Benson engine

[b.lindsey]

Sounds like a great trip Kirk. Hope we will get to see some pictures.

Bill

[kvom]

Just back from Antarctica by way of Buenos Aires and Ushuaia.  The  expedition photographer made a video that I have loaded to youtube:

<a href="https://www.youtube.com/watch?v=T6xGMk6WKDM" target="_blank">http://www.youtube.com/watch?v=T6xGMk6WKDM</a>

Original had a soundtrack that I had to delete to avoid copyright and blocking issues.

[zeeprogrammer]

Very cool, Kirk. Must have been a good trip. 

[kvom]

Apropos of nothing, I have been considering purchasing a 3D printer, one that prints chopped carbon fiber as very stiff parts compared to nylon or fiberglass.  Gears printed this way would be strong enough for engine models, and with a gear design tool any size gear could be produced.

For the Benson, I suspect that the cylinder, for example, could be printed in a way that with the cylinder sleeved and a port plate used.  The print resolution is about .004" with a nozzle size of .0016". 

The printer I'm considering is the Markforged Onyx.

[zeeprogrammer]

The printer I'm considering is the Markforged Onyx.

I'd be interested in why. Got a link to that?

I will be interested in a 3D printer sometime next year but not the kind I build or fuss with. I just want an out-of-the-box printer.

[b.lindsey]

Thanks for posting the video Kirk. One of those once in a lifetime opportunities and looks like you had great weather for it too!!

Bill

[kvom]

To start on actually making parts for the Benson, I decide to tackle the connrod.  It's a finicky part, and I will decide whether to continue with the documented 1:12 scale or do as JasonB and make it 1:8.  Since JL is making the same part concurrently using manual methods, it may be interested to see of our ops match at all.

I chose brass as the material;  easy on the tools and I have a good stock.  Cut a 1.5" slice off a length of 4x.25" brass, squared it, and ran the facemill on one side.



Next I uses a 5/64 endmill to make the cotter holes.  The drawing has the width as 1/16", but all of my 1/16 endmills have a 1/8" LOC.  The width isn't really critical as long as the strap holes are the same.  First set the Z0 using a 1" gauge block.



The second op is to cut the profiles using a 1/8" endmill.  My CAM program is set to leave .05" high tabs at the bottom to keep everything attached to the stock.



The 3rd op cut the relief between the ends and the shaft.



Now a trick I learned over on HMEM.  Fill the slots with Darvon epoxy gel and let sit an hour to cure.  The epoxy will hold the pieces together even if the tabs get milled away on the reverse.



Turn over, facemill to thickness, and cut the 1/32" relief on the back.



The only remaining machining is the 7/32" round slots in the three ends of the rod.  With the work held with the side vertical, a 7/32 endmill would make quick work.  Given that I have a dozen 3/16 endmill but no 7/32 led me to stop work for today.  I suspect a 3/16 would work just as well although the through holes in the bearings would make the walls quite thick.  I'll just order a 7/32 endmill.

And in case you're wondering, 15 minutes in a 250F oven and the epoxy falls off.

[Art K]

Kirk,
That looks like an interesting project, especially if you print the cylinder. Your trip to Antarctica sounded great.
Art

[Jasonb]

Off a good start, If I remember rightly I had to mill my slots from both sides as I used 1/16" wedges even on the larger scale model as they looked too heavy scaled upto 2mm.

[kvom]

Waiting for an order including the 7/32 endmill, so on to another finicky part, this time the "links" for the governor (Mount's part 46).  Start with a 2" length of 1/2" square brass bar, face mill the top, and machine the profile .25" deep.



Reverse in the vise and face mill the bottom freeing the two links.



Next, mount some aluminum soft jaws and mill a pocket that matches the profile.  Use this to hold each part and mill the shaft down to size.



Still needs slots cut in the end, but time ran out for today.

[Tennessee Whiskey]

FYI, aiding and abetting the escape of an engine part may be illegal here down South. Please check with your local officials  . Nice job Amundsen  .

[Dave Otto]

 Tiny little guys they are; looks good Kirk.


Dave

[kvom]

Continuing with my goal to build the governor first, I contemplated the pivot (part 44), which consists of a steel rod that's 1/8" diameter at the bottom but 3/32 over more of it's length.  Mount turned down 1/8" rod using a follow rest, and this could also be done with a box tool, but I have neither.  So my plan was to drill a 3/32" hole through a length of 1/8" rod and glue in the 3/32 part.  I wasn't sure it could be done as is results in a 1/64" wall thickness after drilling.  However, success was mine.  A bit of Loctite 620 holds the two pieces together just fine.



I made two attempts at the upper pivot block and brain-farted both times, so settled for making the stop (part 49).  Cross-drilled some 3/16" brass rod and tapped 2-56:



Then drilled and parted.

[b.lindsey]

Impressive Kirk, those really are some small parts too!!

Bill

[Hugh Currin]

Kirk:

What is this Darvon epoxy? I looked around the 'net and didn't find anything similar. Is that the right spelling? Does it melt out, get soft, or become brittle? After poking around a little I wondered if a low meting point metal could also be used?

Now a trick I learned over on HMEM.  Fill the slots with Darvon epoxy gel and let sit an hour to cure.  The epoxy will hold the pieces together even if the tabs get milled away on the reverse.

And in case you're wondering, 15 minutes in a 250F oven and the epoxy falls off.

Thanks for sharing your process. I'd have used the two holes to try and hold the stock to a tooling plate for machining. Probably would have run into trouble, holes may be to small. Real nice to see alternatives, and the results speak for themselves.

Nice build. Thanks.

Hugh