A Pair of Stuarts

[smfr]

I'm committed the most terrible sin of a model engine builder: starting a new engine before finishing the last one In my case, I got a bit fed up with the painting part of my Muncaster Joys Valve Gear engine, so was eyeing some of my Stuart kits on the shelf to build next. I have kits for both the Twin Launch and the Compound, so decided to build them together, since they share so many parts.

Both are "vintage" kits; the Twin Launch dates from about 1976, and the Compound from around the same time (the plan issue date is 1975), although the castings show some differences, as we'll see. Here are the kits before I started work:



There are plenty of build logs around for these engines, so I'm not going to go into exhaustive detail, but I'll highlight the differences between the two models, and talk about things I did wrong 

Let's begin.

[smfr]

The bases are a natural place to start. Here they are side-by-side, Compound on the left, Twin on the right:



From the top side, the castings look fairly similar, although the feet are a bit beefier on the compound. However, there are some differences on the underside:



The Compound base is more rectangular, and doesn't have the dips where the feet are. Also the central cross brace doesn't curve up like the the Twin. I suspect that the Compound is from a later pattern, where they've made a few improvements.

You can see in the photos that I've taken a file to the base to smooth off any high spots, before checking on the surface plate that they are of even thickness. Then the bottom edge can be milled flat:



I used a face mill to clean up the top surfaces, and that worked well:



Others have reported having issues with gunmetal leaving a non-flat surface when milled, but this face mill left a nice flat surface that just took a rub on some wet & dry paper to get nice and flat.

So now we have two bases prepared for marking out:



Marking out was done while clamped to an angle plate, after squaring up:



and then we're ready to start drilling, tapping, and milling the sides of the bearings:





While in this setup, we need a way to locate the main bearing location easily, so I milled out a 1/4" slot with a ball-end mill:



The uprights just required threading on one end (leaving the other end unfinished until I decide what thread to use to attach to the cylinder block):



When drilling for those uprights, another improvement in the Compound casting was discovered; the corner holes emerge cleanly through the top plate of the casting on the inside, whereas on the Twin base casting, they come out half in the inside corners, causing the drill to wander and the taps to end up non-square. For this reason, the Compound casting seems much preferable!

So that's the bases mostly done. I'm torn about whether to take off the casting texture on the entire part and round the top edge, as others have done. I'm also not sure how to finish the bearing bosses on the base, since they don't match the bearings, but we can leave those decisions until later!

Thanks for reading so far!

Simon

[smfr]

The next job is to machine the main bearings, three per engine.



With six bearings altogether, I had the luxury of machining them in pairs. First, the base is given a skim:



I'm also showing off my new vise in this photo  I finally found screwed vise with a downwards clamping moving jaw that's a good size for my Emco. It's by American Sun, who no longer exist, but it's a beaut.

Anyway, I sweated those bearing halves together (poorly, as it turns out):



found center in the 4-jaw:



and pushed on them with a bit of 1/2" rod to square them up:



Then they were turned:



and drilled 1/4" (the final bore will be 5/16"). After flipping around to do the other side, a bit of rod in the hole helps with re-centering:



Three pairs done, one of which came apart (bad soldering!)



I also had a brain fart and started to open up the hole for reaming to final size on the left pair, but realized that I had gone wrong before drilling out too much. However, that's going to complicate things a bit later!

The stud holes were then located, and drilled and counterbored with an end mill:



Then the various curves were tidied up on the rotary table. The ends of the bearings are curved around the opposite stud hole:



and the top surface finished off:



A pin at the center of the rotary table really helps for this kind of stuff.

To help with the "oops" from earlier, I made a little sleeve to reduce the size of the oversized bore down to 1/4" so I could handle this pair like the others.



Finally a bit of filing takes out the milling marks:



So at the end of all that, we have two bases with bearings in situ:



So shiny!

Simon

[Jasonb]

Good to see you back at it Simon and you have made a good start.

I would leave the top edge square as if it were a full size engine the bed casting would have been planed flat so the bearings and standards all mount to a flat face. If you really want to make it look more like a casting then you could drop the level around all the parts that fit to the base to make it look like just raised areas have been machined.

[zeeprogrammer]

and talk about things I did wrong

I also had a brain fart

3 posts and 1 brain fart. I don't think there'll be much to your first statement. 

Glad to see you posting another project (or two!). Always enjoyable and lots to learn.

[K.B.C]

Hi Simon,

Lookig at your base plates it would appear that bearings are not quite right as when looking at the drawing for the Launch engine the base plate is shown as level with the ouside bearing faces.

The drawing dimension over the base plate is 3" and if you take the bearing centres from the drawing at 1.25",  multiply x 2 =2.5", + 2 x .25" for the bearing thickness brings the total to 3" .
Is your base plate greater than 3" not that it really matters it just doesn't look correct and the eccentrics are well clear of the base plate anyway.

