Greene Automatic Cutoff Steam Engine

[kvom]

The problem with McMaster is having to buy a large quantity to get the 1 or 2 that I need.   

I found that the ball assortment bag had a lot of odd sizes.  I did find a 5/16 for the exhaust ball joint.  It's hard so I'll try the annealing approach.

On the good side, I realized I had a small bag of brass 5/8" balls that I used for another governor.  While I did find that I could hold them in the 5C collet, it was a lot easier with the 6-jaw chuck.  I drilled the center through hole .101", and then found this method of lining up for the cross hole:



With the chuck on the bench, a length of drill rod through the hole keeps the ball from falling through.  Then I used two parallels under the drill rod to level the ball before tightening the jaws.  Then back to the lathe to drill .078" halfway through and thread 3-48.

[kvom]

Spent a bit of time in the shop making the simple lower flyball supports.  Essentially a .3" diameter disc with a center .126" hole and a threaded 3-48 hole into the perimeter.  A length of threaded rod connects a flyball, and the disc is attached to the collar.

[jeff l]

looks like i'll supply the machinable balls to help the builder .

[Dennis]

Good progress Kirk,  its the little stuff that makes a model look exceptional.  Also, thanks for the notes to improve the drawings.
Dennis

[kvom]

I annealed a 5/16" ball allowing me to through drill and tap 3-48.  Now I need to make the cage for the ball joint, which entails drilling two 5/16 hemispherical holes that together will hold the ball captive.  I do have a 5/16" ball mill, so I did some experiments in a piece of 6061 AL.

I touched the mill to the material and used a spindle stop to mark.  Then raised the table 5/32.   I found that the mill likes slower RPMs.  To get smooth finish I used a spotting drill to 5/32 depth to remove pressure on the center of the endmill.  In any case, I did get a smooth hole, but it wasn't deep enough to descend the ball halfway.  Tomorrow I'll experiment with setting the depth control deeper.

[Jasonb]

Can you not 3D mill it with say a 1/4" cutter, I've done male hemispheres so female would be a similar job.

[kvom]

That's certainly an option if the straight drilling doesn't work.

On another front, I was looking online for the necessary bevel gear and pinion needed for the gearbox.  Plans specify Boston Gear G478Y.  Google search didn't show any sellers on Amazon or eBay, and via a distributor they are pricey.  But I did find a close substitute that's quite reasonable.  SDP/SI has the pinion at $13.89 and the gear at $16.58.  I was able to download step files for both these and the BG version, and they are practically identical in size, and fit the governor model.  Both gear sets are 2:1, but the SDP/SI are 36/18 teeth while BG is 40/20.

Gear: http://shop.sdp-si.com/catalog/product/?id=A_1B_3-Y48036
Pinion: http://shop.sdp-si.com/catalog/product/?id=A_1B_3-Y48018

[kvom]

After some dimension discussion with Dennis about some clearance,  I decided to make a start on the center shaft of the governor as designed, which is shown here:



The top 5/16" diameter ball attaches to the upper fly ball links via an axis pin through the cross hole.  The axis goes through the upper section, and the top .25" diameter section rests on the top section where the hole narrows to 3/16".  The bottom of the shaft is where the gear pinion is attached.  While there are nominal lengths for each section I will wait to obtain the gear before finishing.

I had several ideas for attaching a ball to the shaft, but came up with the following.  With some 1/4" drill rod in the lathe, I used a 5/16" ball endmill in the tailstock to slowly drill a pocket in the end of the rod.  I then drilled and reamed a 1/8" hole in the center of the pocket about 1/8" deep.  After annealing the ball with a Mapp torch, I mounted it on the lathe and drilled/reamed a 1/8" hole 3/16" deep.  I then cut a piece of 1/8" drill rod and trimmed to measure to attach the ball to the end of the rod as a type of tenon.  I then liberally applied 638 loctite to assemble the three pieces.  My theory is that this way there is good surface area for the loctite, and the .104" cross hole won't cut the pin completely.





After it cures overnight, I'll drill the cross hole.

[kvom]

Continuing with the center shaft, I cross drilled the ball, and then turned in the lathe using 200-grit sandpaper to remove most of the black surface of the ball.  Then it was time to trim the shaft to the proper length.  The lengths of individual sections of the shaft have nominal lengths, but since the top part may vary from the drawing, I decided to use the SW model to determine the distance from the top of the top to the cross holes' centerline.  This is .541".



