triple expansion engine

[peatoluser]

The longer pivot arms in the curved links have a collar on the end to hold the reversing link bearings in place. decided to use taper pins (1/16") to hold these in place. not having much luck with cross hole drilling in the drilling machine, I decided to mill a V-block to fit the lathe. used a combination of 6 flute countersink & 1/16" slot drill to produce a vee groove in a block clamped to the cross slide.
here's the block beeing milled

and the small journals (5/32" dia.) being cross drilled .I loctited the collar onto the shaft to hold it in place, then after I'd drilled and reamed the hole disassembled with heat, before soldering onto the link.

the v-block worked so well that i ended up making another, but used a 1/2 countersink to produce a bigger vee.
With all the valve parts made, I thought I'd have a trial assembly of the shaft and base. here it is.

Instead of making round oil cups for the main bearings, I decided to try and make them square. A bit like the large oil boxes on full size engines.
Forgot to take photos, but I milled an oval slot in some brass bar using a similar set up to the way I'd drilled the reversing link bearings.
the lids are only a push fit. I tried milling these from solid using the vertical slide. got into all sorts of difficulty with size depth of cut etc.
so bought some solder paint and made them from scrap pieces of 18g brass. It may be an expensive way to buy solder , but a touch of the flame and they were done. I guess it pays to at least think of a couple of ways to do a job before cutting metal
I guess the next job is to make a start on the columns, but befor that, I've agreed to walk the coast-to-coast route. the daft things one agrees to do when drunk ;D. 2 weeks without any shed time. how will i cope!
thanks for looking
peter

 

[peatoluser]

Finaly finished the columns. well except for cleaning and fitting to the base. these were fabricated from 1/8" plate.
first was to hacksaw and file the sides

then tack weld the front and back pieces on

then I welded them up

but making sure i had built the edges up enough to allow filling and emerying to shape

I then tacked up a simple jig

to allow the top,front and base to be soldered on. i was concentrating on clamping everything up square forgot to take photos, but this should give an idea of how it turned out

as I've decided to try and make an open front engine instead of the closed column design, I tacked a piece of 1/8" plate to the centre of the jig to give me the slope for the front columns

the tool makers clamp is only just nipping the bar. In fact, I probably could of left it out. In situations like this, I usualy use a small chisel or centre punch to raise a couple of burrs either end of the bar. These tend to hold it in place while maintaining the joint gap.
and here are the columns ready for cleaning and fitting

thanks for looking

peter

 

[steamer]

Nice fabrication work! I made a cross drilling fixture like that that mounts to my QCTP

Works Great!

Dave

http://i164.photobucket.com/albums/u27/mcandrew1894/P7100003.jpg

 

[Deanofid]

Great job you're doing, Peter. You've sure poured a lot of ingenuity into making so many parts with
the lathe. I have the thought that you could do it all by hand!
Good stuff, this thread.

Dean

 

[peatoluser]

Gentlemen, thank you for the compliments, much appreciated

Dave, I like your stop on the QCTP . I must fit one on mine.

and Dean, I must admit that there are times when all I seem to be using are hacksaw and files, that it feels like I'm doing it all by hand :big:

yours

peter

 

[JorgensenSteam]

Great work Peter, it is interesting to see it start to come together.

Will be watching and waiting for a run.

Great project.

Pat J

 

[peatoluser]

Slow progress, but progress nontheless
to make the crossheads I first squared up some mild steel and then used the lathe to drill the pivot hole and tap the piston hole at 90 degrees, as I can't trust my drill to drill that square. the profile was then filed to shape. the 'foot' was made from phosy bronze and used the vertical slide to mill a locating groove in it. it was then soldered on to the crosshead. heres a photo of the stages

I hacksawed and filed 3/8 strips from some 3/16 plate to make the guides. these were clamped to the cross slide at the right hight and a step was milled in them to suit the crosshead

milling the step

I bolted these to the columns, but instead of using a few countersunk screws , I decided to make them look like full size practice and used 10 ba bolts instead. more by luck than design , the connecting rod and crosshead just miss them although I had to chamfer the guides to stop them fouling the connecting rod.