When I built the Launch engine I made the bearing blocks as near to full size practice and the outside of the bearing slightly averhung the base plate and of course I had to increas the hight of the Cylinder support rods. . I don't know if this applys to the Compound engine as I don't have a drawing for it.

George.

[jeff l]

Simon , nice start on the Stuart's , I would like to see a better picture of your new vise .Jeff

[b.lindsey]

Wow!!  That is an impressive start Simon and some great work as well!!

Bill

[smfr]

Hi Simon,

Looking at your base plates it would appear that bearings are not quite right as when looking at the drawing for the Launch engine the base plate is shown as level with the ouside bearing faces.

The drawing dimension over the base plate is 3" and if you take the bearing centres from the drawing at 1.25",  multiply x 2 =2.5", + 2 x .25" for the bearing thickness brings the total to 3" .
Is your base plate greater than 3" not that it really matters it just doesn't look correct and the eccentrics are well clear of the base plate anyway.

George, I think the bearings are to size, but there's overhang of the base on each end. I had to deal with it when boring (in an up-coming post). I think I should probably just machine down the base to size, and re-create the draft angle on the ends, leaving a boss to create the overall 3" width.

Simon

[smfr]

Simon , nice start on the Stuart's , I would like to see a better picture of your new vise .Jeff

Jeff, there's a 4" version for sale on eBay: http://www.ebay.com/itm/NOS-AMERICAN-SUN-USA-Made-4-Precision-Milling-VISE-4-Deckel-Aciera-LAST-ONE-/351641351902?hash=item51df7536de:g:r64AAOSwl9BWLuk2. You might want to sit down before looking at the price 

Simon

[Dave Otto]

Hi Simon

Its good you see you off onto another project; I always enjoy following along with your work.

Dave

[K.B.C]

Hi Simon,

Looking at your base plates it would appear that bearings are not quite right as when looking at the drawing for the Launch engine the base plate is shown as level with the ouside bearing faces.

The drawing dimension over the base plate is 3" and if you take the bearing centres from the drawing at 1.25",  multiply x 2 =2.5", + 2 x .25" for the bearing thickness brings the total to 3" .
Is your base plate greater than 3" not that it really matters it just doesn't look correct and the eccentrics are well clear of the base plate anyway.

George, I think the bearings are to size, but there's overhang of the base on each end. I had to deal with it when boring (in an up-coming post). I think I should probably just machine down the base to size, and re-create the draft angle on the ends, leaving a boss to create the overall 3" width.

Simon

Good idea Simon, just check that you have 3/4" inside the bearings to let the crank shaft in, you may have to skim a few tho" off the bearing ends to give the shaft freedom.
It won't matter if the base is machined as you say , and it won't effect the bolting down holes.

George.

P.S.   If you decide to make the Stevenson reverse gear and don't have a drawing let me know and I can get you a copy.

[fumopuc]

Hi Simon, good to see you back in business.

[Don1966]

Geezz Simon, I turn my back a your got a thread going. Good to see you starting a new built bud and I will be following along.

Don

[smfr]

Thank you Jason, Zee, George, Jeff, Bill, Dave, Achim and Don for your comments!

I'm catching up here, so have a few more weekends of work to describe.

Now it's time to bore the main bearings. My mill doesn't have the 3" of travel to bore vertically, so I'm going to drill and bore on the lathe. The first thing we have to do is to get the parts on center height. I did this by putting a bit of scrap ally in the vise, and milling it down so that the top surface of the base will sit on the lathe center height:



I had to adjust the fixture height once for each base, since the two bases are slightly different in height, and of course I was careful to do the thinner base first. This is one of the (few?) advantages of a lathe with a milling head; you can mill something down to a specific height relative to the lathe spindle.

That bit of ally was then drilled and tapped for some long BA studs that could pass through the threaded holes in the base, to clamp the base down. This involved some grinding on the Dremel to get corner clearance on the base of the Twin (recall that base had less optimal clearance for the corner holes on the underside).

So I had the base clamped down at the correct height:



Now recall that I drilled one pair of bearings larger than the desired 1/4", but the channel in the base was milled with a 1/4" ball-end mill. Now if I try to drill and ream such a mismatched hole, the drill is going to go all over the place. In addition, the base has some overhang, which would also make accurate drilling impossible.

So I decided to put one of the oversized bearings on each base, on the left side, then I could bore this out to about 19/64", but still drill the other two holes, and finally ream everything.

