Arnold's take on the MEM Corliss

[b.lindsey]

Arnold, you are making great progress on several fronts and its nice to see your updates.

Bill

[Bearcar1]

No flaws, just a great deal of character. Nicely done    It seems almost a shame to cover up such a beautiful piece of the brown stuff (Naaaaaaaaah) Thinking ahead, do you have any plans for paint or just polished metal? (the engine of course) This is going to be one handsome beast when you are finished. 


regards


BC1
Jim

[arnoldb]

Thank you all who checked in 

Jo I forgot all about the reflective brick(s)  .  And yes, I need to get some thin solder wire; that's unobtainable locally or from South Africa, so I'll most likely have to order it in from the UK.  Some solder paste as well for the really small jobs.  My flux is a really coarse powder, and even if mixed with water it stays very granular.  I wonder if pounding it finer with a pestle & mortar would work...

Vince, I'm pretty sure it can be hogged from solid, but it would be a huge waste of material, and could take quite a bit of time to do.

Jim, a lot of that wood will remain visible; I must admit I have a soft spot for teak  .  Rather than wax it like I normally do with teak, I'll varnish it this time.  Oil droplets do get into the wood and stain it if it's just waxed. 
All the steel bits will be painted, that's why I haven't bothered too much about getting very good finishes.  I'm still debating the colour with myself...  I think my favourite dark blue would be a bit on the "heavy" side on this larger model, so right now I'm thinking about a lighter blue.  I think it might also look very good in light burgundy or ruby, but seeing as it will eventually make it's way to my living room, that would not match anything in there, and will stand out like a sore thumb 

Not much of an update for today - I just made the outrigger bearing pedestal.

A block of steel - accurately sized to 33x24x12mm, and milling the cut-outs:


Then I drilled the 3mm mounting holes:


A quick lick with a file on the bottom section to round over the corners, and the job was done:


The vise back-stop came in really handy today as this is a symmetrical part, so once set up, it was just a matter of flipping the part around to carry on operations on the other side.

Not much progress then, but every part made is a part made  .  I had a look at the bearings themselves - I'll divert slightly from the plans for those, and make them from steel with phosphor bronze bushes, rather than all-bronze.

Kind regards, Arnold

[vcutajar]

Arnold

I was thinking also about the crankshaft bearings and my idea was to make both of them at the same time (from one piece) and then split them with a slitting saw.  Problem is that I cannot find phosphor bronze in square section.  Sometimes I think it is only available in round section.  What if I use brass (which is available in square section) for the bearings?  Is it too soft for this application?

Also, I was thinking of making an oil cup for each bearing.

Vince

[arnoldb]

Vince, I only have access to phosphor bronze in round as well, that's why I'm going with the bushings in steel housings. 

Brass should work just as well; it's quite a good bearing metal if you make your crank shaft with steel or stainless steel.  I doubt if any of our engines will see heavy or long periods of use, so brass bearings should last it a lifetime.

The oil cups are a good idea  - in fact, I was also thinking about adding some; it will add a nice bit of detail to the engine.

Kind regards, Arnold

[Captain Jerry]

I have used brass where appearance is important and I have use oillite bushings for quick but I have also used cast iron bushings.  The cast iron seems to give a nice smooth bearing with very low friction.   Is there any problem with cast iron for these low speed, low power, low hour applications?

Jerry

[NickG]

Can't see a problem with cast iron, it's self lubricating properties should make it good, bit like Phos bronze or oilite.

[arnoldb]

Hi Jerry

Like Nick said, I think the cast iron is good to go  - with steel shafts it gives about the same coefficient of friction as sintered bronze on steel, and better than brass on steel (there's a list here)

Both my lathe and mill use steel gibs on cast-iron slideways, and if it's good enough for machines, it's definitely good enough for our small low-use low-power toys.

About the only of the small engines where it matters more is with hot air or Stirling types, where one needs to overcome every single bit of friction as much as possible.  And even having said that, my Phil Duclos "Little Blazer" fire eater runs like a champ with a silver steel crankshaft in aluminium bearings, with just graphite powder for lubrication, and this is my most-often run engine with about 50 hours of total run-time on it.  I know Marv built his one with the aluminium cylinder and piston, and as far as I'm aware his is also still running fine - and most likely has a LOT more run-time on it...

So in my humble opinion, for our hobby model purposes, pretty much anything goes in general.  I have no clue about Internal Combustion engines, so that may be another matter, especially for diesel types.  With live steam, the cylinder and piston materials do make a difference, but that's more related to heat expansion and corrosion rather than friction.  Others may disagree, so keep an open mind.

