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Old December 23rd 18, 05:24 PM posted to rec.crafts.metalworking
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Default Home Made Indexable Dovetail Cutter

I sat down and thought my way through making one. How I would turn it on
the lathe, then how I would fixture it on the mill, and how I would cut it.
In some ways its more of a pain to make than the spring loaded extension
compression tapper. Now my thought if maybe misguided on the tapper was I
planned to make several of them (and I will) and maybe even sell them (which
I probably will not).

For an indexable dovtail cutter I couldn't make one any cheaper (much more
really) than an import from somebody like Shars. I could make one that is
satisfactory, but so does the outfit who makes the ones with the Shars
label. The only real benefit I would get from making one would be the
experience and additional skills in my arsenal. Now that does have real
value. My experience making the TC tapper showed that if only to myself.

The thing is I run a one man homeshop. It’s a real business. Its my full
time job, and it makes a few dollars that I have to pay taxes on at the end
of the year. My time is finite. In fact its probably my most valuable
resource. I have things I want to make using a reasonably stiff dovetail
cutter. I finally decided it was more valuable use of my time to make the
parts rather than the tools in this case. I have not paid myself as much
per hour as I used to charge as a contractor, but time does add up and have
real value. A little over $50 for an indexable dovetail cutter from Shars
smokes the time it would take me to make one (1) and realistically I only
need one. Well until I wear it out or crash it into a part and break it.
Maybe if I needed ten of them all the same...

I like making tools. Its fun and sometimes challenging. I also like making
parts. Its fun and since I do more than 90% custom work its always
challenging. In this case I'll be making parts not tools.

Of course even thinking my way through the process I learned a couple
things. Some I am sure will be painfully obvious to most of you. I may
have even known them myself, but not really consciously.

The first thing you have to do when making a dovetail cutter is select an
insert. In case you missed it that is THE FIRST thing you need to do. When
I was looking up tool and insert prices I noticed sometimes a vendor had the
tool, but they were out of stock on the inserts. Of course I had to make
sure those were common readily available inserts elsewhere. Most were, but
initial searches didn't always show them. I knew I had to have a strong
triangle insert.

TNMG is the strongest triangle insert I know of. Unfortunately it has no
rake angle. That's set by the tool that holds it. Well that just won't
work. If its mounted straight it won't cut because the zero rake will cause
the back (bottom) of the insert to rub and break off that extra edge on the
other side. If its set at an angle it won't cut a 60 degree dovetail.
Something rather less instead. Nope. No good.

TCMT is pretty strong its has some rake angle (7 degrees), and can be
mounted square, but depending on the thickness of the insert may only be
usable on larger diameter dovetail cutters. The trailing edge could still
rub. That's fine I suppose if you are cutting making outside cuts and have
a machine powerful enough to provide suitable horsepower at the lower RPM
required for a larger diameter cutter.

TDX or TDEX (are they the same thing?) have a 15 degree rake. This allows
for small diameter higher RPM (relatively) usage. It has good clearance.
It will not rub unless you go out of your way to plan a tool with poor
geometry. Its also not as strong maybe as TCMT and like TCMT has half as
many cutting edges as TNMG. Ok, for smaller or lower power machines it (or
something very similar) may be the best option.

The difficulty of planning the tool itself. It depends on what you are
going to cut. For something like a lathe tool holder its not all that
important. Really. If its close it will lock up, and the adjusting screw
sets the height. I have seen lathe tool holders made by welding two round
rods to the back of a block. Its not pretty, but in a pinch it works. For
a live (is that the right term) sliding dovetail it might be a little more
important that both sides mate up well. This means making your dovetail
cutter well. It will work best if the cutting edge is EXACTLY on the center
line of the tool. This goes back to insert choice. You need to choose an
insert and plan around its thickness. The reality is if you are pretty
close it will probably work ok, but pretty close is affected by variance of
the inserts as well. If you have done much research on inserts you will
find they have tolerances they are supposed to fall within a range. If you
are at the edge of the acceptable tolerance for your tool, and the insert is
at the edge of its tolerance range you may have a measurable out of
tolerance for your finished dovetail.

Ok, if you have read this far it should be painfully obvious I am NOT a tool
and die maker. Its might also be apparent I spent some time thinking about

Along with reading and looking at manufacturer and distributor information I
also watched a number of YouTube videos of various guys. One was, "I just
picked a insert I had that didn't fit any of my tools," and another was "I'm
just making a single insert tool so the exact depth and position isn't that
important." One clearly did not properly support (in my opinion the unused
edges of the insert. CRINGE! In my early YouTube video watching some of
those comments were taken at face value, but I've learn from watching
YouTube videos you have to watch a minimum of five and preferably ten
different videos on the same subject. Then apply your brain and see what
actually makes sense. A fellow named Randy Richards "RR in the Shop" seemed
to do the nicest job, and several people where clearly trying to copy him in
their videos. The more honest ones said so. There were even videos where
people just showed a Randy Richards dovetail cutter cutting (testing) a

Then there is the nuance of multiple flutes. One flute is very doable for
anybody who takes the time to learn how to do it properly and defines
reasonable tolerances for themselves. The basic preparatory lathe work is
unchanged, The secondary flutes all have to match and you have to be able
to repeat positioning of the insert accurately for every flute. Maybe it
doesn't matter so much for a fast heavy roughing pass (do you even do fast
heavy roughing with a tool like this), but for a semi finish pass and
certainly for a finish pass you are likely to have only one insert doing all
the cutting unless you have been amazing in your tool design, setup, and

My conclusion. I spent more time learning how to make an indexable dovetail
cutter than its equal value to buy several of them retail.

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