Here we are boring that first bearing:



after which the drilling went well:



But next I made a huge mistake  I knew I had a 5/16" straight-flute reamer, but wanted a spiral flute reamer since these holes have a seam between the base and bearing. So I went on eBay and ordered a spiral flute 5/16" hand reamer. Running it on low speed with plenty of cutting oil, I knew things were bad as soon as it started cutting: horrible chatter.



One always hopes that this will improve as the reamer goes in, but in this case it never did, and the finish was awful:



Not only that, but I was holding the reamer in a chuck (not having a floating reamer holder), and the reamer wasn't very true, making the left bearing oversize.





After putting things aside for a while, I decided I had plenty of material on the top of the base, and could mill off a few thou and re-do the base half of the bearings at least, so I took a skim with the face mill:



I also rubbed the bearings on a file to try to take a few thou off those.

Now I have oval-shaped holes, and need to get them back round before another try at reaming. This called for a boring bar that could reach all the bearings, so I turned up a bit of O-1 rod with an offset of about 1/32", leaving a flange which was to become the boring tip:





The business end was then ground down to half its thickness, and hardened and tempered, giving us a 3" boring bar suitable for boring a hole about 19/64" and up:



So I set up for boring again (shimming up my ally fixture to account for the lost height), and skimmed off the bad finish with this boring bar:



Craning my neck skywards, I also realized that on the top shelf I had a set of spiral-flute reamers which included a 5/16" (a nice estate sale find), so I needn't have used the reamer-from-hell in the first place 

Anyhoo that reamer was nicely behaved, and I think left me with an acceptable finish on those bearings:



After all that, the second base went smoothly. Having that shop-made boring bar actually let me do the ideal thing of drill, bore for straightness, then ream, so hopefully things are nice and straight.

So, a bit more excitement doing the bearings than I would have liked, but they seem nice and snug with a 5/16" test bar, and I think weill bed in fine with the crankshafts, once I turn those.

Thanks for following along 

Simon

[Nick_G]

.
Well saved sir.! 

If you had not told us we would never have known. - Having said that I think it's important that we reveal our mistakes as it allows others to benefit and hopefully avoid similar.

Cheers,  Nick

[steam guy willy]

Have just been looking through the Flicker shots of the Muncaster.......Really good and inspiring work happening there.....Looks just like the real thing although it is of course ! and glad to see the use of a file !!  Wonderfull.........

[zeeprogrammer]

Nice post!
Learned several things in there.
Very neat job.

[fumopuc]

Hi Simon, some years ago I have had a similar experience with a cheap 14 mm brand new Asian reamer. Since these days I have started to buy industrial quality machine reamers only. It was a good decisson.

[jeff l]

great save for sure .

[Kim]

Nicely done Simon! A very smooth recovery!  (At least from this side, it may not have felt like that to you at the time! )
Kim

[Johno]

Hi Simon,

The compound from Stuarts that I am building are using very recent casting set purchased late late year. See photo. You will notice that my kit of castings provides a different crankshaft to that of yours. Mine is of cast steel. Those nice people at Stuarts now incorporate square bosses at either end that allow for the drilling of centres to facilitate turning the main shaft and the two crank pins (90 deg. apart) between centres thus avoiding need to make and fit separate clamp-on 'throw' pieces. It was straight forward operation mill the bosses square to form a datum and mark the centres using a surface plate & height gauge. I will take photos and post them.

in the meantime,
regard, Ian

[b.lindsey]

After all that nice work on the bases I am sure glad you could save them Simon. Well done!!

Bill

[smfr]

The compound from Stuarts that I am building are using very recent casting set purchased late late year. See photo. You will notice that my kit of castings provides a different crankshaft to that of yours. Mine is of cast steel. Those nice people at Stuarts now incorporate square bosses at either end that allow for the drilling of centres to facilitate turning the main shaft and the two crank pins (90 deg. apart) between centres thus avoiding need to make and fit separate clamp-on 'throw' pieces. It was straight forward operation mill the bosses square to form a datum and mark the centres using a surface plate & height gauge. I will take photos and post them.

Ian, it's interesting that they changed the crankshaft casting. Both my kits of the same style.

Could you flip over the base casting and post a photo? I'm curious about whether it's more similar to my Twin or Compound casting.

Simon

[rhankey]

Simon,
My mid to late 1960's twin kit had a base just like your twin base.  Like you, it was hard tapping the column holes square.

btw, There appear to be a couple errors in the plans.  Most notably, the vertical slotted slide plates need to be made about 1/8" longer than shown in the plans, else you will have interference around BDC.  In looking at many pictures of other completed twins, by the time most discover the issue, they grind down the cross head washer that rides along the rear of the slide plate.  With a slightly longer slide plate, there is no interference and nothing else seems to be adversely affected.
Robin

[Johno]

Hi Simon,

So sorry for the delay in getting back to you. I have not been able to access my account for several days but it's now all sorted. I attach the photo of the compound twin base as requested.