here they are assembled

Yep, it's deffinately comming together at last.
next stop are the brackets for the reversing shaft and linkages and then i can finaly start thinking about the cylinders

thanks for looking

peter

 

[pete]

Peter,
A awesome and very well done project that makes me feel more than slightly guilty for what I have in my shop. Before your post was started, I wouldn't have believed that a engine of this type could be done with the limited equipment you have. Once your engine has been completed, You really should contact Taig and provide a link to this thread. Your engine would be a super advertising example for them. I'd guess that Jerry Kieffer made a nice amount of spare cash from Sherline some years ago when they used some of his work as an example of what can be built using Sherline equipment. To be honest, This whole thread should be slightly rewritten as a long running multi part artical for one of the hobby machining magazines.

Pete

 

[Jasonb]

Yes thats certainly comming along nicely. Talking of magazines the latest issue of ME has a nice scratchbuilt triple expansion on the cover with accompanying article.

http://www.model-engineer.co.uk/

J

 

[Shopguy]

Peter

Looking good. When done you'll certainly have a fine looking model.
Ernie J

 

[SBWHART]

That's comming together very very well Peter.

It will be a real nice engine when completed.

Stew

 

[ShedBoy]

Nice, real nice. Love the detail, keep up the great work.
Brock

 

[pete]

Jason,
Here in Canada our mail delivery is two behind that magazine. I'm looking forward to it.

Pete

 

[steamer]

Very well done Peter! :bow:

The next few steps are critical...getting the cylinder/crosshead/crankshaft to all line up correctly....take your time.

And a Karma for you for bravery! ;D

Dave

 

[swilliams]

really looks fantastic Peter. Very nice job :bow: :bow: :bow: :bow:

 

[kye]

wow!!

surely im not the only one thinking that that will be hypnotic to watch as the crank is turned over!!!

kye

 

[Harold Lee]

Peter - That is beautiful work. I think to tackle that on the equipment you have is outstanding. I'll be following this with interest.

Harold

 

[Ken I]

I'll second what Harold said, I am so impressed with what you are doing.

Can't wait to see this finished.

Ken

 

[ref1ection]

I'm really impressed with the authentic look of this engine. It leaves no doubt that it's based on a real engine.

Ray

 

[peatoluser]

Well, it's been a while since I posted, so thought it was time for an update. but first, can I say thank you for all your kind comments - they've certainly helped keep me focused on the task in hand and not drift into other projects! - although looking at other peoples build logs I feel I don't deserve half the praise.

the next parts were the reversing shaft brackets and arms which were straight forward soldering and/or filing jobs

the next bit was the operating mechanism for the shaft and this caused a bit of head scratching. the drawings show a worm and wheel arrangement but give no guidance as to number of teeth or pitch etc. I thought about trying to generate a wheel using a tap held in the 4 jaw.
I found this site that gives advice on this method,
http://www.atmsite.org/contrib/JSAPP/wormgear/wormgear.html
but felt i wanted something that would give a faster movement. So I settled on the idea of using a screw and nut similar to the one on imation's paddle engine posted on this board here
http://www.homemodelenginemachinist.com/index.php?topic=16548.0
but it was Zephyrin's comment about the scew that got me thinking. unfortunately.
I've always wanted to try thread cutting on the peatol by the follower method, and figured this would be a good a starting point as any.
I had a 3/4 whit nut and bolt and thought about using these to produce a 10 TPI square thread but I really liked the look of that 8 TPI twin start.. 6 turns and the nut moves 1 1/2"...but how to produce a 4 TPI nut and bolt. In an act of ignorant optimism over intelligent experience I gave it a shot.
the first thing to do was to produce the screw. I chucked a piece of 1" bar in the 4 jaw, centred it , and scribed 8 axial lines down it's length. I then scribed across these in 1/32" steps to give me a spiral pattern around the bar as here

