when to drill holes in cylinder head for model airplane engines?

[jimbo7636]

Maybe its just up to the individual preference but I have seen a few articles describing the order of operations for machining cylinder fins. In some cases it looks like the holes used for bolting it down to the crankcase are put in after the fins are turned and sometimes its described as being done first. I would like to avoid having the drill wander but I wonder if an interrupted cut with a parting tool will be worse of an issue to deal with. Please advise.

Im working on the ML Midge and also Boll Aero 18

 

[minh-thanh]

I did both, but not with that engine
I like to cut the fins first .

 

[Jasonb]

Fins first avoids the interrupted cut as you say as well as the risk of swarf getting into one of the holes and jamming things up.

If you use a split point or 4-facet drill it is a lot less likely to wander as it starts on each successive fin.

 

[L98fiero]

Fins first avoids the interrupted cut as you say as well as the risk of swarf getting into one of the holes and jamming things up.

If you use a split point or 4-facet drill it is a lot less likely to wander as it starts on each successive fin.

And, a stub drill helps as well.

 

[creast]

I built the ML Midge and cut fins first. It does mean some light deburring but is ok if drill with light pressure and slow.
Rich