Luthier CNC

[bluesking]

Following on from my plate design work, yesterday I drilled the various holes:



Everything seemed to go well. I have a mixture of M5, M6 and M12 bolts to accommodate. Many of the holes don't need tapping so I created mostly 5.5, 6.5 & 13mm holes to accommodate the screws.

I also have a bunch of M5 holes that needed tapping. Here I made a bit of a mistake. Really didn't think it would make a difference so I just used a 4mm drill bit I had laying around. Drilling went well, but as soon as I started to tap this happened:



My lack of metalworking experience takes it's first casualty! Today I re-drilled all the offending holes and I think I got away with it overall.

Here's what I have learned:
1) If you want to use a M5 tap, you need a 4.2mm hole. No getting around this. Maybe 4.5mm would also work, but I didn't even try this as 4.2 worked perfectly.
2) If you break a tap in a hole there really isn't any way to recover. You try to drill it out, but because aluminium is so much softer than hardened steel, the drill bit wanders around the tap creating a bit of a disaster.
3) Cutting oil is a mixed blessing. Makes all the work super messy but I think improves results. If doing again I'd drill all the holes dry and use cutting oil just to do the tapping work.

The one hole I messed up was meant to attach to one of my z-axis HIWIN carriages. I'm hoping I can get away with using only 3 out of the 4 holes to mount this. I think this will be fine so I'm not going to bother buying/making a whole new plate for now.