Mike's P.M. Research No. 6 Steam Engine

[macardoso]

This past weekend I had some time to work on the steam engine some more. I've been doing the harder casting parts lately, so I decided to work on some of the easier parts on the lathe.

I started with the Lower Valve Rod, which was a simple rod with a 10-24 thread on one end and a cross drilled hole on the other end. When complete, the part will be bent to shape to fit the final engine.

I started with the 10-24 thread using a die. I have a full set of "Little Giant Screw Plate" taps and dies. They look like high quality tools, however after I ran the 10-24 die over the part, it did not cut 24 threads per inch. It was closer to 21 and very sloppy. Not sure what that was all about. Fortunately I also had a "normal" split die for a 10-24 which ended up cutting perfect threads.



All of the dies have two movable jaws that have screws coming in from the outside which adjust the size of the cut thread. Pretty interesting.



I parted the bar to length but did not yet drill the cross hole.

Next I squared up some brass stock on the lathe for what will become the Upper and Lower Linkages. I was able to get the cut to length within 5 tenths.



I used a 4 jaw self centering chuck held in a 3 jaw self centering chuck to cut these pieces from the short piece of barstock provided in the kit.



I cleaned them up with 600 grit sandpaper and bagged them for later use.



My buddy bought a hardened and ground shoulder bolt to use instead of machining the wrist pin, however it measured significantly undersize on the diameter so I decided to go ahead and make the wrist pin. I've never seen a shoulder bolt be the wrong size?



I've been having a lot of issues with the carriage travel on my lathe being very inaccurate and not repeatable. I'm wondering if there is a damaged gear or loose pin in the apron, or perhaps the rack and pinion is messed up. To cut this part accurately, I set of a 1" dial indicator on a flexible arm.



I turned the thread major diameter for a 10-24 thread and used a split die to cut it. The stock is CRS hex provided with the kit.



I used a VCGT insert to undercut the thread on the end and finish the outside diameter. I turned it to .3125" with .0001" of taper along the .875" length. This is larger than the kit called for, but I only have a .3135" reamer so the fit will match what the kit called for.



I parted the part to length, but paused before fully cutting it off to use a LH internal thread bar to put a 60 degree chamfer on both sides of the hex.



Finally, I reamed an aluminum tube in place in the chuck to .3135" and placed the bolt in there. Tightening the chuck to crush the tube held the part with near zero runout and no marring of the precision surface so I could finish the head of the bolt.

 

[hman]

My buddy bought a hardened and ground shoulder bolt to use instead of machining the wrist pin, however it measured significantly undersize on the diameter so I decided to go ahead and make the wrist pin. I've never seen a shoulder bolt be the wrong size?

Wellll ... Chinese persons do tend (on average) to be of smaller stature than westerners. So it's understandable that their shoulders might also be narrower. Recall the occasional references to the size of Chinese horses on the forum

 

[savarin]

Awesome work, cant wait for the final steam up.
Thanks for showing this makes me want to do something similar.

 

[macardoso]

So I haven't written here in a while because I've mostly been posting about completed parts and lately I've done a ton of parts half way. Over the weekend and last night I finished 6 different parts. I'll do a big dump of those now. I've also done most of the work on the main cylinder including the piston bore and valve bore. It just needs to have the bolt patterns drilled.

Here we go with the updates:

To prepare for the pile of parts I want to run on the mill, I loaded 24 tools into CNC tool holders and preset them all on the bench with my 8" height gage.



This is what my tool table looks like.



And the completed pile of tool holders. This is pretty much all I have. The values were keyed into Mach 4.



The radiused outside was completed with a quick 10 second CNC program with the No. 3 1/4" endmill. The relief pockets were cut using the MPG jogging functions on the CNC as were the drilled holes.



The second part requires a mating slot to be cut through the middle. I opted for a dynamic slot milling operation using a 1/8" endmill. With a light finish pass on each wall I got a great fit on the first try. I did goof and the finish pass clipped the corners of the slot when plunging and retracting. This was just a couple of thou and I blended them into a chamfer with a piece of emery cloth.



Here was the No. 6 1/8" endmill



The completed clevis.



Here the pieces are mated. I failed to get a good picture of the completed parts but they had a 3/16" hole drilled on the ends and a 1/16" cross hole drilled for a roll pin.

After chatting with my buddy, we decided to go off print and use a 45 degree chamfer cutter to remove the razor edge on the part with one tab. It is cosmetic only.

 

[macardoso]

Next I continued on with the inboard head, drilling the bolt hole circle. Something odd to note is the holes are not evenly spaced. This is to allow the bolts to pass into the frame without hitting some webs on the casting.



I had to remove the jaws from my vise to fit the part. It was supported on parallels and gripped with brass shims.





Holes cut like butter. I was moving the parallels around to avoid drilling them and to support the part.



