Here we go again . . . MK4

[routercnc]

Next part is the Z ballnut bracket. All started well . . .

Laying it out


Pilot holes for the threaded holes:


Skim the surface to level it:


Machine pocket to house ballnut:
(Toolpaths are fairly basic from Cut2D - gentle ramp into material, then a series of simple circles. No spiral option. But it gets the job done.)



Profile machined most of the way through leaving a bit holding it in place:




All holes drilled to size, tapped, then on the very last hole backing the tap out - it snapped ! Aargh!

Tap was 12mm into the part and bashing and picking was not working. Flatten the end off the centre punch so that was no good.

Got some Alum powder (about £3.50 off ebay for 2x100g) and mixed up a solution with hot water:

Then dropped in the part, and you can see it bubble straight away (bottom right hole).

After a day there were lots of black specs and a general browny dust settled onto the part (hole now top left).


But even after a couple of days it had only eaten about 0.5mm groove in the top of the tap. At this rate it was going to take weeks.

I tried a masonary bit (3mm tungsten carbide tipped) on a very low speed in the pillar drill and this gnawed away at it for about 15 minutes. The drill kept trying to wander off into the aluminium at the sides, so I flipped the part over and put the drill bit into the hole hoping this would guide it. It made a sound like it wasn't enjoying it much but I pressed on. After another 15 minutes of drilling I got to within about 4mm of the surface, and then the drill broke and got stuck in the hole. Luckily I managed to get it out. I've since put the part back in the Alum solution. I think another go with a 3mm masonary bit will have drilled the last bit out, but I think the thread might be beyond use. I could probably live without that bolt and use the other 5 but it is annoying me now. I'll clean it out and see what to do. Could enlarge the hole then make a plug with a flange on it and press it in from the reverse side, then drill and tap into that. Probably tap it before pressing it in just in case !