Atom Minor Mk III

[bent]

EN8, ah good, AISI 1040 is our Yankee equivalent.   

[Jo]

I found a little casting sitting on the Dining room table  but I am not sure what happened to that cylinder 

The use of a four jaw self centring chuck is no good for holding castings which are not round, so a three jaw must be used. The bottom was squared up using the front of the drill chuck and the jaws tightened. This is rather sticky Aluminium and it was not long before it started sticking to the tip  That has to be removed or the measurements can go wrong and you get a nasty finish, even better remember to use the right type of tip 

The bottom was machined a couple of times until all the casting holes finally went. then I could put the pilot drill through for the spark plug. I have decided to fit this engine with 1/4 * 32 plugs rather than the 3/8" * 24 plugs as it is difficult to find the 3/8" plugs these days and the 1/4" ones are smaller and more in keeping with the engine.

Now we can bore the combustion chamber and using a suitable tool cut the inner rounded edge. Finally adding the undercut into which the liner will fit. Turning round the 1.2mm lip can be used to hold the head in a collet while it is taken to height and the spark plug hole tapped.

The next job needs a mandrel so a dog end of steel has been turned up to fit snugly into the liner recess. This has been secured with a 2BA screw to the mandrel rather than try to use the spark plug threaded hole which might get damaged 

Jo

[Jasonb]

Are you cutting that all dry Jo? Bit of lubrication will help with the sticky stuff no end.

Easy enough to get the 3/8" Rimfire plugs

J

[Jo]

Are you cutting that all dry Jo? Bit of lubrication will help with the sticky stuff no end.

I tried it both wet and dry, it made no difference to the sticking, changing to the correct tip made all the difference.

New 1/4" 32 plugs are less than £10 each as well as looking more in keeping with the engine size and I have 7 spare rim fire ones that size but I would like something more in keeping with the age of the engine 


Mounting in a 5C collet on the dividing head mounted vertically first four holes were drilled, before counter boring with a just over 6mm slot drill.

Mill the top most land for the spark plug and then a series of steps for the fins. I am not going to risk cutting the fins this late in the day 

Jo

[Jo]

There was a moment of confusion when I realised that there was no way that the bottom two fins could not have the same spacing as the others  But having looked at Westbury's original engine yes I found the lower two fins are slightly closer together  Initially the slot was made with a parting off tool and then taken to full width using a suitably profiled/reground parting off tool.

I couldn't find the cylinder so I have started making a replacement in CI which I discovered in his book was the preferred material for the cylinder. I have opted to drill the cylinder before cutting the fins on this one as I fear the fins will be a little weak for drilling after  and of course I do not have a hone for the cylinder bore size 

So it is looking a bit more engine like

Jo

[b.lindsey]

That head looks great too Jo. Did you make the angle cut after cutting the fins?

Bill

[Jo]

Thanks Bill 

Angle cut  The fins had the steps cut yesterday which made them different diameters. Once cut I carefully finished the edges with a hand file  .

Jo

[b.lindsey]

Sorry, I didn't look at the previous pictures close enough. I see now that you cut steps rather than a continuous angle. Guess I had looked on the phone, on the laptop now

Bill

[Jo]

No problem Bill 

Having turned up a quick mandrel using a bit of odd sized ali the cylinder could be mounted up on the indexing head. It is important that the ports go in in the right place so two drills were stuck through the mounting holes and the cylinder squared up to the table. There are four holes for the ports: The exhaust are 4.4mm wide and rectangular so were cut using a 4mm cutter, the exhaust are just round holes 5.5mm diameter. I nearly forgot the little slot in the bottom 

Then back to Mr Silky to have the fins cut: the CI was much easier to cut fins in than either than Ali or any steel even with the interrupted cut The cylinder did however (due to milling the ports) stick on the mandrel and had to be pressed off 

Other than the brass screws the top of the engine is looking much more engine like, time to think about lapping before doing the piston

Jo

[Roger B]

Glad to see you are back on this one  Good progress        Are you going to make an ETW magneto as to go with it? 

[Jo]

Hi Roger, thanks for showing some interest 

Are you going to make an ETW magneto as to go with it? 

  It is not currently part of the plan. I have a very nice ignition box that I use on all of my engines 

Using one of my expanding hones that I made a little while ago - I first turned the outside of one of the aluminium sleeves to be a sliding fit in the cylinder bore. Then coated it with 1000 grit grinding paste, expanded it a tweak and it no time at all the bore was a lovely uniform dull colour (only visible after using brake cleaner to clean the bore.

Piston next.... its a very long piston I still might give that cylinder a quick boil...

Jo

[b.lindsey]

Looks good Jo. You are really moving along on this one!!

Bill

[Jo]

It's cute Bill  when I cleared the Xmas presents off the dining table I rediscovered it from where it had been placed during my recovery.

And having been discouraged a little on the RLE this one is a nice little easy win ... with a rotary valve

Jo

[10KPete]

I've never made an aero engine though I've flown many models both control line and RC. I'm very interested in your techniques, Jo, and follow along eagerly. Very interesting process to watch..

 

Pete

[Jo]

The piston started out as a piece of cast Iron. The bottom was drilled, bored 16.66mm then had a 4mm under cut added about the gudgeon pin internal support. The outside was left oversized at 19mm. Off to the indexing head and the gudgeon pin hole was drilled 15.88mm up from the bottom of the skirt. This hole was then used as a reference to mill the deflector plate on the top of the piston.

The piston now looks about right so it is time to finish the outside.. Mounting it on a mandrel by using the gudgeon pin through a threaded pin to pull it tight, the outside was turned to 0.1mm over sized then the external hone used to take the remainder down.

It has been left just tight in the bore (it had been a bit too tight and got stuck in the cylinder at one point  ) and will now be worked in by hand 

Having moved over and started the connecting rod I have realised I forgot to mill the bottom of the piston  so it has headed off to the 5C dividing head and is clamped up ready for the bottom to be milled out.

The connecting rod is made out of scrap-bin-ium - that's best fast jet aircraft grade scrap-bin-ium. Recognisable by its colour and beautiful machining properties 

Jo