Kind regards, Arnold

[arnoldb]

Well, my new PC arrived on Thursday, and yesterday I spent setting it up properly and loading all sorts of software on it to carry on with my studies.  This being a 4-day long-weekend here in Namibia, I'd decided to spend two days studying and as much as possible of the other two in the shop.  There's some domestic matters that also need attention 

Today's shop session started with two blocks of 12mm plate - already milled to 18mm width before sawing them apart:


A quick job milling them to length on the mill:


Then I drilled 10mm holes through them for the bushes, after using the edge finder to locate the centers and also setting up the vise back-stop for the rest of the operations:


I used the jungle-formula from that Potatograss feller that insists on sticking a square on a hippopotamus to calculate where the flats on the bearing caps would intersect with the curved section when using a 6mm end mill to make the flats - makes machining a bit easier later on:


Then I drilled the mounting holes, and milled the flats out to depth and the calculated offsets:


The 6mm clearance arcs around the mounting holes was too little, so I enlarged that to 8mm by centering up over each hole and just plunging an 8mm end mill down to meet up with the flats after this photo was taken - you can see the rings it created on the flats in this photo where I'm setting up to round over the tops of the blocks:


Rounding over - here's one side just about done.  I was my normal lazybones self and did both workpieces at the same time:


The other side done:


After a bit of filing:


On to the lathe for a change, and I started turning some 12mm phosphor bronze down for the bushes.  PB can be a pain to turn sometimes, but today I think I got something right, as I got a very nice finish with no effort at all:


The finished bushes - turned for a light press fit in the bearing caps, and only drilled through at 7.8mm for reaming to 8mm later on:


I pressed the bushes into the bearing caps with a dab of bearing retainer smeared around the "coarse" finish left by the drill in the bearing caps - a little belt-and-braces measure, as I need to finish the reaming later on.  Then I snapped the latest "progress overview" photo:


Kind regards, Arnold

[vcutajar]

Hi Arnold

Another two pieces of your engine finished.  Thanks for the detailed descriptions of how you do things.  Love them.

I am still carving out the spokes of the flywheel very, very slowly.

Vince

[arnoldb]

Thanks Vince  .  Carving out that lot will be a bit tedious - I've only done much smaller flywheels from solid, and that took a lot of concentration...

I wanted to make a start on the valve covers today.  I thought I had a long enough section of 16mm square brass to turn up the inside covers, but obviously I thought wrong.  So I fell for my own April Fool's joke and spent a couple of minutes setting up the dividing head on the mill to make up some 15mm square bar from 16mm round rod I have quite a bit of... 
...
...
16mm round cannot be milled to make 15mm square  .  Yes, you are allowed to laugh at me  .
Nothing else I have in stock would work without enormous wastage, so I'll try and nip into the metal candy-store this week and dig around for something suitable; it's close to my barber and the couple of hair left on my noggin needs a trim as well - both these haunts are on the other side of town from my normal area of operation.

I grabbed a bit of really crappy 32mm steel and started to turn up the valve disk hub, determined to get a good finish from this steel for a change.  After roughing it close to size, I took a couple of minutes and honed up my HSS cutting bit to a really sharp and smooth cutting edge on an oilstone.  To try and keep that edge while turning, I slowed the lathe down to it's lowest non back-gear speed.  With a fine depth of cut and slow feed, I got the best finish ever in this cruddy steel  - with a bunch of very fine steel wool forming on the lathe tip along the way:

  OK, it may not seem like much - I get better finishes easily on silver steel and even stainless with much less effort, but its a personal thing.  I have a LOT of this specific steel and have never been very successful turning it, so it's a good step in the right direction to use what I have, as well as some more valuable machining lessons learnt.

A quick trip to the band saw had the tuned bit sawed off slightly over length, then I mounted it in a collet to start on the rest of the steps.  I chucked it with the flange out about 2mm from the closer nut face - the reason for this will become apparent later.  After facing the flange down to 1.5mm thickness, I drilled (4.9mm) and reamed through the workpiece with a 5mm reamer:


I drilled a 5.5mm hole to near-depth through that, and followed it with an 8.5mm drill 4mm deep.  The inside of this workpiece serves as a bearing pivot for the valve plate, so good finishes are essential - drills don't give these.  Following the exact diameters to plan is also not that important. Close enough is good enough - it's easier to compensate for differences in size when making the matching valve disk spindle, but the final match between the two parts must be very smooth and light with an absolute minimum of play, otherwise the valve disk will wobble causing binding in all the valve linkages.  Boring to the correct depths can be a pain, so I set up my bed-mounted dial indicator for a bit of help:


The smallest boring bar I have is one ground from some square 4mm HSS - I honed that up really well, and started boring the stepped internal diameters:


Once those were done, I moved the chuck to the rotary table.  The reason I left the gap between the flange and the collet closer nut was so that I could drill the mounting holes without drilling into the closer nut (or collet):

While drilling, I also inserted a bit of 0.5mm brass shim stock in the gap between the flange and the closer nut - even if the drill grabbed a bit when breaking through, this would save dings on my work-holding equipment.

