"We can build that!" The Union Chronicles

[RolandMM]

Bob and Dave, thank you for your encouragement and comments.  Now that the cylinder is permanently attached to the sleeve the bore can be finished.

It is common for the sleeve bore to have tight spots where the shrink area is located.  That is why I leave it undersize and finish it after the shrink has cooled.

Remember the sleeve is still in the chuck just as it was machined with the cylinder shrunk over it.  That eliminates the need to rechuck and assures the sleeve is exactly centered.

Wanting a 1.7500 bore to fit the piston ring, I used a boring bar to bring the hole to 1.7495 ending up with light cuts and slow feed for a good finish.  Then to get a true bore to the exact size I used a homemade lap with 350 grit abrasive.  I dreamed up this lap design years ago and probably got the idea from something I saw and used available materials.

Leaving the sleeve / cylinder still chucked up, I start small so the lap can adjust to the size and lots of oil on the lap and on the tailstock vee-ways.  Then add some grit and slide the tailstock so the lap goes the complete length of the bore.  Lock the crossslide so it allows the lap to only protrude halfway out the back of the cylinder.  If it extends out too far, this goes quickly from a fun easy project to a total disassembly, cleanup, and start all over nightmare. 

Tighten the lap until a drag is felt and by working the tight spot more, soon it will feel the same over the complete bore.  Only then take a measurement and determine how much farther you must go.  The first 0.00025 comes out quickly and as more high spots are removed, the bore gets a polish and removal gets slower.  Usually by the time all the tight spots are gone the size is close.  Finish up by moving the tailstock rapidly back and forth to leave a cross hatch so the rings will seat easily.

NOTE:  In my eagerness to take a picture I did it before I put down newspaper to protect the lathe ways.  Any newspaper will work but use several layers -and- if you happen to have tomorrow's newspaper you should read it first - (and then tell me how you got it).

The lap is simple to make and I have several sizes.  First make the stem, threaded on the end.  This stem works well with a shoulder and can be used with many lap heads.

Then cut a section of copper tube a couple inches long that is about the diameter of the bore.  Slit it lengthwise and if necessary, remove a piece so it will go inside the bore.

Then drill and tap a steel bar to fit your stem and slide inside the copper piece.  Drill and tap a hole, centered front to back, almost through the side of the bar and tap for a NF set screw.  I used 3/8 - 24 for this lap.

Cut the bar lengthwise through the center almost to the stem end and cut the half not tapped, to the slit so it is a separate piece.  Enlarge the tap drill hole in that piece to a body drill size so the set screw can fit inside it and hold it in place.

When you see the pictures it will be as clear as Carborundum grit.  The tapped hole piece fastened to the stem holds the setscrew which holds the loose piece in position and also acts as a crowd screw to enlarge the lap.

Now is time to silver solder the leading edge only of the copper shell to the tapped block so the turning direction will wrap the copper around the loose piece.  Remember to heat the whole copper piece to anneal it as the grit embeds easier.  Drill a hole when done to insert the set screw when assembling and you are ready to lap.

After lapping, I faced the end so it is perfectly square with the bore and broke the inside edge.

Now, and only now, is the time to release the chuck and continue on with the rest of the engine.  Sure nice to have my lathe back!

Roland

[marv in minn]

and now i know how you got such a nice fit on the piston 

[ths]

Thanks Roland, a very useful description. Cheers, Hugh.

[Dave Otto]

Hey Marv

Nice to see you made to MEM! Be careful you just might be asked to post an intro in the Introduce Yourself section.

Roland, thanks for the lesson on making laps; one of the other guys on the forum (Ramon) makes his laps much the same way. 

Good to see a nice progress report on the Union.

Dave

PS. the Regan book should be delivered tomorrow.

[RolandMM]

Marvin!  There you are.  I have been doing all this work and you are getting all the credit, just backwards of the way it should be.

Now that you are here I will tell what you have been doing and you add the details I leave out.

One of the parts with a long lead time was the nameplate.  We had borrowed a very early style and did a rubbing. I scanned it and sent to Marvin who patiently traced it so he could design toolpaths to cut a mold.

Now all the lettering needs to have 1 degree of draft so the wax can be lifted from the mold.  Since most nameplates are curved to fit a cylinder, we long ago decided to cast the wax flat and then curve the brass nameplate.  On larger pieces we have curved the wax before sending it to the foundry but usually it is easier to bend the brass.  Note Dave at the Idaho Division did that when he built his Pacific which is written up in another thread.

We commonly also make a buckle when we make a nameplate.  In this case Marvin made 2 backs for the mold.  One flat for the nameplate and the other rectangular for the buckle.  The picture will explain it well and you can see the design cavity will fit either back.

