Bed for 6040 CNC?

[JasonBModerator @jasonb]

Probably get away with 16mm unless you are the very heavy handed type.

[Steve355Participant @steve355]

Too late, I’ve ordered 25mm. The existing flimsy bed is 20mm so I’m barely losing any Z. And it wasn’t much more expensive.

And I think rigidity increases with the cube of the thickness or something so it’s probably worth it.

Now though I will need to mill a bunch of M8 holes though 25 mm of aluminium, so I’ll need an appropriate cutter for that (?) . Alternatively use the CNC to mark starter holes and do it on my pillar drill.

[Steve355]

On Steve355 Said:

Now though I will need to mill a bunch of M8 holes though 25 mm of aluminium, so I’ll need an appropriate cutter for that (?) . Alternatively use the CNC to mark starter holes and do it on my pillar drill.

Drill them with the CNC…

I used M6 on a 38 x 38 matrix (as a compromise between the number of holes, something that would cover most of the available travel and avoiding various existing fasteners). I think I used 5000RPM for the drilling the 5mm holes, which is on the fast side, but it worked.

I spot-drilled first, then drilled through, then chamfered the tops of the holes. I tapped them by hand which seemed to take ages – might want to look at thread milling them on the CNC, especially if you stick with 25mm spacing.

Some rough video:

Spot drilling

Drilling

Chamfering

(I had to reduce the toolpath radius in the chamfering op as I ran out of machine travel. It looks like the tool is just plunging, but it is, in fact, circling around the top of the hole.)

 

[JasonBModerator @jasonb]

If your spindle is too fast for a 6.7mm drill then as I said bore with teh mill, a 5 or 6mm dia carbide cutter going down in a helical path will allow the spindle to be run faster than a HSS drill.

Thread milling to less than full height will stop the risk of screwing anything in too far and jacking the plate off the bottom, much like a thread stops in a tee nut for the same reason.

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