A Tandem Compound Mill Engine

[wagnmkr]

Nice work so far. Watching with interest.

[deltatango]

Thanks wagnmkr!

Per - the next steps are to convert these:



into this:



which will need a few other bits and pieces along the way.

David

[Admiral_dk]

Ah - I forsee quite a bit of measuring in your future - make sure you get your datums right 

I could see myself using a lot of time to contemplate the best way to solve this - especially the cylinder with all it's holes ....

Still following     

Per

[deltatango]

Yes Per, there's a lot of measuring going on just now:



Any holes marked as on a PCD I'm drilling using the "circle of holes" function on the DRO, all others are marked out and located with the DRO.

However, before any holes could be drilled the castings needed any hard skin removing and cleaning up to size. As with others of this set of castings there wasn't much machining allowance (close to zero on some dimensions) so the first process was a lot of casting fondling to try to avoid mistakes - there looks to be little hope of any replacements.

The seven-tooth cutter came in to it's own on the cylinder block sides and ends:





and the end faces where the covers have to seal given a good finish as well:



Before machining the cored hole for the bore I measured the as-made centre height of the slide which turned out to be 0.009" low:



The other careful measurement was of the lathe centre height above the boring table. In the picture it may be just possible to see the shims under the bottom (datum) face of the block. The angle plate nest was particularly necessary so that the block could be turned end-for-end, my longest tipped boring bar was just too short:



The bore was finished with a between-centres bar which took all my attention to get right so no pictures of that.

Before I get to drill any stud holes there is a lot of detail to add to (actually, subtract from) the block, I'll post that next time.

David

Edited to replace pictures lost due to finger trouble

[MJM460]

Hi David, great to see more progress on this one.  It’s a fascinating project.

MJM460

[deltatango]

Thanks MJM, good to have you along!

I had a major bit of finger trouble when cleaning up my directories on OneDrive and deleted the one that held all the pictures for this build. The originals were still on the local HDD so "all" I had to do to get them back was re-format them to 640x480 and upload to OneDrive. The bit that really took the time was working out which picture went with which bit of text and replacing them in what I hope is the right place. All done now so I'll get back to writing up the build.

With the HP cylinder block nicely squared, and the bore in the correct place, I could start in to drill and (mostly) tap the 142 holes that perforate it. The logical place to start seemed to be for the cylinder securing studs. Getting these in the right place needed an alignment piece to align the cylinder on the piston rod centre line. This piece was just a stub of Al turned to a close fit in the bore and bored at the other end to fit over the boss on the slide. With that and using a shop-made transfer punch the cylinder was fixed down front and back:



and checked with the HP piston and its rod:



With some confidence that the cylinder would go where it was meant to I milled out the steam and exhaust chambers top and bottom of the block:



and drilled and reamed the holes for the valves:



The steam passages were cut with a shop-made cutter, first in the bottoms of the chambers:



then from the bores to connect to the valves:



Two of the pictures above have hints of the Brunswick Green paint I'm going to use for the final finish - hope you like it!

David

[RReid]

I hate it when my fingers twitch at the wrong time! Glad you got it sorted out.
I like both your shop made cutter and it's application. Good ideas to file away!

[Kim]

That's a very neat cutter for your steam passages!  Like Ron said, I'll have to file that one away.
I also like the green color you painted the base.  I think it will make a great looking engine!

Sorry about the loss of your pictures, though I'm glad you were able to recover them.  That's always a pain!

Kim

[Roger B]

That's some good, if slightly worrying, machining. Glad all went well     

Good save on the pictures 

[deltatango]

Thanks everyone!
The little shop-made cutter was 7/8" OD and 0.1" thick, turned from solid silver steel rod, teeth backed off by hand and hardened. I didn't try to reduce the temper any which was just as well because after use it was clear that the inner bits of the 0.1 thickness weren't as hard as the outside. The cutter did the job but needs some TLC before being used again.

The last bit of outside shaping for the cylinder block was to put a 1/2" radius on the top corners. For the first time ever I used the radius function on the DRO with a 12 mm round-nosed cutter to do the work:



The process is tedious but gets there in the end:



The finish is good enough to clean up easily with a file:



The cylinder covers were two rather rough CI castings which I started in the 4-jaw to turn the outside edge and the chucking spigot:



turned round and held in an ER32 collet to machine to fit the cylinder bore (and, for the rear cover, make a recess for the piston securing nut to slide into at the back end of the stroke):



I kept the chucking spigot on as long as possible and used it to hold the parts to mill the clearances to connect to the steam and exhaust passages in the block:



With the same setup the DRO came into use again to drill the ring of 12 clearance holes for 6BA studs and three 8BA tapped holes for forcing screws to help with dismantling:



At first I thought that these three holes were just to stay true to the original but when all the studs are in place it turns out that they're necessary, very necessary! The last act was to remove the spigots, clean up the flanges to thickness and bore out for the O-ring gland:



Then there were eight 5BA, 48 6BA and 24 8BA studs to make but I'm not going to share the boredom of that with the forum, there'll be a progress picture next time.

David

[deltatango]

After a lot of drilling, tapping and screwing in of studs the HP cylinder looks like:



As a change from making holes in CI I made the whole of the piston rod(s) which meant a choice between turning a very long and thin single piece to give the four difference sections all in one, or making four separate parts and devising a way to fit them together - and straight. I chose to fabricate, mostly to avoid having to put a good finish on something so very long and whippy but also to allow the rod to be assembled a bit at a time as the build progresses. The four parts (plus HP piston and O ring) look like:



when separate, and:



when screwed together. The picture shows the method for fitting together which was to turn down the end of one part to a close fit in a reamed hole in the other with a short section of thread at the very end. The whole lot fits together well, when finally assembled I'll put a bit of thread-locker in to keep everything together.

David

[RReid]

That looks like you came up with an excellent solution to the problem; and well executed too. Very nice!

[gary.a.ayres]

From the initial CAD images to the current state of play, this looks fabulous!

gary

[deltatango]

Ron and Gary, thank you! On a very long project like this one the encouragement is very valuable.

The piston rod does look good but final proof will be a while in the future.

David

[deltatango]

The last cast iron parts for this build are the cover plates for the steam and exhaust chambers. These are the rectangular bits with a machining stub in the picture:



There was a chicken-and-egg situation with these bits - how to grip them securely to machine the machining stub? I tossed up trying to grip them by the edges but decided that keeping them square to the lathe axis might be too hard. After a bit of work with a file, the boss that will become a pipe flange was gripped in the four jaw chuck. This didn't look all that secure but both mounting stubs were carefully turned without incident:



With a clean cylindrical bit to hold firmly the other surfaces could be turned to drawing, the outer face and pipe flange first:



and drilled part way through for the steam passage:



then, still holding by the turning stub the edges were milled (and the stud holes drilled):



the last bit of machining was to mill the inner face flat and the part to thickness:



The 8BA threads for the flange studs were tapped and a little bit of hand filing rounded off the corners to give:



Apart from a bit of dust from drilling and tapping a lot more holes in the HP cylinder block there should be no more cast iron swarf to make. I actually like machining CI  (more that gun metal, and there's a lot of that to come) but cleaning up after it can be a pain.

David