Author Topic: A Tandem Compound Mill Engine  (Read 2458 times)

Offline deltatango

  • Full Member
  • ****
  • Posts: 248
  • Melbourne, Australia
Re: A Tandem Compound Mill Engine
« Reply #45 on: February 11, 2020, 01:02:28 AM »
The crankshaft needs keyways for the flywheel, governor pulley and the eccentrics although I'm still doubtful about the eccentrics. Those could be made in two pieces as drawn and located with a key or made in one piece and secured with hidden grub screws. Right now the 3D printer is making the two part versions in PLA so I have something to handle and work out how to get the studs and nuts in (or that it isn't possible). Tug has discussed this in his build and went for the solid version. The other reason for using grub screws is valve timing, if the keyway angles aren't right then your stuck, I may well start with solid, get the timing right, then cut the keyways but all that is in the future.

The crankshaft was set up in v-blocks and brought true to the x-axis of the mill:



Then the flywheel keyway cut:



followed by that for the governor pulley ( angular position doesn't matter here so it might as well be done with this set up):



When I bought the Aciera mill it came with a lot of attachments and among these was a slotting head. At first I thought this was seized but on stripping it down it was just clogged solid with ancient grease. The complete lack of wear makes me think it has never been used and I have been waiting for a good reason to use it - the keyway in the flywheel was perfect for this:



The angle plate not only prevented lateral movement it was also a reference for a square that I used to align the flywheel split line with the machine axis. The simple, square-ended form tool cut well:



although I was probably over cautious with the feed. A little bit of fitting with a needle file was needed to get the key to go in but it all seems nice and firm now.

The family now looks like:



In a couple of hours I should be able to play with the plastic eccentrics...

David
Don't die wondering!

Offline Johnmcc69

  • Full Member
  • ****
  • Posts: 571
  • Erie Pa., USA
Re: A Tandem Compound Mill Engine
« Reply #46 on: February 11, 2020, 02:04:18 AM »
 :ThumbsUp:
 :popcorn:
Excellent work!
...wishing I had a Aciera...

 John

Offline deltatango

  • Full Member
  • ****
  • Posts: 248
  • Melbourne, Australia
Re: A Tandem Compound Mill Engine
« Reply #47 on: February 11, 2020, 03:09:20 AM »
Thanks John,
What I bid for the F3 felt like a lot of money at the time but it doesn't seem that way now! A Schaublin lathe that takes W20 collets would be great but they are very very rare here Downunder.

David
Don't die wondering!

Offline crueby

  • Full Member
  • *****
  • Posts: 9856
  • Rochester NY
Re: A Tandem Compound Mill Engine
« Reply #48 on: February 11, 2020, 05:04:38 AM »
That flywheel assembly is a beauty!

Offline deltatango

  • Full Member
  • ****
  • Posts: 248
  • Melbourne, Australia
Re: A Tandem Compound Mill Engine
« Reply #49 on: February 11, 2020, 05:20:39 AM »
Thanks Chris, just wish I could get somewhere near your levels of productivity!

As yet (tempting fate here) I don't have too many problems with shop elves, apart from the e-stop pusher, and I'm glad of that - just imagine your lot turning it into an elf unicycle and riding around the shop at 3am...
David
Don't die wondering!

Offline Ramon

  • Full Member
  • ****
  • Posts: 1765
  • Suffolk in the UK
Re: A Tandem Compound Mill Engine
« Reply #50 on: February 11, 2020, 10:40:05 AM »
Hi David,

Lovely result on the flywheel and shaft  :ThumbsUp: - you do have me inspired BTW got all the drawings out yesterday  ;)

I know it's looking ahead a bit for you but on my drawings there was a small annotation by Peter Southworth defining the angular positioning of the eccentrics. Do you have that on yours?

I decided I would stick with this and have marked the shaft accordingly (and the C/L of the eccentrics) to ensure this is as close to his recommendation as possible. My thinking was that even if this is out slightly there is enough variation in the linkage make up to make allowance for any discrepancy. Though mine aren't keyed I have the grub screws biting into deep centres for positive location. Unless Peter's anotation is out I'm fairly confident I won't have to remove the straps to adjust the eccentrics.

