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My Atom Minor build


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Not sure if this is going to be a bit boring, but i am sure i will need some advice along the way from you!


Having built the Hemmingway Sparey 5cc diesel (still unfinished business until it runs) I thought another trickier engine would be the ticket to a few more sleepless nights.


Thus I bought a Hemmingway Aton Minor Mk3 box of materials, the large parts/GA drg and the book written by the designer on how to make it.

The book is great. It seems he wrote it just for new-comers like me so I'm following his advice as well as watching the You tube episodes of Paul's Garage Projects.


I will be using the Drummond round bed lathe and the Myford compound slide but have just invested in my first precision pillar drill, all fresh and new from China for £15.99.

I have a new small capacity 240V piston drill that will fit, so all those case screws on the Atom design should be true.


I've treated myself too with a real parting off tool and a small angle plate to help making the slightly awkward crank case.


As i type this, the main case has been faced to 1" width and looks good, the bore for the cylinder is next which needs the angle plate on the face plate I have.


The crank casting only just went into my 3" 4 jaw chuck and was looking very precarious, but with light cuts it was good.


If the regular watchers are thinking, "oh no! not again" let me know and I'll reduce the thread to simply cries for help along the way.

I WON'T be offended.




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Keep going Hillclimber . It can be an uphill struggle at times (sorry about that 😊) but its good to read and see others projects that mirror our own . Ive never made a complete engine but have made all the parts for restoations. Your posts are making my maching fingers itch !

Keep it up . When I started making pistons it was a very frustrating at times but gradually the success rate climbed . 

As for your old lathe , dont give up on that either . My lathe is a Myford ML2 model from between the wars I believe and has it own idiocyncrasies due to some wear but a new one is out of the question.

I admire your persistance with the compound slide though , since buying a small milling machine mine never comes out of the draw as its too awkward in use . 

Keep going please as us older members of the "oily hand society" are getting fewer .

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Posted (edited)

Thanks for the support!


Ok, a few more hours in the garage today.


Today was far more fathoming out how to hold the main casting than machining it.

This lathe is small so has small features. It came to me with a reasonable 'home made' face  plate which is the chosen mthod of holding the casting.

However, the 3" angle plate I now have is HUGE and weighs a ton, I would never balance it out for cutting, so used a nice piece of extruded alum alloy to be the substitute for the angle plate.


This all worked out great and with the instructions to guide me managed to get the cylinder liner bore all done and re-jig the same parts to align the exhaust stub pipe ready for machining tomorrow.

Hope these pics will speak a 1000 words:

_DSC0079 (2).JPG


_DSC0080 (2).JPG



Edited by 911hillclimber
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Had a great day in the garage today making lots of casting swarf, but good results with only one very near cock-up but i dodged the bullet by luck alone. Lots of pics:


Plan was to machine the crankcase casting, front casting and rear all bar the attaching screw holes, still awaiting my £15.75 pillar drill for that.


Finished the exhaust port inside and out and machined the small engine mounting pads, far to small, so was very minimal in my milling.

Spent a lot of time getting parts to fit into my tiny chucks, but got there ok.

The front casting was dead easy, the casting remarkably true, so all machined and reamed, bushes over the weekend I hope.


The rear cover was a pain. It is 'just' too big and lumpy to get into the 4 jaw, so had to chop the bulk of the venturi cast feature and will make a brass substitute and epoxy it in place into the plain hole I've drilled.


The spot facing of the attaching screw hole pads was awkward too as I could not cut them by turning, only using the devilish compound cross slide, but got there.

I made a mistake turning down the rear casting to fit the case, but had left some final material to cut so mamaged to get a nice fit after all, much as the front one is.


The matching of all these features in the casting is laughable. Might file some once screwed together to get most to match, but probably will just leave them.


All the pics:



_DSC0080 (3).JPG

_DSC0082 (2).JPG






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Terrible day on the engine today.

Scrapped all 3 castings trying to get the screws to line up, utter shambles.

At £67 for a new set of castings, I think i'll throw the towel in as I can't think of how to drill the case holes accurately with what I have.

I think you need a milling machine to index the holes and drill accordingly.


The cast lugs are partly to blame as they do not align to the main case well, 3 may be in-line, but the 4th is miles off etc. The rear cover can only fit in one place, and the lugs simply do not align, but the castings are like that everywhere.


Wasting time and money, so will revert to what I'm used to!

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That is a real pain,911 My experience of castings has been very similar, with poor matching of lugs,etc, hence I try to make from bar stock mostly. I think the cause is that these things start out mostly with amateur made patterns, usually with too much taper and not enough machining allowance.


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That's a shame hillclimber,you were doing well there with limited equipment and experience, maybe post some pictures to see if the problem can be resolved. 

Keith, these castings have been available since the late 40's and haven't improved with age,it's about time Hemmingway made some new patterns as these are not fit for purpose, you only have to compare their Sparey casting with the ones I purchased recently too see that 🤨

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I am very disappointed in this. The 2.5mm tapping drill (M3 not 6 ba) just drifted all over the place and while drilling met all manner of lumps and bump imperfection along with buttery drilling too, but the drift was uncontrollable. I made a 'drilling jig', a good lump of dural and drilled 2.5mm and made to suit the location bosses (male and female) of the crank case. The lugs are poor material, the main casting much better and machined well on the lathe.


