Dieter Hartmann-Wirthwein patent engine by Gail in NM

[GailInNM]

I found a bust in my CAD drawings. A stupid snap to the wrong place that then propagated to several more detail drawings. It will take a couple of hours to clean them up. I did get the cylinder heads detailed out enough that l could order material for them, which I did a few hours ago. And, as they were not affected, I made the short connecting rods.

In the first photo you can see a 1/16 diameter spot in the middle each rod. This is to identify them as being made of 6061 alumninum as the final ones will be made of 7075. I only need 8 for the mock up blut of course I made extras to feed the swarf bunnies.

Here is the other side so you can see the three small tabs used to hold the part in place for the final finishing operations. They are 0.007 wide and 0.015 thick. You can also see that I did not all the exit burrs from reaming off the parts on the right end. They are gone now. Just have to clip the parts out with a pair of diagonal cutters and file off the bits of the tabs that are left.
Gail in NM

 

[GailInNM]

I have spend the last few days at the computer fleshing out some of the parts and changing my mind on a bunch of them. Nothing like trying to fit a few things together in CAD to make you wonder about your sanity. But I still have not found anything that would keep this from being a successful runner. Finally today I could not stand it any more and had to get my hands a little dirty. I made a dummy piston out of 12L14 (final pistons will be cast iron) to check for fits. So far every thing looks OK but there may be a bit of interference in one area between the rods. I have plenty of meat there to relieve it if necessary and knew it would be very close. It will be a while before I know for sure as I will have to build a frame with cylinder and bearing mounts and a crankshaft up to be able to check it all. They are all drawn except for a few details that I need to decide on, none of which affects functionality of the parts.

Here it the test fit of parts in one of the center pistons.
Gail in NM

 

[GailInNM]

I have been showing parts photos so I thought you might like to see the general direction I am going with all this.
This is a working SKETCH so parts may appear to overlap as I did not clean them up so one appears in front of another. This is not a finished drawing by any means. It is just one for my own reference but ilf you close one eye ans squint it might give you the idea.
Gail in NM

 

[kf2qd]

I fail to see any benefit to this design. It is just adding complexity and many many more stress and wear points. Complexity rarely adds efficiency. Complexity rarely adds reliability...

 

[GailInNM]

Just because we don't see any obvious advantage to a design does not mean we can't have a lot of fun modeling them. The inventor claimed there were economic and weight advantages from the simplified crankshaft and reduced number of main bearings. Of course neither of these will occur in a demo model such as I am building.

In product development brainstorming meetings we always encouraged any ideas to be presented, even if there was no obvious advantage to them. Sometimes they would spark an idea that would have advantages.



The blanks for the dummy cylinders were turned and bored in conventional manner out of 6061 alumninum. No real care was taken on the bore. I just reamed to 1/2 inch diameter and smoothed the bore out until the dummy pistons were an easy fit. They had been turned a little undersize for this purpose.

After indicating the cylinder in the mill, drilling the mounting holes in the mill was just a case of center drilling and drilling by coordinates.

Then locating the cylinder with two rods inserted in the mount holes the sides were milled. Or so I intended. After milling one side, the rods were repositioned and milling started on the second side.

I did two things wrong and I knew better -- but.... I did not clamp the cylinder tightly and I neither centered the cylinder in the vice or put a spacer in the far end of the vice jaws to keep the vice jaw parallel. As a result the milling cutter snatched the cylinder and the results were ugly.

For the purpose of a dummy cylinder I was able to rework it. If it had been a functional cylinder I would have had t make another one. Then I finished milling the sides withe the part centered in the vice using a stop to position the part.

And finally ended up with two usable dummy cylinders.

After the mishap I spent the rest of the day cooling off by redrawing the cylinder mount and crankcase parts. New parts will be a little more work to make but will make alignment of everything easier at assembly.
Gail in NM

 

[GailInNM]

I got a bit of a start on the crankcase. The crankcase is built up of 7 parts. The base plate, two end plates which carry the outer bearings, two inner bearing holders, a back plate and the cylinder deck plate.

