G'day Chris here, and welcome back to Clickspring.
I'm about to make some brass thumbwheels, with a vintage style rope knurl.
But before I can form the knurl pattern, I need to shape the brass perimeter,
so that the knurling tool will work correctly,
and I'm going to do it using a form tool like this.
The profile of the cutter is reasonably straight forward, but the relief angles require a bit of planning.
I've chosen 10 degrees as the relief angle, and I should be able to take care of these front faces on the mill.
Ideally I'd cut the central section with a tapered end mill, but I don't have one.
So instead I'll drill it out and then finish it off by hand using a file.
So starting with some 1/4" O1 tool steel,
I cut off a section, and then squared it up on the mill.
Using this angle block, I set the work on a 10 degree angle in the vise, and then milled a datum face.
I'm going to use the digital readout and this sharpened carbide rod to mark out some key points and lines.
I milled a small flat for the drill point, and then drilled out the central section of the cutter profile.
Ok so next I need to mill the work down to this reference line, as well as across to this corner,
while at the same time generating the relief angles.
I can take care of the main relief angle in a similar way as before,
by using the angle block to tilt the work in the vise.
And the second angle can be generated by using the swivel base of the vise.
It's not super accurate, but the relief angles don't need to be overly precise,
so its close enough for what I'm doing here today.
This section here needs to be profiled into a curve,
while at the same time generating the 10 degree relief.
I think the easiest way to tackle this is to use the belt sander,
so I've tilted the table to 10 degrees, to match the other face angles,
and then using a 400 grit belt, I formed the curve.
The curved section terminates at the point I marked out with the dro,
and I've sanded as far into the corner as I dared, without risking the profile.
All it needs now is for the curve in the center to be flared out towards the base, sort of similar to this corner here.
I'm using a fine cut file to do the shaping,
and again I'm being as careful as I can to avoid altering that top profile.
A quick rub on an oilstone takes care of the small burrs, and that's the bulk of the hard work done.
The top profile has come through the process mostly unscathed,
and all of the cutting edges now have the required relief.
The last step is to quench harden the steel, and temper the cutting edge to a light straw.
A quick polish on this oilstone, and its ready to be put to work.
A form tool like is a great way to get a repeatable profile onto a short run of parts.
There's a few drawbacks in using them though, that are worth mentioning.
Firstly, there's a lot of cutter surface in contact with the work, particularly when it gets to the full depth,
so it really is quite hard work for a small lathe like this.
This cutter is about 15mm wide, and I'd say that its at the upper limit of what my lathe can cope with before it simply stalls.
Secondly chatter on a tool like this is pretty much unavoidable.
But I've found that using a low rpm and keeping everything as rigid as possible makes it quite manageable.
Thanks for watching, I'll see you later.
If you'd like to see how the rope knurl pattern turned out, here's the video covering that process.
And if you're new to Clickspring, thanks for dropping by.
I post regular home machine shop project videos, so be sure to hit that subscribe button.
Thanks again for watching, I'll catch you on the next video