Stuart 10V Build Log - Complete Beginner...

That would be called a "spring pass" as it takes out any flex or spring in the tool without putting on any more cut..

You will find that the insert you are using is nor really sharp and would be better with a decent depth final cut so it will get pushed off more than a really sharp HSS tool or even a **GT insert, the interupted cut due to the slots in the side of your part won't help either. Depending on the job I will quite often do the last couple of passes with a HSS tool having taken the rest out with CCMT. in iron, bronze and brass I'm more likely to just use CCGT.

Thanks for that.

I've come to a bit of a halt while I wait for some materials to make mandrels etc., and I'm going to add some power to my mill x-feed.

I need some tooling too for the 10V - any advice on slitting saws for the conrod bearing and valve eccentric rod?

Thanks.

Hi,

The bearings could be cut with a hacksaw, then clamped in the mill vice to clean up the mating faces before soft soldering together for drilling and boring then again with a mandrel to turn the OD.

I haven't the plans in front of me but if you are refering to the slot at the end of the conrod this can be done clamped in the milling vice and using a slot cutting milling bit to cut the slot. Drill the hole to bolt together first and gain correct distance, centre to centre then do the finish profiling. As you've found already it may be best to go slightly under size on the milling cutter so you can finish to correct dimensions.

Slitting saws are another tool that will cut oversize and tend to wobble even on a very accurate mandrel, so you will possibly get more control and precision by hand. But there you have two options, the choice is yours.

Regards

Jon

I can't remember how much Stuarts allow for the cut but a saw about 1mm thick would be a reasonable middle of the road thickness - not too thin that it wanders excessively and not too thick that it loads the machine or removes too much metal. Don't get one with too many teeth as fine ones can clog and then start to wander something like 80mm dia and 30-35 teeth would be OK. This will do for both the big end and the half cut in the eccentric strap.

I also like to give the sawn surfaces a skim with a flycutter if there is enough material to allow for it.

Thanks both. I’m pretty sure a cutter will be able to make a better job of it than me with a hacksaw - never could saw square.

Fly cutting the faces might be a tall order - they’re tiny. Maybe milling would be ok though?

cheers.

Got a bit distracted again last week, this time adding a motor to the x-feed screw. I found a ‘how to’ online, and half followed it - it's a much simplified version, but it'll do what I need it to.

First job was to extend the lead screw and cross-drill it for a drive pin:



A simple dog clutch is made from a piece of brass, turned, knurled and slotted at both ends with a “what could possibly go wrong?” slitting saw:





Then drill and tap the end of the bed to take some bolts and spacers for a motor plate:



It’s a 12v geared motor. I’ll be running it through a 15v PWM speed controller. Obviously still needs a casing and control panel, but it seems to work ok on a 15v laptop charger.

Edited By Dr_GMJN on 14/06/2020 21:45:49

So on to one of the critical bits: the cylinder. The black casting is a bit rough:



The drawings have the minimum information, un-toleranced (luckily):



Started by cleaning up the outside by filing:



And painted with red oxide so I can see what’s what.

After looking at online builds and my 10V book, it seems like there are many ways to machine this part. I went with what I understood, and what I thought was easiest. I’m not sure it’s worked out, but more on that later. I scribed my best fit line around one end from the surface, using callipers. Then did a quick check to see if everything was about the right height all around:



Double checked with it in the chuck. I put a parallel behind it to make it as square as a filed casting face would allow:



Then clocked it up to the best fit around the cast circular flange. I did this rather than the bore because there needs to be a constant depth step around here for the insulation plate, defined by the cylinder caps:



And checked the filed face was about right:



Bored the...bore:



Faced:



Then removed and marked out using callipers for the length. I also scribed “B” on the casting so I know this is the lower end and everything is perpendicular (hopefully):



Re-fitted in the chuck using a parallel to seat the machine face on:

I thought about the next operation a lot, but it seemed like alignment by eye was as good as anything. I calculated the bore-face dimension using my bore size, and calculated how much to remove from the cast/filed face. I then scribed a line from the face using callipers. I put the cylinder in the vice and eyeballed the level using a parallel and slip gauge to form a datum plane. This was done both sides as a check, and it seemed to match:



I used the parallel/gauge to set the fly cutter to zero on the DRO for depth:



Then fly cut the face using my new x-axis power feed:



I’m happy with the finish:





I balanced everything together and it seems to be square:







However, despite the cast flanges being equal depth to within about 0.15mm (the book advises to aim to get these the same), the port-face distances aren’t equal, there being about a 0.5mm discrepancy:



I think I can compensate for this error by adjusting the slide valve on its rod.

Also, the faces aren’t parallel. I’ve got an approx. 0.17mm difference front/back. This must have been due to me using the chuck face/parallel as a datum somehow. Perhaps I should have made a mandrel. I don’t think it will really matter so long as the first (bottom) face is normal to the bore axis, but it is annoying to get it so wrong.

So to summarise what I've ended up with in terms of critical dimensions:

Bore: Drg: 19.05mm, Actual: 19.01mm, d= -0.04mm (-0,002"  )

Bore Axis to Valve Face - Drg: 19.84mm, Actual: 19.565mm, d= -0.28mm (-0.011"  )

Average Cylinder Depth - Drg: 28.575mm, Actual: 28.395, d= -0.18mm (-0.007"  )

Max. Cylinder Depth Error (front/back): 0.17mm (0.007"  )

Valve Port Face Width - Drg: 25.4mm, Actual: 25.4mm

Questions:

1) All things considered, are these figures good/bad/indifferent (bearing in mind there are no tolerances on the drawings)?

