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View Full Version : Boring a prop shaft. Best practice?



Chucknuckle
10-27-2018, 07:16 AM
So I'm in the planning/contemplation stages of building Iain Oughtred's Grey Seal, and I've been reading through some blogs. This fine gentleman ran into a few problems (and came up with some brilliant solutions) when boring his prop shaft.

http://greysealbuilder.blogspot.com/2013/11/metal-things.html

http://greysealbuilder.blogspot.com/2013/12/several-new-holes.html

My thought is, wouldn't it be easier to pre-bore the relevant parts earlier in the construction? The line of the prop shaft will be given in the plans, so prior to fitting the deadwood couldn't you pre-drill it? Or from the other way, through the stern post while the boat is still upside down? Or is waiting until the boat is flipped and mostly finished really the best way to do it?

Also, what is the best way to bore a prop shaft? A barefoot auger guide hole followed by a larger barefoot auger of the appropriate diameter? A homemade cutting bar as shown in the blog? Where would one start in making such a thing? Others have mentioned using metal pipe with a cutting edge to basically cut a dowel out of the wood. Has anyone successfully done this and what was their process? Is there another method I'm missing?

And help appreciated!

Peerie Maa
10-27-2018, 08:57 AM
Definitely a boring bar with a cutter. That way you have a guide at both ends and NO risk of being thrown off line.

Chucknuckle
10-27-2018, 10:07 AM
Any tips for boring that initial guide hole though?

Peerie Maa
10-27-2018, 10:40 AM
Any tips for boring that initial guide hole though?

Your proposal of a barefoot auger run through a guide frame is the way to go.

Gib Etheridge
10-27-2018, 11:33 AM
If you build the shaft log with upper and lower "halves" with the division being the line of the prop shaft you can let in a pilot hole right on the table saw before assembling. If you can find the right router or shaper cutter you can do the entire job before assembling. Assuming that there will be a stern post aft of the log you can then use the pilot or completed boring in the log as a guide to drill out the post.

If a square in cross section "boring" will work you can do it with a dado blade then add a liner bedded in whatever seems appropriate, which could be epoxy around a glass tube or tar around a bronze tube, tar because you may need to remove the bronze tube someday due to corrosion.

Jamie Orr
10-27-2018, 11:41 AM
So I'm in the planning/contemplation stages of building Iain Oughtred's Grey Seal, and I've been reading through some blogs. This fine gentleman ran into a few problems (and came up with some brilliant solutions) when boring his prop shaft.

http://greysealbuilder.blogspot.com/2013/11/metal-things.html

http://greysealbuilder.blogspot.com/2013/12/several-new-holes.html

My thought is, wouldn't it be easier to pre-bore the relevant parts earlier in the construction? The line of the prop shaft will be given in the plans, so prior to fitting the deadwood couldn't you pre-drill it? Or from the other way, through the stern post while the boat is still upside down? Or is waiting until the boat is flipped and mostly finished really the best way to do it?

Also, what is the best way to bore a prop shaft? A barefoot auger guide hole followed by a larger barefoot auger of the appropriate diameter? A homemade cutting bar as shown in the blog? Where would one start in making such a thing? Others have mentioned using metal pipe with a cutting edge to basically cut a dowel out of the wood. Has anyone successfully done this and what was their process? Is there another method I'm missing?

And help appreciated!

I think this is an excellent description of how to do it. A friend and I re-bored my boat to change the shaft angle, we made our own boring bar, the single cutter was made from an old drill bit.
http://www.gartsideboats.com/faq/boring-long-holes.html

Jamie

Gib Etheridge
10-27-2018, 02:05 PM
I've never seen it done but it seems to me that it would be easy, on the bench, to cut a deep dado into the side of the log, install a tube, then fill the remaining space with wood in epoxy with perhaps a couple or three vertical thru bolts or lags for the belt and suspenders effect. If the bolts were accessible one could even skip the epoxy and have future access to the shaft from the side, but I don't know how that would be useful.

stromborg
10-27-2018, 05:48 PM
http://straydogboatworks.com/oughtred/pics/large/largedwgs/Grey-Seal.jpg

The engine is under the cockpit, yes?

A number of us Eun Mara builders laminated the deadwood from a number of smaller pieces, more work initially but less movement of the timbers being better for the epoxy. I think you could figure out the shaft placement on the loft floor and build it in.