Sunday, 23 June 2019

Finishing operations - Z axis bracket

Counterboring the fixing hole:
Not much point bothering to create a toolpath for this. The hole needs to be bored out 12.5mm to clear the bolt head, so I'll use a handy 1/2" 4 flute end mill. The shoulder is 44mm below the top surface.

I set the origin in the middle of the top of the 10mm hole, then double checked that the bottom hole was at the same X,Y position. The Renishaw probe only just manages it. The reported hole centre was claimed to be within 10um, which is fine by my standards.

Done. The bolt sits just flush within the counterbore:

And I drilled the 3 fixings using Fusion 360 CAM.

Manually tapped the three M6 holes:

And made up three matching bolts to suit the ballnut dimensions:

The slight issue-let is that the holes in the ballscrew are claimed to be 5.5mm diameter ie for M5 clearance. Of course, Fat Boy has committed to using M6 fixings and the holes in the ballnut certainly aren't M6 clearance. The screws I have made up (22mm long) are almost but not quite able to go through. 

Lesson: change to M5 threaded holes (4.3mm tapping?) next time (if there is a next time) and somehow open the 3 ballnut holes out sufficient to get the M6 fixings through on this example. I would use a carbide burr if I had one - or possibly use a carbide end mill. I'll check to see if I have a 1/4" end mill which would be ideal, having a degree of additional clearance over an M6 fixing, then use The Shiz to place them and control the feed carefully.

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