Off-center drilling jigs for shafts

Kelly_Guy said:
I have a lot of near perfect dowels (in terms of runoff) where the center grain line from one end runs the entire length, but is not quite at the center of the other end. Since I stress over details (whether the topic warrants it or not), I thought I would try making some jigs to "center" drill the dowels at a bias to straighten out the grain center to center.

In the first picture, the 3 jigs, made of delrin ofcourse, are bored to just larger than the OD of my shaft dowels for a snug fit. The depth of the bore is 2 inches. The 3/16" holes drilled through the solid portion is about 3/4" long. A #2 center drill fits very snug in the hole, so it locates well drilling by hand. The jig on the far left has the center hole drilled offcenter .04", the middle one .08", and the one on far right is .16" from center. Regarding the two shaft dowels above the two jigs, I drew a line from the intended joint end following the center grain line to the other end, and then selected the appropriate jig that comes closest to where the grain line runs. The 2nd picture shows the sleeve over the dowel, with the #2 center drill in place. Obviously, the hand drill is removed for the picture.

The .04" offcenter jig can be used for the joint end in conjunction with the others at the tip end to cover a wide range of offsets when taking into account both ends, .04", .08", .12", .16", or .20". I also scored a V mark on each jig on the side where the center hole is offset toward as a witness mark to help line up the jig on the dowel when drilling.

They seem to work pretty well, so I thought I would share the pictures and idea. I imagine this has been done before, but I came up with the idea myself and figured out how to drill the holes in the jigs accurately in terms of the .04/.08/.16 offsets.

I would be glad to make a set of 3 (bored to your specs) for a resonable price if there is any interest.

Kelly

jig1.jpg




jig2.jpg
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Once you locate where you want your centers to be drill a small center with a hand electric drill put the shaft between centers and turn it true before you install an insert. If you do it the way you are showing it will not be true to the center line of the shaft.
 
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macguy said:
You should put the shaft between centers and turn it true before you install an insert. If you do it the way you are showing it will not be true to the center line of the shaft.
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Sorry, not sure what you mean by installing an insert. The pictures are not about installing an insert, they are about establishing the initial center drill holes for turning between centers so that you completely eliminate grain run off in near perfect dowels.

Kelly

EDIT: I see you edited your post. I guess I see what you are saying, but these are 1" dowels before any cuts are taken. They are a long ways off from having an insert installed in them, and once turned between centers to a sufficient diameter that there is no oval (very likely the first taper on most of them) at the tip end, the ends can be faced, and new center holes drilled while chucked up in the lathe after facing so the angle of the center holes are true to the axis of the shaft.
 
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Kelly_Guy said:
Sorry, not sure what you mean by installing an insert. The pictures are not about installing an insert, they are about establishing the initial center drill holes for turning between centers so that you completely eliminate grain run off in near perfect dowels.

Kelly
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Ok then that is what I was saying. It looked like you were wanting to install an insert off center to keep the center line you wanted before turning the shaft. I just find the line I want and tap a little dimple and turn off the high stuff giving me the center line I want.
 
macguy said:
Ok then that is what I was saying. It looked like you were wanting to install an insert off center to keep the center line you wanted before turning the shaft. I just find the line I want and tap a little dimple and turn off the high stuff giving me the center line I want.
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You can certainly eyeball it and tap with a punch or center drill by hand or whatever. I just wanted something more repeatable and systematic for shaft dowels, and didn't trust myself to always get it positioned exactly where I want to and not push it out too close to the edge. With the largest offset jig, I know the hole will only be .16 offcenter, still plenty of meat at the tip end to work with once turned round. I still have to decide which end is which, and which line I want.

I just eyeball like you said for butt stock squares when I want to straighten out grain or maximize figure.

Kelly
 
What happens to the spine of the shaft as you're off-set cutting to eliminate run-off ? Doesn't it wind-up off center as a result ?
 
KJ Cues said:
What happens to the spine of the shaft as you're off-set cutting to eliminate run-off ? Doesn't it wind-up off center as a result ?
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No. If that were true, every shaft that has grain run off to begin with would have a spine that ran off. The spine is defined by the center of the dowel, and runs through the dowel in the same direction as the grain lines, but does not necessary follow a grain line. It is independent from whether there is any grain run off, but it is correlated with the position of the center grain line for whatever section you look at. The spine you see is the pattern made from the flecks in the wood, not a grain line.

If you take a square, unless the grain lines run diagonally through the square, the square will have two "quarter sawn" sides, and two "flat sawn" sides. When turned round, the spine will be at the center of the quarter sawn sides, regardless of run off the length of the square in a typical straight grained piece of wood. Offsetting the center drill perpendicular to the axis of the shaft (the axis that shares a perfectly centered grain line with no run off) to reduce the run off will not make that spine pattern go away when turned between the new centers, and will only strengthen a theoretical spine if it affects it at all.

Kelly
 
Kelly_Guy said:
No. If that were true, every shaft that has grain run off to begin with would have a spine that ran off. The spine is defined by the center of the dowel, and runs through the dowel in the same direction as the grain lines, but does not necessary follow a grain line. It is independent from whether there is any grain run off, but it is correlated with the position of the center grain line for whatever section you look at. The spine you see is the pattern made from the flecks in the wood, not a grain line.

If you take a square, unless the grain lines run diagonally through the square, the square will have two "quarter sawn" sides, and two "flat sawn" sides. When turned round, the spine will be at the center of the quarter sawn sides, regardless of run off the length of the square in a typical straight grained piece of wood. Offsetting the center drill perpendicular to the axis of the shaft (the axis that shares a perfectly centered grain line with no run off) to reduce the run off will not make that spine pattern go away when turned between the new centers, and will only strengthen a theoretical spine if it affects it at all.

Kelly
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Dude you know a lot about wood!!!
 
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