Another Comber / Coomber build

Gallery, Projects and General > Project Logs

<< < (2/15) > >>

arnoldb:
Hi Benni

At first it does not make sense; don't worry :thumbup:. If you have a look here it might become more obvious.
The animation does not show how the porting to the cylinder works though. In the last photo of my cylinder block, the two holes at the end of the axle must still be blocked off. This is a cross-section of what the cylinder & steam passages looks like:

The slots that are milled in the port faces connect up to holes in the main bearing as the engine is turning - providing the steam / air path. This is what the main bearing looks like to allow for steam and exhaust connection:

Hope this helps :D

:beer:, Arnold

Stilldrillin:
Off to your usual great start Arnold! :clap: :clap:

I hadn't the faintest idea, just what a Coomber engine was/ is....... :scratch:

Google Images came up trumps! :thumbup:

Good luck! Watching quietly. :wave:

David D

saw:
Thanks Arnold but I am not shure. :doh:
I am awere that there is a lot off diffrent steam engine, but I don't think that I ever have seen this kind of engine before.
If I understand, well not right now, I will go back to my own engine for some adjustment, and thinking of you're engine, then maybe there will go up a candle :smart:

arnoldb:
Cheers David :beer:

Benni, don't worry :thumbup: ; this type of engine is a bit less known, as I think it is inefficient and as a result was unsuccessful in industry. I like these weird engine designs, that's why I build them... The next engine I have in line to build is the "Kimble" engine, and I'm busy putting my own set of plans together for another weird engine that I have not seen any models or pictures of real ones of... If you have any specific questions on what you don't understand on this engine, or any detail you want more pictures of, please ask :thumbup: - I'm happy to try and help.

Today's bit; I wanted to have more done by now, but time has a way of running out...

I started on the cylinder heads; some 25mm square Aluminium bar clocked up relatively on center in the 4-jaw chuck:

Remember, when centering up square stock, make sure you have enough travel on the dial indicator to clear the edges, and manually push in the tumbler when rotating the stock :med:

Faced off - I like it when I get a near-mirror finish like this:

Then some more taken off to leave a 0.5mm thick step.

The step is a nice push fit in the cylinder bore to keep the head concentric, and one needs a nice sharp point on the toolbit to prevent rounding in the corner, otherwise the head will not sit flat against the cylinder face.

The workpiece was then center drilled with a 1mm center drill, and drilled about 8mm deep with a sharp 2mm drill that I know does not drill over size. This hole should actually have been reamed to about 2.02mm, but I don't have a 2mm reamer, so I'll lap the hole out later. I just made a point of retracting the drill bit slowly from the hole; a sharp drill can leave a fairly good finish in the hole if this is done.

Then I used the parting tool (after a quick hone on it) to remove a fair bit of material on the other side:

Just a couple of straight-in parting cuts to the same depth; have I mentioned how much fun parting plunge cuts can be through the square section? ::)

The other cylinder head followed, using the same method. The one on the left shows the face that points into the cylinder, and the gory one on the right what it looked like after the parting off on the other side. Not quite as bad as it looks; it's got some cutting oil stains on it as well:

To clean up the messy face, I just chucked up a bit of 2mm rod in the collet chuck, leaving a short length protruding to engage the holes in the cylinder heads, and took a bit of carton and stuck it over that:

Then I used the revolving center in the tailstock to tightly press the cylinder head to the front of the chuck, and with light cuts turned the face and boss to final sizes:

To clean up the face of the boss was another matter; one cannot get close enough without damaging the center; something I REALLY do not want to do. So I moved away the tailstock, and with a narrow strip of emery pressed against the face with the forefinger of my right hand, I started the lathe; the pressure keeps the cylinder head engaged against the collet chuck, and because the contact area against the paper is larger than that of the emery on the face, there's sufficient drive to finish it. NOT the best way to do things; it would be better to stick the cylinder head to a mandrel (with superglue or double sided tape) or clock it up in the 4-jaw against a backstop to finish machining.

A piece of 2mm rod passes easily yet closely through both holes with very little binding. A Little lapping will sort the binding out in just minutes:

Next I set up to drill for the cylinder mounting screws. I marked one side of the cylinder out just for visual reference, then found the left back edge of the cylinder block, dialled in the location of the first hole, and set the X and Y dials to 0. A quick check locating the other hole locations on the handwheels turned out well:

Then I clamped one cylinder head to the block and drilled the four 1.6mm holes needed to tap for M2.

I really need to invest in some spotting drills... I'm still using a center drill to spot the holes before drilling.
Flipped the block, and did the same on the other side using the other cylinder head clamped down.

On to tapping the holes in the block. For tapping M2, I use the cruddy-looking tapping handle and tapping guide shown:

I'm a big old wimp - When I get around to tapping holes in a cylinder block, I religiously follow through the holes with each tap in the set; cleaning the tap after each hole. It may take much longer, but after having put a lot of time, material and effort into the cylinder block, the last thing I want is to have it ruined by breaking a tap in it!

One thing I have found to be really convenient is to use a countersink to lightly countersink around each hole before tapping. I just do it by twirling the countersink between fingers until there's a spot just slightly larger in diameter than the thread size:

This serves multiple purposes. On a cylinder face, it prevents tapping from raising a burr above the level of the face, keeping it nice and flat. It also seems to help to make the tap start easier into the hole. And last, the tangent surface of the countersink reflects some light when looking through the hole of the tapping guide, making it easier to locate over the hole.

For this engine, I'm going to use 2mm countersink screws to retain the cylinder heads. I just clamped each cylinder head in a loose vise, and on the drill press drilled the holes out to 2mm clearance and then countersunk them, using the drill press depth stop to limit depth:

I also milled each cylinder head down to final size on the square ends, and ended up with this:

Next I need to start laying out the base. As I'd increased the cylinder dimensions, the bearing posts need to be relocated from the original plans. To get a feel of what things would look like, I compared the cylinder block to my existing Coomber's:

I think it will look OK - just a bit chunky maybe, because it's fatter. But I didn't expect one thing... :bang: :bang: The new cylinder was meant to be the same length as the original with the same stroke... It's about 3mm longer! - had a look at the plans, and the fuzzy dimension on the printout says it all... The cylinder block was supposed to be 13/16" long, but on the printout it looks like 15/16" and that's what I made it, so it's 1/8" too long... That means I'll have to increase the size of the cam - the original is already very close in clearance and there's no way I can keep to the original cam size now. Seeing as I have 1/8" more stroke available, I might as well adjust the cam for that as well.
I guess my sister's going to get a bigger engine than I thought :lol:

Regards, Arnold

saw:
You are working nicley, like a painter :bow: :bow:

Navigation

 Message Index

Go to full version