Author Topic: Benson engine  (Read 40195 times)

Offline kvom

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Re: Benson engine
« Reply #225 on: August 15, 2017, 10:25:54 PM »
I spent most of the day making the forks that go on the ends of the operating rod, which connects the governor to the inlet valve.  Basuically the same part as the eccentric forks and made the same way, although at half the size.  All went well until after the final op. which was tapping them 0-80, at which point I find that my 0-80 screws are too loose to hold.  I'm not sure what went awry as I drilled the holes with a #55 as before.  In reality I'll probably just glue them on when it comes time.  Possibly some JB weld and redrill could work.



Still need a bit of polish.

Offline kvom

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Re: Benson engine
« Reply #226 on: August 20, 2017, 09:26:03 PM »
I received my printed rocker arms from Shapeways this weekend.  I ordered a version in polished brass for use on the engine, but since versions in plastic were quite cheap and didn't add extra shipping, I ordered one (yellow) in "strong flexible" plastic and another (black) in "hi def acrylate" to get a example of these materials.

Cost for the brass version was $14.00, black $5.57, yellow $2.73.  Shipping $4.99.  Order accepted on Aug. 7, shipped on the 17th.



All three versions seem quite accurate, although the holes vary a bit.  They are drawn as 1/16" diameter.  A 0-80 screw passes cleanly on the brass version, but are tight on the plastic and need to be screwed through to widen the holes.

A test fit shows that I made the diameter on the mating collar of the bottom pivot block a bit too large, so I'll need to reduce it to fit.
« Last Edit: August 20, 2017, 09:30:04 PM by kvom »

Offline Jo

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Re: Benson engine
« Reply #227 on: August 21, 2017, 07:51:58 AM »
I received my printed rocker arms from Shapeways this weekend.  I ordered a version in polished brass for use on the engine, but since versions in plastic were quite cheap and didn't add extra shipping, I ordered one (yellow) in "strong flexible" plastic and another (black) in "hi def acrylate" to get a example of these materials.

That is very interesting: are there any printing marks on the brass rod?

Jo
Enjoyment is more important than achievement.

Online Jasonb

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Re: Benson engine
« Reply #228 on: August 21, 2017, 08:57:31 AM »
As the brass is investment cast from printed wax and then polished I would hope most of the layering will have been lost, they do say fine surface detail can be lost when it is polished so that should take care of layering.

how do the parts measure up for length? Did you have to send then with a shrinkage allowance for casting or do shapeways take care of that?

Offline kvom

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Re: Benson engine
« Reply #229 on: August 22, 2017, 08:13:08 PM »
The easiest dimension to measure was the outside of the 'C' feature, which I mic'd as .380", where the drawing was .375".

The separation of the holes in the brass part match up with those in the black plastic part to within the tolerance of a 0-80 screw passing through both together.  Seems evident that Shapeways accounts for shrinkage, if any.

I machined the lower pivot block diameter down so that the arm fits well.  Shop time has been curtailed by eclipse watching and other things.

Offline kvom

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Re: Benson engine
« Reply #230 on: August 23, 2017, 04:50:17 PM »
Added the rocker assembly to the entablature, and it fits well.  I ran out of 0-80 washers and nuts and ordered some yesterday, so I'll need to get the delivery to finish that part.


Offline kvom

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Re: Benson engine
« Reply #231 on: August 27, 2017, 04:41:32 PM »
One issue I'm struggling with mentally is the throttle valve (part 42).  How do I get the cross hole to end up horizontal when the valve is screwed into the steam chest?  One idea is to thread the end of the bar stock, screw it in tight, and then try to scribe a guide line for the rest of the machining.  Alternatively, just machine according to the drawing and use some shim stock between the valve and the steam chest to allow proper orientation (perhaps a thin layer of epoxy would work too).

Online Jasonb

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Re: Benson engine
« Reply #232 on: August 27, 2017, 04:53:30 PM »
Turn it from round stock and leave the square part just over size. Screw the valve chest onto the throttle valve and use a square against the valve chest while you grip the round stock in an ER block or indexer, remove valve chest square up the 4 sides, drill and tap for the spindle gland and round off around the thread.

Offline kvom

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Re: Benson engine
« Reply #233 on: August 27, 2017, 05:22:34 PM »
I was hoping to find a way that didn't involve disassembling the engine.  I should have done this work beforehand.   :Doh:

Offline kvom

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Re: Benson engine
« Reply #234 on: August 28, 2017, 10:41:17 PM »
Another tiny part needed to finish the engine:  throttle lever


simplyloco

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Re: Benson engine
« Reply #235 on: August 28, 2017, 10:45:30 PM »
Sounds like this small change will do you some good!  :)

Online crueby

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Re: Benson engine
« Reply #236 on: August 28, 2017, 10:45:57 PM »
Yikes. Best let the junior shop elf make that one - teensy!

Offline kvom

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Re: Benson engine
« Reply #237 on: August 30, 2017, 10:01:03 PM »
I remade the forks for the operating rod today, since the previous ones had been drilled with the wrong size tap drill for 0-80.

Getting close to being done with this engine.




Offline J.L.

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Re: Benson engine
« Reply #238 on: September 18, 2017, 09:27:36 PM »
 Hi Kirk,
How goes the engine?
John

Offline kvom

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Re: Benson engine
« Reply #239 on: November 16, 2017, 12:11:15 AM »
After spending 3 weeks in Japan, I've had 2 weeks of jet lag.  I don't remember having this much trouble getting sleep cycles back in step from previous trips to Asia.  Must be age-related.

Finally decided to get back in the shop yesterday and today to get back to the engine.  I won't go into the multiple times taking things apart and reassembling, but I came to the conclusion that my "system" of clamping the column and entablature to the base with a threaded rod needed some improvement, mainly to keep things from rotating while tightening.  I also saw that when running the force of the piston rod caused some visible rocking of the column.

With the bracket on the column, I verified that the piston rod would pass freely as long as the column was in the right position.  So I put a thin layer of epoxy between the column and base, oriented so that the bracket wasn't binding, and clamped the column until the epoxy cured.  Now I could mount the entablature and use the threaded clamp rod to lock it without the column possible turning.

After assembly (no governor), everything turns much more smoothly.  I'll do the timing next time in the shop and shoot for a run.

 

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