I bought a Prusa MK3 printer the other day, and decided to print out the patterns for a jumbo-sized Dake engine as a trial run.

So far I am quite impressed with the little printer, and it has basically been running 24/7 for over a week without any problems.

This will be on the large size for a model engine, but I like to straddle the line (or cross it) between models and small workshop engines.

My eyesight is not good these days, so this is basically an engine version of a large print book for the visually impaired.

The engine will be poured in gray iron using my backyard oil-fired furnace.

I will probably pour permanent patterns in 356 aluminum first, since the plastic tends to get brittle over time, and some of the printed patterns are pieced together from multiple printed pieces.

Edited By PatJ on 10/03/2019 17:07:01

This is my furnace in action.

The crucible lift is at 1:00.

Edited By PatJ on 10/03/2019 17:10:35

I had visions of building a Dake one day, but I wanted a build that was more true to the original Dake design, so I studied the Audel's information, and drew a fairly exact scale Dake engine.

I posted my Dake drawings on an old website in about 2011, and a fellow named Stu Hart saw them, and asked if he could build a Dake model from the drawings. I told him that one day I would build and perhaps publish a Dake myself, and so I told him he could use my drawings, but that he should morph his build into something a bit different, and not just outright copy my design.

I have never seen the article, but I am told that Stu published the "Potty Dake" in Model Engineer.

No doubt it was an excellent build, given the engines I have seen that Stu has built.

Below are the drawings that Stu had, and these were the genesis for the Potty Dake build.

These were my second atttempt to draw a steam engine, and at the time, I could only draw in 2D.

Looking back on these drawings, they seem rather crude.

The isometric views were hand-sketched in 2D autocad, and so are pretty rough.

The geometry in these drawings I believe is valid though, and I paid close attention to that.

This is a barstock build design, because at the time, I never dreamed I would learn how to cast engine parts.

The format is large (ARCH-D which is 24"x36&quot.  These days I generally use an 11"x17" format, which is much easier to plot and handle in the shop.

Edited By PatJ on 07/07/2022 02:09:16

So now that I have the casting thing down, I am dusting off the Dake 3D printed patterns, and I intend to start casting some engine parts.

Many of the parts will be fairly easy to mold.

I will probably touch up the 3D printed patterns, to reflect that this is no longer a barstock build (add a few fillets here and there).

The most complex shapes to mold will be the valve body and its multiple passages, and the crankcase cover with its multiple passages.

The remainder of this engine should mold up fairly easily.

The plan is to make these castings in gray iron, and I think I can accomplish that.

For those not familiar with the Dake, this design appears to have been an almost carbon copy of a Roots engine that was patented about 20 years earlier than Dake's patent.

Dake made some slight changes to the Roots engine (at least that is my speculation; Dake could have actually created an almost identical engine independently, but I sort of doubt that).

I am surprised that the patent office allowed Dake to patent an engine that was so close to the Roots design.

I have never seen any Roots engines like this design, but the Dake version was a very successfully manufactured engine, with quite a few of them sold commercially.

This is a two-cylinder engine, with no dead-centers.

The pistons are shaped like a piece of toast, ie: they are flat on two sides and roughly square in shape.

The inner piston rides inside of a hollowed out outer piston.

The design seems laughably impractical, and yet my Dad's Dake engine is an amazingly smooth running engine, with no appreciable vibration.

It took me quite a while to wrap my head around how all the passages work in this engine.

The center piston also acts as a slide valve, and the port faces are build into the crankcase housing.

The valve body is for reversing the engine, and it works in a fashion very similar to a Westinhouse air brake valve, if you have ever seen one of those.

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These cuts are from the Audel's book that my Dad used to make his Dake.

The Dake engine design varied over the years, and no two appear to be exactly alike.

Even in these cuts from the same article, the ports in the inner piston vary.

I have seen rounded ports in the inner piston too, along with more of a teardrop-shaped port.

I am not sure what is going on exactly in these cuts, since in the second cut, the ports at the top of the crankcase are 180 degrees out. The ports in the crankcase should be as shown in the first cut.

Some engines had reversing valves, and some did not.

Some had the reversing valve remote-mounted, so the engine could be operated by a valve at ground level, with the engine at the bottom of a mine shaft.

The tapered shims in the bottom of the crankcase allow the slack to be taken up on the outer piston.

Dake offered metal gaskets for the crankcase cover in increments of 0.001", so that the clearance between the pistons and cover could be adjusted.

The counterweight on the crankshaft offsets the weight of the center piston to some extent.

The last cut shows the engraving I used as a guide for which Dake model I wanted to mimic.

I added the reversing valve, since most Dake's seemed to have that feature, as shown in the second cut.

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Edited By PatJ on 07/07/2022 02:52:52

Thanks all. I must admit I had to take my Dad's Dake engine apart and study each piece in order to finally fully understand how this engine works.

Here is a writeup I made about the Dake in 2010.

I can't guarantee that everything in this writeup is 100% accurate, but it reflects my understanding of the Dake engine.

The inner piston is pinned to the crankshaft, and it can only move up and down within the outer piston.

Pressure applied to the outside of the inner piston can only move it either up or down.

The outer piston is constrained by the adjustable shims in the bottom of the crankcase, and it can only move side to side.

What gets confusing is the inner piston is also the valve, with 4 ports in it.

The valve face where steam is admitted and exhaust is released is the back of the crancase, which is the cover facing away from the crankshaft/flywheel side.

Edited By PatJ on 07/07/2022 12:33:34

Much as I love the banter of the tea room topics, I can only use those to avoid shop work for so long.

It is rather hot this time of year, with temps hovering around 100F every day, and about 70% humidity, so really no excuse is too flimsy to avoid shop work.

The only way to finish an engine is to start on an engine, and so I have started working on the base pattern for the Dake.

When I created the drawings for my Dake, I was not into backyard casting, and so everything was set up for a barstock build.

This is coming back to haunt me a bit, and so I am having to fill the base pattern with wall patch compound.

I could go back and reprint the base pattern, but I think at this point I will forge ahead, and just salvage the 3D prints that I have.

As I got into foundry work and pattern making, I realized the importance of things like draft angle, fillets, overhangs, machining allowances, etc.

What I do now is complete my 3D engine models without many fillets (perhaps no fillets), and with no machining allowances.

Then I create the 2D drawings, which reflect as-machined dimensions.

Then it is back to the 3D model to add fillets (using too many fillets initially really clutters up the 2D drawings), and add machining allowances. The fillets and machining allowances can be toggled on and off in the 3D program.

And finally, in the 3D slicer program, I add a shrinkage multiplier of about 1.015, just prior to 3D printing the patterns or pattern pieces.

My Prusa is too small to print the entire base pattern, so I printed it in four pieces.

I had some slight bed lifting issues with one piece, and so I epoxied my base pieces together with them all being on a flat surface, and I will work out the warpage issues with filler.

Since this pattern will be fragile, I think I will cast a permanent pattern in 356 aluminum.

The filler is a mix-on-demand powder, used for patching wallboard.

If I had set up my 3D model correctly, and if the 3D printed patterns all been perfect, then I would need very little filler.

Alas this is not a perfect world, and so I am using a rather gloppy approach with the filler.

Most of the filler will get sanded off, and luckily this filler sands relatively easily.

The Durham's wood putty does as advertised, ie: it dries "hard as a rock", and so I don't use Durhams, since trying to sand it ruins the nearby wood or plastic pattern.

Edited By PatJ on 23/07/2022 03:46:33

Edited By PatJ on 23/07/2022 03:51:23