Retlas

[Jo]

It is looking very good Andy 

I noticed that in your enthusiasm you posted two huge (+3M bytes) photos the same. Did we miss one?

Jo

P.S. The poor guys who are trying to see the forum on their mobile phones will find it takes forever for those big pictures to download 

[Chipmaster]

Ooh er sorry, can those pictures be deleted so that I can have another attempt. I have wanted to delete attachments to replies before posting but the 'clear attachment' button hasn't worked for me.
Andy

[Jo]

Removed.

Once they are attached to remove them you have to un-click their attachment box 

Jo

[Chipmaster]

Thanks for doing that Jo, I'll correct that posting later on when I'm using my pc.

Andy

[Chipmaster]

A recess for the larger timing gear was formed in the base casting but quite a lot of machining was required to reach the required diameter and depth of the finished recess. I was concerned that I might form a hole instead of a recess.
If it had gone wrong there was plenty of support for the timing gear axle and I knew I could patch a hole from inside the base if necessary. Milling with the boring head was a very noisy affair - lots of screeching right through to the final cut yet the tool appeared to be cutting perfectly well.
Andy

[Alyn Foundry]

Hi Andy.

Great progress !!

This might be the first Retlas to have straight pushrods ?

I added extra material to the inlet and exhaust pads of the cylinder and also added extra to the back of the valve chest castings.

Re the screeching, was your boring bar a little on the slender side?  Alex would have said that you had made dust not swarf, he always made swarf!!   

Kind regards, Graham.

[Chipmaster]

Hi Graham, yes ok dust all,over the place, vacuum doing overtime with all this iron dust. It was a half inch boring bar about four inches long and the boring head is an old Enco that seems to be in good order. I wonder if the geometry of the tool was a factor because there was negligible end rake in the position / mounting of the triangular insert. Or perhaps my poor old Archdale milling machine is telling me somthing.
Off to the monthly meeting of the Black Contry Live Steamers tonight.
Andy

[Chipmaster]

The crankshaft was a job I that I approached with some trepidation.  Retlas has a stroke of 3", the largest crank I have made so far is the 2" stroke  crankshaft for my Alyn Foundry Gardner O Type which was machined from flame cut steel plate. Machining a Retlas sized crankshaft from the solid  would consume a lot of time and I wasn't keen on machining the crankpin between those webs.
So, with my confidence boosted by Jason and Graham's advice I made a fabricated silver soldered crank using 12" of 3/4" ground EN1A mild steel and an eight inch length of 1.5" x 5/8" flat mild steel.
Couldn't obtain 1.1/4" x 5/8" so I had to mill the 1.5" x 5/8" steel flat down to size for the webs. After the material for the webs was reduced to the correct width it was sawn in half and the two pieces glued and bolted together. The webs were marked out and the holes for the 3/4" shaft and crank pin bored out on my lathe to ensure they would be parallel. The big end is 5/8" diameter and 3/4" wide, I stepped the ends of crank pin down to 1/2" to fit in the webs. A gap of 0.001" was allowed in the joints for the solder's capillary action. Correction fluid painted over the crankpin kept the silver solder off the bearing surface.
The pictures below tell the story, I was very pleased that the crankshaft  stayed straight after being subject to the heat of the soldering process. Some cleaning up and polishing remains to be done, that can be done while some other job is on the lathe or milling machine with the power feed engaged.
Andy

[Chipmaster]

The two eccentric straps were machined next, each step was pretty straightforward . Boring out the centres was left as the last operation because thin iron castings like these can be delicate  . I finished these the day before I broke my Stuart Major valve chest which was much thicker. http://www.modelenginemaker.com/index.php/topic,3389.0/all.html#lastPost
Anyway the machining is done they just need a bit more cleaning up.

Andy

[Roger B]

That crankshaft turned out very nicely   

[Chipmaster]

Yes thanks Roger  I was both pleased and relieved with the result.
The next job on the crankshaft will be to mill kegyways in the shafts for fixing the flywheel and timing gear. I have found the fitting of Gib keys to both models and full size engines to be a time consuming process, perhaps due to the limitstions of my equipment or technique.
So, hoping to get a better / faster result I'm waiting for the delivery of Gib Head keys from Tasman Industries, Stourbridge UK http://www.keysandpins.com/ecommerce.
I'm going to fit 3/16" keys rather than the 1/4" specified because a 1/4" keyway in the timing gear appeared to remove too much material for comfort?
Andy

[Alyn Foundry]

Hi Andy.

This forum moves fast, I had completely missed your post on the crankshaft! It's looking great.

I have to agree with your intention of going with 3/8" keys, more in keeping with the original.

In the early days we used to hand file the keyway, both messy and inaccurate! Alex suggested the Du Mont broach and bush system. Expensive yes, initially, but over time they really paid for themselves. I now have all the imperial sizes from 3/32 " to 3/8" . We discovered very quickly that the bushes supplied were of no use for our application being far to short, so we made longer ones to support the broach over the full length. We used thin strips of shim Steel for the incremental cutting method.

Gib head keys have a taper of 1:100 as does the broach, I know I'm going to get a " ticking off " for this but we just pushed the broach, on the final cut up to the last tooth to enter and then pushed it back out.
It was Roland ( Mery engine ) who suggested bushes with the 1:100 taper so you could push right on through.

The keys are usually slightly oversize requiring a little hand finishing we used a medium, flat oilstone to remove the last thou or two. The final result was a well secured and true running flywheel. Oh another tip, put your keyway between spokes as sometimes they are stubborn to remove necessitating the use of a drift which can be passed between the flywheel spokes, much more difficult when there's a spike in the way!

Fiddly bits to come!!

Kind regards, Graham. 

[Jasonb]

I prefer to make my keys from rectangular key steel, if you leave it on the bar it gives you plenty to get hold of so its easy to pull out while tweaking the fit. I have made a few bushes with a tapered slot so it cuts a matching taper in the flywheel.

Also watch the taper, metric are 1:100 but imperial are 1:96 (1/8 to the foot) not that it makes a lot of difference in our sizes.

[Alyn Foundry]

Hello Jason.

I assume that you've machined a taper on your rectangular key steel? 

With so many of our engines using 1/8" Gib head keys I bought a box of 200, they worked out at 60 pence each........ A real time saver!!

Kind regards, Graham.

[Jasonb]

Graham, yes I machine the requiered length down to a slight taper and then hand fit as needed. I have shown it in other threads but this is how is set a taper, 1:48 in this case



What you can't see in that earlier photo is the pair of mole grips on the end of the keysteel which can be tapped with a hammer to withdraw the key, once happy with the fit I say off the key leaving enough of the rectangular section to form a head