Wobbler help

[grimm]

Hi All,

It's not a locomotive so I hope that this is the correct forum. I'm currently building an Elmer's #26 boiler and engine. I have almost finished the boiler and alcohol tank, so I'm starting on the engine. Here is a link to the plans:

http://www.john-tom.com/ElmersEngines/2 ... Boiler.pdf

What is confusing me is the drill jig to determine where the ports need to be. From the diagram it looks like you need to use the crankshaft with the jig, but if that is the case, why the locating pin? If you need the locating pin, then why the 1/16 hole in the jig? I wish he just put the measurements for the ports on the diagram, then I could just dial it in with the DRO.

Here is what I have finished so far:



Thanks,

Jason

[prlawiii]

Grimm,

On the frame, the holes must be 3/8 inch from the center of the cylinder pivot. The drawing shows that the locating pin is centered 1 1/4 inch from the center of the cylinder pivot, and the part of the locating pin which moves the jig is 3/16 diameter. This will raise the jig 3/32 (1/2 of the diameter) plus the edge of the jig is 5/32 from the center of the pivot hole. So the centerline of the jig has been moved 8/32 (1/4) from the center of the locating pin (3/32 + 5/32). The sine of the angle the jig was raised is 1/4 divided by 1.25, which gives an angle of 11.54 degrees. The height of the holes above and below the center line of the pivots will be the sine of that angle times 3/8, or .0757 inches. The horizontal distance of the holes from the center of the pivot pin will be the cosine of that angle times 3/8, or .367 inches

At least, that's my reading of the drawing.

[RET]

Hi,

The combination of the drill jig and locating pin is just a simple way to locate the inlet & exhaust holes accurately for those who don't have a DRO. Remember, these drawings have been around for a long time and were meant to be used by those with just the most basic equipment.

When you locate the drill jig in the dotted position on the drawing & clamp it in place, you can drill the exhaust hole. The locating pin goes in the crankshaft hole. When you flip the jig over and locate it at the complimentary angle on the other side of the pin, the jig will be in the right position to drill the inlet hole. Both holes are 1/16" dia.

Hope this helps.

Richard Trounce.

[grimm]

Grimm,

On the frame, the holes must be 3/8 inch from the center of the cylinder pivot. The drawing shows that the locating pin is centered 1 1/4 inch from the center of the cylinder pivot, and the part of the locating pin which moves the jig is 3/16 diameter. This will raise the jig 3/32 (1/2 of the diameter) plus the edge of the jig is 5/32 from the center of the pivot hole. So the centerline of the jig has been moved 8/32 (1/4) from the center of the locating pin (3/32 + 5/32). The sine of the angle the jig was raised is 1/4 divided by 1.25, which gives an angle of 11.54 degrees. The height of the holes above and below the center line of the pivots will be the sine of that angle times 3/8, or .0757 inches. The horizontal distance of the holes from the center of the pivot pin will be the cosine of that angle times 3/8, or .367 inches

At least, that's my reading of the drawing.

prlawiii - That is brilliant! Thanks, but I should have told you that, for some reason they combined both Elmer's #25 and #26 into a single pdf. So if I take your math and apply it to #26 I should get:

The holes must be 15/64" from the center of the pivot, the locating pin is 15/32" from the pivot. The locating pin that moves the jig is 1/16" in diameter. This will move the jig centerline (half locating pin + jig edge) 3/32".

The angle would be 11.24 degrees.

The height of the holes to the left and right of the center pivot would be sine of the angle times 15/64" or .0456".
The vertical distance would be .2295"?

Sound about right?

Jason

[grimm]

Hi,

The combination of the drill jig and locating pin is just a simple way to locate the inlet & exhaust holes accurately for those who don't have a DRO. Remember, these drawings have been around for a long time and were meant to be used by those with just the most basic equipment.

When you locate the drill jig in the dotted position on the drawing & clamp it in place, you can drill the exhaust hole. The locating pin goes in the crankshaft hole. When you flip the jig over and locate it at the complimentary angle on the other side of the pin, the jig will be in the right position to drill the inlet hole. Both holes are 1/16" dia.

Hope this helps.

Richard Trounce.

Thanks Richard,

That makes a lot of sense, I forgot that these plans were made before all the fancy stuff we have now. I'm assuming that the extra hole is so you could use the jig with the crankshaft, maybe to double check the hole placement?

Jason

[prlawiii]

Grimm,

Sorry, that I didn't notice that there were two engines and didn't pick up on which one you were making. Your numbers are right, except that I get .0455 for the side to side displacement, because I kept the angle in calculator memory to probably more decimal places than significant number theory would allow.

Herman

[xo18thfa]

Jason: Here's a photo of that kind of jig. You need a little spacer on the center pin since the jig can't sit flat.

[grimm]

Thanks Bob,

I see now, you used the jig off of the crank. So the spacer is why Elmer uses the locating pin instead of the crank, or you could do it either way? Makes sense.

Jason

[grimm]

I have finished building the wobbler engine and boiler. Here is a couple of pictures of the engine:





It took about 2 months to build the engine, I'm just happy that it works. Although I'm still having some problems with it.

Here is a short video of the engine running. Sorry for the bad video, it was hard to both run the engine and shoot the video as well.

http://www.frostyfoot.com/grimm/images/ ... _anim1.mpg

Jason