Gray, yes I would think it possible to close the holes off at the top. As you say the “void” would still need to be open somewhere to allow the unbonded layers of metal powder out much like you would need a way to remove the sand from a traditional core.

Mike Tull over on MEM forum has just had some nice exhaust manifolds and other pipework printed for his Mercedes GP Engine  which is otherwise mostly CNC machined on small Emco machines

Costing can be a bit variable sometimes quite good other times it seems expensive when compared to casting. But a lot depends on what you are after, if it is a one off casting or a batch then pattern making costs will be higher for a single but can be spread over the cost of a batch. But can be worth it where fine detail, complex cores etc are wanted that may be hard to cast or involve more costly core boxes etc.

Some interesting recent posts over on MEM which go along with what David has said, the prints can attain the same strength as solid or cast metal.

Although the basic structure is fine in aluminium there could possibly be issues with it as a bearing surrface picking up both for the revolving crankshaft and the sliding cylinders on the port face. I went with a bronze sleeve for the crankshaft as it is not something that could be automatically oiled while running unless you go to pumped oiling which you don’t see on many small steam engines. The cylinders on the other hand can be lubricated with either displacement lubricators if using steam or inline oilers when running on air for longer periods.

The usual 3D printed aluminium is AlSi10Mg though you can go for 6081 which is the old HE30 and they heat treat to T6. Someone on MEM did the maths and in theory that short length of male threaded steel I had in the print should fail before the aluminium threads strip out. I’m not going to risk one of these prints trying but next time I order will just have a block of metal printed to try and pull the thread out. A simple drop of oil is enough for my <10min runs

At the moment there don’t seem to be that many doing 3D prints directly in bronze (or brass and iron), but they all offer a service where the model is printed in wax and then investment cast in bronze but that does put the price up

If you have seen my article in the current mag then there are several people using 3D metal prints to recreate old model aero engines where you can’t get the castings anymore like this Sugden Special. They don’t have problems with their heads popping off be that for compression ignition diesels or high performance competition engines. These engines would have had bearings and liners added originally so that side of things is taken care of.

I think accuracy and finish are likely to be better.

No hoping that you have allowed the right amount for shrinkage. No problems with the two mould halves not lining up and leaving a step at the parting line. Machining allowances can be included but fairly minimal and there is no need to worry about draft angle or flash around loose pieces as they are not needed. You can also print thinner than you may be able to do so with castings which is useful for models where you may want to cast something that was say 6mm thick in full size and your 1/4 scale model can still do it at 1.5mm where as you may have had to cast at overscale thinkness to be sure the meatl flows.

You are also not going to get voids, areas of shrinkage or hard spots in a print that you can with a casting

Finish more consistently as you don’t have a fettled parting line that ends up smoother than the “cast” surface. Also given the surface finish I have been seeing lately on the now commonly used bound sands the print is going to have  a better surface as the tendancy seems to be to just dump a load of the freshly mixed sand into the cope or drag and just push it down. This gives a reasonable finish on the horizontal surfaces but the more vertical they become the rougher they are due to the sand not being packed well against the mould

I did actually ad a small boss to the intended print file but it was not on the one I actually got printed, you can see it on the rendering at the start of the thread. Though I was still able to add an oil hole with CSK around it.

I may have a few of the other 5 prints available.

A piece of wooden dowel was turned down to a firm fit in the cylinder, loaded with a mix of oil and 600g silicon carbide powder and the cylinder lapped.

The piston material was then faced and turned 0.2mm over diameter before being drilled & tapped M3

It was then screwed onto the piston rod for final turning to diameter using the cylinder to gauge the size and a small oil groove added. No photos of the piston rod as it is just a piece of 3mm stainless steel tapped M3 at both ends.

A small offcut of brass was milled to a 5mm x 5mm square section, the end squared up and a hole drilled and reamed 3mm for the crank pin.

It was then held end up to drill and tap for the piston rod. After sawing off the end was rounded over concentric to the pin hole.

Again no pictured of teh cylinder pivot as it is also just a piece of 3mm stainless threaded at both ends. The spring adjusting nut was turned from 8mm brass and rather than a hex hed like I used on kelsey I formed a half round bead and then using just one wheel of a pair of diamond knurls cut a good representation of a rope knurl.

And I think that just about covers all the parts.

After a successful test run the engine was stripped, cleaned and painted.

Still not too late to guess how long it took me to complete.

Thanks, keep the guesses coming, I’ll leave it until Sunday evening to let you know how long it took me.

Although I have posted the videos in the Kelsey thread I will put them here so it is all in one place

During the test run and while doing the video above I could not get Willy to run as slowly as I would have liked, he was a bit stiff and he needed a good flick to get him going when the regulator was at a low opening but as I wanted to get the completed video out before the end of the year run as it was.

With a little more time I had a fiddle and there was a bit of tightness when turning the flywheel over. I tracked it down to the big end which was a bit tight on the pin, running a hand reamer through the previously machine reamed 3mm hole just eased it enough to free things up. I think what had happened was that I rounded over the big end by screwing it to an arbor and using the rotary table, the cap head screw had brused the edge of the hole slightly.

With the engine back together and no change to the pressure it ran a lot slower and if the crank was in the right place would self start as the regulator was opened – something it did not do before.

One other bonus of this fiddling was that I found the small adaptor for the airhose I had made could be screwed in too far and partially block the inlet drilled passages. With it not screwed in so far there was a good improvement in speed, going from 2700rpm as seen at the end of the first video to 3687rpm an increase of almost 1000rpm for the same pressure but with no restriction to the passages😀

How long did it take?

I recorded my time on this one and totalled it up when the engine ran, I added a flat to the crankshaft afterwards so then added that on which can be seen on mt “working drawings”

Guesses in no particular order

8.55   Grindstone Cowboy

12.30 Andrew Crow

7.30 Colin Heseltine

8.20 Diogenes

9.45 Danni Burns

7.30 Keith Beaumont

12.00 Mark Eastwood

36.00 Dalboy

Well you were all over some by more than others. The building time was 6 hours 35 minutes which does not include painting which was just a rattle can job.

I may have a couple of the spare 3D prints available if anyone wants to PM me.

No and I don’t before I run a part on the CNC either. I just check it all goes together and rotates and moves as it should in CAD.