A Stuart Twin Oscillator

[crueby]

That box angle plate t slot thingy is neat, where did you find that?

[Sanjay F]

I hope the link works:

https://www.ebay.co.uk/itm/282572204072

[crueby]

I hope the link works:

https://www.ebay.co.uk/itm/282572204072

Yup! Thanks!

[Sanjay F]

The day started with the realisation I had positioned the standard the wrong way round on the box angle plate so the arms would touch the milling table when tipped over 90 degs  Corrected that and then used a face mill for the 1st time rotating just short of 2000 rpm as suggested; it does produce a very nice mirror finish

I remember from a previous build about drilling of brass and reducing the angle on the drill bits so they wont grab; sacrificed a set of drill bits and made them specifically the 'brass' set and drilled the crankshaft bearing coming in from either side and finishing with a reamer. The swarf does look different after the modification

Finally milled the tops of the arms in preparation for the drilling of the steam passages. I must admit I'm not the best at interpreting drawings. From the cross section below and from what I have read, I repeat the steam passage machining on the otherside of the standard and its just offset to make the inlet/outlet passages?

Lot's more operations to go on this little piece 

[Jasonb]

That's it both sets of passages are the same if you look from front or back

If you have a look at my Kelsey build and the link to my drawinsg it may make it a bit clearer as the passages are quite similar.

https://www.model-engineer.co.uk/forums/topic/v-twin-kelsey/

[Sanjay F]

I figured it out, but I wish I'd seen your drawings a few days ago it would have saved some time head scratching! I remember looking at your build a few months ago as well 

The box angle plate has proved its worth, I'm sure there are many ways to hold the standard and make the necessary holes and steam passages, it definitely made it easier for me. I started with the horizontal and then vertical passages, then tipped the whole setup over by 45 degs each way, the drilling was slow with frequent swarf clearance and plenty of oil and used the 'paper' method to see when the drill bit broke through.

This is where I've ended up this evening ....... enough for the day, start again tomorrow with fresh head & eyes 

[Chipswitheverything]

Things are looking good with this quite intricate multi-directional machining of the casting.   That little box plate has definitely proved its worth , straight from arrival!  Dave

[Sanjay F]

The next part is equally intricate and requires the several holes to be made and positioned correctly. I'm following a 2011 Model Engineer build (starting issue 4396) which suggests making drilling jig to assist. The writer of the article thinks its worth the effort (I'm hoping so), but only time will tell as I have made it, but not used it and obviously the jig needs to be accurately made otherwise .......

Its quite ingenious the way the jig pivots on the bearing axis allowing each arm to be correctly drilled and also the jig on the reverse side makes the holes for the steam inlet/reverser mechanism

CAUTION:

They are quite a few measurement errors which have been identified and corrected in the build, but in later issues, so future builders take note and make sure you read the a few issues ahead of where you are ....... see below. I have also found a couple of uncorrected errors when making the jig.

- The holes on the reverser are 5/64" and not 15/64"
- The spacer which holds the jig pieces at the correct distance apart should be around 0.780" (width from one side of the crankshaft bearing to the other, not 0.593" as stated

Again fresh brain required as all the holes are different depths etc and don't want to mess up ......... tomorrow methinks 

[Sanjay F]

Not a great morning making the valve steam passages ...... I drilled everything correctly only to find the deeper holes did not intersect with the angled steam passages. The build suggested opening up the holes in the valve surfaces which I did but still no joy. Then it dawned on me to open up the angled steam passage from 5/64" to 1/8" which worked so repeated on the other arm, everything is interconnecting.

I'm not sure what effect all these mods will have but I really do not like the look of the top and bottom set of furthest holes in the LHS arm 

[rstreift]

Having built a single oscillator engine, I don't have the experience to make helpful comments.  The holes look functional and with the connections it should "run".  I'll be interested in what you figure out.

About that box angle plate, I can see where it would have made a couple of past machining tasks a bit more efficient (and therefore "fun").

[Jasonb]

I'd be worried that the gap between the top two holes is less than the hole in the cylinder which could lead to you being connected directly from inlet to exhaust, do not pass go and don't collect £200.

Also on port faces try and keep th eedges of teh holes as crisp as possible so no deburring tool just a rub on some fine Emery laid on a flat surface.

[Sanjay F]

I agree and am annoyed I followed the build suggestion and not my own thinking! I guess its a suck it and see type thing, however, I was thinking of a possible solution and that is to JB Weld the top of hole and the drill the LHS where which is the steam passage side (blue arrrow). The gap should be 0.100" and I have 0.046" - I think it may be worth doing anyway?

Everything else panned out fine

[Sanjay F]

Done, the gap is approx where it should be - will measure it when dry and trim if necesarry, what's the worst that happen?  :'(

[Sanjay F]

Hmmm….more peculiar goings on; the valve face should be 7/16” (0.4375) from the centre line of the cylinder it’s at 0.438” and the other one is bang on 0.4375”, so nothing to remove??

[Sanjay F]

So while the JB Weld dries there is an alternative solution which I was discussing with Michael who is also mid-repair with his Stuart D10, and that's to plug and re- drill. The advantage is I now know the bottom of the valve port is accesing the steam passage so can plug the top and drill a hole of the correct diameter and position using the drilling jig......only time will tell!
 

In the meantime onto cylinders which are prepped and ready for boring and have been left slightly oversize until the boring has been completed