came with a number of gears from 15 Teeth to 125 teeth, but the main cluster counts up in 5's, ie 30 teeth, 35 teeth etc.

By swapping the gears around you can get many TPI threads, and after considerable swapping about this was achieved, took 2 hours in all...This Drummond was sold as a budget lathe capable of thread cutting back in the day.

Those familiar with powered machines will appreciate the fright of the risk that the tool crashes into the chuck/work piece and the damage that can ensue, and thread cutting is one of those risky things, so the trick is to drive the spindle very slowly, ie 20 turns/minute of less. This way you can stop the lathe and risk of the crash.

So, the first mod to the lathe is to allow the spindle to be turned by hand, that is add a hand crank to the spindle substituting the electiric drive motor totally.
Oddly, this was dead easy(!) and a plug socket welded to the 1922 gear clamp nut allowed me to put a good double ended ring spanner on the socket end and add a wood handle for comfort when turning the spindle.

I made a 'bolt' to engage the gear train to the dog clutch to the lead screw, and with the gear set got 24 tpi for a cross slide/ tool post movement of 1 inch.

Hope you are keeping up at the back!

Next came a test, so with a simple pointed tool bit and some steel about 5/8" dia I first covered the steel bar protruding out of the chuck (about 1.25") with marking blue.
I added a 'cut' on the cross slide and wound the spindle. This grazed the surface like a scriber would and a nice clean helix was 'cut' into the steel surface.

Wound the spindle back and the tool free of the steel bar. The leadscrew remember is still all engaged together (important fact), NEVER disengage the lead screw.

Added a real cut, about 10 thou, and wound on again to cut a start to the thread which exactly followed that scribed helix previously, which started the thread cut form, it actually worked!
Further back and forth and I had a nice thread on the bar, my first self cut male thread since i was 16 on a lathe. (actually a square acme thread on a simple screw jack, still have it).

Harold, my tutor as an apprentice would be proud!!

With this, I bought a set of internal and external thread cutting tips and also some old school 3/16" HSS for the old tool holders I have, so now fully set up with tools, and getting closer to 'All the gear, and no Idea' elevation.
Time now to study the design and the drawings and decide which part to make first that is the simplest.

Enough boring words, a few pics taken along the line to amuse.

Anyone notice the head-scratching I had with the last picture?

Got a few hours into the engine this afternoon, back to finishing the decorating tomorrow...

I was going to start on the easy bits, but having looked at the drgs, there aren't any.

So, to get stuck-in I've started on the cylinder which is steel Not free cutting steel but some nice stuff. Cuts well enough but my lathe struggles at times with lack of power in the motor, but getting there with many light cuts.

The bar provided is huge due to the cylinder having the mounting plate on it and machined from the solid to keep the mounting dead square to the cylinder, so turning down from about 1.5" to 0.9" to rough the part out.

The drgs are all imperial, but irritatingly in fractions, not decimals, so first task was to convert all the fractions to decimal using the Fabulous Zeus engineers book.

Just how many of these have been printed and sold and used and replaced over the decades? Mine is from 1976.

Seems nobody has spotted the tooling geometry above??

This project will go quiet for a while as progress may be a bit slow.

Been darting in and out of the garage between decorating (99.99% done) and various domestic errands, but some progress.

I've made a LOT of swarf.
This steel in the pack from Hemmingways is really nice stuff, miles away from leaded mild steel.

After a lot of bulk cut down it came to the sensitive stuff, cylinder boring (needs to be very fine) and the first 24 tpi external threading in the build.

When I was 16 as an apprentice, by the end of my 1st year my nick-name was Micrometer Eye, and so far I can still live up to that.

The bore is tricky as the general shape of the cylinder hampers easy chucking due to the mounting disc (soon to be square) which forces me to clamp the top end of the bore in the 3 jaw chuck.

Trouble with that is it is easy to distort the bore into a tri-lobal shape. Not good for compression (no rings in this engine).
Still, you can rough cut the bore to about 1/32nd and then relive the clamping of the chuck to gingerly finish the bore dia using a nice fresh tip.

This is what i did and it seems ok (my micrometer eye says so).

This accomplished, I turned to cutting the 24 tpi thread. The design of this engine is made for machinists. The relief either side of the thread is the root diameter of the thread, so when the cutting tip starts to 'scribe' the thread helix you are at the root dia of the thread, so : Stop Cutting.

To my amazement it all worked, the thread is cut on the cylinder so just the awkward cutting of the ports to do, not so easy.

Cutting the ports starts with accurate marking out, the transfer port especially is critical, and I'm not sure how to do that as I type. I'll sleep on it.

Some pics to amuse:

Closing in on the final bore...



Gears all engaged and the lead screw locked in for the thread cut..



Here we go, 24 tpi on it's way..



Looking almost good!



Looks almost right, but port time next..

Following.
When do you plan on having it finished?

TBO Rob, as and when.
This project is a substitute for a 2 wheel Cyclemaster which is what I really wanted to do this winter, but space is at a premium. You know how small my garage is, but both garden sheds now full too!

I would hope to be finished doing the machining and fitting up by end March/April ('24), but running it may be an issue as 16" dia props are near unheard of.
That is a big prop and shows what a bruiser this engine is.
Bit scarier to start than a twin plug high comp 320 bhp flat 6.....

So far it has been a great project, lots of skills coming back making all these fine machined parts, but something (will) might go wrong.

Operator error comes to mind.

Looking good! I'm following with interest! I'd love to take on something like this. It would be a great skill builder.

I've got a lathe and a mill, but they are both in bits awaiting the completion of my garage extension (3 years and counting! Builders going bust, Grr.) and I have no real idea about how to put them back together or set them up! They were acquired from a close friend's grandfather, now deceased, so I can't ask him unfortunately.

It is all about accuracy and repeatability of movement. My little Drummond is from 1922 and has lived a busy life in a small village garage in the lake district, cost £180 working.
I spent some time getting a lot of wear out of it and it is simply superb, BUT you need good keen rigid tooling to fine machine the parts, this has cost about £100 so far max. Great value for money.

I really enjoy this task and having a real purpose to use the lathe is a big cherry on the top. I would die for a small miller, but have no room for one anywhere, my double width short garage here is full of the 911, the Lola race car and my Yamaha YB1, the lathe and bench etc., probably looks like that Lake District garage!

I could extend the garage quite a way, but cannot justify the cost at my age v the benefits.

Big projects like the 911/Lola are now behind me, the bikes are easy but space hungry, so this engine is perfect, have to be realistic!

Having a lathe and miller and some other bits opens a new world of learning. I was very lucky to have had such a good apprenticeship for 5 full years with tons of practical experience thrown in, and paid to get a technical education, HND etc.
If you can, get those machines done!