PM Research #4 - Quarter Horse Vertical Steam Engine

[RReid]

I'll second and third what Chris and Mike said. I do both things fairly often. I tend to prefer boring to reaming whenever possible. Not only is it cheaper (and I'm cheap), but I can (try to) get the exact fit I want (tight, snug, running, loose,whatever). Besides, what better way to exercise your newly hot-rodded lathe?

[propforward]

Well that settles it!

I may have been a bit gun shy after my last boring adventure, but today every cut I made that I finished with a spring cut came out at the dimension I was shooting for, so given that I should just keep going. The finish in the bore right now is pretty reasonable, so with a bit more care should end up just fine.

Thanks everyone for your comments - very helpful and greatly appreciated!

[crueby]

Spring cuts are your friend!   When boring out, one thing I like to do (when I remember anyway) is to test out speeds of turning/feed and depth of cut before reaching final dimension, to see if changing anything slightly will give a smoother finish. Sometimes need to adjust the boring bar up/down slightly or put in a fresh insert - better to find out before that final pass! With proper setup its normally possible to get a nice shiny smooth finish.
 

[larry_g]

A couple of things that worked well for me on my engine.

On the eccentric strap the print has you drill through the threaded rod connection point and into the strap so that the hole in the strap becomes an oil hole.  I moved this oil hole around so that it is between the rod and the connecting bolt.  This allows easier oiling and access to the grub screw in the eccentric so one can adjust the timing without removing the eccentric strap. ( Thank you Keith Appleton)  Also with mod you can line up the grub screw hole with the oil port and fill it with oil, making it somewhat a reservoir.

On the valverod to the flex joint connection I deleted the pin and made this connection threaded. I extended the length of the coupling so that it had plenty of thread length. My thinking was that as designed you could only adjust the valve position by one thread pitch at the eccentric strap and I wanted something finer.  Once running I could adjust the valve position, while running, by turning the valve rod by hand and getting the best running that I could. 

These two changes made getting the valve timing and position very easy and for me it was a success.

lg
no neat sig line

[propforward]

Hi Larry,

Thanks for those suggestions. They are solid improvements and I think I will implement both of them. The threaded connection you mention for the valve rod is a lot like the design on the PMR#1, so I'm sort of surprised PMR didn't already include it here. Thanks for mentioning it. I am also planning on making a tapered lock collar for securing the flywheel to the crank shaft, copying Stan Shires on that one.

No work on the engine last week - crunch time at work on a big project. Lots of overtime, then we had a weekend away. Hopefully get back in the shop this week.

Dratted work. Got to pay for the hobby somehow though, and have money available for materials in retirement. Ho hum.

[propforward]

Haven't been in the shed much the last 2 weeks, what with trips, overtime and a night at the opera thrown in. What time I did get in was mostly making some jigs and fixtures. But I did get this finished today.





 Not very much to say about it. I have plans for more interesting parts in the coming weekends, so I'm looking forward to that.

[propforward]

Back at it again, and picking up on the crank bearings.

First thing was to get the blocks to the correct height. Touching off with a DTI and using the DRO suggested about .09" to come off. Easy enough. I clamped both blocks next to each other for the best chance at height matching.




Checking the final height:



1.375 was the nominal sought dimension.



I'll take that.

Sweeping across both blocks suggests coplanarity and flatness within .0005 to .001 - I'll take that as well.

So then I set the blocks up one at a time on a fixture plate, to protect my mill table. I used a .750" gauge pin to visually align the casting to the mill axes - basically just centered the pin on each boss of the casting.


After doing that I touched off on the front and rear of the casting base, left and right, and showed that the edges of the casting were within about .020" of parallel to the mill axes. I figured that was good enough - I want to get a decent visual and have bolts centered in their bosses as much as possible, rather than have a rough casting edge very straight and bolt holes obviously off center. It's a balancing act the whole time.

A quick look once the center of the casting was established shows that the center point is about right.



Then it's a matter of drilling and tapping. As much as I like to make a mountain out of a molehill, and post umpteen pictures per step, I can't bring myself to show those operations.

End result seems OK though.



I repeated the process on the bearing cap - which you can see is still attached to the bearing block. The idea being that it is a bit easier to hold the cap by clamping the bearing block.

Again I visually aligned the bosses as best as I could, choosing the center oil hole boss as a zero point. No pics of the process, but after straightening the cap to the mill axes, and establishing a center zero, I traced the part back and forth with the point of a center drill just to make sure it was not obviously off.





After drilling I finally separated the cap from the block, and did a test fit.






Other one:



I'm well happy with these. The casting edges of the mating parts align very nicely, and everything is centered pretty well. The holes are all accurately placed, so these are in a good place for drilling and boring for the crank shaft. I also have to clean up all the flash now - I deliberately left that in case I needed to blend between caps and blocks - and also need to machine the sides of the bearings to the correct width.

So anyway, that was fun. Not particularly complicated, the trick was to understand the casting and locate everything accurately but also matched visually to the castings.

[MJM460]

Hi Stewart, good to see you back on the job, it is going very well.

I think you got the balance pretty much spot on.  Not a mountain, and really helpful emphasis on the critical aspects of dealing with the vagaries of castings. 

The bearing blocks are looking great.

MJM460

[propforward]

Thank you!

I intend to make studs and nuts to attach these, and will likely attempt to make the studs a “close fit” for better alignment. The holes called out on the drawings have a lot of clearance. While I decide what “close fit” is to be in this situation, I may move on to the next part.

[Grateful Ted]

I’m enjoying your build.
I’ve always liked the PMR #4 & #6 engines.
Thanks for documenting it for us.
GT

[Michael S.]

Hello Stuart,
the idea of ​​making the screws with a tight fit is a good one.
You may have to do this before drilling out the holes for the crankshaft bearing. So that the lid cannot slip.

Michael

[propforward]

Very definitely Michael - the main advantage is to holding the caps to the blocks securely and maintain alignment during boring.

Not to mention studs and nuts will just look much nicer on the finished engine.

[propforward]

I have to either make or acquire a rounding bit to make the studs the way I want, and I haven't decided how I want to machine the sides of the bearing blocks yet (angled or flat basically), so while I make up my mind on all that, I moved on to the cylinder.



The aluminum alignment plug fits the cylinder nicely after filing out some flash from the ID, so this seems like a good way to hold the thing for the first passes to machine each end clean. I spent some time measuring the casting and ascertained that the rough bore is quite straight - within .020" or so - so aligning off that should maintain visual appearance reasonably well.

Setting up for milling the first face:



The casting is about .3" long, so a decent amount of machining stock. I took the first face to mostly clean (about .100" removed).



Then inverted and did the same the other side - now clamped directly to the table to get the faces parallel. the aluminum plug has done its job at this point.



The print shows that the circular boss on the side of the casting should be centrally located, so I used my height gauge to touch off between the high spot on the boss and each face. From those measurements, and a measurement of the overall length, I calculated how much to take off each end to keep the boss in the center of the casting.



So then I went back in the mill to finish cleaning up the faces. No pictures - looks the same as previous set ups.

Once complete, I was within .002" on length (tolerance was ±.01" so I''m happy), and the boss measures exactly the same to each face. End flanges are within .020" of each other on rough thickness measurements. Overall this has balanced out very well.



Then into the lathe to bore it out.

Quick set up to get it clamped roughly in place.





The aluminum plug came back into play to get the part centered. The live center is being used just to hold the plug against the surface of the cylinder. Coarse adjustment first using a drop indicator:



And then fine adjustment. Same approach.



Then clocked the face to make sure it was true:



Setting up the boring bar so it isn't over extended needlessly, and checking the rotation of the faceplate and part to avoid any collisions during machining.



First step was to get the bore to clean up. Once I had done that I did some experiments with spring cuts, which caught me out last time. This time I determined that I needed 3 spring cuts to make sure that I hit dimension, and avoid a taper in the bore. Having learned that I set out to hit the center of the tolerance range (shooting for 1.500" +.002 / -.000 per drawing).

My testing suggested that my measured bore typically came out .0002" over what was shown on the DRO. Not sure how reliable that is at this point, as using those spring loaded plungers for measuring bores is a little trickly, but I remeasured multiple times.

Final result:








I'm rather pleased with this - I measured it at 1.5009" throughout the bore. The plunger feels like it has an even drag through the whole bore, so overall I'd say this has come out well. It could certainly use some honing, which will be for another day, but even if I don't do that I think it will bed in quickly and easily.

With that done the next step is to machine out the valve guide bore. I have a plan for it, but I'm out of time for today, so that's the next installment.

Ciao!

[mikehinz]

Stuart, the cylinder came out great!   

I do have a question for you.  Why did you bore the cylinder on your lathe vs your mill?  I've done it both ways and to me, the setup is typically easier on the mill and I can't tell that the bore is in any way inferior to doing it on the lathe.  i do tram the mill though before boring anything critical, just to make sure the head is square with the table. 

Anyway, great work and I look forward to how you'll do the valve bore.

Mike

[propforward]

To be honest - just because I’ve never tried boring anything on the mill. Figured I’d go with what I had a (very small) amount of experience with. But as I was finishing facing the cylinder I did think that really boring out on the mill would save a lot of set up, as well as reducing the risk of getting the bore out of true to the faces.

I also considered leaving stock on one end to face off on the lathe for the same reason - should have done that really, but it all worked out.

So boring on the mill is very likely be what I try on the next engine.