2) Do I need to correct anything?

3) I tried to machine to my marked-out lines on the casting, because I had no flat datums to touch on to, to use handwheels/DROs. What's the best procedure for this? I can only think to machine a datum, remove form the machine and measure, then re-fit to the machine and cut to depth using the read-outs (at least for parts that I can get access to measure).

4) Any comments on the methods I used, and how to avoid errors in future are, of course, welcome.

Next job: steam ports. Thanks!

Edited By Dr_GMJN on 14/06/2020 22:51:16

Thanks Jason, that's all good. I guess the non-parallel cylinder faces were a result of the jaws moving the workpiece. I'm pretty gutted about it, but I'll know to double check the seating next time.

Question about lapping:

Plain hardwood plug, tight running fit, #600 SiC and oil, run the cylinder along and back with the wood rotating?

Same with the standard.

But how do I lap the piston to the bore with the #1000 in terms of which bit to hold, and which bit to move, and how to align? Same with the crosshead and standard.

How should the initial fit feel?

Thanks.

That's it for the cylinder, lap in the lathe & run fairly slowly 100-200 rpm and just work it up and down the wooden lap.

Piston, machine it but leave say 5thou over diameter and then mount onto the piston rod. Hold assembly by rod and get that running as true as you can and then take a couple of light skim cuts off the piston trying it into the cylinder after each until is will just enter. you can do the last bit by hand holding by the rod and work the piston into the bore with a tiny amount of 1000g and plenty of oil or it could be done on the lathe. I don't always lap the piston just leave it as the turned finish so upto you.

Have a look at my Filer & Stowell thread a bit later and I'll show the cross head being lapped for that

Out of idle curiosity I thought I'd measure the variation in width on my two recently squared up cylinders. Taking three points on each, one has a maximum variation of 0.1mm and the other is 0.05mm. Of course the variation doesn't matter. What is critical is that the bore is perpendicular to the face that controls piston alignment. What the other face, which is just a cover, does isn't important.

Andrew

Hi, if you are worried about the end faces, you could always make a slightly tapered mandrel, and carefully polish the taper on, and taper it so the cylinder goes about 3/4 of the way on, put a bit of thin oil on it, then gently tap the cylinder block on tight while the mandrel is still in the chuck, and then take a skim off the end of the block, I guess only one end will be off, the end machined at the same time as the bore should be square. Whenever I make a Stuart engine, or any other for that matter, that is the way I always machine the second end. One the end is faced, remove the lot from the lathe and tap the mandrel out.

Chris Gunn

Thanks guys. I think regarding the cylinder I'll not try to correct it. It's a bit short anyway. If I mess up, I'll probably be way under size. If I had any excess at all, I'd probably do it using Chris's mandrel suggestion. There's a description of how to make a tapered mandrel on the Harold Hall website. Seems easy enough. I will know for next time though to do that by default. As I mentioned, there are different methods outlined online and in books, but I chose the one that seemed the most straightforward and paid the price.

Had a spare hour and a half, so started on the valve chest, while the dimensions of the cylinder port face and lagging were still fresh in my mind:



I tried the approach of cleaning up the outer surfaces, measuring, and re-cutting to size using the DROs, and with scribed lines as a sanity check:





All faces were square and dimensions were spot-on to the limit of what I can measure, so that’s one method I can hopefully use from now on:





However, this still leaves the cast bosses to machine. After machining the sides, they may not now be in the exact centre of their respective faces (they appear to be less than 0.5mm out, but that's measuring to a cast surface, so may be more, may be less. I need to turn these in the 4 jaw chuck, but I couldn’t think how to centralise them accurately. I've seen a DTI used on each face in turn, and any difference in reading on oppsite sides corrected. This seems a bit dodgy, since it relies on getting the DTI pointer on precisely the same point, at the same angle on each opposing face. Any discrepancy in rotation angle will give a false reading. I suppose you are supposed to rock the chuck and take the minimum readings, but it seems a bit hit and miss. Anyway I’m going to try this centering ring I made from some scrap brass, and hopefully the result will be OK:



It’s a tight fit over the edges of the chest, and the idea is that I’ll fit it over the 10mm or so of the part protruding from the jaws. The back face of the ring will butt up to them. If I can center the part using a DTI on the ring, the excess material removed from the bosses should leave me with the finished drilled, tapped and reamed features bang in the middle, and the chuck jaws should ensure they are central within the box:



That’s the theory anyway. I might check using teh DTI on opposing face method, just to see what the numbers are.

Edited By Dr_GMJN on 15/06/2020 22:20:03

This is the valve slider as supplied in the kit:





Shame - in a strange way - because I was hoping to be able to say I’d machined everything myself when it’s finished, and it looks like a simple thing to make.

Looks like someone has machined it for you, you can see the marks

A split bush is easier, and quicker, to make than a tapered arbor for holding work:

The split bush shown was used to face the gland to length, turn the boss to diameter and face the back of the flange. Width of the flange and height of the boss are parallel to better than 0.02mm. A split boss can also provide a high clamping force. Here's one being used to cut a 6DP gear in EN24:

Andrew

Thanks Andrew, how do you make the bush?