Re: [MedievalSawdust] Cutting octagonals on a slope
- For this math to work:
1) Save the cutoff, then tape it back on afterwards to keep two flat sides -
one flat on the tablesaw, one flat on your taper jig.
(if the cutoff is too small, cut something out of scrap to use)
You don't have to keep the octagonal cuts, as the calculations are based on
your original flat sides.
2) I assume you have a taper jig which you used to make the first tapers.
sides S: 8
Angle A = 90-(180/S)
taper jig J: atan(sin(T)/tan(S))
blade tilt B: asin(cos(S)*cos(T))
These numbers give you half the angle, so multiply times two (I was using them
for tapering staves).
3x3 -> 1.5x1.5 = .75 taper per side @ (unknown distance).
assuming table height of approximately 30" we'd get:
T = atan(.75/30) = 1.432deg
A = 90-(180/8) = 67.5 deg
J = .593deg
B = 22.493deg
So, your blade should be at 44.985degrees (might as well be 45),
and your taper jig at 1.186deg
I haven't actually done this for outside cuts like you are doing, but I'm
fairly sure the math works the same compared to the mugs I was making.
On Sun, Dec 02, 2007 at 09:17:37PM -0600, Rhys Terafan Greydragon did say:
> Greetings all,--
> I am hoping someone knows a good trick for "octagonalizing" a sloped
> piece of wood.
> I have a 3 x 3 that is sloped on all 4 sides down to 1.5 x 1.5...
> (that is what I want).
> What I now want to do is octagonalize it so all 8 sides are even and all
> narrow down evenly from the big end to the small end. Anyone have any
> tips, tricks, or good ideas??
> I can do it with a drawknife and a spokeshave, but I am looking for a
> Master Rhys Terafan Greydragon terafan@...
> Brewer, Tent and Furniture maker, and other things I can't remember...
> Visible links
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- Rhys,Consider using a band saw with a tapering jig. Cut each of the tapers but do NOT cut all the way through. leave some room at the bottom and shut off the saw and pull the piece off and give it a turn If you leave about 1/2 an inch still connected you still have a complete thickness at both ends of the piece which should allow it to be solid in the jig.You can then cut through the rest of the way with a tool of choice or if you start with the piece about 1 inch longer, you can very carefully cut off that last inch with a power miter / chop saw.Please work out any problems out on a test piece first. And let us know how which ever idea you use works out.Johannes MachiavelliOn Dec 2, 2007 9:17 PM, Rhys Terafan Greydragon < terafan@...> wrote:Greetings all,I am hoping someone knows a good trick for "octagonalizing" a sloped piece of wood.I have a 3 x 3 that is sloped on all 4 sides down to 1.5 x 1.5... (that is what I want).What I now want to do is octagonalize it so all 8 sides are even and all narrow down evenly from the big end to the small end. Anyone have any tips, tricks, or good ideas??I can do it with a drawknife and a spokeshave, but I am looking for a power-tool-method...
Master Rhys Terafan Greydragon terafan@...
Brewer, Tent and Furniture maker, and other things I can't remember...
Lord Johannes Machiavelli
Shire of Rokkehealden
Kingdom of the Middle
- If you have assess to a good library there is an article in Wooden Boat
#91 on mast building that includes a very simple tool to scribe accurate
lines for octagonalizing a timber. The relevant couple of sentances are
Start by taking the mast from a rectangular to an octagonal section.
For our mast we made a set of simple marking gauges from scraps of 3/4x1
1/2 lumber, with finish nails for the guide pins and scribers. In use,
the gauges are held diagonally across the mast, the guide pins
determining the angle. As this angle changes with the dimensions of the
mast, the gauge automatically divides the face into the correct
proportions for the octagonal section. The circular saw was used to
rough out the octagonal shape. Be careful here - make sure you don't
stray inside the guidelines. The jointer plane is ideal for completing
this stage accurately.
I don't know if I can do an accurate drawing but it looks something like
l Scrap lumber
l l l
l short internal nails are the scribers
l long external nails are the guide pins
a b c
Hope that helps. If necessary I can scan and send the two pages from
that article about it.
jay sabath wrote:
> Consider using a band saw with a tapering jig. Cut each of the tapers
> but do NOT cut all the way through. leave some room at the bottom and
> shut off the saw and pull the piece off and give it a turn If you
> leave about 1/2 an inch still connected you still have a complete
> thickness at both ends of the piece which should allow it to be solid
> in the jig.
> You can then cut through the rest of the way with a tool of choice or
> if you start with the piece about 1 inch longer, you can very
> carefully cut off that last inch with a power miter / chop saw.
> Please work out any problems out on a test piece first. And let us
> know how which ever idea you use works out.
> Johannes Machiavelli
> On Dec 2, 2007 9:17 PM, Rhys Terafan Greydragon <
> terafan@... <mailto:terafan@...>> wrote:
> Greetings all,
> I am hoping someone knows a good trick for "octagonalizing" a
> sloped piece of wood.
> I have a 3 x 3 that is sloped on all 4 sides down to 1.5 x
> 1.5... (that is what I want).
> What I now want to do is octagonalize it so all 8 sides are even
> and all narrow down evenly from the big end to the small end.
> Anyone have any tips, tricks, or good ideas??
> I can do it with a drawknife and a spokeshave, but I am looking
> for a power-tool-method...
> Master Rhys Terafan Greydragon terafan@...
> Brewer, Tent and Furniture maker, and other things I can't
> Lord Johannes Machiavelli
> Shire of Rokkehealden
> Kingdom of the Middle