Stuart Triple new build

More progress
Now for what I consider the hardest part on this model. The reversing screw the drawing calls for 3/16 20TPI 2 start thread. I gave this plenty of thought and decided I would make this by making a tap to produce the nut then screw cut the thread on the shaft using the nut as a gauge. Checking my history I decided to make the thread stub acme as acme threads came into use about the 1890's and as I do not know exactly the date this model is a copy off, checking google I found triple expansion engines were around this time frame so that is what I decided to build. I checked with my tooling supplier could only get 16 TPI stub acme full form tips so again this is what I used.
First up the tap I used silver steel as I was only tapping bronze.



I hardened the silver steel using a blow touch did not try to temper as it is a long time since I did any serious heat treatment it did end up quite hard as I only had to tap through 3/8 dia bronze it worked well




I made 2 nuts just in case I had any issues.

Next I cut the 3/16 thread on the shaft. My lathe is a Prototrak out of the USA I am semi retired these days and as you get next to nothing for used machinery I decided to keep my lathe it is great at this type of machining, I can program any pitch required so this thread was pretty straight forward. The only consideration with this thread was setting the screw cutting tip at the require helix angle for this thread it required 9 degrees on the holder so I machined a wedge to give me the required helix angle it worked great.



The thread for the reversing screw came out great




Next I made a simple wheel to fit on the shaft and bracket to fit to the model along with the reverse screw lever all came out great



And an up to date of progress

Very informative. I did a 2-start reversing screw for a larger model where I found a commercial tap and turned the shaft to match. I never thought about making the tap myself, nor using acme threads.

Maybe a bit late, but when I made mine I found it needed more than the 1” of thread shown on the drawing I needed 1 1/8” minimum to achieve full movement of the expansion links.

Hi Steamingandy
I agree with your observations I have not fastened things yet I looked at that very aspect and thought the same thing and I have a second reversing shaft made which has 1 1/8 of thread if required. I like suggestions from readers of this blog if they see things to make my life easier with this build. Keep the suggestions coming.

One other thing the shaft holding the expansion link arms, drawing says 6 15/16“, make 7 1/4” and trim down when you have the expansion links connected to the valves. Had to be longer on all the ones I have done.

Thanks again already corrected this mistake on the drawings 1st one made as per the drawings 2nd one as you said 7 1/4 "
Thanks again

Now for the next part reasonably straight forward, the Guide bar bracket first skimmed the sides to get a parallel then was able to hold lightly in the mill vice to machine to thickness worked well then drill and ream the 4 holes. I drew it up in AutoCAD and produced a program to machine the outside profile using a fixture I made first, see attached photos and YT link, The YT video was shot after I had actually finished the part as I forgot to do it as I was machining.










Link to YT machining


https://youtube.com/shorts/Sqy7el7fT_o

Hi All
Updated photo to this stage

Now to do the Cylinder Block very straight forward machining job I have a surface grinder in the shop so can get very exact sizes when needed.



Many holes to drill and tap 7BA, Port holes mounting holes a total of 86 holes it took some time to complete, luckily no mistakes.
Joining the two castings was a bit problematic supplied with the kit are are some cheese head screws I did not like them as they are quite large for where the join needs to be so I had some M3 stainless SHCS which after milling a small pocket did a great job of joining the two castings.



Next I machined the valve chests for the HP and LP ends of the castings see attached photos along with the valve rod glands





This week I will start putting studs into the cylinder block and fitting the valve chests then proceed to machine the valve rods and the 3 slide valves which will need some slight modifications as the ports in the castings are not exactly as per the drawings, not exactly certain on what to do yet to get them working correctly but will tackle that this week. Till then cheers.

I briefly had the castings for this engine before passing them along. It seemed to me that most of the small castings were easier to recreate from billet.

Worth drilling the cladding holes in the cylinder block (easy to mount) before you get to much sticking out of it

I like that idea will checkout before I get too much hanging off the cylinder block.

Also as KVOM mentioned, yes some of the small castings are easier to make using billet stock I have done this myself as the castings are very hard to hold so billet works.

Emers said:

Also as KVOM mentioned, yes some of the small castings are easier to make using billet stock I have done this myself as the castings are very hard to hold so billet works.

Click to expand...

I've been following your thread. I'm curious, how difficult would it be two build the cylinders from CI? (or steel) Also, is there a reason the two cylinder sections are built in too parts? Is it possible to build the two as one?

Hi Richard
It would be very difficult to build from CI or steel as there are steam passages cast into the walls of the castings and it needs to be in 2 pieces as there is a cavity between the 2 castings for the slide valve to operate actually a valve chest.




Hope this explains things

Emers said:

Hi Richard
It would be very difficult to build from CI or steel as there are steam passages cast into the walls of the castings and it needs to be in 2 pieces as there is a cavity between the 2 castings for the slide valve to operate actually a valve chest.
View attachment 137134

View attachment 137135

Hope this explains things

Click to expand...

Thanx. Yes, it explains a lot. However, I thimpfks that it would be possible to carve this in CI. I wonder what Stuart would charge for just these two castings. (and how much shipping would be to USA). There is another triple expansion engine I am interested in, I thimpfks with a condenser. As far as I know, there are no castings available for this other one.

Hi again
Stewart do sell individual castings they will quote cost plus postage to you just one email will get you a price.

Emers said:

Now for the next part reasonably straight forward, the Guide bar bracket first skimmed the sides to get a parallel then was able to hold lightly in the mill vice to machine to thickness worked well then drill and ream the 4 holes. I drew it up in AutoCAD and produced a program to machine the outside profile using a fixture I made first, see attached photos and YT link, The YT video was shot after I had actually finished the part as I forgot to do it as I was machining.

View attachment 136892


View attachment 136893


View attachment 136894


Link to YT machining


https://youtube.com/shorts/Sqy7el7fT_o

Click to expand...

Hello,

Did you insert bushings into the fixture, or are the stand offs machined from a complete solid? Do you keep these fixtures? I struggle to decide if it is easier to just make new fixtures occasionally or store and prepare them to be able to re-align them later. I would be interested how others do it.

Greetings Timo

Hi Timo
That fixture has inserts I made that fixture for that job and they are all kept together but if I can do simple mods to be able to do other parts I will modify and hopefully not have to make the original part again.
Cheers
Emers

Emers said:

Hi Timo
That fixture has inserts I made that fixture for that job and they are all kept together but if I can do simple mods to be able to do other parts I will modify and hopefully not have to make the original part again.
Cheers
Emers

Click to expand...

Hello,

thank you for reply . The insert will be something that I have learned today for future use. "archiving" fixtures vs making new ones will be always my gamble. The day I scrap one I need another part.

I keep following Greetings Timo