Here is the complete part. I ordered a 1/2-20 bottoming tap to finish the center hole deeper.



And fitted in place on the cylinder (sneak peak!)

 

[macardoso]

Remember this little guy? This is the inboard valve head. I finished the lathe work a while ago but needed to do the bolt hole pattern.



I made a super quick (read TOO quick) fixture by tapping a 3/8-24 hole into a piece of scrap aluminum and threading the part onto it as firmly as possible.



The holes were spotted and drilled to the print. I got a little aggressive with the first hole and the part spun slightly. Fortunately the drill bent and didn't break or mess up the part other than a very minor amount of bell mouth on one hole. This was acceptable and I was able to finish the part after holding it down better and drilling more slowly.



Complete. You may also notice the kitchen peeler got my finger

 

[macardoso]

These shafts were next on my list to check off the list.



My friend wanted to keep one shaft a little extra long to allow him to attach additional hardware. The shaft and keyway were lengthened by 1".

The part was indicated flat within 5 tenths then centered with the electronic edge finder.

I used the Mach 4 multiline MDI to write a quick G-code program to slot the keyway in 3 passes. The fit was perfect on the key.



A couple of quick wipes with an Arkansas stone removed the razor edge.



I repeated this process for the second shaft.

 

[macardoso]

Easy one done last night.

I had finished OP1 and OP2 on this valve a while ago. I set it up in the vise on parallels and indicated it flat. Then used the electronic edge finder to locate the center of the stub end.

I drilled the cross port with a 3/16" drill followed by a 1/4" endmill. I was cutting a cross hole pretty close to the diameter of the part, so I wanted to use the end mill to keep it on diameter and straight. It came out great.



I then added the 1/16" cross hole for a roll pin. I used a 1/8" endmill to spot face the hole before spotting. The witness mark from that operation is still on the part.



And finished! It took me a long time to really understand how this valve works. The cross hole allows the inboard side of the cylinder to exhaust to atmosphere through the middle of the valve to the ouboard side of the valve cylinder.

 

[BGHansen]

The next part I tackled was the Base. It is a fairly large casting and requires facing the top, bottom, and drilling/tapping 16 holes.

View attachment 317223

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I first clamped the part upside down. I used a 1/2" HSS roughing endmill to face the bottom of the part, moving whichever clamp was in my way. The change in clamping pressure around the perimeter created a few steps in the face but they won't be visible when this is assembled. Not sure how to do it better. After about 1/3 of the way around the part, my spindle load meter started to climb, the finish got worse, and the cut got louder. I stopped to find my endmill was worn to a smooth corner. It must really not like the scale right at the surface of the casting. I switched to a carbide roughing endmill from Hanita and has no further issues.

View attachment 317222

I then flipped the part and skimmed the top faces for full cleanup. This actually took the part underside on the height, but was the preference of my friend who owns the kit.

Right before I started on this side, my CNC computer had a glitch and wouldn't respond to the mouse or keyboard (touchscreen was fine). I had to fully reimage the PC including setting up Mach 4 again. That sucked and chewed up 2 weeks of shop time. But everything is running fine again.


View attachment 317226

After taking 2 weeks off from working on this, I wasn't in my flow, wasn't paying attention to the print, and made a big oops. The mounting pads shown below were for 10-24 screws, but I pre-drilled them #7. With permission from my buddy I will have to modify the plans to use 1/4-20 bolts here for the pillow blocks instead.

The process of indicating this part to be straight on the table without any precision surface to reference, and to center the holes on the various bosses took many hours of fiddling with the indicator. I probably spend twice the time on setup as I do actually cutting.

View attachment 317227

Here is the mating part with the intended screw (left) and the 1/4-20 screw (right). It will look and function fine, but I'm mad at myself for not paying attention.

View attachment 317228

Here are the pads completed. I also drilled the 4 mounting ears at the bottom.

View attachment 317232

Kate needed to do a final QC.

There was also several hours of bench work to remove the flash from the edges of the casting.

View attachment 317234

-Mike

Many die makers in our tool room at work say, "the sign of a good machinist is how well they can hide their F-ups". Great work and saves.

Bruce

 

[macardoso]

I took a little hiatus from this project as I picked up an industrial robot and I've been working on getting that running. Here are some updates on the project as I start back into it.

Here the the inboard head. This seals the main cylinder from the outside.


The component starts as a casting with a remnant of the casting gate hanging from the side.



I rough machined the back of the component to establish a datum.



Next I turned and CNC drilled/tapped an aluminum fixture ring to use on the next operation.



The bolt hole circle was drilled and spotfaces were added under the screw heads at my buddy's request.



I bolted it to the fixture and used my 4 jaw to get the ring shaped boss in the center of the part running fairly true. The OD was turned to size.



Using some brass shim stock, I finished the back side features.



And here is the finished component! Ready to be painted.