The cylinder deck plate is the most complicated and I started with it. Photos tell most of the story. ^he plate is 3/16 thick and just over 3 inches long.

Gail in NM

 

[Path]

Gail in NM

Keep'em coming, great photos. Can't wait to see it running.
Thanks for the updates.


Pat H.

 

[GailInNM]

Thanks Pat.

All of the crankcase plate work is finished. Everything is 3/16 inch thick plate except for the base which is 1/4 inch thick. The bearings were test fitted bult won't be installed until later. The test fit up just has a few screws to check for fits as it will all have to come apart later.
Gail in NM

 

[ddmckee54]

Gail:

I'm assuming that the two flanged bearings shown in the photos are for the camshaft. Is the cam going to be stiff enough that it won't flex with no support in the middle? I realize that the loads on a model camshaft are fairly small, but then again so's the cam.

Just wondering,
Don

 

[GailInNM]

Don,
I think that the cam will be stiff enough. The root shaft diameter is a little bit larger than I would normally make it if I had additional bearing support. But, just in case, I have a center bearing support on the drawing that I can add in. It is open on the top side so it can be slid into place with the engine assembled. Since the deflection forces will mostly be downward and some front to back from friction on the tappets the open top will not affect anything. Since it would be a plain bearing I would make it a couple of thou oversize so it would not touch unless there was some deflection.

The cam, as drawn, is fairly gentle and combined with low speed operation should not put too much load on the cam. Besides< I have to make it run before I worry much about such details.

Thanks for the comment. It's too easy to overlook details that others may catch.
Gail in NM

 

[GailInNM]

With the bearing mounts inside the crankcase ready I thought I would make up the crankshaft. I will still eed to make some other internals before it has anything to do but it will give me something to diddle while I am thinking on the next parts.

I tarted with a 3-1/2 inch long, or so, length of 3/4 inch diameter 1144 stress proof steel. Turned it down to 0.687 diameter and then turned 2-3/8 of one end down to a finished 0.250 diameter to good fit for the main ball bearing races.
Then I whittled down the remainder to leave a 1/8 inch wide crank web and a roughed out crank pin.

Now to turn the crank pin. I could do it in a 4 jaw chuck but I normally make up a turning fixture. It takes about the same time as setting up the 4 jaw so there is no real time advantage either way. I will cover the fixture next time.
Gail in NM

 

[GailInNM]

The crankpin turning fixture started life as a length of 1-1/8 diameter 12L14 steel. Nothing scacred about the 1-1/8 except I bought a bunch of bar ends that size and about 5 inches long from a screw machine shop.

I turned down about 3/4 of an inch to 1.000 diameter and then cleaned up another 3/16 inch so it was smooth and concentric with the 1 inch diameter. Off to the mill where I centered it in a vee block with an indicator. Drilled and reamed two 1/4 inch holes with 0.1875 offset for the throw dimension. I did two holes because it makes it easy to set the fixture up for slitting with just two rods in the holes resting on the vice jaws. Then pull the rods and cut the slot.

Before cutting the slot I milled a pocket for the crankshaft about 1/16 inch deep. This aligns the crankshaft and provides insurance that the crankshaft will not turn in the fixture.
Gail in NM

 

[GailInNM]

The fixture with the crankshaft was held in a one inch diameter collet in the lathe. First the crank pin was roughed out with a carbide insert turning tool and then finished with a high speed steel turning tool that had close to a zero radius on the tip. Not great for stress on the crank pin to crank disk interface but for all this engine will get run it will be OK.

After polishing the crank pin the connecting rod was test fitted and after oiling it was run in for a few minutes. Easy to do now with the crank pin on center.

Notice the step on the end of the crank pin. This is to engage the other half of the crankshaft and drive it. Since it is not necessary for basic operation of the engine I will not build the second half of the crankshaft at this time.
Gail in NM

 

[AussieJimG]

Thank you Gail for the information about the crankshaft turning fixture. I have been thinking about this for a while and you have given me some new ideas.

And the thread is quite absorbing. I look forward to a dose of Gail each morning - it's much more interesting than the newspaper.

