DIYbanter - View Single Post - Replace cutter-head on JWP-16os

dpb

wrote:
On Jun 25, 8:05 am, Jack Stein wrote:
....

I would think only a fraction of the surface would be cutting since
the head is made up of lots of small cutters in a circular spiral, so it
would seem LESS hp would be required than from a 15" knife contacting
all at once?

I don't think that's a good assumption at all. The same work is being
done.

Integral, yes. Instantaneous, no.

The work in the straight-knife version is accomplished in three peaks
with essentially no work in between. In the spiral head multiple knife
head, there are 72 (otomh, roughly right, anyway) knives in 4 or 5 (that
I don't remember) spiral rows. Consequently, there are instead of three
impacts to do the total same amount of work instead of just three, the
actual peak work at an instant is reduced and averaged over more,
smaller-effort-each, work intervals. On at least the Byrd heads, the
cutter faces are also angled slightly instead of being parallel to the
face so that they tend to have a shearing cut that, similar to skewing a
plane reduces the effort as well as helping to reduce tearout on
difficult wood.

Anyway, the main reasons I want one is it handles wild grain better, but
also makes a lot less noise. I don't care much about the noise part but
I figure the reason it makes less noise is because it cuts more
efficiently, ie, needs less HP due to just one small cutter in contact
at a time.

I would expect knives to be a lot more expensive, though.

I don't know what they're going for now; some years ago I did some
comparison and a complete replacement set were about 3X the cost of a
full set of straight knives. But, since the inserts are 4-sided, the
effective cost would be about 4 sets for the price of 3 or roughly a
third less overall. That doesn't account that a set of solid carbide
straight knives may be resharpened at least if there isn't too deep of
knick, etc., but I think knife cost would work out to be roughly
equivalent in the long run from what I have looked at.

That said, I've not owned one; simply from looking a catalog data in the
past and it hasn't been within the last year or so (altho I wouldn't
think relative costs would have changed much though I expect absolutes
are higher than back then)...

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