Stuart 10V Build Log – Complete Beginner…

[geoff walker 1Participant @geoffwalker1]

Dr G

You can mill the rough cast outer rim of the cylinder concentric with the bore

Pass short length of silver steel about 8mm diameter through the bore.

Clamp the cylinder in a machine vice but push the bore down on to the s.s bar which will be resting across he top of the vice jaws

Take a light skim of the rim with the cutter and lock the cutter

Rotate the cylinder a few degrees at a time and take more skims making sure for each skim the bore is resting on the s.s

Keep rotating until the whole rim is skimmed and finish with a flat needle file

Sorry no photo

Geoff

[Dr_GMJNParticipant @dr_gmjn]

Thanks Geoff – I understand. Might give that a go – better than filing from the start.

[Dr_GMJNParticipant @dr_gmjn]

Thinking more about Geoff’s cast O/D machining method:

Am I right in thinking it would work better for a symmetrical ring than an asymmetric cylinder casting?

Because of the port face bulge, it won’t hang vertically on the bar (or at least only at one point), so it would be an estimation job to get the orientation correct to achieve a consistent wall thickness?

But if the bar was a fit in the cylinder, all rotational positions around the arced portion would give the correct thickness?

[JasonBModerator @jasonb]

It does not have to hang vertically, just ensure the work is pushed down against the supporting rod to get a constant thickness. The wall thickness is set by the cutters height above the support bar which remains constant whatever angle the work is at.

Here I was making a cylinder from solid and used the method on the smaller diameter, you can see the facets that the method produces.

Quick bit of filing to blend them in.

[geoff walker 1Participant @geoffwalker1]

Hi Dr G

Trust me and Jason, last post, the method works.

Here is a photo of an inverted engine, same one as Jason's which uses a 10v cylinder. You can see the machined outer surface is concentric with the lower cylinder cap. The tapered section is held horizontal in the vice but still with the bore resting on the s.s. bar

Also did the con rod using the same method, 3mm bar through 6.5 hole

[Dr_GMJNParticipant @dr_gmjn]

Thanks Guys – what I meant was this:

If the part touches the bar at it's apex, then no problem:

But if the part is clamped in any orientation where the contact isn't at the apex, then the wall thickness will be less. This diagram is obviously exaggerated, but shows what I mean:

I thought with an asymmetric part, it might be possible to get the orientation wrong if you happened to roll the part slightly when applying downward pressure.

It seems like it works fine in practice though, so I'll give it a go.

Cheers all.

[Dr_GMJNParticipant @dr_gmjn]

Another weekend spent messing about with equipment rather than making engine parts. At least the 3D printed power feed controller cover is done and fitted:

That’s about if for modifications to the mill I think. Just need some bearings for the lathe handwheels, and a couple of DROs for it. Still wondering what the neatest way of fitting them is though. They do look messy on an ML7.

[Dr_GMJNParticipant @dr_gmjn]

Ok, so I made the split-ring fixture, I didn’t have any brass, so used mild steel.

I can get no better than 0.003” runout, as measured on the protruding bit of turned o/d of the cover.

Is this ok or should I make another and try to get 0.000”?

One slight issue is getting rid of the radius in the corner of the mounting pocket – I don’t want to heavily chamfer the cover edge. I’ve put some ink on the internal seating face, but it only touches at the edge. Not sure it’s affecting the runout much, but it’s definitely not seating over the full face area.

Thanks.

[Dr_GMJNParticipant @dr_gmjn]

…or get it to zero in the 4 jaw chuck?

[JasonBModerator @jasonb]

HSS with no tip radius and slightly undercut.

[Dr_GMJNParticipant @dr_gmjn]

Ok I’ll try that. What about the runout error for this component?

[JasonBModerator @jasonb]

Which side did you end up machining first?

Edit, just looked at previous page which was not how I suggested so you will want better than the 0.003" you are getting.

Edited By JasonB on 22/06/2020 18:14:48

[Dr_GMJNParticipant @dr_gmjn]

Posted by JasonB on 22/06/2020 18:13:03:

Which side did you end up machining first?

Edit, just looked at previous page which was not how I suggested so you will want better than the 0.003" you are getting.

Edited By JasonB on 22/06/2020 18:14:48

Not quite sure what you mean by side? The top cover is finished, it's the bottom one I'm working on. I turned the location spigot, made the split clamp and was going to do the drilling, reaming an tapping all at once on the other side. I'd assumed that the split bush method meant that the order wouldn't be too critical, ie that the undersized thread method was intended for reversing straight into the 3-jaw chuck, without the split bush.

I didn't appreciate that I'd need to use both methods. Ah well live and learn.

Is it recoverable? I've still got the cap O/D and spigot machined concentric in one setup, but no hole. I've still got enough material to make another cap if necessary.

[Martin ConnellyParticipant @martinconnelly55370]

If you machine the spigot, OD and the piston rod hole at the same time then the piston rod is concentric with the spigot and therefore the bore, which is what is required. If there is a packing nut and packing on the other side concentricity of the thread is less critical and the hole in the packing nut can be slightly larger than the piston rod to allow for any error. The piston rod hole can be used to set the cap correctly in a 4 jaw chuck using your split ring to hold the cap to machine the outside face and details.

Martin C

[Dr_GMJNParticipant @dr_gmjn]

Thanks Martin – I misunderstood that the two methods were independent of each other. No problem, I’ll re-machine it, and this time I’ll also get some brass for the split-ring and use an HSS tool.

so to confirm – the hole in the gland nut should not be reamed, or should a reamed version self-centre on tightening?

