Tapping M4 threads in Octura x4 series

[northernmike]

Has anyone done this? I'm about to attempt it. Any advice would be appreciated! I'll let you know how it goes..

[martin]

The correct size hole for a 4mm x .70 thread is 3.3mm, Octura 1/8" bore prop is bored 3.2mm so the tap will be slightly tight when tapping so you need to take care when tapping using good quality high speed steel taps & thread cutting oil. The most difficult thing tapping a prop out is getting the tap running spot on true to the hole, Not always easy with a slightly under size hole either. Martin.

[northernmike]

Thanks Martin! Maybe I can find a 3.3mm drill...

[martin]

You have to be carefull drilling props as their not the easiest thing to hold so care must be taken & keep fingers well clear. Especially when drilling bronze as drills do bite in bronze. Martin.

[northernmike]

Yes - I'm looking at my vise and thinking very hard about it now. Perhaps I'll need to make a fixture.

[northernmike]

[martin]

Excellent, Screw it onto shaft or reverse it on the tap & rotate to see if its running true. Martin.

[northernmike]

Runs true to my eye, but but better metrics will follow. Did not enlarge the hole - 3.14mm as supplied. On Graupner M4 stubs it is snug, but consistent.

Supported in basic vise and tapped by hand - no mechanical alignment - 60 degree bites at a time, no lube. This is trial #1, of course - I expect to have to improve my methods. If I don't have to - I will call it fantastic luck.

The entire process took about 20 minutes.

[northernmike]

Well, it's not very true.

http://www.youtube.com/watch?v=r7_EEgxjF30

Oh, well. Better next time.

[dasboata]

that could be from the tip on your tap

[northernmike]

that was a haiku! ...

perhaps... but i doubt it. i may try it anyway.