Regards - Tug
"I ain't here for the long time but I am here for a good time"
(a very apt phrase - thanks to a well meaning MEM friend)

Offline deltatango

  • Full Member
  • ****
  • Posts: 248
  • Melbourne, Australia
Re: A Tandem Compound Mill Engine
« Reply #51 on: February 11, 2020, 12:15:27 PM »
Hi Tug,
Thanks! Well, it would be great to see your build make progress again. Maybe we can restart, or even start, one or two others?

I know there's no need to look at fixing the eccentrics anytime soon but I do like to get each part finished in its turn, OK I try to ignore the OCD but that isn't always possible  :)

The drawings that Bob P sent me also have the extra sketches that help with the angular positions of the eccentrics but I still had a hell of a time interpreting them. Please take a look at the attached drawing and let me know if you think the keyway positions are correct. Just looked again myself and see I need to add an arrow for direction of rotation and a note to confirm that the crankshaft sections are viewed from the crank end. If Arnold T drew all this up and got it right then he was something special!

I've just been cleaning up the 3D prints of the two-part eccentrics, I'll play with these soon to work out if I want to make the real ones that way or follow you with solid and accept the possibility that the crank might have to come off sometime in the future.

Regards, David
Don't die wondering!

Offline Jasonb

  • Full Member
  • *****
  • Posts: 6963
  • Surrey, UK
Re: A Tandem Compound Mill Engine
« Reply #52 on: February 11, 2020, 04:59:57 PM »
I wonder whether those angles are optimised for running on steam, if you are going to be running on air it may be worth going for something with a bit more adjustment.

Don't let Tug get distracted I'm waiting for him to get on with his "Twin Shaft"  ;)

Offline Ramon

  • Full Member
  • ****
  • Posts: 1765
  • Suffolk in the UK
Re: A Tandem Compound Mill Engine
« Reply #53 on: February 11, 2020, 05:45:38 PM »
Hello again David,

I gave quite a bit of thought as to whether to make the eccentrics more scale like and from two parts as they ideally should be. Came down in favour of impression rather than realism mainly due to the time I wanted to give to them. Also, in the way mine were made (from the drawing) there was little space to get a functioning nut in without a lot of secondary machining of the cut out and subsequent thinning (and likely potential for distortion) of the outer wall thickness.

I still feel comfortable with that decision but would encourage you to go the two part route if desired as it will certainly look much better.

Your angles match mine for the Corliss and exhaust but I do not have any indication for the slide valve ? Wonder why?

Ne'er fear Jason - Twin Shaft and Corliss intentions are 'on the bench' together - hopefully get a start on them by the end of the month :) possibly sooner  :) :)

Regards - Tug
"I ain't here for the long time but I am here for a good time"
(a very apt phrase - thanks to a well meaning MEM friend)

Offline deltatango

  • Full Member
  • ****
  • Posts: 248
  • Melbourne, Australia
Re: A Tandem Compound Mill Engine
« Reply #54 on: February 11, 2020, 09:38:11 PM »
Jason's point about running on air vs steam hadn't occurred to me - I doubt I'll be building a boiler big enough to run this engine on steam.

With that point, and Tug's experience, in mind the solid eccentrics with grub screws look like the way to go. Maybe a two stage process, solid first, then when the timing is optimised re-make with keys? I'll have to think about how best to secure the crank, maybe a taper pin left over long until the final fix?

David
Don't die wondering!

Offline Ramon

  • Full Member
  • ****
  • Posts: 1765
  • Suffolk in the UK
Re: A Tandem Compound Mill Engine
« Reply #55 on: February 12, 2020, 09:37:07 AM »
Apart from the engine in the Wide a Wake and my first, a Stuart Twin Victoria, I've made the slide valves in other engines (destined to run on air only) with no lap, the length equalling the port spacing. Whether this gives any great advantage I'm not sure but the engines do run better - that is smoother - at slow speeds.  How this will translate to Corliss valves I'm not sure - it's been a bit too far ahead to really contemplate.

