Winner Pm Research Engine #7

[kvt]

Ok, what part failed. The getting them level with the mill table or the holding them, Based on your comment about the super glue it may not have held the way you wanted or something. The home made ones look nice. I have been busy and have not even made it out to work on mine for over a week. The base is still sitting on the mill table waiting to be lined up and leveled again.

 

[tomw]

It was a combination of factors that led to the failure. Mostly it was about finding a good way to hold them solidly and on level. My failed solution was to use an aluminum plate that I glued the big ends to, and then supported the small ends on shims.

Thanks fro reading.

Tom

 

[Hawkeye]

I ordered my engine kit this evening. I can see that I'll be reading your account several times when I get working on it.

 

[kvt]

Tom,
here is what I was thinking on them, Clamp it in the Sherline vice, by the small end or as much as possible, and shim it to put it as much straight as it would go, Then use an endmill on the big end to cut the sides on it, then remove and clamp by the newly done big end now do the small end. If we squared the big end off properly we should now be able to have both ends set, and can hold by one end and drill the other, then do the switch again. Yea it is a bit of a pain, but I think it should work. these would almost have been better as blocks of stuff to cut and shape rather than castings from what I see and happened to you. If I get a chance to try it I will let you know.

 

[T Bredehoft]

At one time in my varied career, I was required to Blanchard grind the ends of some connecting rods. (approx 18 in long.) The big end was thicker than the small end and they were symmetric. We had jigs made for each of the four differing grinds. The first and second grinds were of the big end, the third and fourth for the small ends. We did four rods at a time, mounting them on each fixture, and in the case of the first of the set, leveling them crosswise in the fixture with a separate piece of fixture. It was a complicated process and one no one wanted to do. The very first grind taking 20 minutes to half an hour to set up and 5 minutes or less to grind. Two rods per engine. This particular engine had as a third piston on the crank, a double ended compressor piston, for natural gas. The engine ran on Nat Gas and compressed it also, to send it on its way in a pipeline. The power pistons were about 6" dia., 3 1/2" stroke, producing with a turbine, 75 hp.

 

[kvt]

I think I have seen some of those around, From the Texas panhandle they had both gas and oil pump stations all over the place. I always though it was funny they use the Natural gas to run and pump it as well, what if something went wrong, but never saw one fail and cause much of a problem (fire ball type). I always thought a sealed electric motor might be safer.

 

[tomw]

Hawkeye,

I hope you find it enjoyable. Let me know if I help with clarifying anything.

Tom,
here is what I was thinking on them, Clamp it in the Sherline vice, by the small end or as much as possible, and shim it to put it as much straight as it would go, Then use an endmill on the big end to cut the sides on it, then remove and clamp by the newly done big end now do the small end. If we squared the big end off properly we should now be able to have both ends set, and can hold by one end and drill the other, then do the switch again. Yea it is a bit of a pain, but I think it should work. these would almost have been better as blocks of stuff to cut and shape rather than castings from what I see and happened to you. If I get a chance to try it I will let you know.

Ken,

Yeah, I thought of something similar after I had screwed up the rods I have, if I understand what you are saying. The only problem would be the shimming and holding it well enough by just one end. They are pretty flexible little pieces.

The other thing I was thinking was putting them, one at a time, flat and by the big end, in the vice. Drill the big end hole and then use that to mount it to a fixture with some sort of fitting you could indicate from. You would still need to shim under small end to make it level, and probably shim under the thin section of the crank and clamp there to prevent the wobblies. But once clamped, you could mill and drill the small end, flip it and re-shim, and then mill the other side of the small end. It would be a lot of monkey business for two small pieces, and you would still need to thin the big end somehow.

Let me know how it progresses. I'm going to keep pondering.

Cheers,

Tom

 

[tomw]

The next things I did were the crank throws and crank bearings.

The crank throws are bronze castings. The first step was to use the belt sander and some draw filing to remove the sprue and smooth the surface a bit. I then mounted the casting in my three jaw chuck. The central boss was then turned and faced. According to the drawings, the height of the center boss is not critical, but the height (or thickness) of the crank throw as a whole is very critical (the drawing has a .xxx dimensional callout, so +/- .005). From crank throw is drawn with what looks like half of the thickness being taken up by the boss, so I faced the boss to a height of 3/16". The diameter of the boss is also not critical, so it was taken down until it was nice looking. This is probably an optional step, but it makes for a much better surface for the chuck to grab in the next step.