Since this was a very short run (3) I did not bother to cut vents and just used strips of tape to get the mold to fill.  The pins are the cores to make the mounting holes.  It is easy to locate holes when making the mold but difficult after the tag is made.

Roland

[marv in minn]

in order to make a tag or buckle mold, i start with a photo, rubbing or ideally an original tag .
then comes the process of finding a font that is close and then modifying it to match the original lettering.
this entails changing the shape, spacing and elements of the letters and adding flourishes that complete the design.
this process can take up to 40hrs like the Kansas City Lightning or Samson tags.  the Union and Pacific tags were fairly straight forward.
i have to make sure the letter size and spacing will be able to fill when Roland injects the wax and be sharp to read.

i use Surfcam 3 axis CAD_CAM program to draw and create the tool path.
for the engraving, i use a carbide single flute cutter ground on my Deckel cutter grinder with 2 to 5 deg draft.
i have to allow for the shrinkage of the wax (.017) plus the brass(.006) which comes to .023 per inch.
i also have to cut the mold in reverse so the end product will read correctly. (Dave, be quiet  )
i've heard that mold makers are backwards people, i've only been one for 44 years and still walk toes first. 

to cut the Union tag cavity, i used cutters with diameters of .187, .062, .012 and .007, the programs ran for about 6+ hrs.
the back plate has both locations for the plain tag and a buckle back where the tag cavity is the front of the buckle.

i now let Roland inject all of the waxes.
i tried it one time and wound up spraying his garage ceiling and my beard with green wax when a core pin blew out. 

[RolandMM]

Marvin,  Glad to get some details and maybe it is not as easy as you make it look.  Using a .007 cutter may make readers think this type of project can be done on a desktop mill.  Send a picture of the mill you use to cut delicate parts like nameplate molds.

The green wax story would almost make a new thread .......

Roland

[Dave Otto]

The green wax story would almost make a new thread .......

Or at least a little comic releif
The quality and detail of investment casting still amazes me.

Dave

[marv in minn]

Warning!! this is a working shop, not a show case

i use an older Milltronics Partner1 that was rebuilt to factory specs.
it uses Cat 40 tooling and can run up to 5000rpm.
it is one of the only full size CNC machines that can run on 220 single phase so i don't need a phase converter for it.
i also work on full size engines and machinery so this works best for me.

so far, i have not found a benchtop CNC that satisfys my needs

re: green wax,  at least everyone else thought it was funny   

[RolandMM]

Time to catch up on the Union Engine.

As previously mentioned, parts requiring castings were addressed first. One of these were the governor weights.  This was an easy mold and Marvin turned it right out.  It helped that we had been able to borrow a complete Union governor so had a good pattern.

Marvin cut the mold in an aluminum block and I injected wax and made several patterns.  Then off to the foundry, carefully wrapped in dollar bills for padding, and a few weeks later the bronze castings arrived looking good.

There was some machining to be done on them.  We had decided against cores because this was a short run.  A simple fixture with a hole to hold the ball and a clamp plate worked well.  It was fussy to get everything square and true and in addition to drilling holes, the dog had to be undercut so the spoolpiece didn't bind - but then I am getting ahead of myself.

Roland

[Alan Haisley]

It's amazing how much cleaner investment castings look than the cast iron, aluminum or brass sand castings. Ignoring material costs, how do the prices compare for the two processes?

Alan

[Dave Otto]

Hi Roland

Nice to see an update; looking forward to the next one.

Dave

[tvoght]

It's good to see an update Roland. I assume the castings were not received in the same packing material in which the patterns were sent...

--Tim

[RolandMM]

Alan, Dave & Tim,  glad to know someone is watching. The lack of comments makes me think no one cares.

Investment casting is expensive.  With green sand you use a pattern on a matchplate, usually made of wood and the foundry charges by the flask.  In other words whatever you can get on the matchplate is included.    I can get one (1) flywheel, bearing caps, a cylinder head, and other small parts on a matchplate.

With investment castings, there is the cost of the wax, now $8/pound + shipping, the postage of the patterns to the foundry and the postage back needs to be included.

Then there is the mold.  We make ours of aluminum because we can.  If you hired it made it would be thousands of dollars.

Now Alan,  to get to you question. My foundry charges $40/flask for cast iron.  The investment foundry charges $160 for one (1) flywheel.  Same cast iron, same size but there is a world of difference in detail and surface finish.

Morrison & Marvin Engine Works uses a lot of investment castings and our casting sets are exquisite but not cheap.  We strive to have the quality all other casting sets are compared against.

Here is a picture of the Union Governor mold with a wax pattern.  Also the finished Governor Balls showing all the machine work.

Roland

[Roger B]

Thank you for that interesting oversight of casting methods and costs    Quality costs remains true