then, using first a 3 corner needle file, then a six inch one, I attempted to file a thread around the bar, but not after re-chucking the piece to bore both ends 5/8" and drill right through with a 6mm drill (this way it gives me 2 bites of the cherry to get a good fit on the lathe spindle, and makes it easier to thru drill the 6mm hole) . why I didn't just cut a card template of one helix and use this to mark the thread I don't know.
here's the bar with a plug loctited in for turning it

for the nut, I bored a 1" hole in a piece of 1 1/2 by 1/2 bar and drilled it to accept a 5mm bolt that i had turned a cone on the end.that's all that was going to be pulling the saddle along , but that bit worked surprisingly well. A scrap piece was welded on to it so it could attach to the bar that is bolted to the saddle

and here it is on the end of the spindle

I turned a suitable blank for trying out then set up for cutting the thread. then what could go wrong did go wrong.
i initially had it supported by the tailstock, but the tool easily deflected the work, so made a quick and dirty travelling steady and bolted this to the block i had bolted to the saddle. it's in use here cutting the first thread.

then i was surprised how much effort I needed to turn the spindle, so thought i would make a 'pre-cutting v shaped tool' to rough out the cut before finishing with the 1/16 wide cutter.
then the tool dug in and turned the work in the jaws putting it out of phase with the thread master.
the chuck fouled against the block I had screwed to the saddle so had to have the work protruding even more
next the master itself came loose, so had to strip down and drill for a grub screw (you can see it in one of the above photos)
then the tool broke, so I reset up with the finishing tool, but finally managed to get the first thread cut. It wasn't pretty - it was out of sync. with some of the other efforts- but cut nonetheless.
to cut the second thread, i had come up with the idea of initialy using a piece of 1/8" scrap to pack the tool out to cut the first thread (hence the use of the toolmakers clamp in the previous photo) and then remove this to give the required offset. unfortunatly something went wrong and it got offset too much so when I cut the second thread you can see it's slightly out of phase.

it was then I realised I hadn't given much thought to cutting the internal thread, and moving the tool to cut the second thread. the conventional type of tool was out, if for no other reason than trying to grind it free hand, so i ended up coming up with the idea of filing a hook type tool- i only needed to thread for 1/2 depth- from gauge plate. the first one was too slender and bent when cutting, so made a second but modified the way i offset for the second cut . here they are

and here it is cutting a piece of scrap brass (I counter bored the back first for tool clearance)

the tool width is 0.070" and I drilled a 6.7mm clearance hole
did it it fit the screw? well of course it didn't! but it was trying to. it seemed to be just missing catching one of the threads, so I clamped the screw in the vice, putting some..er.. spanner flats on the thread, and using a light hammer and spanner, gave the nut a few taps while trying to turn it. both threads eventualy caught and I was able to run it on abou 1/2" before it went tight. well with the use of a needle file and some 400 grit grinding paste , within 1/2 hour I was able to run the nut the full length of the screw!

it's undoubtedly only catching on one helix and the threads wind themselves round the screw more drunkenly than i find my way home on a friday night, but work it does! it is good watching the nut race along the screw with a few turns, much better than with a die cut thread- one turn of 3/8 whit moves 1/16", here its 1/4. I will definately remake this. Might even see how much it would cost to get a proper follower and nut made by a local machine shop. And i would urge anybody to have a go, especialy with a screw cutting lathe. even if you only produce a single 8 TPI or 10 TPI square thread. they realy look the part. i think the stumbling block is cutting the internal thread, but the tool doesn't need to be HSS or long and can be easily file and hardened from gauge plate or drill rod. give it a go. It's well worth the grin factor at the end.


Oh, and PLEASE don't ask why I didn't use the compound slide to move the tool. I have one some where, but so seldom use it, it never entered my head.