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When I wrote previously, I thought you had done this end flange prior to machining the gauge plate base, and crank main bearings. Thus making the gauge plate was a way to translate the bore/flange machining for the cylinder to make the bearing alignment. I didn't appreciate the gauge plate base was simply a way to make a method of clamping the base casting to the right-angled plate.
I feel you missed the point about my Vee-block idea.
The Principle axis of the engine is the Crankshaft. By "Principle", the axis MUST be identified, and secured by machining very early, so most other critical machining can be taken from this axis.
Of course, to permit repeatable setting-up, the underside of your casting had to be machined first. But that is NOT a running / working surface except for a reference to "other machines"etc. when finally mounted.
The Secondary main working axis is the cylinder-bore axis.
Your odd brass and aluminium insert is a little "weird" (in my head) as you set it into a casting, (Not sure how or where it relates to the casting?) then you precisely aligned this to the Quill axis before boring for the cylinder to mate. I am not sure what all this is really doing...? It seems an Imprecisely fitted bar is being precisely aligned, so the imprecision exists in the machining of the casting?
My sequence (Because that's what I was taught in the 1960s when boring cylinder blocks!).
1: Ensure the underside of the base casting is flat with a reasonable alignment to the CAST bearing and cylinder mounting holes. - This is where an appreciation of Datum alignment is required to understand the castings are NOT perfect and often need compromise, if inadequate machining allowance is not provided. The base grinding set-up is where your brass/aluminium bar could help, but scribe lines on the casting work fine for me. I assume the casting is about right, I.E. plus-or-minus 1/8" from where everything should be. "By eye" marks are better than that, so are adequate to decide where the casting is mounted for the flat underside to be ground. - But you have done all that.
2: From the flat base surface, the bearings can be positioned and machined to form the PRIMARY DYNAMIC datum. This is used to mount the base casting on the precisely set-up angle plate. - But with "freedom" to re-position to the Crank-axis.
3: From this datum, the bore can be set: at Exactly the correct distance for the bore axis to be to align with the Primary dynamic datum. I.E. if the bearings were set at 1.457 INCHES above the flat base underside DATUM, then the bore shall be centred EXACTLY at that same dimension. That will centre the bore on the crankshaft axis.
4: With test bar in the bearings, the test bar can be set in Vee-blocks, and the test bar used to clock to ensure it is exactly perpendicular to the Quill. (In case your Vee-blocks are NOT the same size, muck anywhere, imperfect machine alignment, etc.). THEN the base casting can be securely clamped to the right angled plate surface.

You can still use this alignment to eliminate all the TINY errors that are in-built from the machining of all the components by using this as the set-up for BORING the cylinder. All the other stuff is holding the parts together. This BORING to be perpendicular to the crank axis is the PRECISION that makes a good engine.
Sorry if my explanation is a bit crude - Boring even?
If I am wrong will any experts tell me where I am wrong, as I appreciate life-long toolmakers know best - and my friend and mentor is unfortunately past-it now.
j is doing a really careful job, being precise in setting everything to DTIs, etc. But I "worry" that following the wrong sequence or datum can lead to an "Imprecise" engine that disappoints - and we all want this to be the best he can make.
All is not lost: The final boring to the crank axis is the key.
K2

My brass bar was used to ensure that the casting was reasonably straight and that the middle of the journals was in alignment with the center of the cylinder flange. Obviously from a casting it can never be exact but there is little room for plus-or-minus 1/8" on these castings. Not in the middle of the flange webs will see catastrophic results when the flange is bored through.

Now that my fixture plate is securely in place all parts will be machined with reference to the primary datum which is the edge of the plate closest to the bearings. I can't use v-blocks until the bearings are fitted and bored. Granted I could have waited until then until machining the flange but that ship has sailed now and had sailed long before you made your suggestion.

As you say, I could easily grind the flange face using v-blocks and an angle plate if things do not go well. That is always an option. With a bit of luck my bearings will be aligned with my reference and that won't be a problem.

There are many ways to skin a cat precisely.
 