Given this, the bottom of the 1/4" section should be even with the bottom of the top section.  I marked this point and parted off, then drilled and reamed a .186" hole 5/16" deep.  The 5/16" section is to be loctited into the end.  The length of this section is then determined by the bottom edge of the bottom section.  Again this length is marked and parted off, and the end is drilled and reamed .126" 1/4" deep.



The 1/8" section to be glued to the end will have the pinion gear mounted.  While the SW model shows a fixed length section plus a final threaded section for a nut, the gear will be held in place by a 3-48 grub screw.  The section will be long enough to allow the position of the gear to be varied vertically to mate with the large gear.

I received the gear set.  Both had to be reamed to slide smoothly onto their axes.

[kvom]

To connect the two lower parts of the governor body, a circular pocket is machined into the gearbox.



Good fit.   



The 4 pieces all together in position for the first time.



In order to proceed further, I need the last two pieces, the upper ball arms.  These are tricky parts, and after considering many ways of making them I think I finally have a good sequence of ops.

[kvom]

Having drilled the bosses of the gears for set screws, I installed the large gear into the gearbox to have the reality of the situation made clear:



The top of the bevel is closer to the flat milled for the bottom of the center section, and the length of the gear's boss means the bevel is too close to the center.  This means that the boss length needs to be shortened to move the gear teeth away from center enough to mesh the with the pinion.  I can also see that I need to drill a hole in the flat somewith larger than the pinion to allow  it to engage the large gear.

Then too, the bottom of the center section needs a hole at least larger than the boss of the pinion, and the pinion will extent up into the section's body.  This the center shaft will need to be shortened to match.



This then implies that the setscrews for attaching the pinion may not be accessible via the gear box opening.  I need to model this anew to determine how to proceed.  But that will have to wait as I am off on a 3 week trip on Wednesday and won't be back at it until mid-March.

[sco]

Make a new boss and Loctite it to the other side of the gear?

Simon.

[Jasonb]

If you put the large gear on the other way round you will then be able to access the small gears grub screw to fix it to th eshaft and then slide the larger gear already fitted to its shaft into place and screw on the side cover.

Or put a hole in the bottom for access and slide the vertical shaft complete with small gear in from below if you want to keep the larger gear that way round

What did the original drawings show?

[kvom]

If you put the large gear on the other way round you will then be able to access the small gears grub screw to fix it to th eshaft and then slide the larger gear already fitted to its shaft into place and screw on the side cover.

Or put a hole in the bottom for access and slide the vertical shaft complete with small gear in from below if you want to keep the larger gear that way round

What did the original drawings show?

The large gear would normally go the other way;  I just tried it this way to see if there is more spaced to play with.

The boss on the gear is .20" long.  I could remove half of it and leave room for grub screws.  If that's not enough I can mill a pocket on the inside of the cover to get a bit more.  Simon's idea would work well too if the other options don't.

Even with the cover and gear removed it's not clear if I'd have access to the grub screws for the pinion if they need to be high inside the center section.  The drawings show the pinion secured by a threaded section at the bottom of the shaft, but that means it's not adjustable vertically.  The SW model doesn't show the gears at all.  A solution I'm pondering would have the upper section removable so that the pinion could be accessed.  I'll have to see once I modify the center section.

[kvom]

I had some more time to play with this.  First I drilled the top with a .47" hole to allow the pinion to enter the case.  Then bored a 1/2" hole .150" deep into the inner side of the cover, which is .21" thick.  Now I could adjust the position of the large gear in and out.  Using the pinion on a piece of drill rod centering with the  Mark IA precision eyeball, I got the large gear pretty close to where it needs to be.

It seems that all I needed with the cover was a hole half as deep.  So now to retain the gear shaft I'll need a bushing on the shaft between the gear and the cover.  Or else remake the cover.  It seems I could have removed .075" of the boss with the same result.

With the gears meshed, the teeth of the pinion are all inside the lower box, but the boss will be inside the center section.  The grub screws won't be visible from the bottom case.  Therefore I'll drill the center section 1/2" to allow the main shaft to be inserted and removed with the pinion attached.  The position of the pinion will be able to be determined before the center and lower sections are attached permanently.