And Now for the Twin

A special section just for steam engines and boilers, as without these you may as well fit a sail.
Mike Rometer
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Re: And Now for the Twin

Post by Mike Rometer » Wed Jun 11, 2014 11:48 am

It has 3 degs taper towards the bottom, Ron, allowing sand filling to the top edge, first.
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Re: And Now for the Twin

Post by DetroiTug » Thu Jun 12, 2014 1:51 pm

Hi Mike,

If I'm understanding correctly, the smaller outside diameter is on the bottom in the pic? The largest OD should be on the bottom. Mounted to a board like in the pic below makes it much easier for them to make the molds.

Image

The silver coating is a release agent they use.

The board is just 1/2" MDF with a coat of west system epoxy applied.

-Ron
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Re: And Now for the Twin

Post by Mike Rometer » Thu Jun 12, 2014 2:08 pm

I was advised to do it that way because of the under-shape. It will apparently be pushed into the sand (for the bottom shape) and then filled to the top edge, hardened, and then the top-box filled. If it had been flat underneath, then yes, the taper would be the other way. The under-side is 'all machined' so any 'indiscretion' in the moulding isn't a problem.

I could have made it flat bottomed and machined the shape.
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Re: And Now for the Twin

Post by Mike Rometer » Sat Feb 24, 2018 11:58 am

Well, I really hadn't realised that it was quite so long since I did anything other than think about this job. Over 3 years! I have to say I have not been totally idle, I did finish off a 16 year long loco project. (long, that's both the time and the loco :lol: )

I have now made a start (re-start?). I've been thinking a lot about Mike's thoughts on pistons and that part is getting there. I'm not a 'drawing worker', I will/can use them when required, but generally if I can visualise what is required, then I just get stuck in and make it. Someone else can draw it afterwards if they wish.

The cylinder cover pattern has been discarded as that was one of the hang-ups, getting enough patterns together to make a trip to the foundry 40 something miles away, i.e. 160 miles total over some of the worst Motorway in the country, worthwhile.

Some slices of continuous cast iron bar have been obtained locally and the covers are now almost complete. A far simpler way to go. Shouldn't have wasted the time on the pattern in the first place.
Cyl Cover (4) (600 x 450).jpg
Cyl Cover (4) (600 x 450).jpg (54.31 KiB) Viewed 21861 times
Several thoughts are now in the air. Normally 6 fixings per cover, but should they, for looks reasons (or any other) be studs (I hate making short studs!) and nuts (what nuts), or bolts (which sort, hex, socket head etc.)? Also as the two covers are 'fitted' together between the bores what is the best orientation of the fixings, one between the cylinders (11 total), or avoid that place (12)? I propose to use the mill's DRO P.C.D. function so they can all be drilled in one settup.
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Re: And Now for the Twin

Post by fredrosse » Sun Feb 25, 2018 11:37 pm

As far as cylinder head bolting goes, the best arrangement depends on available dimensions. If you could "fill in the blanks" of the attached drawing, I would be glad to suggest something.
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DIMENSIONS NEEDED
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Re: And Now for the Twin

Post by DetroiTug » Mon Feb 26, 2018 2:58 pm

Mike,

Good to see you back on the twin again. Studs vs bolts? Studs and dome or acorn nuts are more traditional and definitely look better, but for ease of use, the bolts are a better option. Which is mechanically better? I would say the bolt as there can be more thread engagement. One thing to keep in mind though, sometimes threaded holes for cylinder heads will protrude in to the steam passages which are in close proximity to the ports, a bolt left installed for a long period of time may corrode to the point making removal nearly impossible, so that is definitely a consideration for the use of studs and nuts.

I dislike making studs as well, when I was younger, any part replicated over ten times led to undesirable boredom, nowadays, I'm down to about two identical parts. McMaster-Carr here in the states sells studs in different grades, which is probably another vote for bolts over homemade studs which will be soft and have a higher likelihood of twisting off if fowled.

Socket heads are typically a no-no for traditional steam, they weren't invented until around the 1920's? 30's? Though, they are easy to get along with, when I built the Southworth pumps, I used them to make servicing easier dockside.

Traditional hexhead bolts, the one's that I have worked with have a head height near equal to the distance across the flats, the top of the hexhead is usually radiused. Have never seen any sort of grade slashmark or makers marks in older lathe made bolts, that's all done in a header machine now (high speed press) and threads rolled on.

-Ron
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Re: And Now for the Twin

Post by Mike Rometer » Mon Feb 26, 2018 4:46 pm

fredrosse wrote:As far as cylinder head bolting goes, the best arrangement depends on available dimensions. If you could "fill in the blanks" of the attached drawing, I would be glad to suggest something.
Thanks for that Fred. The bore is 2.5", the liner is 1/8" wall (0.125"), and the centres are approximately 3.3" (within a thou or two). I'm thinking twelve, but the centre four will be slightly close.

