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prop; after market,

Old 02-22-2021, 04:03 PM
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Default prop; after market,

Can I just drill prop hole straight through?

prop, not available, ( that came with plane has an internal shoulder. 0.128" hole dia for 0.328" and a 0.122" hole for 0.025. essentially precluding mounting prop backward, further establish the "internal shoulder" as the connection of prop to motor shaft.

after market prop ( does not have internal shoulder. the connection of prop to motor shaft would be flat plate 3/4" od .125 id that rotates with shaft. no interference with anything.
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Old 02-22-2021, 04:46 PM
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OK .... NEVER drill a prop hub ... you cannot g'tee it being straight or centred. Many people have ruined props doing it. Once drilled wrong - its virtually impossible to correct.

What you need is a TAPERED REAMER .... these are carpenters tools for opening out mounting holes to fit dowels etc. that are not exact fit for drills. DO NOT buy the rubbish Hobby Shop ones - they are too soft a metal as they are designed for plastics on model cars etc.

You can find these in Builders Shops .... Home Depot .... DIY etc. They are hardened steel and like mine - last a lifetime literally.
I carry one in my flight box for use on the field in case I have to fit new prop.

Some will tell you to buy the Stepped Reamer ..... forget these - they are designed for set diameter shafts and cannot cater for those often found to be a little out. Even if you ream too much ... then just ream to fit a shaft adaptor ring.

Here's APC Propellor Co statement :

Engine Shaft Hole Alignment

The propeller hub aft surface and aft hole are precisely defined during molding. However, post-molding shaft hole drilling may induce minor angular miss-alignment of the propeller with the engine shaft. This hole miss-alignment is avoided by use of a tapered reamer to slightly enlarge the propeller hole forward of the aft surface. This causes the propeller to precisely register with the engine shaft at the aft surface and hole.
Their Tech site :

Well worth a minute reading.

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Old 02-22-2021, 04:52 PM
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OK ... lets clear up another item :

Shaft holes in prop hubs do not need to be uniform front to back lin constant internal diameter. The hole only allows the shaft to locate centrally in the hub and if the hole is tapered - it makes no difference as long as the shaft is held centred.
The thrust and work of motor to prop is transferred via the back flat surface of the prop hub and the 'thrust washer' on the shaft. Tightening the two together till friction locks them together is how thrust is transferred.

Again check the APC link I gave.
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