Gallery, Projects and General > The Design Shop
An experimental engine
arnoldb:
Thanks Benni, Stew, Nick, David, Eric & Bernd :beer:
Stew, aye - the wiggle wire; just wish I remembered it earlier... There's a funny thing about the smaller sizes; I think I'm getting used to them. Now I'll wait for the lads with the funny white jacket :lol:
Nick, I went with the D valve as I have built one before on Elmer's Grasshopper. Of all my engines, that one is the easiest and smoothest runner. In fact, I considered using the same cylinder dimensions for this build, but it would be too large, and scaling would present a couple of problems. Piston valves was also an option, but they can be leaky by nature and I want to use as much steam as possible on this small scale.
As to the save on the hole; Bogs and many others have shown this type of method used - it's one of those things that can save a lot of time and work, and if done properly is nearly - and in some cases completely - invisible. On a personal strive to perfection on a home-built project it's a no-no depending on point of view, but when restoring historic pieces or simply saving a complete re-build on an experimental workpiece its always an option.
Today's bit; I had shortened shop time due to a personal commitment that paid off handsomely in a bottle of good single malt :)
First job was to drill the mounting holes on the sides of the cylinder block - 2.5mm for tapping M3 later:
I drilled out all the mounting holes in the cover plate, valve plate and valve chest stock to 2.1mm by clamping the lot together:
Then on to milling out the valve chests - I got rid of a lot of the excess material by drilling two 6mm holes in each:
And then started milling to the scribed lines with a 4mm end mill. Apologies for the out of focus photo:
The other chest received the same treatment. I think I'm due for a new 4mm end mill though - the flutes on this one leaves two "lines" on the sides.
Some may have by this point wondered what I'm going to do about the valve guides and packing glands... I had decided on doing things a little differently - that's what experimentation is all about - and make up longish press-fit guide & gland combinations, that can be pressed into holes in the valve chest. As these would be subject to steam pressure and heat eventually, I opted to go for a design where they would be pressed in from the inside of the valve chest with thin flanges to prevent them going out should heat and pressure loosen things. Seeing the things might be better...
So on to the lathe for a change. Material for the valve guide combinations is 6mm stainless steel rod, which I turned down to 4.01mm for a length of 8mm, threaded the end M4 for a length of 3mm using the tailstock die holder and then drilled and reamed out to 2mm in the center. Then I started parting it off leaving a 6mm diameter and 0.2mm thick "flange" on the end:
Then I drilled and reamed 4mm holes in the side of the valve chest:
Pressing the guides in from the inside was a bit daunting. The bits were coated with some loctite, and then I resorted to using a spanner and hammer to bash them home using the big vise as a guide. Brute force, and I paid the price by missing a hammer blow - no guesses where that one landed :doh: :
I should have made a proper pressing jig; would have made for a much better outcome :bang:
Surprise, surprise... Things are offset ::) - the valve ports are offset by 1mm towards the inside, which will become the outside of the cylinders :palm: :
I'll see how things pan out from here; I'm thinking it will be usable as-is, otherwise I'll have to make a new valve plate. Now I'm glad I made the valve plate separate from the cylinder blocks.
Time to sample that malt :beer:
Regards, Arnold
NickG:
Shame about the offset Arnold but it looks like there's room to make some offset valves to suit.
arnoldb:
Thanks Nick - yes, for now I think I can get away with offset valves. Not ideal though; and I'm actually more disappointed at myself than anything :coffee:
My IT project's going well at work, so I'll have a bit of time for the shop this weekend :ddb:
Stole a couple of hours in the shop today, and got down to some bits.
First off, grabbed the M2 taps, and sat down and tapped all the holes on the top of the cylinder using my crude tapping guide and handle. It looks like one piece in the photo, but actually I set the tap depth in the top "handle" so that it will bottom out the handle on the guide at the correct depth:
::) I really need to get around to making a tapping stand... It will have to be a wee bit more robust than Rob's version though :lol:
The mounting holes needed to be tapped M3 - but as they are pretty shallow and I want to get maximum depth of thread, I had a bit of a problem; one that seems quite common. My M3 "final" tap; the last one of the set of 3; has a sharp point:
A quick step to the bench grinder,and with the excess ground off to leave just three threads with taper for engagement in the hole:
Most bolts I've seen will get well down to final depth of thread in a hole tapped with a tap like this; and one could always file that slight taper at the very end of the bolt to go down into a hole completely.
Tapping down to the hole end; on aluminium I just use the second and last taps, and to the top left, you can see my "tapping fluid" for aluminium; ordinary methylated spirits:
And I'm way too lazy to use a tapping guide for M3 - I just free-hand it...
When I looked in my stock for M2 threaded rod, I was all out ::) - so I ended up making some from 2mm bronze brazing rod, which is nice and tough to use for studding on lighter-duty applications. I just start it off clamped in the collet chuck and with the tailstock die holder, and a couple of manual turns by hand to make sure the thread is properly engaged. Then I power up the lathe on a low speed (on my Myford, surprisingly, lowest non-back gear speed is fine) and hold on to the die holder and let it run through. It does need quite a lot of tapping fluid to cool things down and lubricate the die, and my left hand is never far away from the lathe clutch in case something goes wrong:
I made up four lengths of rod, and threaded some M2 nuts on - to be used in the next step:
After I took this photo, I ground the excess sharpish points off the rods using the bench grinder; not ideal use of it, but it's very little metal to remove.
Having four separate pieces of threaded rod makes life easier for the next step; a dab of loctite on the tip of each rod, and screw it into the cylinder block until it is finger tight. Then a light additional twist using pliers on the non-threaded bit of each rod, and they tighten up nicely into the block:
A coffee break later - to allow the loctite to cure a bit, and on to the next step. All the nuts are screwed out to a height where their top end allows adequate space for the valve plate, steam chest, steam chest cover, slightly thicker nuts, and a little extra in case some packing is needed and an allowance for clean-up. A whole mouthful; but rather too long than too short at this point. I also dug up my favourite sharp electronics side cutter:
The side cutter trims off the rod quite well, but still deforms the tops and hence threads at the tops slightly:
That is the main reason why I added the nuts in the first place... Once the nuts are unscrewed, they clean up any thread deformations, allowing nuts to be easily screwed back on again later. ::) This was REALLY taking the long way around to handing out a handy tip :lol:
With the cut ends of the threaded rod cleaned up a bit on the bench grinder again, it was easy to screw on the nuts again; hence ensuring that the rods would screw into the block without problems, and the second set of studs was started, and later finished exactly the same as the first lot:
End of work today; the whole lot assembled and some rods shoved in the valve holes:
I took that lot inside together with the bit of copper pipe that will most likely become the boiler, and compared sizes against Fred the loco:
It's nice to start getting a visual comparison and while the previous two photos don't mean too much, it does start to give me an idea of what's needed from the frames, which will be up next. Some Thinking is required :med:
Regards, Arnold
sbwhart:
Comming along well Arnold :thumbup:
Is O gauge 13/4" between the tracks ?
Stew
Gerhard Olivier:
Nice progress Arnold :beer:
Keep it coming
Gerhard
Navigation
[0] Message Index
[#] Next page
[*] Previous page
Go to full version