We are not talking of skinning cats. You need to have an open mind, but when it comes to critical alignments, the bore must be truly square to the crank axis. You appear to me to be coming at it indirectly via a bolted on plate. I am proposing a direct set-up from crank axis to cylinder bore (not flange face), that avoids acumulated errors of a number of interfaces.
As it stands, you are set-up to have a job that is less than perfect, IMHO. Luck does not exist when making good engines. Good set-up strategy helps though.
You can still make the cylinder, fit it to the base casting, then set-up from the bearings with a straight bar instead of crankshaft fitted in the bearings, in order to finish boring the cylinder. That way you'll recover from any accumulation of error in the various set-ups so far.
But my advice is just that. "Good luck" ( I don't believe in luck but you seem to need it) with whatever way you choose to make the engine.
No problem to me, I can only advise.
K2
 
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Part 4 - Bearing Journals​

Next job was to mill out the bearing journals. This involved setting up the sole plate horizontally. To minimise any errors I bolted my fixture plate directly to the mill ways and aligned it carefully using the end flange as a reference. This took considerable time as I was using a 'tenths' indicator. I could not get it any better than 1 tenth - 0.0001". So hopefully that will be good enough!

IMG_8982.jpeg


I used the diameter of the end flange to locate the vertical centre of the bore. This and the end of the flange is where all dimensions are measured from so it is important to get this as accurate as possible. To double check I machined up some aluminium as a tight fit in the bore and machined that down to my zero height. I removed this and checked against it's diameter only to find I was out by 0.001". This was corrected in the DRO.

I was worried that tapping out the plug may have affected my alignment, so I double checked that once more and made sure everything was where I expected it to be.

Using a brand new 8mm carbide end mill I took my journals down to the centre of my bore. Then I made the slot through the middle. This was a simple matter of machining almost to depth before expanding the width before making a cleanup pass to final width and depth. Creating a new coordinate system in the DRO which is centred on the bearings really helps at this point.

Then it was a matter of machining the sides of the journals before drilling and tapping the four 5BA holes.

IMG_8988.jpeg


The next task was to take the crosshead slide down to it's finished height of 5/8" below the cylinder axis.
Once this was done I drilled and tapped the 6 holes for the crosshead slide guides.

IMG_8990.jpeg


Once that was all done I could tear down the setup and mount the bedplate at 90 degrees so that I could finish the mounting boss for the valve guide. This proved to be quite tricky as my hobby mill is not large and it took me a couple of attempts to find something that would satisfy all requirements.
IMG_8991.jpeg


Last job was to cleanup the valve guide flange. This was problematic as it didn't quite have enough material available. I took it down below spec as it should not be too hard to either increase the thickness of the mating part or to introduce a packing shim.

IMG_8992.jpeg

So finally that is pretty much it for this casting. It doesn't look like much but it really was a lot of work. There is one more hole to add which bolts the bottom of the cylinder in place, and I need to spot face the cylinder bolts, but those jobs can wait for now.
 
It's coming along well

I don't find dowels are often needed. Provided you do all the main machining with out removing the casting from the machining plate then the same edge of the machining plate can be clocked true for each setup.

I also don't drill tapping right through plate and casting, etc, I just note the DRO readings when drilling the casting and use them to place the holes in the plate

The theory of the Vee blocks is OK but a lot of hobby mills simply won't have the head room to allow the casting to stand on end and get a boring head/bar into place. That's assuming the tram is true.

This is my well used machining plate, I've lost count of the number or open crank IC and steam engine castings that have been on that but they all run so must be OK. its 10mm thick 100 x 300

20240611_095126[1].jpg
 
It's coming along well

I don't find dowels are often needed. Provided you do all the main machining with out removing the casting from the machining plate then the same edge of the machining plate can be clocked true for each setup.

I also don't drill tapping right through plate and casting, etc, I just note the DRO readings when drilling the casting and use them to place the holes in the plate

The theory of the Vee blocks is OK but a lot of hobby mills simply won't have the head room to allow the casting to stand on end and get a boring head/bar into place. That's assuming the tram is true.

This is my well used machining plate, I've lost count of the number or open crank IC and steam engine castings that have been on that but they all run so must be OK. its 10mm thick 100 x 300
It's especially tricky to do the bearings first as pretty much every feature on the engine is dimensioned from the cylinder flange. It's hard enough to decipher the expertly hidden dimensions on this drawing without having to work backwards! If it was good enough for Tubal Cain, it should be ok for me I think.

