Author Topic: A Tandem Compound Mill Engine  (Read 28856 times)

Offline Admiral_dk

  • Full Member
  • *****
  • Posts: 3717
  • Søften - Denmark
Re: A Tandem Compound Mill Engine
« Reply #180 on: February 22, 2023, 12:25:48 PM »
Another part ticked of the list  :ThumbsUp: and I'm sure you will apreciate it later, that you used a lefthand thread in one end - as it give infinite adjustability without disassembly  :cheers:

Per

Offline vtsteam

  • Full Member
  • ****
  • Posts: 753
Re: A Tandem Compound Mill Engine
« Reply #181 on: February 22, 2023, 03:00:47 PM »
Fine looking parts, and great to see a filing button used to help make them! A love to see traditional hand work methods, and their results. :ThumbsUp: :ThumbsUp: :popcorn: :popcorn: :cheers:
Steve

Offline cnr6400

  • Full Member
  • *****
  • Posts: 2660
Re: A Tandem Compound Mill Engine
« Reply #182 on: February 23, 2023, 12:24:44 AM »
 :ThumbsUp: :ThumbsUp: :ThumbsUp: :popcorn: :popcorn: :popcorn:
"I've cut that stock three times, and it's still too short!"

Offline ettingtonliam

  • Full Member
  • ****
  • Posts: 128
Re: A Tandem Compound Mill Engine
« Reply #183 on: February 23, 2023, 03:25:45 PM »
Another method I've used when I didn't have a suitable left hand tap/die, was to cut one end 40 TPI and the other end 32TPI, so turning the rod gave a differential adjustment between the ends of approx 5 thou.

Offline steamer

  • Global Moderator
  • Full Member
  • *****
  • Posts: 12691
  • Central Massachusetts, USA
Re: A Tandem Compound Mill Engine
« Reply #184 on: February 24, 2023, 12:17:44 AM »
It's coming along swimmingly!

Dave
"Mister M'Andrew, don't you think steam spoils romance at sea?"
Damned ijjit!

Offline deltatango

  • Full Member
  • ****
  • Posts: 373
  • Melbourne, Australia
Re: A Tandem Compound Mill Engine
« Reply #185 on: February 24, 2023, 04:50:44 AM »
Thanks for looking in, everyone!

The adjustment of the valve gear is likely to be tricky enough without having to dismantle everything to change the length of links. The use of different threads on each end is a new idea for me - thanks. In this case though I may need a couple of mm of adjustment.

On the original drawings the ends of the rod ends were left square across, but this looked a bit crude, so I rounded them off. This is one place where I think it is easier (and more satisfying) to use hand methods, the time taken to set up the rotary table etc. etc. just doesn't seem worth it.

David
Don't die wondering!

Offline deltatango

  • Full Member
  • ****
  • Posts: 373
  • Melbourne, Australia
Re: A Tandem Compound Mill Engine
« Reply #186 on: October 11, 2023, 04:22:17 AM »
This project has been making progress but in such small increments that I didn't write them up at the time. Now there is quite a lot to catch up with, although many of the small parts needed for the HP cylinder valve gear were tedious and not very interesting to make. I'll pick out a few of the interesting ones to get the build log up to date.

The steam lever (see attached drawing) takes the drive from the eccentric rod and opens each of the steam valves in turn. Making this is complicated by having to turn a circumferential groove with an offset centre:



I chose to make the part on the end of a stub of round rod and adding the small, rounded end as a separate piece epoxied in. After drilling the two holes and defining the outside limit (above picture) the part was re-centred to turn the  groove in which the trip blades will run:




then turn a length concentric with that for holding the part later:



and that was held in the dividing head on the mill table to cut and drill the slots for the trip dies:



The mounting stub was also necessary for tapping the 10BA screw holes for securing the hardened trip dies:



The separate piece with a 1/8" hole was JBW'd in place and the outside shape finished off:



After all the messing about the part looked like:




If there were a "next time" I might simply round over the end and not bother with the fabrication step but it did work.

More shortly.

David

Don't die wondering!

Offline Admiral_dk

  • Full Member
  • *****
  • Posts: 3717
  • Søften - Denmark
Re: A Tandem Compound Mill Engine
« Reply #187 on: October 11, 2023, 08:46:24 AM »
I can see a great number of small things to make - just on that sheet alone ...!

But good to see that you're still making parts  :cartwheel:

Per     :cheers:

Offline MJM460

  • Full Member
  • ****
  • Posts: 1638
  • Melbourne, Australia
Re: A Tandem Compound Mill Engine
« Reply #188 on: October 11, 2023, 11:05:57 AM »
Good to see that you are still on the job.  It’s been a big undertaking.

Always fascinating t see how those intricate parts are made.

MJM460

The more I learn, the more I find that I still have to learn!

Offline wagnmkr

  • Full Member
  • ****
  • Posts: 904
  • Lindsay, Ontario, Canada
Re: A Tandem Compound Mill Engine
« Reply #189 on: October 11, 2023, 12:22:37 PM »
Don't know how I missed this build. Fine workmanship with all the small parts.
I was cut out to be rich ... but ... I was sewn up all wrong!

