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AdeV:
Hi Gerrit,

It would be simple enough to shim the bed... but I can't guarantee it won't move horizontally, which would bugger up my milled slots  :doh: Anyway, for my purposes, it's good enough, I'll be drilling right through into the plastic anyway. I'm also not 100% convinced it's completely flat either - I believe there are programs out there to "map" the bed height for these type of machines; not something I plan to do, but probably worth doing if you're doing a very fine engraving (but, if you're doing very fine work.. would you do it on an unmodified sub £150/$200 machine from China...?)

AdeV:
Can you guess what it is yet?

 :lol:

OK.. that's not fair. This little mini-project took a couple of hours on the lathe, once I'd finished procrastinating. I'll keep the writing short this time...

Photo 1: Some copper bar I bought ages ago to make spark eroder electrodes from; but which is proving rather useful today; and a lump of "mystery steel", I think it might have been a ginormous pin out of something, but goodness knows what. It's a bit of a bear to cut, but the price was right: £free  :med:

Photo 2: After chucking up the copper bar, turn around 1/2" down to 0.656", the major diameter for a 3/8" BSP thread. Chosen because it fits comfortably inside the diameter copper I have, the thread count is decent for such a big thread, and I have both taps and dies and the tooling to fit them  :headbang: I really need to sort my taps/dies/tapping handles/die holders out... a boring job for another day. Photo 3 shows the stringy, gummy, razor sharp swarf that copper makes. It's evil stuff to turn. I did wonder about work hardening it, but apparently it's its day off?  :scratch:

Photo 4: I cut a gutter at what will be the mating face, just so I could run the die right up to the shoulder & know it's cut full depth all the way. Follow up with the die, and a 19tpi thread file just to clean them up a bit.

Photo 5 & 6: Cut the threads down so around 3 were left (the part was far too tall), then parted off, leaving approximately 0.1285"/3.26mm of original diameter copper. OK, I admit it, those measurements were made just now as I write this... I left "enough" on.

That's it for the copper... for the moment.

AdeV:
Moving on, the steel goes in, and using one of those new-old carbide bits I was asking about the other week, was roughed down to something approaching its final dimension. The cutter is amazing - it needs a huge depth of cut, and it needs to be really thrown at the workpiece, otherwise it makes blue/black chips. Fantastic for hogging off big bits of material, which is handy, as that's what was needed today  :palm:

Photo 1: The heavy cuts have been taken, and the middle drilled out to 15mm to a depth of just under 1/2" (pointy bit), leaving approx 0.400" usable depth.

Photo 2 & 3: Setup for tapping (taper tap, followed by a plug tap (not shown). I start it under power @ 17rpm, but stop after a few turns and take over tapping by hand. I want to feel the bottom of the hole before the tap breaks, not afterwards...  :zap:

No photos of the finished thread. Well... that's not strictly true - I took three photos, and you can't see the damn thread on any of them! The contrast in the metal just isn't big enough... it all just looks like it's had a boring bar fitted with an axe head up its spout... Anyway...

Photo 4: After a bit of a cleanup with a brush, the copper part is now screwed in (whilst the thing is still on the lathe). It's a decent fit, requiring a pair of pliers to move it the last few turns. All remaining operations will try to force it to tighten up, so I'm not worried about that gummy muck from digging in and breaking the tool (you can absolutely guarantee it would do it if the cut was trying to loosen the thread....).

Photo 5 & 6: Trimmed down to the same OD, with just a skim taken off the copper. The surface finish really is that bad. I should have probably used oil.

Photo 7 & 8: Almost there now! The part has been parted off from the stock, turned around in the chuck & faced, and given a generous chamfer. In use, the copper side sits downwards - hence, a copper-bottomed project*

One more operation done (but not shown), I've drilled/tapped an M6 threaded hole in the side, about 1/2 way up, and above the copper baseline (but drilled/tapped into the copper slug). This will take a copper screw, with a smaller hole drilled down its centre... except that I don't have an M6 die I can adequately hold just now, so we're at a temporary haitus.

Anyway.... can you guess what it is now?  Answers later/tomorrow...

AdeV:
Lacking patience, but recalling that I recently bought an indexable threading tool.... much haste was made to the lathe! Miracle of miracles, the threading tool was already in a QC toolholder! No height adjuster yet ( :palm:) so I just eyeballed it in, after turning down ~10mm of that copper bar to 6mm. Got a fantastic surface finish... I wish I'd photographed it, but it was being turned into an icky thread anyway...

So: Switch the lathe into French Mode, reverse the reverser, etc. and dial in a 1mm thread pitch... and off!

I wish I'd recorded it with a video camera (or even a stills camera TBH), because it worked surprisingly well, even though I thought I'd lunched it at one point with a slightly over-aggressive cut. Still, after 6 or 7 passes, feeling my way to depth, it got to the point where it'd screw in, part way at least. That'll do for me tommy! So, I drilled a 1.5mm hole through the middle (that cost me a 1.5mm drillbit, I just HAD to have one more peck at it didn't I?  :wack: Screwed it into the main lump as far as it wanted to go & parted it off with a hacksaw. Using the same hacksaw I cut a slot across the middle for a screwdriver.

The result can be seen in photo 1, with a 50p for scale. If you're watching this in the colonies, that's about the size of a silver dollar. But not the value, unfortunately...

Next up, thread a wire through the 'ole (photo 2), solder it up (hence the copper; photo 3), and screw it into the block as tight as it'll go given the means I have to actually tighten it (i.e. sod all!) See photo 4 for the finished item.


Now, as I'm sure you've guessed, this is the probe "puck" for my CNC machine (hence being here in this thread  :palm:) There's a couple of ways I'll be able to use it. Toolbit mounted in the motor is electrically attached to the motor body - which is great; so I'll attach a wire to the motor body going back to one of the probe pins. The other will go to the puck. If I'm drilling a circuit board, I can simply place the puck on the PCB, and use the copper surface itself to get the Z=0 point. If I'm engraving/drilling something non-metallic (or a single-sided PCB copper-side-down), then I can simply measure down to the puck itself, which - serendipitously - is exactly 15.55mm high. So probe to the puck, set Z at 15.55 minus the stock height.

So, there we go! Just got to connect it all up to the machine, maybe make a little holder so it sits out of the way when not in use, and that's another useful feature of the machine enabled  :thumbup:


FAQs:
Q: Why the copper screw?
A: I did actually make another one, which I tried to solder the wire to directly. Problem was the solder froze waaay to quickly, and I just couldn't get enough local heat into it to make it melt again. And it looked a mess.

Q: Why didn't you just make the whole thing out of copper?
A: Shut up.

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