The crankshaft throw rough casting.​

After removing the sprue and a little draw filing, I mounted the throw in a three-jaw chuck.

I machined the side and faced the end of the boss. The height of the boss was brought to 3/16". The parallels are somewhere under one of my toolboxes. Do as I say, not as I do.​

The piece was then flipped and grabbed in the three jaw chuck by the newly machined boss. I did not want to mar the newly machined surface, so I cut a small strip of aluminum shim stock to wrap around the boss. The jaws then dig into the aluminum and not the nice shiny bronze.

I fashioned a protective shield for the boss from some aluminum shim stock.​

I then faced the surface, taking cuts until the piece was .375 thick. To get it to the right thickness I first did enough facing to make the surface smooth. I then removed it from the chuck, measured its thickness. I then rechucked it and took the rest of the cuts. I only removed it for the one measurement, as I wanted the surface to the absolutely perpendicular to the crankshaft mounting hole (next step). Unfortunately, I have no pictures of this process.

I then center drilled, drilled and reamed the hole for the crankshaft to 1/4".

Drilling the 15/64" hole for the crankshaft on a nicely faced crank throw. This was followed by reaming to 1/4".​

The next step was to drill the hole to which the f*****g connecting rod is connected to the crank throw. The distance between this hole and center of the crankshaft needed to be accurately determined. For aesthetics and balance, this hole also need to be along the center line as defined by the center of gravity of the throw. I found the centerline of throw using a ruler, my opti-visor, and some swearing (yes, I like Oxford commas). As kind of illustrated below, I would pick a point some distance from the hole for the crankshaft and find the middle of the narrow bit on the throw. I did this for three points, and then used a straight edge and scribe to connect the dots. This line now identifies, reasonably accurately, the centerline of the throw's center of gravity.

A rough illustration showing how I roughly determined the centerline of the crankshaft throw. The light gray bit is supposed to be a ruler (or scale if you prefer).​

The crank throw in a three jaw chuck mounted to my rotary table. Note the scribed line. Along this line, .375" from the center of the crank hole, will be drilled a #38 hole for attaching the connecting rod.​

I then mounted and centered my rotary table, and then mounted the 3 jaw chuck with the crank throw still in its clutches. I moved the X axis .375. I installed and aligned wiggler, and used the rotary table to bring my scribed line under the center of the spindle. And like Robert's your Mother's Brother, I could now drill the #38 hole that will be the point of attachment for the g*****n connecting rod.

Using a wiggler to indicate the centerline under the center of the spindle, .375" distant from the center of the crank hole.​

The grub screw hole to fasten the throw to the crank was then drilled. I did this by holding the throw vertically in the vise, and aligning it by eye so the grub screw hole would be on the opposite of the side of the boss that faces were the little s**t of a connecting rod attaches. I used the crankshaft itself to make sure the hole through the boss was perpendicular to the axis of the grub screw hole. Then I used an edge finder and some arithmetic to find the horizontal center of the boss and drilled the hole. All holes were then tapped with the appropriate tap and fluid.

A shop still-life, showing how the grub screw hole was located and then drilled. I don't show a center drill, but I did use one.​

Tapping. That is a 5-40 tap.​

The above steps were done for both crank throws.

I then made what the kit calls the crank bearings, but really they are the bearings for the connecting rods. Anyway, those are pretty basic. Read the captions on the photos below for more details.

I used 1/2" 12L14 CRS for the bearings. The kit supplies a chunk of 5/8" CRS. It seemed silly to remove more metal than I had to, so I made the switch. If I had had 3/8" CRS, I would have used that.

I faced and then turned the stock down to the 5/16" outside diameter. BTW, I love turning leadalloy.

Drilling the central hole. I center drilled things to get it started, and then I drilled deep enough so I could get both bearings done at once.

The inner pilot diameter was then turned. To get the shoulder as small as possible I did this turning with a very sharply pointed HSS bit (not shown). Here are I am getting ready to cut off the first completed bearing.

The crank bearings completed. Both bearings have been de-burred.​

And this is how things look at this stage:

Until next time, Cheers,

Tom

 

[tomw]

Next up are the eccentric hubs and eccentric straps.

The kit provides a length of 5/8" CRS, probably 12L14, from which to fashion the eccentric hubs. There is a concentric groove and a 1/4" hole for the crankshaft that is offset .100, for an eccentric throw of .200.

