Benson engine

[Jasonb]

Don't let Jo catch you using screws, you know what she is like wuth her studs

[kvom]

Jo's studs?  Tell me more!

I might try making some later, but for now I'll just get screwed.   

[Jo]

I don't talk about my studs anymore, I embarrassed some of the members with my tales of what I do with them  and they have rarely been seen since 

Jo

[kvom]

The past two days I've started on the pieces that will eventually become the cylinder.  Taking some advice from Jason and will try JB Weld to stick them all together.  All the parts except the port block are made from a length of 1.5" diameter bearing bronze I had left over from the Joy build.  The port block is brass, and I started with some 1" square brass bar.  The profile was CNC milled;  luckily I had a good endmill with a 1.5" length of cut for this part.



The concave portion matches the .75" outside diameter of the cylinder.  I didn't have a 5/8" reamer but did have a 16mm.  Go figure.



Ovr

Next op was to mill the spigot for the exhaust, which also brings the port face to correct width.



Next, mill the spigots on either end, bringing the port face to final length.



Over to the lathe and drill/bore to obtain a close sliding fit to the cylinder.



Now turn and part off the missing flange for the cylinder.



Final job of the day is to use the form tool I made a few weeks back to make the decorative ring (astragal).



It will need to be cut open to fit around the port block.  Seems it's a lot simpler just to start with the casting. 

[crueby]

The cylinder parts are coming together nicely!

What was the reason for making the flange for one end of the cylinder a separate part rather than turning it in on the original bar?

[kvom]

So the astragal could be slid in.  If I had turned it and the flange integrally then fitting the port block would be difficult.  OTOH, I could have tried to do it like Justin, who cut  the astragal to make it wrap.  I am thinking of leaving the engine unpainted and so wanted the astragal uncut.

The other benefit is that I can ensure a close fit between the flanges and the port block this way.

[Gas_mantle]

Looking good Kvom :-)

I've learnt something new today - didn't realise those decorative rings were called Astragals

[J.L.]

Kirk, this is masterful work. You must have an engineering background. Your work is so clean and precise.
John

[zeeprogrammer]

I don't talk about my studs anymore, I embarrassed some of the members with my tales of what I do with them  and they have rarely been seen since 

The members or the studs? 

Sorry Kirk. I couldn't resist.

[zeeprogrammer]

'astragal'...I'd never heard that term before. Comes from Greek and Latin for vertebrae.

Great looking part. 

[kvom]

I learned the term astragal only from Jason where he mentioned it in JL's build.    Today's work was to make the steam chest, and since JL already made this it's not a mystery part.  After sizing the stock (I happened to have some 3/8x3/4" brass bar, the first ops on the CNC mill were just to drill the mounting holes (2-56 clearance) and mill the interior pocket.  A 1/8 endmill would have been quicker, but none of mine had flute length < 1/4".  So I found a 7/64 with over 1/2" flute length, but which I could feed at only 1.5 IPM.  That pocket took nearly 30 minutes to mill, but I had a book to pass the time.  On a manual mill I'd have chain drilled out the center first.



Then stood it up in the vise to profile the elliptical spigot and drill the necessary hole.  Mounting screws are 1-78.



This is certainly the smallest steam chest of any of my previous engines.  An interesting observation is that Solidworks allows me to draw the spigot as an ellipse and when saving as DXF converts it to a polyline with 96 segments.  I am wondering where in SW configuration is the setting for the tolerance that controls the segment generation.

The problem with closeup photos is that you can see all the places I need to clean up.

[kvom]

@JL - I graduated with a mechanical engineering degree but worked as a software developer my entire career.  All the mechanics has left me other than some concepts.  But I can look up things and understand them (sometimes).

[Flyboy Jim]

I learned the term astragal only from Jason where he mentioned it in JL's build.    Today's work was to make the steam chest, and since JL already made this it's not a mystery part.  After sizing the stock (I happened to have some 3/8x3/4" brass bar, the first ops on the CNC mill were just to drill the mounting holes (2-56 clearance) and mill the interior pocket.  A 1/8 endmill would have been quicker, but none of mine had flute length < 1/4".  So I found a 7/64 with over 1/2" flute length, but which I could feed at only 1.5 IPM.  That pocket took nearly 30 minutes to mill, but I had a book to pass the time.  On a manual mill I'd have chain drilled out the center first.

Then stood it up in the vise to profile the elliptical spigot and drill the necessary hole.  Mounting screws are 1-78.

This is certainly the smallest steam chest of any of my previous engines.  An interesting observation is that Solidworks allows me to draw the spigot as an ellipse and when saving as DXF converts it to a polyline with 96 segments.  I am wondering where in SW configuration is the setting for the tolerance that controls the segment generation.

The problem with closeup photos is that you can see all the places I need to clean up.

Oh sure...........just keep it up with all this CNC stuff............it's getting more interesting all the time! 

Jim

[Flyboy Jim]

@JL - I graduated with a mechanical engineering degree but worked as a software developer my entire career.  All the mechanics has left me other than some concepts.  But I can look up things and understand them (sometimes).

If it's any consolation, I graduated from college in 1966 with a degree in Electronics Engineering Technology. I worked in the field for 6 years before buying a Commercial Salmon Troller and heading to sea. About the only thing I remember about electronics is Ohms Law.  For years I've always wished I would of taken Mechanical Engineering Technology. Would of been much more useful through the years.

Jim

[kvom]

Today's goal is to make a simple part with few ops needed.  The valve rod gland is made from some 3/4" round brass rod held in a 5C collet.  First on the lathe drill the center 3/32 hole for the valve rod.



Then move the collet and work to a collet block and set vertically in the CNC mill.  Drill the mounting clearance holes (.081") and mill the two profiles.



Check that the spigot fits the steam chest.  If it were too large it could be turned down on the lathe before parting.  As it happens I have a good fit and just needed to part it off.





A bit of sanding to remove the tit left by parting and it's done.  Glands for the piston and valve rods will be done the same way.