It will all go in a box now and eventually I will order £67 of fresh castings and start again, but will get my friend to make a steel gauge plate jig i can bolt to the case and ends to get holes to match.

This drilling is very hard to align without a milling machine and being able to position the pilot in X and Y accurately, but could take them over to Phil and get him to drill them on his miller along with the cylinder head bolts  too.


I'm too embarrassed to picture the mess...

Will re-open this thread when I get fresh castings.

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Is it not possible to thread and plug the holes?  When I have been confronted with trying to line up bad positioned lugs etc. I make a drill jig from ,say, 1/8th" perspecs with the  same bore/plug as the casting and then you can eyball the positioning of the holes,rather than work to dimensions and then reverse for the mating part.


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Several things have crossed my mind, plugging was one of them, alum 'solder' another for the twp covers and all the 8 lugs. The case would have to be plugged.

Doubt you can get M3 aluminium screws to act as plugs, steel ones could lead to a wander due to the hardness over the alum if you get a 'half-hole' line.


I have found my drill to be lacking, too much play so I'm shimming it to try to stop the wandering. I have used the centre drill from the lathe to eradicate 'wander', hope to report a success tomorrow.

Have the morning to my self tomorrow so can try a few things.


Thank you for the ideas and support, is helping a lot.

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I've ordered my aluminium 'welding/solder rods that melt at 300 DegC and need a proper welding set (gas) which I have, so the castings could be a Big Blob on the floor soon...

Found some alum screws too which will be used to fill the tapped holes in the main case. Will Red Loctite them in place, leave to set and cut off flush etc.


Fixed my £15.75 pillar drill by turning two very thin shim/sleeves for the head stock which was tricky, and took 3 attempts, but done and now the drill drills on the counter sink and stays true to the scribe lines. Used a pilot drill off the late to spot the holes first like a good boy!

With that done, found a very nice piece of flat machined alum 8mm thick plate and made an accurate drilling jig, with raised boss on one side to locate in the case, and a female recess to locate on the end plates.

This way the 4 holes will all be the same on all the parts when I've repaired them.

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Hi hillclimber. I dont want to teach you to suck eggs but have you used the low temp rods before ? If not make any holes you intend to fill bigger and taper them with a counterdi k or similar. Also make yourself an abraidi g rod from a length of stainless steel . Gr8nd 5he end to a sharp point . When you have filled the hole or tinned the edge as you do when soldering use the rod through the molten metal to scratch through any oxide that formed this way the alloy will fuse with the part and be very strong. Dont heat tye rodor repair area but heat the whole part . 300 deg rods should be safe on proper aluminium . Ive used them on zinc alloy with good results  . Some zinc alloy cases do still blister even at 300 deg though . 

Good luck and show us your progress.

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Sounds good, advice always appreciated. all a bit like chamfer the edges to be welded for best/total penetration. A good counter sink hole is easy as you know. This is for the end plate lugs.

For the main case I have M3 alum screws on order so will red loctite them in and flush to the machined face.


Once done I will intal steel M3 studs and hold the lot together with nuts.

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Filler rod arrived today, I even read the instructions!


Decided to test trial the job first, so found some nice alum sheet, 16 swg and formed a simple corner joint, about 30mm long. Thought I would try the butane torch first as per the instructions as it is butane gas.


The torch could not get the sheet alum hot enough to melt the rod. 

So, reverted to my mini gas welding set that will gas weld 16 swg steel well, that should do!


No, the sheet got hot ok, infact to melting point, but the rod simply would not take to the freshly cut surfaces. I opened the intended welded joint by hand after quenching.


Frustrated (as ever) with this saga took, the cast back plate to the vice and csk sunk the one lugs with a centre drill, so the surfaces were very clean. The hole is about 2mm dia x 5 deep, open, the csk is open to about 5mm dia and 4 mm deep, a good funnel I hoped.


Heated the casting gently for a minute or so and focused on the one lug.

Heated and dabbed the rod to the csk hole, nothing happened, hotter still and the rod sort of lost it's tip on the surface, but did not flow, just there as a small lump. Tried more and the casting lug as good as melted.

What rod was there picked out after quenching with a scriber.


So, I conclude the casting are made of peanut shells, melts at a temp lower than the rod (300 degC) and the rod will not take to the casting, or sheet aluminium or peanut shell castings.


All in all a waste of time, money and gas.

Maybe one day I will buy some new castings for £67 and try machining again, but do not feel inclined to carry on.

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In a word,no,quite frankly your best bet is to go and download a set of drawings from outerzone.com for one of a number of engine designs that are made from barstock and then try and make friends with someone that has a tig welder that can repair the Atom cases in the meantime. 

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Hi Hillclimber . Where did you buy the rods from. There are some on ebay that claim to melt a5 300 deg but actually melt much higher. Ive just repaired am AM 25 crankcase lugwith som 300 deg rods20240405_102619.thumb.jpg.36a37a75fa729dfa477d9d06fe66adb5.jpg

You can see its a slightly different shade after shaping and bead blasting



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