Reducing the diameter of a dowel?

[T i m]

Hi all,

Well, it's not a dowel as such but a 1.8m long dinghy oar and I would like to reduce the diameter of the shaft from 45 to 40mm (over about

1m).

I was wondering if there was any 'clever' way of doing it, without requiring a lathe big enough etc but whilst retaining the concentricity / straightness and with std d-i-y level tools?

One way I have thought of is to run the grip and near the blade in some sort of basic 'bearing' and then use a router on a long slide running up and down whilst turning the oar by hand?

Once down to the right diameter (plus a bit, too late for a spar gauge [1]) I should be able to bring it back to the required finish by hand with glass paper.

How do / did they do them in the boatyards pre automation or would they always start off with some round timber?

Cheers, T i m

[1] Unless I fed it though a thicknesser (that I would have to rig up) taking it back to a square section and back to round after that?

[michael adams]

Spokeshave ?4.62 Toolstation

For shaving either spokes or oars.

More expensive models are probably available, the blade is sharpened same as with a hand plane.

michael adams

...

[GB]

Why does it need to be round? When I rowed, the oar shafts were more oblong in shape, with one side completely flat. They were also hollow, but I doubt your dinghy oars are.

Can I ask why you need to reduce them, anyway?

[T i m]

;-)

I think I have one somewhere. ;-)

The only thing is, I'm not sure how 'concentric' I could keep it over the meter of length of oar I need to do. Whilst it doesn't actually matter too much if it's not spot on or not, I was rather hoping for something more semi-automatic that meant I would end up with the right diameter and it still be as true as it is now. ;-)

Cheers, T i m

[T i m]

Valid question ... the quick answer is because:

1) It is at the moment. 2) It will then match the existing and otherwise identical oar I have that is 40mm diameter. 3) So I can get a pair of plastic collars of the same ID and know both oars will fit in the rowlocks. ;-)

Yes, the skulls for our skiff are more like that.

Far too basic for that. ;-)

You can, 'it', and potentially answered above. ;-)

The smaller (8') folding boat came with a pair of oars that looked like they were made from broom handles with some planks fixed on for blades (well, not quite that bad but you get the idea) so I picked up a second hand 'pair' of real oars where one had the collar missing.

Then when I had them picked up and I saw them my first thought was that the shafts were different diameters, and they were, hence my question.

If there was an easy solution (that mostly did itself) I wouldn't mind doing it, partly for the s&g's and because it then gives me a pair of lighter oars to use with this fairly light folding boat.

So, with the router mounted on the bench like a sideways spindle and something that allows me to move it (or the oar) up and down while it trims of about 2mm off all round ... ?

Cheers, T i m

[Brian Gaff]

Might one ask why not make whatever it is to fit into a bigger version to accommodate the size? Brian

[T i m]

Of course one might ask Brian. ;-)

Because, apart from looking a bit strange, packing the thinner oar out somehow to allow it to fit the same size collar as the bigger oar would potentially create a step between the oar and the collar, not allowing the oar to slide out into the rowlock so easily.

Also it means the fatter oar will remain a bit heavier (not sure I'd notice that in use though) and generally, not make 'a pair' of oars.

So,, if I could and could do so easily (as in I don't mind spending a bit of time rigging up a jig as long as the job itself is quick and gives the effect I want).

Cheers, T i m

[nomail]

Take a substantial chunk of wood and a piece of plywood, screw them together and bore a small pilot hole through both, remove the plywood and open out the hole in the wood to be a close fit on the original shaft, bore a hole at right angles and slightly to one side of the main hole, fix a router to the top so that its shaft/cutter pass through the second hole, open out the hole in the plywood plate to be the size of the modified shaft and reattach it to the block of wood. Start the router, put the shaft into the large hole and slowly rotate it, adjust the router depth to give a size that just fits through the smaller hole. Bob's your auntie's brother!

[dennis]

Make a trough 1m long cut a couple of u shapes to hold the dowel at each end of the trough. Make the height of the trouh so that the spoke shave just takes the right amount off. Rotate and shave. The little bit left at the end should be easy to do after the main bit is done.

[T i m]

Hey, yup, that's a clever way. ;-)

So, whilst it would only be about as true as the original oar, that would probably be good enough (for what it is for etc).

Yes, he is actually. ;-)

I think the shaft is thinnest near the blade so I think the ply part with the bigger hole will have to be going on the handle end first, followed by the cutter and the bigger block with the new diameter bored though it (or something). ;-)

I think the trick will be getting enough alignment length for our guide block and getting it down to the right diameter at the extremes at both ends (nothing I couldn't then finish by hand of course). ;-)

Cheers, T i m

[T i m]

Two battens ... ('Contiboard' maybe as they will be level, flat and rigid) on edge on a base board and the 'U' bits across either end ...

Set the U shapes down low enough to get the right final diameter with reference to the top edges of the trough.

The only thing with that is you would have to make sure the oar stayed down in the grooves and I'd probably have to get someone else to turn it (compared with the tube / router solution). However, if I pulled it down at the U bearings, friction might hold it down and still sufficiently me to do it a few degrees at a time.

Sure.

Well, that's another solution, thanks. ;-)

Cheers, T i m

[Brian Gaff]

Hmm, does seem to me to be a bit of a job though. Besides if you wanted lighter oars then.... I'd hate to be in a boat and snap an oar. Brian

[T i m]

Yeah, it's mostly the 'see if I can or I won't bother using the oars' sort of thing.

It's not really that Brian, it's just to make the oars an actual pair and to allow me to be able to use the same size collars etc.

Quite. However, these will still be 5mm bigger diameter than the supplied oars and I don't believe they have any issues with those.

Cheers, T i m

[michael adams]

Before you start you cover the length you want to reduce with dark shoe polish or similar. Then polished up. When you've shaved all that off and are back to clean wood you repeat the process all over again. And repeat until you've reached the desired diameter. Ideally you'd probably want the oar held in the jaws of a workmate.

michael adams

...

Whilst it doesn't actually

[T i m]

Like using 'engineering blue' on steel. ;-)

Interesting solution (thanks) but I think I need something more reliant on mechanics and less on 'craft'. ;-)

e.g. The ideal solution will be one that I can't get wrong. So, as long as I hold the oar in a way that allows me to rotate it reasonably freely (so supported the blade and by the handle) and then move some form of spinning cutter (router / plane etc) up and down the length, or something that fits the oversize oar snugly but allows me to rotate the oar under a cutter ... whilst held off the oar by 2mm or so, we should be good.

With an ideal solution it will probably take longer to set up than to do. ;-)

Cheers, T i m