Pilot Holes

[IrishPiper42]

Seems to me that this can only work for concave bores, not convex ones. Concert pitch bores tend towards concave, but flat pitch bores are (mostly) convex.

Bill

No, it works for both concave and convex bores.

-Mike

[o'corragain]

Quote:
Seems to me that this can only work for concave bores, not convex ones. Concert pitch bores tend towards concave, but flat pitch bores are (mostly) convex. Bill


Could you elaborate a little more on convex and concave bores?
Thanks, David

[o'corragain]

Quote:
Seems to me that this can only work for concave bores, not convex ones. Concert pitch bores tend towards concave, but flat pitch bores are (mostly) convex. Bill


Could you elaborate a little more on convex and concave bores?
Thanks, David

I think I figured it out, please correct me if I'm wrong. A concave conical bore would be one in which the rate of taper would increase at a point {or points} and then return to the original rate. A convex bore would be one in which the rate of taper would decrease at a point and then return to the original rate. If this is correct how would you be able to complete the convex bore with a reamer, or would you have to ream it to a straight, smaller size and then enlarge the lower part of the bore up to the convex point with the proper reamer and finish the upper part with some other tool? Thanks, David

[PaisleyBuddy]

I've noticed that, they have a little bend/give to them...

Mine doesn't; however it is much heavier in weight than the North American reamer I have seen, which suggests the latter is perhaps an alloy rather than tool steel,but what do I know.

[mirabai]

I've noticed that, they have a little bend/give to them...

Mine doesn't; however it is much heavier in weight than the North American reamer I have seen, which suggests the latter is perhaps an alloy rather than tool steel,but what do I know.

The reamers I use have 4 spiral flutes, are definitely hardened tool steel and do flex when trying to follow a warped bore. This is a particular advantage of this type of reamer in this context since it is able to flex evenly at any position, as opposed to a D or flat cross section reamer. The advantage of a less flexible reamer is that it will want to correct a warped bore which could be good if there is enough wood left before reaming.

Tim B.

[billh]

by 'convex' I mean that the bore lies "outside" the straight cone formed by connecting the throat and bell. By 'concave' I mean that the bore lies "outside", i.e. is smaller than, that cone.

Another way of putting it is that a convex bore is "fatter" in the middle than a perfectly straight-sided cone with the same average rate of taper would be.

You can form a concave bore with multiple long reamers having different rates of taper. Obviously you can't do that with a convex bore, since the rate of taper at the bell end is smaller (steeper) than it is higher up (nearer the throat).

With short section straight reamers you could make at best a rough approximation of a complex bore, especially if all those straight reamers have the same rate of taper; you end up with something rather reminiscent of the "Penny Chanter", with steps here and there.

Bill

[ausdag]

by 'convex' I mean that the bore lies "outside" the straight cone formed by connecting the throat and bell. By 'concave' I mean that the bore lies "outside", i.e. is smaller than, that cone.

Bill, do you mean 'inside' for concave?

Cheers,

DavidG

[billh]

Yes, I meant "inside" for concave, thanks for catching that David.

Bill