One or two observations regards Stuart castings; They go back to 1890's first based in Henley-on-Thames, the company has changed hands on a number of occasions, at one point they were based in British Channel Islands. They now are based Bridport, Dorset, UK in my neck of the woods, infact I have visited them several times now and have purchased my casting kits directly from them. it would appear that they are now owned by a well established foundry that operates from the same site hence the present castings are in my opinion very good. Although my kit of castings were purchased late 2015 the drawings are dated 1954 and the associated drawing for the reversing gear 1955, each with the Henley-on-Thames letter head. The drawing of the crank shaft only shows that to be achieved and makes  no reference to the type of base component supplied.  In fact the accompanying material itemises 'materials not supplied' and refers to bar stock required to fabricate a crankshaft. Hope the photo help with your build.

Ian

[smfr]

Well, it's (checks calendar) six years later, and I've been making a bit more progress on these fellows. Some updates coming soon. 

[steamer]

Looking forward to it Simon!

Dave

[smfr]

We're still back in 2016 for the next few updates. I started working on the cylinder blocks. Here's the compound cylinder block being filed so I have a flat surface to rest on for initial marking up and machining:



and then we can go over the top with the face mill:



and take a rougher to the ends:



I seem to recall some of those messy bit near the ports were pretty hard; chilled I suppose.

So here we have the two blocks mostly cleaned up:



Oh, but what's that little hole in the Twin's block? 

[Dave Otto]

Hi Simon, good to see that you are still around. You are one of the many that I have often wondered what happened to?
I always enjoyed your work and looking forward to seeing more.

Dave

[smfr]

Bet you didn't know there was a water-cooled version of the Stuart Twin Launch  :



I sent this picture to Stuart Models, and they send me a new casting, no questions asked, even though this original casting set is probably from the 1970s or 1980s.

Anyway, here are some other shots of the two cylinder castings:





I think its was around this time, while waiting for the replacement casting from Stuart, that this pair got put to one side, and other hobbies took over for a while. We'll pick up more recent work soon!

[tghs]

fun to watch ,my compound kit had very bad HP cylinder rings,, I emailed ST a photo, within minutes they replied to see if I needed anything else as long they sending the rings

[Kim]

Hi Simon!
Great to hear from you!  Looking forward to watching the continuation of your build! 
Kim

[smfr]

Fast forward to December 2020, and we have the new casting from Stuart cleaned up, and it's looking much better than the holey one:



Now I can find the center line, and mark them both up:





and then drill for the supporting columns:



It's good to have these holes be accurate, so they are handy as a reference line for later operations. For example, the setup to mill the sides of each end:





I then used a roughing end mill to clean up the bore of the new casting:



and remove some excess material from the valve faces:

[smfr]

Now it's time to bore the bores! I made some gauges, and used an end mill shank for the 3/4" (later I would find an end mill with a very precise 1" shank in the drawer which I could have used for the Twin 1" cylinders). The 1.001" gauge is 0.998" on the other end.



To ensure that the bores are perpendicular to the base of the casting, on my little mill table that I don't really trust, I bolted some bits of Al to the table and skimmed the tops to the same height:



Then I could clamp the cylinder blocks down onto those for the boring operation:



The gauges were useful, backed up by a telescoping bore gauge:



Big ol' counter sink to put a chamfer on:



The Twin bores ended up on size, with a decent finish, and maybe a thou left for honing.

The large bore of the Compound also turned out well:



The smaller bore didn't go quite so well; things went slightly wonky because I didn't snug up the quill of the mill, so it ended up a couple of thou oversize and could still use a bit of cleanup with a hone. Will a 0.753"-ish bore be OK with the supplied cast iron piston rings?

[smfr]

Columns! All 10 of them. Rather than use the stock supplied with the kits, I used 1/4" precision ground stainless rod:



I did experiment with putting a fishbelly on a test rod which I think would look nice, but the rear three columns need a spot to hold the valve slide support piece, so shaping those would get a little more tricky.

[Jasonb]

Good to see you back on these.

[tghs]

you should be fine on the HP bore,, test fit the rings in the bore mine were tight..

[john mills]

the gap on the rings when  in the bore would be slightly larger try them in the bore and see what it is  will still work
John

[fumopuc]

Hi Simon,
good to see you back in business.

[Michael S.]

Hello Simon,
I used the cast iron piston rings on my compound.
That worked well. The compound first ran a lot with compressed air. I later tested it with steam. The machine ran much better then. Then she was suddenly stuck!
This was not due to the piston rings but to the failure of the displacement oiler.
The steam pressure during the test was 6 bar and the steam temperature was therefore too high.
So it is better to use an oil pump.

Michael