Wednesday, February 26, 2014

Action Verbs

"Lathing" is yet another term, like "painting" or "sewing," in which the activity directly indicated by the verb is the smaller part of the total activity.

In painting, you spend far more time in sanding, dusting, taping, and otherwise doing prep work, than you do with a brush or rattle can in your hands. In sewing, the larger part of your time is cutting and pinning, not putting in stitches.

And in lathing, a whole lot of grinding tools, checking measurements, tightening bolts for every actual metal-removing pass.

My lathe learning project is progressing:

This is an excellent learning project for the lathe, as it requires a good variety of operations. Today was grooving, cutting a chamfer, cutting a radius, knurling, drilling, and parting. And many of these operations can be accomplished with a variety of techniques, providing even more chance to learn.

The front grooves here are supposed to be 3/32" according to the plans I drew. The parting tool I ordered from McMaster-Carr arrived Monday -- but unfortunately it doesn't fit in any of the tool holders at TechShop. However, I found in the bit bin a 1/8" parting tool that someone had already partially re-ground for a smaller size. I took over that project and made a custom shape just deep enough to make the cuts I needed.

The next operation to try was the angle. I unlocked the Compound Rest for this, setting it up so I was traversing with the Compound Rest instead of with the Carriage. Several cuts back and forth along that angle, and I had the chamfer I needed.

This was also possibly the way to do the nose radius. I set up for doing this freehand (you operate both the crossfeed and compound rest simultaneously), but decided I didn't want that much a test of my dexterity just yet.

McMaster-Carr to the rescue again. I'd also purchased a pair of cheap carbide-insert RH turning bits. Which are basically a blank of tool steel -- high-speed-steel -- with one end ground and a carbide insert brazed on. So I flipped one over, and using the corner of the grinding wheel created a custom radius tool of high-speed steel. All those videos on grinding tool bits seems to have helped!

Then there was knurling. Stuck the live center back in (if I was really smart I'd flip the thing over and knurl towards the headstock). There's a fair bit of conflicting advice on knurling. Or, rather, there is a school that believes you need to calculate your radius carefully to be a multiple of a whole number of teeth. And there is another school that thinks that knurling tools are designed to slip a little, and will adjust if you give them a chance.

I align with the latter. Particularly when you think about actually cutting a knurl; as you drive in, the effective radius is going to change.

One trick I picked up from the many videos I've been watching is that you don't want to tiptoe up to the knurl. You want to move the tool in aggressively and give it a good chance to start. Well, this advice seemed to work. The main issue I had is I'd cut the angle in the grenade just a little too steep; I couldn't bring the knurling tool all the way in without it rubbing against the other side of the groove. So I had to compromise and bring it in at a slight angle relative to the working face.

Drilling did not go so well. Well; I got a hole, and I didn't break off the bit inside. That's all to the good. But the hole is awful. According to more reading, I needed to take it even slower, backing out the bit even more frequently than I had. I also think I'll get better results not trying to drill through the entire grenade from the front; just drill past the internal shoulder, and do the longer hole from the other side with a larger drill bit.

I also didn't manage to get a good fit with my first try at turning down the 3/8" stock to the right diameter for the button. And I crashed the headstock -- okay, tapped the headstock -- cutting up to the shoulder on that piece, and that was a really good signal it was time to shut down for the day and clean up. Getting the interference fit on the rear of the grenade is going to be an "interesting" exercise and that's best left for another day.

And, yes, that's why the rim looks odd; after the spring is inserted and the plug pressed in, I'll face to the final dimension. And also adjust the shoulder on the rim, and do a little radius on the rim itself.

Meanwhile, the holocron is getting painted:

Okay, that was acrylic wash over Krylon hammered copper. Except that something didn't like the Jenkins Happy Medium I'd used to cut the acrylics, and I ended up having to strip that paint job back to primer and start over again.

And the circuit is coming along:

It is hard to see in this pic (what with the incredibly messy desk and all) but this is me testing the capacitance sensor. A wire is taped to the underside of one of the acrylic pieces making up the holocron body, which in turn is being held by my third hand jig as I wave my hand over it. So far, the sensitivity is less than I would like, but I can get a solid trigger by touching or nearly-touching the side of the holocron, and that's all I really need for this.

There will be a full entry on the build later. Once it is all working.

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