Hello and a part-built blowfly

[Lisa]

The left cylinder looks a bit nicer than the right:

Correctly positioned and into clean metal all the way through, just have to finish fly-cutting the front face. The bore still looks low in the casting, but as before there's nothing to be done about that, the critical dimension of bolting-face (frames) to bore centreline is correct.
Once the fly-cutting is done, I need to grind up a couple more tools for the boring bars, then I can turn the cylinders round and flycut the rear face and bore to finished size in one setting.

Meanwhile, the bottom of the smokebox saddle is mostly flat now.

Just need to do some clamp hopping to get the last bits, then I'll probably flip it over and just skim over the top so that the top and bottom are truly parallel. Then upside down again to mill around the outside of the bottom flange, which will be a little interesting as the Y(?)-axis of the mill doesn't have enough travel to go all the way round; so I'll probably do the sides, then turn it 90° and do the ends.

[Lisa]

Here's the larger of the two boring bars set up to cut, I ground up a tool for it yesterday, and got back to boring today.

The back face has been fly cut at this point, so the cylinder is at the correct length. One minor niggle is that the holes for fixing the end covers should be 5/16" deep according to the plans, but there's only 1/4" of metal on the flanges after finishing the cylinders to length. So another area where the casting is upsetting things a bit. On the plus side, it does mean I can go for through holes, which will be easier than bottom tapping into a blind hole.

This is the cylinder pictured on the previous page with the bore all over the place; the bore is no longer off centre, I'm finally taking a full cut all the way through. At this point I measured the bore to see how oversize I'd have to be, but it's at 1.486" (or so says the calipers, I don't have a 2" mic'), so pretty much just right for a finishing cut to 1.5" (or maybe a thou under, then hone it); pure dumb luck, but I'm not going to complain.

[Jim]

There's no 'dumb luck' there Lisa not only have you bored out the cylinder to size but ground up your own cutter, that's skill.
You're doing a great job I must say and really getting your money's worth from your lathe. Lovely to watch the progress.

Jim

[Lisa]

Thanks Jim, I was expecting to have to go oversize with the bore, and 14 thou is pretty close, but at least it's close on the right side.

[Lisa]

Ignoring the cylinders for a bit, I finished milling the bottom of the smokebox saddle casting flat and square.

I also skimmed across the top to ensure the top and bottom are truly parallel as mentioned; this helped greatly with the multiple clampings required to mill around the sides of the bottom.

Dad was watching on and seemed to be quite enjoying himself.

[Lisa]

To improve my measurement capabilities I bought a set of telescopic bore gauges, and the cylinders have been sitting idle while I waited for them to arrive.

They arrived this morning (along with the latest AME, which has an interesting article on LBSC in it), so I finished boring the first cylinder this afternoon.

Fingers crossed on the last cut of half a thou, as accurately as I'm able to measure the bore is now 1.499"; just right for honing to finish it off.

[Lisa]

The front cylinder covers, which I turned up a while ago, fit quite nicely in the bore at last.

This also shows up how far off the casting is.
Urgh, rust.

[steamer5]

Hi Lisa,
You have got to be very happy hitting those numbers! I know I would!

Cheers Kerrin

[Lisa]

Thanks Kerrin, the last cut was "faith-based machining" as in "oh goddess please don't let me f*** this up."

[Lisa]

While boring the second cylinder earlier today (well, yesterday now), I got curious and measured the distance from the bolting lugs to the cast-in drain cock spigots; wondering how far out they'd be as a result of the bore being low in the casting. But oddly enough they're bang on central to the bore, which is surprising considering how far out the end faces are.

Dec 25, 2016 14:58:32 GMT simon48 said:

Hi Lisa,

I have the same lathe as you, and to use the official faceplate I had to remove the cover as it hits the edge of the faceplate and you cannot start the lathe.
I now run the lathe without the cover! Just leaving the arm set asif it was in the down position.

Simon.

I've been wondering if I can't move the cutout switch for the (now removed) chuck/safety guard, it seems the switch could be used to make a stop for the carriage. I already have the mechanical stop I made a while back, but an electrical cutout would be useful for having the lathe shut itself off when taking long cuts (such as boring cylinders, though a bit late for that this time around).

[Roger]

Oct 23, 2017 9:30:18 GMT Lisa said:

Thanks Kerrin, the last cut was "faith-based machining" as in "oh goddess please don't let me f*** this up."

That's a great term, I might have to borrow that one....  "faith-based machining" There's an awful lot of that in CNC machining!

[Lisa]

The boring is done. Though I still need to flycut the rear face of the second cylinder, then it's onto ports and passages, after honing.

Speaking of honing, this one's done:


Just a flex honer in the bench drill does the job.

I should clean that mess up, problem is that I'd never find anything then.

Also the faces need to be machined (at least closer to) concentric with the bore. This will either involve a rotary table in the mill, or some kind of mandrel in the lathe, we'll see.
The faces are also getting lapped on some oily emery so that they're flat, and smooth, and just generally less likely to blow a seal.

[fostergp6nhp]

I wouldn't bother lapping joint faces as unless the machining is really rough they will seal fine with a gasket. The gasket under the safety valve unit of my miniature Traction engine holds a hydraulic test of 300psi and the faces were only fly cut on the mill.

[Lisa]

They're probably fine as you say, but I'm just not entirely happy with the finish from the fly cutting.

[Lisa]

Today I almost finished the second cylinder, just 0.5mm to go in fly cutting to get the rear face done and the cylinder to length.

Dad was in the workshop with me enjoying himself, so I made a little video of it all.

www.youtube.com/watch?v=ndJTb9TbzFo

[Lisa]

I finished the last of the fly cutting earlier today, then spent a bit of time cleaning, oiling, disassembling, reassembling, and just generally getting the lathe back into general use mode again.

... After double and triple checking that I really did want to remove the boring setup now.


I bought a fixed steady for the lathe today as well. There's two fixed steadies available for this lathe, so I got the larger 50mm one which should be more versatile than the 30mm one, hopefully. It will at least let me face and centre drill materials that won't fit through the headstock, which will be handy.

[springcrocus]

Good move, Lisa. Cast iron dust and oil equals grinding paste. I always like to clean up really well after machining cast iron.

The cylinders are coming on well, great job.

Regards, Steve

[Lisa]

I grew up with (overly dramatised) tales from dad of lathes being destroyed by cast iron dust. His aim of teaching me to keep the machine clean and lubricated worked though. The same can not be said for benches however.

[Lisa]

Just a simple little job today of turning the chucking spigot of the rear cylinder covers true, while going over the lathe, adjusting gibs and such, so it's back in peak condition.


I also got invited to join in on a group build of 6" scale Ransomes Simms & Jefferies traction engines; I'd jump at it if I was working (for that matter the idea of selling a kidney crossed my mind), but alas I had to let the opportunity pass.

[Lisa]

Playing around in CAD a bit tonight. Blowfly was designed with packing for the glands, which I'd much rather replace with o-rings, so I came up with this:

It's basically as designed, but with the thread shortened on the gland nut, and a pocket put in for an o-ring. The aim being to seal the o-ring on the diameter, and give it a little space for it to 'roll' along the piston rod; not much, the pocket length is 1.5*o-ring diameter. As such, the gland nut doesn't put any pressure on the o-ring, just traps it in place.
Anyway, I think this should work.