G'day Chris here and welcome back to Clickspring.
One of the cutting tools required to make this impossible dovetail puzzle
is a narrow taper dovetail cutter like this.
It has an included angle of 22 degrees, and 4 teeth formed by milling 4 straight flutes.
Each tooth has positive rake generated from the way the flutes are milled past the centerline,
And I'll grind in some relief angles behind each tooth after its been hardened.
Starting with this section of oil hardening tool steel,
the first step was to turn the basic profile to shape.
And of course I'm going to need something for the chuck hold onto when I start forming the
tapered section of the cutter, so I'm turning the profile for the shank first.
The cutting teeth need to be concentric with this shank, so I'm removing the 3 jaw chuck,
and using an ER Collet chuck from here on, to give a better result.
There's quite a bit of work sticking out from the collet,
and its all supported by that narrow shank,
so a bit of tailstock support will be needed to get an accurate cut.
Once that support was in place, I formed the tapered profile of the cutter.
At this point the workpiece is essentially a cutter blank, ready to have some teeth formed,
so the next step was to transfer it to the mill to cut the 4 flutes.
Now that most of the shaping of the cutter is complete, it can be taken to a red heat,
quenched in oil to harden, and then slowly tempered it to a light straw color.
Now ideally I'd form the relief angles using a tool cutter grinder, but I don't have one,
so I'm freehand grinding them using this bench grinder.
I'm keeping the contact with the wheel quite short to keep the heat generated to a minimum,
I don't want the temperature to rise so much that it softens those cutting edges.
And at this point the cutter is basically complete, it just needs to have the small burrs removed,
and the cutting edges honed.
And I found that its a particularly easy cutter sharpen; it sits comfortable on the bench,
and a small oilstone runs neatly down the flutes.
OK, so with all edges honed and ready to cut, lets give it a run and see how it performs.
I've used a standard end mill to remove the bulk of the waste stock
from this test piece of aluminium, so that I put the lowest possible burden on the cutter.
And for the most part, it seems to perform quite well.
As always though, there are some limitations.
For one thing it can't be run very hard. If the cutter heats up too much,
the carbon steel will become annealed, and immediately lose its cutting edge.
Its a light duty cutter suited to relatively soft materials.
The speed of the cut at the top of the tool is also much slower than at the bottom,
and the cutting geometry at the top is less than perfect too.
So while the bottom is forming nice chips,
the top is a little more inclined to rub the metal rather than cut it.
It wasn't a huge issue, and a partial solution was to take a finishing pass on either side,
as well as use some abrasive paper to knock down the burr, but still, it's not ideal.
And finally, it's unlikely that the taper I formed on the lathe has survived my
freehand grinding of the relief angles, particularly as I resharpen it.
The accuracy was fine for the project I used this cutter on, but I think its fair to say
that freehand grinding of the relief limits the cutter to relatively low precision work
like profiling and contouring.
Having said all that, it cuts aluminium surprisingly well,
and seems like a reasonable option for low volume, low precision work in softer materials,
particularly if there's nothing available commercially.
Thanks for watching, I'll see you later.
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Thanks again for watching, I'll catch you on the next video.