Ron, I'm glad to be back on it. I've located a supplier of Stainless dome nuts. The studs I've found so far are threaded the same both ends. Not what I was taught, but probably the modern way.

I've also measured the distance between the port edges and it is 3.5" exactly, so I think for safety a stroke no longer than 3.25" that will allow a 1/4" for rings, and on that thought I may go for two in the one groove or even a single Clupet ring. The Clupet doesn't need to to be wider than about 0.187" (they're made to order) which will mean it will never get fully to the edge of the port (assuming I don't B.U. any crank, or rod dimensions).

I've been looking for suppliers of M.S. bar stock (crank) who will cut slices, so far no luck locally, but maybe further afield.
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Re: And Now for the Twin

Post by DetroiTug » Mon Feb 26, 2018 7:55 pm

For laying out a bolt circle, it's very easy with a calculator.

Work in one quadrant of the circle, we'll calculate everything in the Northeast quadrant X+ and Y+ directions.

For a 12 bolt circle, two inches in diameter, that means there are three hole spacings radially in that quadrant.

90 degrees in a quadrant, so the holes are 30 degrees apart. First hole going up from the horizontal is 30 degrees, second hole going up is 60 degrees. same form the vertical center line, 30 to the first, 60 to the second.

On the Windows scientific calculator or any scientific calculator, you know the degrees, so enter 30 and then press "SIN" and that equals .5" over 1" which is the radius of a 2" circle. For different diameters just multiply the radius times the SIN in decimal dimension. Now for the 60 degree, same thing just enter on the calculator 60 and then the "Sin" key and that is .866".

So the top hole in the bolt circle working from the center of the circle, would by Y1 - straight up
the one to the right clock-wise is X.5 Y.866
The next one clock-wise is X.866 Y.5
The next one on the horizontal or X axis is X1.

All the rest are the exact same dimensions in negative and positive going around the circle in their respective quadrants.

Another Example, 8 bolt circle is 45 and then SIN. Which is .707" so the radial hole position is X.707"Y.707" if this were a 3" circle, then it would be 45 SIN X 1.5 which is the radius. Then it would be X 1.06" Y 1.06"

Work the quadrant, can even rotate the bolt circle a few degrees, and the same method can be used to calculate the hole positions.
And it's really that easy, not sure you were asking that, but in case anyone is wondering.

-Ron

Incidentally, the same calculator function is used to set a SIN bar with Jo-blocks.
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Re: And Now for the Twin

Post by Mike Rometer » Mon Feb 26, 2018 9:27 pm

DetroiTug wrote:For laying out a bolt circle, it's very easy with a calculator.

Work in one quadrant of the circle, we'll calculate everything in the Northeast quadrant X+ and Y+ directions.

For a 12 bolt circle, two inches in diameter, that means there are three hole spacings radially in that quadrant.

90 degrees in a quadrant, so the holes are 30 degrees apart. First hole going up from the horizontal is 30 degrees, second hole going up is 60 degrees. same form the vertical center line, 30 to the first, 60 to the second.

On the Windows scientific calculator or any scientific calculator, you know the degrees, so enter 30 and then press "SIN" and that equals .5" over 1" which is the radius of a 2" circle. For different diameters just multiply the radius times the SIN in decimal dimension. Now for the 60 degree, same thing just enter on the calculator 60 and then the "Sin" key and that is .866".

So the top hole in the bolt circle working from the center of the circle, would by Y1 - straight up
the one to the right clock-wise is X.5 Y.866
The next one clock-wise is X.866 Y.5
The next one on the horizontal or X axis is X1.

All the rest are the exact same dimensions in negative and positive going around the circle in their respective quadrants.

Another Example, 8 bolt circle is 45 and then SIN. Which is .707" so the radial hole position is X.707"Y.707" if this were a 3" circle, then it would be 45 SIN X 1.5 which is the radius. Then it would be X 1.06" Y 1.06"

Work the quadrant, can even rotate the bolt circle a few degrees, and the same method can be used to calculate the hole positions.
And it's really that easy, not sure you were asking that, but in case anyone is wondering.

-Ron

Incidentally, the same calculator function is used to set a SIN bar with Jo-blocks.
It's even easier with the Digital Read Out P.C.D. function, set the block straight on the bed, find the centre of one bore, input the rad, and number of holes and the start angle (first hole) into thr DRO, then follow the dials. Drill the six, then move it over to the other bore centre (measured with the DRO) and repeat the sequence. :o :D
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Re: And Now for the Twin

Post by DetroiTug » Mon Feb 26, 2018 10:58 pm

The old DRO's I used to run around 25 years ago didn't have such a feature, sounds nice to have though. The method I suggested will work with any mill even those with just dials. How does the DRO tell you where the hole is, does it automatically set itself to zero incrementally on each hole?

Of course, nowadays we use CAD and CNC machine tools and it takes a lot of the math out of it. When I wrote that above I had to double check myself, it's been so long, but thought it would be useful for anyone running a manual machine and didn't want to kneebone the rotary table around.

-Ron
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