Agnes.... 1/16 Scale Pollit & Wigzell Tandem Compound Condensing Engine.

[Jasonb]

Jo whats the best way to generate the helix when using the slotter or shaper?

[pgp001]

I have played about in Solidworks a bit, and it really does need to be a proper helical shape, otherwise the two will not mate together back to back.

I looked at taking step cuts, but it is going to end up looking like a spiral staircase and probably still need finishing with a file anyway, so I had come to the conclusion that it will have to be set up for spiral milling, I did wonder about using some sort of sheet metal ramp/cam and just hand feeding them a bit like some of the spiral gear attachments we have seen.

Phil

[Jasonb]

I suppose if the steps were small enough maybe 1 or 2 degrees you could get a fairly good finish.

As you say the flat ramp does not quite mate on the ramp but the faces that take the load do.

[Jo]

Jo whats the best way to generate the helix when using the slotter or shaper?

You do it the same way you do for a milling machine. The only difference is you are using an up and down tool rather than a round and round one which means you get square edges right into the corner and if you shape the tool correctly the ramp should also be smooth.

Jo

[pgp001]

Just a quick update on progress, I am busy making the barring engine at the moment.

This is the full size one, so you can see it is tiny in comparison to the flywheel it has to turn.



The model starts off by making the worm and wheel, the worm is a bit complicated in that it is also the crankshaft and eccentric.
All this was machined from solid.

Blank for worm wheel being formed on the Alexander milling machine using a Tom Senior dividing head.



Teeth on the wheel were cut on Mikron hobbing machine, it was a real fluke that I had the correct cutter for this.



Transfered to the boley & Leinen jig borer in order to produce the cruciform section spokes.







Here is the embryo crankshaft having the mating worm put on.





I made this fixture for turning the crank and eccentric pins, but it was a failure I am afraid, being made from aluminium it was just not rigid enough.



So I modified my Keat's angle plate to do th job and that worked much better.





You get a sense of the scale of the finished shaft next to a ruler.



More to follow.
Phil

[Gas_mantle]

Looking good Phil, nice work :-)

[fumopuc]

Hi Phil, fantastic. Thanks for showing your progress.

[Ramon Wilson]

Lovely work Phil -particularly those cut outs - very nice milling all round 

Regards - Ramon

[jadge]

Great looking worm and worm wheel. Presumably there is no need to gash the worm wheel first when using a hobber? Assuming that the worm wheel is based on an integer value DP how did you set up the lathe to cut the irrational pitch worm?

Andrew

[pgp001]

Andrew

The worm and wheel are 0.1" circular pitch, so the worm was a straight forward 10 TPI thread with the correct ACME profile to match the worm.
All I had to do was work out the diameter of the wheel blank and put the root radius onto its OD with a ball nose slot drill prior to hobbing the teeth.

Phil

[jadge]

Phil: Thanks for the information. I guess it makes sense to do it that way round so you don't end up with an irrational pitch for the worm. It's a very impressive looking worm wheel.

Andrew

[pgp001]

Next up is the base casting, mostly just straight forward squaring up and milling pockets etc, there are quite a few 10BA tapped holes that needed a bit of care as well.









Then onto the split bearings, these were made from a piece of recycled cast brass musical box bedplate that is about 150 years old.
I faced up a couple of blocks and soft soldered them together whilst they were being machined.









The outrigger bearing was next, but I got carried away and forgot to take any pictures until it was done apart from this first one just skimming up a datum face to work from.



So, that's where I am up to at the moment. Here is a trial assembly of what I have done so far.







Phil

[Dave Otto]

Nice work and progress Phil!

It is always fun to see an update on this amazing engine and project.

Dave

[10KPete]

A first glance at those pics and one thinks "Wow, that's a nice engine." Then one comes to the pic with it on the
tapping pillar.....

That engine is tiny!!

Beautiful work.

Pete

[Jasonb]

Looking good Phil, would make a nice little project in itself.

Are you going to add some rod to the counterbored holes to bring them up to look like cast bosses?

J

PS PM waiting for you on the other side