Cheers

[Martin ConnellyParticipant @martinconnelly55370]

I would expect the packing nut to be slightly over the piston rod size. If there is any misalignment in the holes in the cap and packing nut there will be some binding due to pressure on the sides of the rod. If you reamed the cap and nut together then what happens if you tighten or slacken the nut slightly and there is a now a misalignment of two reamed holes?

Martin C

[JasonBModerator @jasonb]

My method was as martin's for the same reasons. See my post at 16.46 on the 17th.

The split ring should enable you to get the part machined cover to within half a thou or better, aluminium will do rather than expensive brass.

Drilled nut will do

[Dr_GMJNParticipant @dr_gmjn]

I'm re-making the lower cover, starting by turning the spigot:

Its a push fit onto the lower cylinder, so that's OK:

Drilled and reamed – it's a brand new Dormer reamer, and is the right diameter:

….but the piston rod supplied doesn't fit; it's about 1.5 thou oversized:

Any ideas on how to overcome this? I've left the cover in the lathe for now. The next job was to remove it and make another split ring out of aluminium.

Thanks.

[JasonBModerator @jasonb]

Get a 4mm reamer as I suspect you have been supplied 4mm rod not 5/32" or buy some 5/32" stainless rod.

[Dr_GMJNParticipant @dr_gmjn]

So after some false starts, I finished the lower cover this evening.

Turned the inner spigot, drilled and reamed:

Close fit into the bore, all ok there:

5/32” rod supplied was oversized, but I eventually got it to fit by some polishing in the chuck:

Then, after two failed attempts, made the split bush to hold the cover while machining the reverse side:

Matched to jaw #1, I checked runout of the coverWith a DTI. Virtually nothing this time, much less than 0.001”. I then pushed the rod into the hole and checked that:

Quickly wished I hadn’t; 0.004” runout.

Anyway, I can’t keep re-doing this cover. It’s getting the better of me and I need to move on. It must have been the drill that wandered, despite me being very careful.

I made the recess the right depth for the cover, so it was a simple matter to turn down the boss:

Close fit in the standard; ok:

Drill & tap:

Finished:

The standard diameter is a fraction more. I might turn it down to match – it should also reduce the depth of the edge flaw In the casting a bit.

The reamed hole is very shallow, significantly less than its diameter (as per the drawing). I’m wondering now if it was meant to be reamed at all. The drawing doesn’t say so, I just assumed it did. The packing nut also isn’t specified as a reamed hole. I think maybe they should be a close fit, but not to a ream tolerance. The combined length of the assembly, plus packing would probably form a good enough sliding location. We will see how it assembles I guess.

[JasonBModerator @jasonb]

Hopefully that 0.004" will be a lot less on the entry side which is where it affects things.

[Dr_GMJNParticipant @dr_gmjn]

To test Jason's theory, I put the cover back in the fixture and put a finger gauge in what’s left on the reamed hole:

I’m getting a maximum reading of about 0.00075”. I suppose my previous reading could have been made worse by any clearance between the rod and hole, and error in the rod. Plus I guess a small inherent error with the split ring itself. Anyway, I don’t think I can get better than that.

Still puzzling over whether this hole is actually that important with respect to the accuracy required: When installed in the cylinder and standard, the piston/rod/crosshead assembly appears to be fully constrained axially and in all rotations normal to the axis, without the need for a fit in the cylinder cover hole. My assumption is that the main function of the lower plate hole is just a location for the packing seal, in which case a bit of clearance might be beneficial. As it is, it seems like any error in the location of the hole could cause binding on the rod, but in reality if the hole was oversized, the packing would compensate and self-centre on tightening the gland nut. The packing wouldn't need to serve as an axial location – that's covered by the piston and crosshead.

The only thing I can think of that would require the hole to be a perfect fit, was if the intention was that it, combined with the crosshead, served to perfectly centralise the piston in the bore such that it never touched the sides. That would appear to be a huge ask though.

Comments/clarification welcome. Cheers!

Edited By Dr_GMJN on 26/06/2020 12:26:46

[Martin ConnellyParticipant @martinconnelly55370]

You want the piston to be a close fit in the bore and the cross head to be a close fit in the standard. The piston rod hole should be close to the piston rod but not rubbing. The packing will hopefully then seal around the piston rod whilst aligning itself to the correct position for the assembly to work correctly.

Martin C

[Dr_GMJNParticipant @dr_gmjn]

Thanks Martin, that was my assumption. It will be interesting to see if it’s a sliding fit when all three things are assembled. If not I suppose I could lap the cover hole to the shaft – assuming the piston and cross head move freely?

Ill cross that bridge when I come to it. Next job – drill and tap all location holes/studs.

[Dr_GMJNParticipant @dr_gmjn]

Today I co-ordinate drilled the covers, standard and cylinder block. Started by triple checking my calculations, then set the cylinder in the vice and finding the centre of the bore, which I set to be 0,0

Dotted the co-ordinates as a sanity check:

The gasket PCD was a bit small, but after checking yet again I could find nothing wrong with my calcs, so went ahead and drilled and tapped each of the 10 holes in turn:

Then, on to the top cover. Used the inside of the vice jaws as the y-reference:

Clearance drilled:

Same with the lower cover, but gripped by the lower boss:

Then the standard – I put it in the vice using the feet edges as a reference for clocking the hole array:

Clearance drilled :

All de-burred:

Studs test fitted, everything clicks into place, although the lower cover only fits in two orientations:

The gaskets have a bit of stretch, and do in fact fit ok:

The lower nuts fit, but their corners *just* touch the machined radius unfortunately. I can correct it though:

But all in all, happy with that.

Edited By Dr_GMJN on 26/06/2020 19:00:31

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