Duclos Huff and Puff

[techonehundred]

I recently started a new project. Phillip Duclos's Huff-n-Puff. I wanted to do something a little smaller for a challenge. I had been a little leery to work with the small stuff and after doing a few parts and my highly trained experience of 5 tapped holes of 0-80, I am now enjoying the challenge. with this I also have some questions. When I get to the valve rod cam and the flywheel, It is going to be very close with the tap that I have. The flywheel has a 3/16" thick body and 3/4" dia. The crankshaft diameter is 1/16". It says to use a 0-80 setscrew. I don't yet have a bottoming tap, I have a tap from the local train hobby shop and it is obvious the tapered threads on it are too long. will a bottoming tap have enough room to create a full thread before it goes through the 1/16" hole drilled in the flywheel? If not what do I do here? Hope this is clear as mud.
Here are some pictures of progress so far.

The engine is 1/4" Bore and Stroke.

 

[GailInNM]

You probably don't need a bottoming tap. When you drill the set screw tap size hole, drill past the shaft hole to provide run out room for the taper on the tap. It will also be helpful if you open up the tap size hole to a clearance size except for the last 0.09 or so before the shaft so you wont have so much to tap. If the tap is not long enough to provide threads all the way, then open up the clearance hole a short distance to allow the body of the tap to go in the hole a short distance as needed.

None of this will unbalance the flywheel enough to affect the engine operation as it is not a high speed engine. If you wanted to be a perfectionist, you could drill a second hole opposite the set screw hole to rebalance the flywheel. I would not bother with doing that however.

Your parts are looking good.

Gail in NM

 

[mklotz]

Another approach in situations like this...

Drill the tap drill size hole through to the crankshaft hole.

Thread only enough of this hole to allow the setscrew to sit below the circumference of the flywheel.

Drop in a short brass rod that will reach from the bottom of the setscrew down to the crankshaft. Insert setscrew and tighten. The brass rod will transmit the clamping force down to the crankshaft.

This technique works well with larger diameter flywheels when you don't have a tap long enough to reach the bottom of the hole or the shank diameter of the tap is larger than the tap drill size hole.

 

[ChooChooMike]

Marv,

That's a GREAT tip for the setscrew !!

Mike

 

[winklmj]

I like the set-screw + plug idea too.

Could also run down to the train shop and buy another taper tap and grind off most of the taper.