A Simple Uniflow Engine

[gary.a.ayres]

I have a question: when I get back to making a replacement crankshaft, should I use precision ground mild steel or silver steel for the shaft itself? Or is is six and two threes?

These are the UK names for these steels, anyway - not sure if it's the same elsewhere.

[Jasonb]

I generally use PGMS when building up a crankshaft. M-Machine pack it better than other suppliers.

[gary.a.ayres]

Great thanks Jason.
Will check them out for PGMS.

 

[gary.a.ayres]

Bringing to dimension and squaring off the edges of the base plate in the mill:



Haven't got much done in recent days as we have been somewhat overtaken by  events here. The small island on which I live went overnight on Friday from having been extremely well controlled for months, and life apparently back to normal, into a second hard lockdown following an unexpected spike in community-seeded covid cases.

Lots to organize, arrangements to make, meetings to reschedule... and while this is clearly a dark cloud that no-one wanted, the silver lining for me will be quite a bit of extra shop time over the next few weeks. If it's possible to find a little bit of positivity in a negative situation, then I say do so.

[gary.a.ayres]

Not very exciting stuff really, but...

... With one of the long sides of the base plate milled to a clean edge, the other edge was marked using a combination square. This left a narrow strip of uneven width between the rough-sawn edge of the plate and the scribed line. Rather than spend ages milling it down to the line, I decided to chain drill it and remove most of the metal that way. Because the strip was of uneven width I used a step drill to be able to optimise the size of the hole at any given point without having to change drill bits. The floorstanding drill press (which has been converted to 3-phase with variable speed and runs like a dream) made short work of this:



The swivelling action of the bench vice was ideal for holding the plate for hacksawing between the holes:



That done, the base plate is now back in the mill and clocked in. A couple of passes were taken before I called it a day, and the second edge should be clean and parallel to the first tomorrow or the day after.

[gary.a.ayres]

The baseplate has been squared up in the mill and the two sides offered up to get a sense of the layout. Because of the bend in the original crankshaft I have reverted to a piece of round bar of the same diameter to guide alignment of the frame sides on the baseplate:



Once one side was aligned it was clamped  with toolmaker's clamps and taken to the mill to spot the holes in the frame support bars (aluminium angle) on to the base plate. A wiggler/wobbler/centre finder/whatever it's called with a ball end was used in the mill to locate the holes:



That done, one side of the frame (still in the form of a blank) was fixed to the baseplate. All fixing hardware remains temporary at this point:

[gary.a.ayres]

The frame is now assembled in very basic form, with the two sides (which are still blanks due to be shaped later) attached to the base:



Since the crankshaft is now a reject due to being bent, I just used some 12mm round bar to test the alignment, with a drill chuck attached to the end to make it easier to manipulate. It was hard to turn the shaft and at first I thought that the alignment was out, but then I realised that the sides are leaning inwards at the top to the tune of just over a milimetre. Pushing the sides apart at the top made it easier to turn the shaft. To remedy this I'll add two or three cross-braces between the frame sides at the top. These will widen the gap between the sides at the top, and will also make the structure more rigid.

Don't be confused by the belts and pulleys you can see in the photo - I just sat the assembly on top of the belt sander attachment of my woodturning lathe to take the picture.

[propforward]

Looking good Gary! It's all progress. 

Those step drills are kind of fun. They definitely have their place, and it looks like you put it to good work.

[gary.a.ayres]

Thanks Stuart.

Yes - I don't use the step drills very often, but they were good in this application.

Forgot to mention that I now have a leak in my home workshop roof here in Guernsey! It's just a shed, but I'm a bit mystified because I just gave the roof a new coat of very sticky fibreglass stuff last Summer. It really shouldn't be leaking already, but it is... and now we're back in lockdown again here I can't go out and buy more of the stuff at this point in time. Fortunately the leak is just above an area of open floor, so a bucket under it will suffice for now. Not a good feeling though.

Never a dull moment...

[gary.a.ayres]

Three cross-braces were made from aluminium round bar, each marked out with the surface plate and height gauge to a length corresponding to the distance between the inside faces of the frame sides at the bottom of the frame and turned to length on the lathe. The braces at each end of the frame were drilled, tapped and fixed by screws via holes which were pre-drilled in the frame sides. The one in the middle is just wedged into position:



Together, these push the sides of the frame out sufficiently to bring them into parallel with each other. As a result, the test shaft rotates freely in the bearings, which with a little running in should allow the new crankshaft to turn just fine. A satisfying evening's endeavours.

The cross-braces will be kept when the frame sides are cut to a hopefully more elegant shape, and repositioned to do the same job as they are doing now.

[gary.a.ayres]

Starting on the structures which will anchor the cylinder in the engine frame.

Two lengths of 32mm aluminium round bar were cut to make cylinder support pillars. The pipe jaws on the vice are great for this kind of job:



These were turned to length and drilled through with a 6mm clearance hole. They raise the cylinder so that the centre of the bore is at the same height as the centre of the crankshaft. Long M6 screws or studs will pass through the base plate, up through these pillars and will be screwed into blind tapped holes in the bottom wall of the cylinder. For aesthetic reasons I want the cylinder to sit horizontally rather than at an angle so that requires it to be raised up:



I know this makes the cylinder sit quite high. This is because the crankshaft also sits quite high in the frame in order to be able to accommodate the flywheels. With only the two support pillars the cylinder wouldn't be anchored rigidly enough, so the plan is to bring in two cross-braces from each side of the frame to the corresponding side of the cylinder wall, again threaded into blind tapped holes. I suspect that arrangement will hold the cylinder firm, but if it doesn't I'll consider additional ways to secure it.

Meanwhile, here is the cylinder on its support pillars rougfhly positioned inside the frame, just to give an idea...

[gary.a.ayres]

Four cross-braces for the cylinder were turned to length from aluminium round bar. They will be drilled through with 6mm clearance holes and with M6 screws or studs will secure the cylinder at four points to the frame sides. Here is a lashup of them with no fixings:



Even with them just wedged into the frame like this the cylinder sits pretty solidly in position. The braces are located two fore and two aft of the exhaust ports, so no interference there. Fingers crossed that when secured with fixings the whole assembly will be stable enough when the engine is running. I suspect it will be, but if it isn't I'll just have to find a way to add more anchoring elements.

[crueby]

Looking good!  Will the side panels have designs pierced through them?


 

[gary.a.ayres]

Thanks Chris.

They will be cut to a curved shape and will have round holes of various sizes drilled through. I'd get into triangular holes etc. if I had CNC, but I don't. I suppose I could mill them in the conventional manner but it would be a long haul and risky of errors. Round holes will be fine this time though.

Hope to have CNC one day, but don't have it yet...

Cheers...

 

[crueby]

I did some clock plates once with angled and triangular holes, trick was to drill the corners first, and clamp the plates to a tooling plate on the rotary table to line up the sides of the openings for milling, like doing spokes on a gear or flywheel. The design you describe sounds like it will look great!