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Quick prop bore centering for small props

By hand only and no precision guaranteed.

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Chuck Plains25/04/2016 12:06:19
1096 forum posts
244 photos

I should have thought of this ages ago. I'm using a pilot drill + countersink wood working drill. The only issue is that all the countersinks are 10mm diameter.

The pilot drill in this instance is 5mm, which fits the prop center perfectly. Yes, it's a cheap prop and the through hole is not necessarily accurate, but it's going on a foamy slow flyer.


Quick and cheap prop centering

These were a cheap set of countersinks from Ebay  and the adjustable countersink cutters are not hardened. So, ironically, although they wouldn't be any use to regular carpenter, it means that I can probably turn one on my lathe if I need to reduce the cutter. And I also reckon I can make bigger cutters and depth collars.

Edited By Chuck Plains on 25/04/2016 12:06:58

Edited By Chuck Plains on 25/04/2016 12:10:01

Edited By Chuck Plains on 25/04/2016 12:11:00

Chuck Plains25/04/2016 18:40:58
1096 forum posts
244 photos

Just as a by the way, the pilot drills in this are sized at 6.0mm, 5.5mm, 5.0mm, 4.5mm, 4.0mm, 3.5mm and 3.0mm.

I'll be putting one of the countersink cutters up on my lathe this evening, to see if I can just reduce the size to the standard 9.5 that most prop makers use for their usual bore spacers.

Biggles' Elder Brother - Moderator25/04/2016 19:17:18
15748 forum posts
1460 photos

Nice cheap and cheerful solution for a low stress application. smile


Chuck Plains25/04/2016 23:21:43
1096 forum posts
244 photos

Well exactly.

The cutter turns out to be case hardened at the business end, so I had to reduce the diameter using my diamond lap stone. AND I have to say that the whole lot of them are not very concentric. But it was not made with precision in mind. Some are better than others.

I've now drilled out the center of one cheap orange prop and countersunk the hub to 9.5mm. An APC prop spacer fits nicely, but the whole deal is slightly eccentric. As expected, the center bore isn't exactly central. But for slow and park flyers, this should be fine.

small center.jpg

Low speed with the drill/driver.

low revs.jpg


spacer fitted.jpg

I have a prop balancer arriving soon, so I'll throw it on that and see what's what. But I've already flown two different props after resizing the bore in this way. One was my slow stick and the other was a foamy trainer/practice jobby. Both worked ok, with no noticeable vibration.

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