The eccentric plan, should I be able to stick to it.​

The first step was to create two grooved parts of the correct length. I faced the provided stock, and then turned the first groove. I used my .031 wide carbide grooving tool, which allows for cutting on the side of the tool. I would plunge cut both ends of the groove as indicated on the plans and then turn between those points to about 10 thou less than the final depth of .075. Each sweep I would take about 15 thou. Then using my "wire gauge", 1" mic, and some arithmetic, I took the last few cuts to the called for depth. The scare quotes are because I used a drill bit as my gauge. Or is it gage? What is the difference?

Cutting the first part of the groove with a carbide groovy tool. The groove is .100 from the end of the part, and will be .100 long by .075.​

I then cutoff this first part and repeated the above steps for the second, hopefully identical part.

Yup, cutting off the part.​

A now grooved part was then mounted in my 4 jaw chuck. I need to be able to offset the part from the spindle center by .100 in just one plane. To make this easy, I had previously fashioned some thin v-blocks. I use these v-blocks and some small parallels to mount the piece in the chuck. The piece was then centered in the chuck. I prefer the method outlined by David Lemereis in this video for chuck centering. This has been posted on this site before, but it is worth mentioning again, in my honest opinion. What sort of jerk gives his dishonest opinion? Psychopaths, I suppose.

Mounting the part in my 4-jaw chuck. It is only roughly centered here. Once centered, it will be offset along one axis .100.​

With the jaws snug, but not tight, I then offset one axis .100. The really nice thing about the v-blocks and parallels is that you don't have to worry about getting the other axis out of center, since those jaws remain snug on the fixture the entire time. You also don't need to worry about getting scratch marks on the piece as it moves past the jaws.

The hole for the crankshaft was then drilled and reamed to 1/4".

Reaming a hole! Holy moly, look at that! Wow!​

Then I machined the piece to create the lobe-like bit, aka counter weight. On an engine this small I imagine this part is optional, but it does make the part look better, and it is called for on the plans.

Roughing out the counter-weight lobe on the eccentric hub. The visible steps are eliminated during the finishing cuts.​

The trick here is paying attention. I did not want end up going to far, so I turned the lobe to about 10 thou less than the correct diameter and about 10 thou less than the correct height (depth). I then went back and took light facing cuts towards to lobe and then would back the bit out along the Z axis. In this way, I would increase the height and decrease the diameter of the lobe and leave behind a nice smooth surface.

Wow, was that clear as mud or what! Maybe the sketch below will help understand these last few cuts.

Imagine this is a sketch of the eccentric hub. The grey area is going to be removed as the cutter follows the arrow. Note that the cutter is at an angle to give clearance for both facing and turning in one somewhat smooth operation.​

This process was repeated for the other eccentric hub. I used the trick of only loosening two adjacent jaws to swap in the second piece, thus ensuring my centered offset would remain undisturbed.

Both pieces were then taken to the mill and their grub screw holes drilled. I used the same process as on the crankshaft throws. These holes were then tapped for the 5-40 set screws.

Center drilling for the grub screw hole.

Finished eccentric hubs.​

The material provided for the eccentric strap, or simply eccentric on the plans, consists of a short piece of brass tubing. The tubing O.D. is fine, but the I.D. is too small to fit over the eccentric hub. This I enlarged by boring until the eccentric hub just slid into the bore. It is a sliding fit, so there needs to be about a thou of play. Otherwise it will bind and/or gall when running.

The provided stock for the eccentric straps are these two bits of brass tubing.

Boring out the tubing so the eccentric hub will slide within it.

Checking the sliding fit of the eccentric hub in the eccentric strap. Slides like a weasel chasing a rabbit down a hole.​

I then faced the piece to the correct width (length?).

The plans call for a 45° x 1/32" chamfer. I put this on using a straight, brazed carbide bit set at 45°. To chamfer the other side, I flipped the piece in the chuck and bump aligned it to get it running true before doing the cut.

A chamfering I will go.​

Each strap was then taken to the mill, where I milled a small flat on the O.D. and drilled and tapped the hole for the valve connecting rod.

Putting a flat spot on the outside of the eccentric strap. The lock nut for the valve rod goes against this surface.

Finished eccentric straps. Or eccentrics, as the plans call them. This strikes me as an odd name for these parts, as they are, in fact, very symmetric.​

That is it for today. Until next time.

Cheers,

Tom

 

[T Bredehoft]

Thanks for the excellent descriptions of your work. I made a small (4" tall) two cyl steam engine many years ago, considerably different from yours. Only had a one sheet plan. I did a lot of engineering to get it done.

The cyl block was hard brass, the base was cast iron, the rest was mostly drill rod.