Jim

 

[GailInNM]

Glad it has given you some ideas Jim. That's what forums are all about.

Here is the latest development. Everything clears so far. Now to make some bell cranks and mounts for them.
Gail in NM

[ame]http://youtu.be/eoC6cqL97Ho[/ame]

 

[GailInNM]

The bellcrank and associated parts that get stuffed into the pistons are completed. I still need to make the bellcrank pivot mount and an outer arm support for the pivot. Once these are done I can fit both cylinders and pistons to one side and see if I need to "adjust" any dimensions. There should be 0.005 inch clearance but machining tolerances can eat that up quickly with this many parts.
Gail in NM

 

[petertha]

That engine has some funky kinematics. Very interesting indeed.

Can you elaborate on your pins with the e-clip ends: material type?, hardened after? grooving tool used?
Is the end result Aluminum-On-Steel with most of these links? (ie no bushings).

 

[GailInNM]

Petertha,
All the small pins used in this engine are 12L12 steel. The mating parts that they run in are made of 7075-T6 Alumninum. The 7075 is harder than the 12L14 and they run well with each other. 2024-T4 also works well. Many commercial model engines used 2024 connecting rods directly on a hardened steel crank pin ant that is much more severe duty than these pins will ever see as they are only in a rocking motion and not making full rotations.

The main connecting rod is also 7075 and it is running directly on a crankpin of 1144 steel. All the steel pins are lightly polished but not hardened. I typically finish polishing with 1200 grit abrasive paper using a metal backing to keep things flat. It is not really necessary to use bushings on a small demonstration engine like this. I do have the room on this engine to put a bronze bushing o the main connecting rod big end but did not think it would be worth the bother. One of my "Tiny" Hit-n-Miss engines has over 1000 hours with a 2024 conrod on 1144. It is a little bit loose now but well within acceptable tolerances.

For grooving I use a Nikcole carbide insert grooving tool 0.5 mm wide (0.019 inch). The e-clips are E-6 clips with the groove diameter 0f 0.052 inch. The width could be narrower as the recommended width is 0.012 inch but I am too lazy to grind a special tool for them. Other people like to use the Warner HSS insert tool with a 0.015 wide blade and it also works well.

Gail in NM

 

[GailInNM]

The penny in the photo lin the previous post has to be the worst looking penny I had in my pocket. I did not notice it until I posted the photo. Made me feel guilty about using it so I took all the pennies in my pocket and dropped them in the ultrasonic cleaner and then reserved the best looking one for future photos. With all the crud on the parts I need to start running them through the cleaner before photos. I will clean all of them before final assembly.

All that has been productive has been to make the pivot pins for the bellcrank. One photo of the pins and one showing where it gets installed.

With the pivot pins in hand I assembled all the conrod linkages and found I did have a bit of a rub between two parts. I could turn the engine over but there was a binding spot. It was where I thought I might have one but it was not because of tolerance build up. I had changed one part a bit and did not plug the new numbers into all the drawings that used it. Good news is that there is an easy fix and it is under way. Since things are apart I am also making another small change the while not really necessary will make assembly easier. Another hour or two and I can start assembling all over again. More photos then -- with a clean penny.
Gail in NM

 

[GailInNM]

It's been apart and back together several times now and is finally working smoothly.

First I slimmed down the small connecting rod and that got rid of the bind. For additional security I also took off a little of the main rod.

But I could still get a tick when turning it over in the lathe and taking out the slop in the linkages by pushing things around with a stick. I could have just relieved the spot with a needle file but I put a little 45 degree bevel on the spot with a drill/mill cutter that I have. Then for what I hope is the final assembly I played with it for a while.

The end of the pivot pin will get captured by an outboard support at final assembly and keep the bellcrank in place as well as supporting the pivot pin.

Back to the lathe for some more testing and every thing seems good. The video shows the engine upside down so the free con section will hang down by gravity and not get caught in the rest of the linkage.

[ame]http://youtu.be/hZyoh8yHMEA[/ame]
Gail in NM