Help understanding Elmer's 24 drawing

[drysdam]

On page 3 of the PDF, look at the base. I have two questions about it:

1) What are the "drill 1/8" holes about? I can't figure out what is supposed to go in those holes. Worse, looking online, I see one person tapped them for some reason, but the end of that article doesn't show them screwing anything into them that I can see.

2) What do the circle C marks on some of the holes mean? Not "clearance" since there's also a circle C on a linear dimension on the right end. Similarly, on the bear part, same page, there's a 1/8" hole that has both a circle C and a circle S.

All the text says is that both these parts "need no comment"...

My gut says to leave out the 1/8 holes unless I find I have an extra part that needs to fit there and to cut the circle dimension parts to the numbers as given and forget the circles. Thought I'd ask before throwing away a couple hours work...

 

[drysdam]

Ah, someone on the NEMES mailing list pointed out to me that the appendix lists C and S as meaning close fit and smooth respectively. Still no idea about the mystery holes, though. Maybe for mounting to a wooden base? Doesn't seem like they'd have to be through holes for that.

 

[kvom]

My guess on the 1/8 through holes is a means to secure the base to a larger sub base, as the flywheel probably makes the engine unbalanced when running.

 

[Tin Falcon]

I see what you are talking about. I also see the narrative stated the base and bearing need no explanation.

My though the are holes to mount the engine to a wood base as that is common practice. threading these holes would allow machine screws to come from the bottom of the wood base and screw into the metal base. Look back at the previous plan sets for an explanation . often a designer/author will start the first few plan sets with lots of detail and explanation . assuming you will build in sequential order. By the time you get to 24 little expansion should be needed . that is unless you start with # 24.

I looked at a couple other lowered number plans the base/ foot on many of the engines have two unexplained holes. I would use these holes for screws to mount to a wood base. You can make these holes blind from the bottom if you wish. And tap for machine screw. That is if the base metal is thick enough and in the case of #24 it is.
Tin