I've taken the angular location of the eccentrics as drawn at face value and fixed them as such. Thoughts so far are that any adjustment can be made either in the linkage or on the valve lever itself. My plan is to replace the square drive to the valve with a tapered seating so allowing variation - certainly on set up - possibly fixing with a drop of Loctite if required once settings are established. Thinking of course is only part of the equation  ::)

You have the nub David - once that crank is fixed those eccentrics are there to stay - well mine are for sure ;)

Best - Tug
"I ain't here for the long time but I am here for a good time"
(a very apt phrase - thanks to a well meaning MEM friend)

Offline gbritnell

  • Full Member
  • ****
  • Posts: 2059
Re: A Tandem Compound Mill Engine
« Reply #56 on: February 12, 2020, 03:01:07 PM »
What a gorgeous flywheel!
gbritnell
Talent unshared is talent wasted.

Offline deltatango

  • Full Member
  • ****
  • Posts: 248
  • Melbourne, Australia
Re: A Tandem Compound Mill Engine
« Reply #57 on: February 18, 2020, 06:07:52 AM »
Thanks George - I'm pleased with it as well!

Still working on bits associated with the crankshaft, and before thinking any more about how to make the eccentrics, I made the governor pulley. This is a straight forward piece that started as a rather rough gunmetal casting. This had a cast-in line marking the diameter and I cut along this with a slitting saw:



Note the very carefully judged sliver of metal being left behind by the saw, this kept the top piece in place so it didn't fly off when the cut finished. Next time I do a job like this I'll know to set it up like this deliberately  :D .

The two halves were soft soldered back together. In this picture you can just see that I should have marked this out for myself and no relied on the cast in line:



Set up in the 4-jaw the bore was finished to size and one face cleaned up:



This was then superglued to a mandrel turned in place on the 4-jaw SC chuck and the outside and other face finished:



The mandrel moved to the rotary table and a drawing made with the set of angles and offsets needed for machining the four cutouts (the drawing is attached as a .pdf file):



After heating the mandrel to both break the superglue bond and de-solder the joint two 7BA studs were made up using 2.4 mm stainless TIG welding rod and the whole lot fitted together:



The slightly rough patches are the consequence of not quite getting the original split line across a diameter as there is very little metal to spare on this casting. As the part will eventually be painted the rough bits can be cleaned up later.

Now I have no more excuses for not getting on and working out how I'm going to make the eccentrics.

David
Don't die wondering!

Offline Flyboy Jim

  • Full Member
  • ****
  • Posts: 1800
  • Independence, Oregon
Re: A Tandem Compound Mill Engine
« Reply #58 on: February 18, 2020, 01:56:59 PM »
Nice writeup on the machining process for this part.

I like those clamps on your rotary table.

Jim
Sherline 4400 Lathe
Sherline 5400 Mill
"You can do small things on big machines, but you can do small things on small machines".

Offline deltatango

  • Full Member
  • ****
  • Posts: 248
  • Melbourne, Australia
Re: A Tandem Compound Mill Engine
« Reply #59 on: February 19, 2020, 03:35:24 AM »
Thanks Jim, I made five of the clamps to a design in either Model Engineer or Model Engineers Workshop, I've tried to track down the reference but so far it's eluded me. Hopefully someone else on the forum will recognise them.

A few days ago I 3D printed samples of the eccentrics for the tandem compound so I had some bits to handle whilst I made a decision about making them split (as drawn) or solid. In the picture the slide valve eccentric is on the right, Corliss valve eccentric (there will be two of these) on the left:



The studs are 7BA and on the slide valve eccentric it is possible to fit standard 7BA nuts using tweezers and needle-nose pliers but it's awkward and getting a spanner on the nuts to tighten them properly just about impossible. The one nut I got on for the Corliss eccentric is an 8BA thin nut tapped out to 7. Getting it in there was tedious and tightening it impossible. I'd really like to hear from anyone whose has made the parts to the original drawings but, for me solid eccentrics will be the way to go. Tug has pointed out that even with everything fixed it will be possible to adjust the valve events so I'll get on and cut the keyways in the crankshaft and make the crank. Making the eccentrics will keep until I've made the straps, it will be easier to turn the eccentrics using the straps as gauges; the other way around isn't really possible.

David
Don't die wondering!