Benson engine

[kvom]

Sorry, it's Devcon Epoxy Gel.  Brain fart.  There's also a Devcon Epoxy without the gel that won't work as well.  That one cures yellow.  Can be bought at HD or Lowes.

The holes in the links are 1/16, so pretty small for screws.  However, the two ends are the same diameter so they can be held in a vise.  The advantage of the soft jaws is that the zero is fixed and makes it easy to swap parts without remeasuring.

[kvom]

Today's jobs were to finish the two links (I had drawn them wrong in SW) and try to build the governor  lower pivot block (part 48).  The pivot block started with some .75" hex brass bar and ended with a lot less material.  Lots of ops on this part,  but I didn't stop to take pics.  Here's a poser shot of the links and pivot block on the shaft.



I also got my McMaster order that included some 9/16" brass balls.  I drilled and tapped two of them 1-72.

[kvom]

I'm going to remake the conrod after messing up milling the half-round slots in the ends.   

In an effort to get something finished today I worked on the top pivot block (part 47).

The first op was drilling and profiling on the CNC mill.  This part measures .5x.185x.185 inches, so quite small.



Using the machinist vise held in the Bridgeport vise I machined off the stock from the bottom.  After tapping the center hole 2-56, I flipped it in the vise to drill the hole for the pivot shaft and mill the 5/64" slots.



Shown mounted on the pivot shaft:

[kvom]

Spent the past few shop sessions trying to make the arms for the governor, with several failures.  Today I tried a new technique, starting with some 1" round brass bar held in a 5C collet centered on the CNC mill:



Being able to first surface the end on the lathe makes this form of stock easier to prepare than brass bar.  The CNC mill machines the profiles of the arms .100" deep; then drills the 1/16" center holes with a center cutting endmill.



The collet then goes back on the lathe, and the arms are parted off leaving a very thin layer on he bottom.  The two arms can then be separated with scissors.



Then mounted on the small vise, and the bottom later is machined off.  After measurements the same setup is used to bring each piece to .078" thick.  This was harder than it might seem as I ruined two by taking off too much.  One issue was that my parallels weren't the right height on hold them and I was relying on some shim stock.



Finally the 1/16 endmill is used to cut a cross hole in one end and a length of 1/16" drill rod is glued on.  After curing, the blocked hole is redrilled.



The next step is to attach the 7/16" diameter balls to the ends with glue.

[kvom]

I can't find anywhere that Mount talks about the pins that hold the governor together.  Since the holes are 1/16 (.0625"), I'm thinking I need some 0-80 screws.  Any other ideas?

[Jasonb]

I just made some flat headed pins and threaded the end, for your size I would go 1/8" dia head by 1/16" long and then a plain 1/16" shank with the end threaded.

[kvom]

1/16" major diameter thread is a 0-80.  $12.90 from AME for a die. $8.71 for 25 steel nuts. $6.38 for 25x3/8" steel screws. $2.22 for 25 steel washers.   Think I'll go with screws and nuts.  Not as elegant but should work for the purpose.  Interesting to see what JL decides when the time comes.

[kvom]

Looking at the governor pivot bearing, Mount specifies a "3/16x40" thread, which as far as I can find does not exist in normal standards.  10-32 seems closest to the M5x.5.

[Jasonb]

It is one of our ME or Model Engineer standard thread forms, I think it would be like a 10-40UNS but if you have the 32tpi one that should do.

Some of the model pipe threads that PMR do would also fit the bill

[crueby]

Looking at the governor pivot bearing, Mount specifies a "3/16x40" thread, which as far as I can find does not exist in normal standards.  10-32 seems closest to the M5x.5.

the 3/16-40 must be standard somewhere, I have taps and dies for it. I think I got them originally for the touch hole plug on a flintlock I was building, so maybe its a gunsmith item. Did some looking, PM Research has them here:
https://www.pmmodelengines.com/shop/tools/straight-pipe-thread-taps-dies/

Dont remember where I got mine, it was about 10 years ago.

[kvom]

I made the pivot threads 10-32, the die I have.  Here's a family shot of the governor.



I ordered the 0-80 screws/nuts/washers to tie it all together.  I still need grub screws for the stop and top pivot block plus the gear to drive it.

[90LX_Notch]

Kirk-

What about using pressed pins rather than 0-80 hardware?  I think pins would look cleaner.

-Bob

[kvom]

I would have needed to drill the holes in the pivots smaller and arms/links larger.  As it is all are 1/16.  The arms and links need to pivot freely.

[tvoght]

Others have mentioned that PMR uses "3/16-40" for 3/16 inch model pipe fittings. I'm pretty sure I bought a 3/16-40 tap from them and the tube was marked #10-40.

The major diameter of #10 being .190, it's pretty much the same thing. McMaster-Carr sells #10-40 taps and dies.

--Tim

[kvom]

As you can see in the photo I just used 10-32.  It's not a critical specification.