Another Comber / Coomber build

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madjackghengis:
Well Arnold, it looks like you're making some pretty good progress there. Thanks for the video of your running engine, it's much better than the other video showing the basic mechanics of it. Thanks for the connections to Elmer's engines as well, I expect to find some interesting projects for the future from among them. I like the fact you are using plans, but not tied to them, and willing to modify and adapt, it makes each engine unique unto its self that way as I see it. This engine is kind of like a wobbler that the cylinder travels in a complete circle to complete its porting of steam and it makes for a very interesting looking engine when running. Very nicely done she should be a real beauty when she's running. :jaw: :beer: Cheers, mad jack

arnoldb:
Rob, both Johns and Jack - Thanks Gents :beer:

Jack, Elmer's engines are well suited for beginners, but I know of quite a couple of experienced machinists who get just as much fun from building them. About half of the engines I've built so far are Elmers; on most of them I worked to the plans, but now that I've started to grasp how things go together on paper and what to look out for when making my own changes, I'm getting bolder about doing that. The basic Elmer engines are very simple in appearance and does lean themselves to a bit of change and "customisation".

Stole two hours in the shop after work today :dremel:

I used an old "incorrectly made" needle valve stem to find the location for the first mounting hole to drill in the columns and zeroed the X and Y dials on it:

Then I started drilling the holes, just by feeding in the coordinates on the mill. The third hole was a bit of a disaster; the 1mm center drill I was using to spot the hole location before drilling snapped it's tip in the hole:

I used the sharp side edge of a pair of needle-nosed pliers to grab on to it and gently tried to reverse it out of the hole. A bit more snapped off, and after poking around in the hole with a sharp scriber I could feel there was a bit left. Out of sheer desperation, I plunged the snapped center drill in rapidly, hoping that it would deflect and then pick up and extract the bit of HSS trapped in the hole together with the swarf:

:ddb: It worked; after that plunge, scratching around in the hole with the scriber I couldn't feel any hard bits in there, so I drilled the hole to size without any further fiasco, and the last hole went well as well:

Tapping the holes went well; in the background you can see the bottle with the purple-coloured methylated spirits I use for tapping aluminium:

I wasn't in the mood to set up the rotary table to round over the tops of the bearing columns, so I used a 16mm drill bit's shank to support the columns and started milling away facets - a quick job, but just make sure there's no swarf trapped below the drill bit (or supporting rod):

This is what the columns looked like fresh off the mill; the glue holding them together came loose in the process, but fortunately they need not be held together any more at this point:

Getting rid of the facets is easy - a couple of light strokes (literally about 10) with a sharp file around the outside, and you can see the difference:

A quick rub over emery, and that's where I stopped for the day; there's still some tool marks left, but I'll remove those later, as I need to do a bit more work on the one column and also press in the bearings once made:

:beer:, Arnold

saw:
Arnold, you are stiil going strong, nice progress :clap: :clap:

Stilldrillin:
Well saved, and nice end result Arnold! :clap: :clap:

After just such a snapping, last year. I stopped using centre drills.

I always use a 3mm spotting drill, in the lathe and mill....... :thumbup:

Not one hiccup since! :D

http://www.ebay.co.uk/itm/3MM-NC-SPOTTING-DRILL-90-DEGREE-COBALT-SPOT-DRILL-NEW-/140596402738?pt=UK_Home_Garden_PowerTools_SM&hash=item20bc32da32

David D

Henning:
Great work!

Nice touch on using the drill bit as an axis to mill the facets to get the rounding. I have saved that in the murky depths of my twisted mind until i get a mill.

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