U Groove -- Tapered ! --

1 view
Skip to first unread message

Karl Hakmiller

unread,
Nov 17, 1994, 5:51:00 PM11/17/94
to

BW>From: wil...@clemson.clemson.edu (Bill Willis)
BW>Date: Tue, 15 Nov 1994 21:57:10 GMT
BW>Subject: U Groove -- Tapered ! -- How?


BW> Anybody know how to cut or otherwise wind up with a tapered,
BW>semi-circular cross-section trough in a 3 foot length of wood? I want to ma
BW>two of these to glue up to obtain a tapered hole through what will later be
BW>turned round.

I'd use a router and a shopmade jig. The jig would consist of a
base and two sides sloped to yield the desired taper over the 3
foot length of the blank. A blank that had been sawed in half
along its long axis would be clamped into the jig so that as the
router rides up the sloping sides it will make an ever shallower
cut. A cove bit with the diameter of the maximum desired bore
radius should do the trick.
---
* QMPro 1.01 ******* * H2O is hot water and CO2 is cold water.

Bill Willis

unread,
Nov 18, 1994, 8:38:31 AM11/18/94
to
In article <9411180...@drs.state.ct.us> karl.ha...@drs.state.ct.us (Karl Hakmiller) writes:

>BW> Anybody know how to cut or otherwise wind up with a tapered,
>BW>semi-circular cross-section trough in a 3 foot length of wood? I want to ma
>BW>two of these to glue up to obtain a tapered hole through what will later be
>BW>turned round.

>I'd use a router and a shopmade jig. The jig would consist of a
>base and two sides sloped to yield the desired taper over the 3
>foot length of the blank. A blank that had been sawed in half
>along its long axis would be clamped into the jig so that as the
>router rides up the sloping sides it will make an ever shallower
>cut. A cove bit with the diameter of the maximum desired bore
>radius should do the trick.

That'll work pretty well with the use of a homemade reamer, which someone else
suggested, but I think you mean to use a core box bit with no more than the
minimum diameter of the U -- otherwise, the cross section of the small end
would have too large a radius.

Thanks,


Bill Willis

bak...@delphi.com

unread,
Nov 22, 1994, 1:39:55 AM11/22/94
to
Bill Willis <wil...@clemson.clemson.edu> writes:

>In article <9411180...@drs.state.ct.us> karl.ha...@drs.state.ct.us (Karl Hakmiller) writes:
>
>>BW> Anybody know how to cut or otherwise wind up with a tapered,
>>BW>semi-circular cross-section trough in a 3 foot length of wood? I want to ma
>>BW>two of these to glue up to obtain a tapered hole through what will later be
>>BW>turned round.
>

Hi,
I think I see a way that might work. First you need a
simple router jig that's sort of a combination fence and
base at least a little over the three feet you mentioned.
It's just a fairly stiff piece of wood (1/2" Baltic Birch
plywood is what I use) with a fence rail (make it at least 2-
3 inches wide so it can be easily clamped) glued to it such
that when the router is moved along the fence, the router bit
will cut flush to the edge of the base.(When you glue on the
fence leave a little extra and trim it with the bit you're
going to use.)
Next lay out the radii on each end of your stock. Use a
cove bit (I think that's what it's called, it'll cut a
semicircle shape) the same diameter as the tapered end and
set the depth so that when the router is sitting on the jig
the bit will cut down to the deepest part of the larger
diameter hole. Shim the jig at the tapered end so that the
bit will cut just deep enough to cut a semicircle rather than
a groove. Clamp the jig to the work so that the center of the
bit will travel along the centerline of your cutout, and make
a pass. Don't forget to put the shim at the tapered end. The
idea is to flare the jig at the wide a little and make
another pass, flare the jig at the wide end a little and make
another pass etc., etc., etc. Each time you flare out the
jig, you're going to have to shim the jig a little so that
the bit will always be cutting tangent to the layout line at
the wide end. With a little bit of sanding you should wind up
with half of a pretty true tapered cylinder.
It sounds pretty tedious, but I'd bet that with some quick
release clamps, a supply of shingles, and a convenient way of
clamping the jig relative to the stock (largely oversized
stock would be ideal) it wouldn't take more than an hour to
do the machining.
It just occurred to me that the shim for the tapered end
should be beveled to match the angle of the jig for the first
pass so that as the other end is raised the depth of cut
won't change. It would also be a good idea to use some
intermediate shims for each setup so that the jig won't sag
into the work. They wouldn't need to be clamped or anything
like that, just stuck in here and there to keep the jig flat.
I'm not sure how well I've conveyed my concept, but if you
want to ask about any of it, feel free to email.
Good luck,
Steve Baker
PS Let me know how you make out.
Reply all
Reply to author
Forward
0 new messages