Strictly.... “ Hot Air “

[Twizseven]

Well it's taken best part of two days but now have a power cylinder. 

Once the base was flat and squared up drilled the two mounting holes and the two transfer port holes which allow air to pass between the power cylinder and displacement cylinder via the main body.  Then over to the large 4 jaw chuck.  I trued the cylinder up using the outer surface of the cylinder and then checked that the two machined faces on the base were square (in both directions) to the face of the chuck.  Faced the end of the cylinder, it was a little on the hard side.  Boring the cylinder was taking around 20 minutes for a return journey as I had it on the slowest feed I could get.  Again the first 1/8" was hard.  Gradually worked way out to just under the requisite 2.25" and left it overnight and finished off this morning.

Turned cylinder round and fitted in 3 jaw chuck to machine the governor end.  The 1" diameter hole which passes through to the main bore just cleaned up with about 20 thou to go.  The larger diameter bore then put in to a depth about 10thou past the pair of transfer port holes.

Over to mill to face of the governor flange and drill/tap the fixing holes.  Finally drill the 3/16" hole for the linkage rod in the two flanges on the top.  Was hoping to have plain hole one side and tapped hole the other but had to abandon this idea.  The holes were  bugger to drill as the material was hard, started to tap the lower hole but decided discretion was the better option and stopped before the tap snapped in the hole.  Drilled the hole out and passed a 3/16" reamer through it.

Colin

[Twizseven]

I was doing really well, the piston was almost complete, fitted beautifully, just had to face off the boss on the top.  Put in 3 jaw on Colchester, coke can shim to protect it.  Really slow 5 thou DOC to clean up the face.  Tool dug in and threw piston out of chuck.   It changed shape slightly.    Scrap   after taking my time.  Ordered new casting of GC.

Was going to abandon workshop and read a book but decided to make the governor plunger.  At least that bit went okay.

Happy New Year to you all.

Colin

[Dave Otto]

Ouch, sorry about the mishap with the piston; hopefully the next one will go better.

Dave

[Twizseven]

That makes two of us.
Thx
Coli

[Alyn Foundry]

New year greetings.

Colin, your piston doesn't look as bad as I was imagining during our telephone conversation.

There's a replacement on its way but in the meantime you could try a little " rescue " work.

I'd suggest getting it very hot in the forge, around a mid towards bright Orange for several minutes. Allow it to cool naturally. Make a suitable mandrel to pick up the thread you've put in the piston crown. You can now " clock " the crown diameter for truth. If you centre the mandrel you can add extra support with your tailsock rotating centre. By getting the piston hot it should have " grown " a little and also might have relaxed back to a more round condition. I use " radiused " tips for cast Iron, general work, as this gives a much smoother surface finish.

With any luck you should be able to remove a few thou and bring the piston back to size. Although the drawing shows a plain, flat side many of the full size engines had shallow reliefs to help reduce friction in the cylinder bore. That small " nick " in the side won't affect anything at.

The governor looks great, cheers Graham.

[Twizseven]

Following Grahams advice the piston has had 20 minutes at 800degrees in furnace.  Just about to go and make a mandrel and see if can resurrect it.

Colin

[Twizseven]

Having cooked the piston as per Grahams suggestion I was amazed by how much it had grown.  Just under 10 thou on diameter.  Made a 1/2" mandrel with 2BA thread and stuffed it in the collet chuck and screwed piston on.  It looked pretty true all things considered so proceeded to cleaned up the piston boss and face and then turned diameter back down to 2.2495.  It cleaned up reasonably well.  Can still see couple of marks in it, but going to go with it for now.

Last piece to machine is the main platform.  Will try this on big lathe tomorrow.

Colin

[Alyn Foundry]

Pleased to read things turned out well Colin. 

Do take your time in setting up the platform as it will pay dividends later.

Cheers Graham.

[Twizseven]

Fettled the main casting and went to have chat with friend, Tom, who had his own engineering business for last 4 years.  Had a chat about brazed carbide tooling and borrowed a spare green grinding wheel of him.  His view was to mill the casting rather than turn in lathe.  Chatted about milling cutters and appropriate speeds.  Came back and set up in mill with flat side down resting on two parallels with couple of bits of thin card to get level.  I had what should be a nice 4 tip facemill cutter which fitted in my large Clarkson collet.  Ran it nice and slow but had a very rough, almost grooved, finish.   Could not work out what was wrong  :headscratch:b and Tom came up for a look and bought his spare R8 3 tip facemill.  Swapped over to this and achieved a beautiful finish.

Looked at my facemill and found that for some reason two of the opposing tips were slightly lower than the other two.  Gave it a quick clean and it appeared a little better, but is now awaiting complete disassembly and a visit to the ultrasonic cleaner.

With a decent finish on the circular underside the casting was turned over and the top face milled.  This machined really nicely but needed a little more machining off than I expected to completely clean up.  Finished off with a 1.5thou cut with about 1/2" stepover.

Really pleased with the finish achieved.  Its about 20thou undersize on height but this should not cause any problems.

Next step is a bit of boring, drilling and tapping.

Colin

[Jo]

Coming on nicely Colin 

Jo

[Twizseven]

Thanks Jo.  Happy New Year to you and hoping you are keeping well away from the dreaded bug.

With a bit of luck will get the cold side bored and the displacer rod hole done tomorrow and maybe even the three screw holes.  This will just leave the tapped holes for the bearing pillar and power cylinder.  I have bought paint and primer for it all, but need to do a little bit with some JBWeld on the 3 leg base prior to painting.

Colin

[Roger B]

I have always been surprised how much things grow when heated with CI piston rings and silver steel  It can be a good rescue operation 

[Alyn Foundry]

There are many " roads to Rome " Colin but you're nearing the finish line.

Having not had a milling machine for several years after the lathe I discovered many tricks to get the job done. With the Robinson platform you can reduce the number of operations to a minimum.

Don't get me wrong, I wouldn't be without one these days and funnily enough the Denbigh has become a lathe on more than one occasion. Particularly when I had to machine flywheels of over 14" in diameter. It has an effective three foot swing.... 

Cheers Graham.

[Twizseven]

Setting of the main casting in the 4 jaw chuck was fun.  By the time it was centred on the lower periphery the the casting missed the lathe bed by about 1/8".  Used a tailstock revolving centre to help hold the casting against the chuck jaws.  I was running at lowest speed 54rpm as did not like the idea of casting spinning too fast and having to take interrupted cuts.  The only downside is the bearings are very very noisy on that particular gear.  I felt the next gear up which is a lot quieter was a bit too fast for my liking (85rpm).

Trued the face up and then bored out the cylinder.  Took it out to 3.35inches and then removed tailstock center to enable me to measure with internal mike as I took next few cuts to 3.4".  Just before took the last cut I faced the inside top face.

Centred, drilled and reamed the 5/16" hole for the displacer rod.

Put the tailstock center back in and then machined the 1/16" O-ring groove on 4.1732" diameter.  Finished off with a cleaning up the periphery of the casting and putting a champfer on lower edge.

Off to the mill to use the DRO's hole positioning feature to do the three holes to mount to base.

In order to position the  holes to fix the power cylinder and the bearing mount, all the linkages etc are assembled and placed on the main casting.  The linkage to the displacer rod needs to be set vertical and this then positions the power cylinder which is clamped in place.  The bearing mount is then moved around until the whole assembly moves easily and does not jam up or get stiff in any position.  When this is achieved the bearing mount is clamped in place.  The holes are located on the main casing using transfer punches through the power cylinder and the bearing mount.

Just need to source some small headed 0BA and 2BA bolts to fix the two components.

Then have a choice: test then paint or paint then test.

Colin
 

[Admiral_dk]

Nice to see it this close to running conditions - must give some satisfaction