Thank's for your comment. That's a wonderful fixture plate. I hope mine ends up looking just as well used!
 
Creasy, FYI, I found the valve rod guide to be problematic, nearly impossible to get its bore lined up perfectly with the valve rod, I used shims above and below the screws that hold it onto the boss in the base in order to tilt it into alignment, but if I ever have to take it apart and re-assemble it, I'll probably leave the shims out, bolt it down tight, and "tap" it into alignment as the bronze used in Stuart castings is very soft and malleable (at least the old castings, if they've recently changed to brass that could be different).

Also, I did not use a machining plate, but dang that's brilliant, and I wish I had the brains to have thought of that :) !!!
 
Creasy, FYI, I found the valve rod guide to be problematic, nearly impossible to get its bore lined up perfectly with the valve rod, I used shims above and below the screws that hold it onto the boss in the base in order to tilt it into alignment, but if I ever have to take it apart and re-assemble it, I'll probably leave the shims out, bolt it down tight, and "tap" it into alignment as the bronze used in Stuart castings is very soft and malleable (at least the old castings, if they've recently changed to brass that could be different).

Also, I did not use a machining plate, but dang that's brilliant, and I wish I had the brains to have thought of that :) !!!
Thanks very much for that tip. I have been worried about that forever. It seems like a crazy design. Especially if you consider the steam chest would most likely have a gasket. Problems seem to be inevitable.
 

Part 5 - Reverse Counterbore​

The back side of the cylinder flange is very curved and I wanted to make sure that the nuts that hold things down have a flat surface to press against. I could not use a normal counterbore because the bearing journals are in the way so I needed to make a reverse counterbore. I have noticed that many builders either ignore this issue or in one case I found they had used a very narrow washer below the nut. I think that is quite a good solution but really I think best practice is to counterbore the flange and let the nuts do their job.

After failing miserably I found this very useful article about the subject: Making Counterbores from Drill Rod in the Home Shop

I chose a simple design with two cutting edges and a removable alignment shaft held in place with a 3mm grub screw.
IMG_9029.jpeg


I used my cordless drill and It worked very well although it did leave a mark on the side of the casting in one spot. I have fixed that with some jb-weld so it should not be a problem after the paintwork is done hopefully.

counterbore-1.jpg
counterbore-3.jpg
 
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Not an unusual way of making a spot-face on a reverse side of a job, but more usual to align by using the milling machine. But surely better than the cast surface., for the nuts to impinge. I should insert a plain washer beneath each nut. (Possibly brass instead of steel?). This should avoid local stress concentration and subsequent deformation of the cast iron where it contacts the nut, which can cause slackening of nuts if the metal relaxes in service. And use of a spring washer can also apply some axial spring to help maintain contact pressure. (Belville washers are best for this application, but I doubt you will find them so small.). As it is a model, it is "unlikely" you'll have a problem, but good to make "unlikely" into "never".
I well remember how cast iron and aluminium cylinder heads always used to show "bruising" where the head bolts/nuts etc. had been tightened down without proper washers. A very good reason to re-torque after a few hundred miles of running-in!
A tip. If you ever need to "stick" a washer in place while assembling, you may find a small dab of (breakable) loctite will be adequate. To prevent the loctite then glueing the nut to the threads, use a greased thread. Disassembly then is easy and washers stay nicely in place for the next time. Loctite on some threads that may be re-torqued (or need re-tightening) is not a good idea, as the loctite will give the wrong torque when re-setting the fixing. Correct torqueing of fixings should be done on free-running threads, clean and lubricated for the most accurate and repeatable settings. Usually joints are torqued where special attention is required to achieve a high torque, or to PREVENT over-torqueing, as well as to get consistency of applied torque across a series of fixings. Models rarely see a torque wrench. Torques are so small we all rely upon "feel" - and sometimes (I) get it wrong. My next tool purchase should be a low range torque screwdriver, that takes sockets, hex bits, etc.
https://www.ebay.co.uk/itm/16601263...d0JtH04lkxln8oKztFvEjki6E=|tkp:BlBMUPCzns6EZA

K2
 

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