Offline deltatango

  • Full Member
  • ****
  • Posts: 373
  • Melbourne, Australia
Re: A Tandem Compound Mill Engine
« Reply #190 on: October 13, 2023, 12:21:36 AM »
Thanks for looking in and for the encouraging comments - Per MJM and wagnmkr!

Other small parts that made me stop and think before cutting metal were the trip dies - sharp wedge shapes with a large hole at one end and only ~5/8" long. As with other small bits these were easiest to make on the end of a piece of stock, keeping them attached as long as possible. First rounding over one end then milling one face of the wedge:



then turning over and milling the other face:



The "sharp" end had a small radius filed on after detaching from the stock:



The second part had to be cut off from the stock before fitting filing buttons to form the rounded end.

David
Don't die wondering!

Offline deltatango

  • Full Member
  • ****
  • Posts: 373
  • Melbourne, Australia
Re: A Tandem Compound Mill Engine
« Reply #191 on: December 24, 2023, 07:03:51 AM »
The function of the trip dies is to lift the trip blades (these carry the motion from the steam lever to the valves) is to release the valves to close at the cut-off point. The trip blades were made on the end of a piece of square key steel (almost all of my square steel stock is key steel):



and then case hardened.

Most of the other, very numerous, small bits were made from what had been bought in as free-cutting stainless to reduce the amount of corrosion and maintenance in the future. Some of the steel machined quite well, other bits were a pain and the whole process of finishing off the HP gear was time consuming and became tedious, I guess that all large projects have times like that. I'm not going to re-visit this period in great detail!

The last parts needed to complete the HP cylinder were the castings for the dashpot body, bracket and lever bracket. These were missing from the casting set and I don't know if they were ever available. There was a choice here between machining from the solid (the straight-forward easy way) or learning how to make my own castings; of course I chose the more interesting path.

With the 3D CAD models for the parts already created turning these into masters for lost PLA casting was simple enough :



learning how to produce useful castings took rather longer. I'll start in on describing that in the next post.

David
Don't die wondering!

Offline Roger B

  • Global Moderator
  • Full Member
  • *****
  • Posts: 6090
  • Switzerland
Re: A Tandem Compound Mill Engine
« Reply #192 on: December 26, 2023, 08:34:17 AM »
Some nicely made Fiddley bits  :ThumbsUp:  :ThumbsUp:

I'm looking forward to the casting adventure  :)  :wine1:
Best regards

Roger

Offline MJM460

  • Full Member
  • ****
  • Posts: 1638
  • Melbourne, Australia
Re: A Tandem Compound Mill Engine
« Reply #193 on: December 26, 2023, 09:38:55 AM »
Hi David, good to see the progress continuing.

It will also be interesting to follow your casting adventures.

I hope you had a happy Christmas.

MJM460

The more I learn, the more I find that I still have to learn!

Offline deltatango

  • Full Member
  • ****
  • Posts: 373
  • Melbourne, Australia
Re: A Tandem Compound Mill Engine
« Reply #194 on: January 08, 2024, 01:43:34 AM »
Thanks to all who those following along and good wishes for 2024!

The casting story is largely about treating everything you read online with skepticism. It is also about not trying to save money; that really doesn't provide anything but frustration. What follows condenses several weeks of experiment into a short description; it isn't intended as a set of instructions for lost-PLA casting but will give hints about what not to do.

I already had a stock of fine cristobalite sand so when I read that ordinary plaster-of-paris was all that you need to turn this into investment plaster that was what I tried. Well, this may work for lower temperatures, but it didn't cope with casting bronze at around 1000 C. I'd also read that all you needed to do to form the molds was to use cardboard tube to contain the investment while it sets which sort-of worked but obviously didn't provide any support during burn-out. Several molds cracked at this stage. Time to stop messing around and look at what was available to buy locally from a real local supplier. What I found was "Gold Star Omega+" investment powder (from Australian Jewelery Supplies in Melbourne). I could also see that casting flasks were just steel tubes and that sprue bases could be 3D printed:



The condition of the mild steel flask is the result of burning out to the instructions for the Omega+ which require several hours at 750C as the final stage. The burnout was tedious but at least I was now getting useful molds.

As to the type of PLA to use, I started with ordinary white filament which almost works but still leaves a small amount of burnt residue in the mold. PolyMaker "PolyCast" filament is made for the purpose and prints can be polished with iso-propyl alcohol. It also burns/vapourises away completely. There are other materials available but having found one that works I'll stick with that (at least until I change to a resin printer, that is).

I already had a muffle furnace that had been discarded from work (I found out why and had to rebuild it but that's another story) for burn out and bought in a small electric furnace advertised for jewelry work. This is claimed to reach 1200C, well above the liquidus of bronze, but I'm not so sure about this and will have to experiment a bit more. A gas fired furnace may be needed to get the metal hot enough to pour well.

After three sets of failures I managed to get some usable castings for the dashpot body and its two brackets (useable, not perfect!):





After the use of rather a lot of filler on the body all three machined up to be usable and I'll describe that process in the next post.

David

Don't die wondering!

 

SimplePortal 2.3.5 © 2008-2012, SimplePortal