Chris's Marion 91 Steam Shovel

[crueby]

Well, that went remarkably easy!


For the expanding mandrel, started with a 1-1/2" 10-32 SHCS, and turned/filed the outside of the head to be a slight taper, around 5 degrees or so. Then took a 1-1/2" length of brass round bar, turned one end to be a close fit to the hole in the eccentric straps, and drilled through for the 10-32 SHCS. The first inch was counterdrilled to the size of the narrow end of the tapered screw head, and the rest tapped 10-32. Since the slitting saw was already set up on the mill, moved the chuck over to the mill and used it to make two cuts at 90 degrees to each other in the end of the mandrel to let it flex out as the screw is run in.

Then moved the chuck back over to the lathe, and put the first part in - tightening the screw down made the madrel grip the inside of the part very tightly, and the shoulder made sure that the part was square on the mandrel. Few passes to turn the part down to thickness, loosened the screw, and the part came right off for test fit on the eccentric. Needed another thou off to fit well, so back on the mandrel for another pass.

This is what the mandrel looks like:

First part done, turns well on the cam:

And the rest cut down as well, including the two spares:

Very happy with how easy that worked, have to keep that option in the bag-o-tricks for the future! I think it holds plenty tight to use it to mill the outside shapes as well. One end gets milled off round, the other as well but with a tab sticking out to hold the arm that goes to the Stephenson link. The tab will have a shallow slot to hold the arm, which will be temporarily screwed on then silver soldered in place.

[fumopuc]

Hi Chris, may be for the next time.
https://www.2spi.com/category/crystal-bond/

[crueby]

Hi Chris, may be for the next time.
https://www.2spi.com/category/crystal-bond/

I have some of that, works pretty well. The things that the mandrel does so much better is self-aligning the parts to center, and allowing me to remove the part to test fit, and put it back on again very easily. It is a one-size tool, but it would be possible to turn the rim slightly smaller if needed for another part later. All in all, it only took a few minutes to make and saved a lot of time making multiple parts.

[cnr6400]

Gotta hand it to you, I never saw anybody make an expanding mandrel with a deli slicer before! 

Well done! the straps look like a great fit to the eccentrics.

[crueby]

Gotta hand it to you, I never saw anybody make an expanding mandrel with a deli slicer before! 

Well done! the straps look like a great fit to the eccentrics.

Getting hungry, gotta go make lunch....!

[derekwarner]

'the top/bottom caps and cylinder are not held together with studs at each end, the studs actually go all the way through and are held by the end of the crosshead guide'

This isn't all that different Chris, providing that the headcap & endcap are spigoted to the barrel, and the opposite side of the headcap spigoted to the individual crosshead......[the only downside is a stripped tapping in the crosshead/s]

I find this crosshead tappings surprising, as it does not have any redundancy considering the machine in itself is  absolutely in the highest levels of impulsive nature

I suspect the tie-rod bolts would have been rolled threads [over machining] as the rolling production imparts parallel grain structure and as such far greater strength than a machined thread & the change of section etc

Derek

[crueby]

Derek, this setup was new to me, though I have not inspected that many machines in this fine detail. I figured it had at least partly to do with the inaccessibility of the back side of the crosshead guide, since it is up against the gear train holder for the slew drum. As the pic a few posts ago shows, the machinery space is crammed in as tight as a front wheel drive compact car today.  Gotta get that time machine working again and go visit the Marion factory in 1905...

[crueby]

Yesterday and today saw the rest of the shaping done on the eccentric straps, started out by using the rotary table on the mill to tap the bottom end of the straps down to dimension using several shallow passes.

Took off the curve on the end of the top half in the vise, indexed off the tops of the tabs even with the top of the vise so once the first one was done the rest were all the same height.

Then turned them sideways in the vise, and milled the slot for the control arm end. The ends of the arms will have their corners rounded off to match the inside corner radius left by the end mill.

Back onto the rotary table to take the sides of the upper strap down to size, which left the inside corner at the top tab still to do.

So I laid the table down horizontal and finished off the top tab sides:

Here are the finished straps, ready to put on the control arms.


The arms will be made out of some 1/16" flat steel bar, temp screwed to the straps and silver soldered in place. There needs to be a block at the other end of the arms to form the clevis which goes around the bottom of the Stephenson link, that will also be soldered on and shaped. All the arms need to be the exact same length to keep the timing correct for forward and reverse, so shaping/drilling that end block will require another little alignment jig.

[zeeprogrammer]

Fascinating. 

I wouldn't mind seeing a closeup photo of the 10-32. The mandrel work is going into my reference book.

[crueby]

Fascinating. 

I wouldn't mind seeing a closeup photo of the 10-32. The mandrel work is going into my reference book.

Sure thing - here it is, just took a stock bolt and chucked it in the lathe, filed a taper on the side of the socket head:

The hole it goes into is tapped at the bottom, then is counterdrilled out to a diameter just over the size of the narrow end of the taper, so the farther it is run in the farther it pushes out the four segments of the mandrel. Works very well, I did notice that since the mandrel is brass, that the end of the hole got worn back in use, so the bolt had to go in a little farther, but that is not a problem unless making many many parts. Making the body out of steel would solve that, but the brass was much easier to fabricate from.

[zeeprogrammer]

I did notice that since the mandrel is brass, that the end of the hole got worn back in use, so the bolt had to go in a little farther, but that is not a problem unless making many many parts.

Thanks Chris.  And thanks for the additional explanation on the wear. I had noticed the bolt seemed to go in a little farther and had wondered about it.

[crueby]

Combination of wear and I did trim a bit off the socket to give room to fix a goof on one strap.

[Flyboy Jim]

I really like that mandrel Chris.  Like Zee..........I'm going to file that away. Oh yeah.............the parts aren't to shabby either!

Jim

[steam guy willy]

Hi Chris ...just a technical question about the straps and sheaves ...if one or the other had a segmented periphery would there be less wear/friction happening ???  I have never seen this modelled before but would it be a valid 'thing' to do ???? Answers on a post card &&&&&& !!!!

[crueby]

Hi Chris ...just a technical question about the straps and sheaves ...if one or the other had a segmented periphery would there be less wear/friction happening ???  I have never seen this modelled before but would it be a valid 'thing' to do ???? Answers on a post card &&&&&& !!!!

Hi Willy,


I don't think I have ever seen that on a engine, model or full size. Was it done on full size ones anywhere? It would reduce the contact area, so less friction, but might give places for debris to collect at the edges if the segments, causing more wear there? It could give the straps stress points to bend/break at if they were notched. Dunno, never thought of that, good question for those who have dismantled more old engines...