On to the valve disk spindle, and I turned it to a close match to the valve disk hub from phosphor bronze - just testing the fit along the way and taking off imaginary 1/4 thou in-feeds in the final stages on the cross slide by reading the dial between the lines.  A very sharp toolbit is essential for this.  If you think you're seeing a bit of a hollow on the middle step, you are correct.  The corner to the next bigger step was not quite sharp enough because of the tool radius, so I used the rear parting tool to edge into the corner, but slightly over-did it  - hence the hollow.  The rest of the section is spot-on and will function as expected.  You'll also notice I added some generous chamfers to the sharp edges - this should prevent binding in the corners of the valve disk hub:


Back to the mill and rotary table, and I milled the needed square section on the spindle:


Off to the lathe again, and after parting off the spindle, I ended up with today's bits for shop time:


Where they fit together on the cylinder block:

Also visible is the reason I asked about paint in the "20 Questions" thread - we've had a terribly dry spell so far, but the last two days the rain came belting down and immediately there's rust on the block and mountings, so I need to get some paint on there soon, or oil it up and have to remove the oil later...

Another very interesting thing I noticed in the shop - or maybe it's my imagination.  On Saturday when I worked in the shop, it was still well into the 30^oC temperatures here, and today it was just 20^oC - and all the machines felt tighter to operate.   Is it just me getting old bones, or can a 15^oC change in temperature make such a difference in the feel of the machines?

Kind regards, Arnold

[b.lindsey]

Arnold, the progress overview shots are looking really nice....its starting to take shape...thanks for the update.

Bill

[vcutajar]

Thanks for the update Arnold.  It will be interesting to see how you will make the square hole in the valve disk.

Vince

[Don1966]

I am really enjoying your progress Arnold. Some superb work as usual and she's shaping up great. Your photos are top guiltily also.

Don

[arnoldb]

Bill, Vince & Don, thanks Gents 

Not much progress to report...  Today was all about butchering - earlier this week a sheep and an oryx walked into my freezer, so those had to be taken care of...

Then I managed to fit in a bit of shop time, and the butchering continued; not some of my best work - on the valve disk.  It's dimensionally correct, but does not look too good, so I might have to re-make it later, taking a bit more time to make it look better.  For now it'll do - I'd like to get the valves and linkages going, as this is an area where there could be a couple of unforeseen problems.

I sawed and milled a bit of 3mm plate to size for the valve disk, and located edges to zero up the DRO on the center of the square hole. Then I started spotting hole locations - the exact center of the square hole, as well as four positions offset 1mm in both X and Y.  I'd decided to use a 1mm drill to get into the corners of the square section for a start:

Nearly made a booboo with the calculations there; You might see two additional spot marks offset by just 0.5mm...  The funny little man in my tummy kept screaming at me that something wasn't right, so I stopped, thought, and realized the error before spotting in the correct locations.

While I was busy spotting hole locations, I did the rest as well:

The locations where the disk arms will mount are on a 33mm PCD, but not at a convenient angular spacing to use the DRO's PCD function, so I just used a quick bit of trigonometry to calculate their proper X and Y locations.

Then drilling started.  Unfortunately I skipped taking a photo here, and I know Vince is interested in this bit, so I'll describe.  I drilled 1mm holes through the spotted corner locations for the square hole, as well as through the center. 
Then I drilled through the center location again with a 2.5mm drill - hoping that the center 1mm hole would tend to guide the drill and prevent it deflecting.  This seems to have worked, and the drill deflected only a tiny bit when it broke through - this time there is a photo of the result:

It's slightly deceptive - the 2.5mm drill left burrs in the 1mm corner holes but went through nicely on center.

Some more holes drilled - this time 1.4mm and tapped 10BA.  This is the area in which the size of the engine was determined to an extent - being the smallest fasteners that will be used.  Note that on the plans these are not shown as tapped holes, but I think they should be, as they will be used to mount pivots for the disk arms.:


As a last step, I plunged a 3mm end mill through the "square" hole to get rid of more material.  I could have done this earlier, but all the previous work needed the small drill chuck to do, and for this I had to switch collets.  Just me being lazy.:


Off to the big bench vise, and a small triangular needle file and a couple of strokes later, the hole was square.  I used the triangular file, as it's easier to file out sharp corners for me with it than with a rectangular file - which still tends to make rounded corners.  This was my smallest needle file, but it was still too big for the hole, so I only had about 25mm of usable travel on it.  I just carefully worked my way around the hole filing away the same amount on each face and testing regularly with the spindle for a fit:


And ended up with a nice snug fit - with no free play at all:


Back to the milling machine, and some more trimming:


Once again back to the bench vise, and this is where the butchering started.  Got a couple of bits too close while hacksawing out the excess:


And further butchering - instead of making up some filing buttons, I eyeballed things for filing to shape, and in a place or two took away too much metal...  The results:

Like I said - not very good to look at - but adequate for now - all the holes are in their proper locations.

Mounted on the cylinder block - and standard M3 nuts and washers are too large...  So I guess that besides making studs, I'll be making nuts and washers as needed as well:


Kind regards, Arnold