Spar gauge.

[squib]

There was a post recently about rounding timber and it seems that the tool needed for marking out is a spar gauge, the nice thing about them is that they can mark timber that has been tapered in the square first .
Here is a pic (hopefully) of the style we used to use.
The two pins are spaced 7, 10, 7 from memory and the gauge is skewed across the spar, the gauge only marks 8 sides then by eye to 16 and then 32 and sanded.
I used to really enjoy spar making as it allowed the use of the adze , drawknife and my old wooden hollow or bollow planes none of which get much use these days.
I suppose i ought to mention, even in the handtool section, that my old makita handplaner took a serious bashing making masts!
cheers Squib.

 

[bugbear]

The two pins are spaced 7, 10, 7 from memory and the gauge is skewed across the spar

So the (e.g.) left pin is 7/24 of the way across, which is 0.291

That's more than near enough for the purpose of the gauge - the true value should be

1 - sqrt(2)/2 ~= .29289321881345247560

(it's simple octagon within a square geometry)

BugBear

 

[squib]

I am glad i remembered right then , thanks BB.
Here is a pic of a nice one that is a copy of one in Mystic Seaport museum.

 

[Alf]

Knew I'd got mine stashed online somewhere; here 'tis. What a beauty, eh...? Seem to have done 5-7-5; I will await BB to tell me how far off I am. I used pencils rather than pins 'cos I was marking up octagons, so wouldn't be removing the pin mark. Very useful little device; good idea to highlight it, Squib.

 

[knappers]

Just spotted this thread, and may be being a bit thick, but what for / how is this used?

Si.

 

[Steve Maskery]

Just spotted this thread, and may be being a bit thick, but what for / how is this used?

Si.

It's used for marking a square section of timber into an octagon. Wen the corners are cut off to the marked lines, producing said octagon, the nxt lot of corners is removed and so on until the workpiece is round in section.

FWIW this is how I mark a square blank for sawing to an octagon before turning:

Set a pencil gauge to the distance from one corner of the square to the centre of the square. Then mark down all the sides of the blank at this setting. Those lines are the octagon lines, so by sawing to them the workpiece becomes much more amenable to being turned without knocking off huge corners.

I don't know if this produces a mathematically true octagon, but it good enough for workshop use in this application.

S

 

[bugbear]

Seem to have done 5-7-5; I will await BB to tell me how far off I am.

5/(5+7+5) = 0.294

Interestingly that's MORE accurate than squibs 7-10-7 at 0.291, given that we're aiming for 0.293

BugBear

 

[knappers]

:-D Thanks Steve.

Si.

 

[squib]

Here is a link to a famous firm of spar makers, no connection to me, and it shows the gauge in action and how the mast is made.

http://www.collars.co.uk/downloads/Maki ... n_Mast.pdf


And here is the theory and i think its a little more accurate than mine as for mast and spar making one is only roughing out at this stage.

 

[Alf]

Seem to have done 5-7-5; I will await BB to tell me how far off I am.

5/(5+7+5) = 0.294

Interestingly that's MORE accurate than squibs 7-10-7 at 0.291, given that we're aiming for 0.293

Eye thank ewe. *takes bow* (Pretty sure I nicked the proportions from a message on The Porch akshully )

 

[Steve Maskery]

I think it's all wrong.

I thought that might get your attention.

The original sketch at the top is OK, but the Veritas one (and I'm not knocking LV in general, for whom I have a great deal of time), does not take into account the diameter of the guide pins. They are measured on centres but have a finite diameter, which alters their guide positions.

It would be more accurate if the outside spacing were increased by the radius of the guide pins, but even that would change if the angle of presentation changes.

I'm not arguing with the efficacy of the system, you understand, just the accuracy and precision of the mathematics.


Pernickety Steve

 

[Alf]

I think you should take into account the width of the pencil line too, Steve... For the record, you should blame me rather than LV. For the purpose it's more than accurate enough, but yep, for the engineer's amongst you, it is indeed an abomination. It's worse - the dowels aren't even at 90°. Eeek! Don't worry, I'll report for my stoning in the forum square tomorrow morning... :lol: