What diameter hole for the connector to inlet port on an oscillator?

[student123]

On a novice build of the littlemachneshop oscillating engine

http://littlemachineshop.com/Projects/OscillatingEngine.php

I have a Taig lathe & a cheap & cheerful drill press.
Will be test running on compressed air.

I've drilled the two vent holes in the ali upright, for one hole drilled 2.5mm then tapped part way through 3mm for the inlet connector to fit into.
(the second hole I drilled 3mm in error, but that can be an outlet vent -unless I can glue a tube in place?)

To create a 3mm conector my plan is to drill through the shaft of an M3 bolt (ie to create a tube with an M3 ext thread). What diameter hole should I drill?
Alternative suggestions welcome.

Mike

 

[arnoldb]

Mike, a 1mm or 1.5mm hole should do the job for an M3 bolt/screw.

I had a look at the plans - the port holes are specified at 0.125" ~= 3.2mm, so the one you drilled through at 3mm is actually closer to size than the 2.5mm you chose - you don't want the port holes on a wobbler too small, as it will cause it to perform poorly. But rather a bit small than too big!

You might be better off opening the port hole you want to tap to 3mm as well, and then drill it part-way 3.3mm and tap for M4. Then a bit sawn off an m4 bolt or screw with a 1.5 or 2mm hole through would work as air connector.

If you can find tubing with a suitable OD to fit in the hole, it will work just as well if you loctite it in if you are only going to run the engine on compressed air. The loctite is a bit of a no-no for running on steam though as there is heat involved that could cause the loctite to loosen.

Regards, Arnold