Through slot in aluminum tube

[mattthemuppet2]

don't forget too that to hit 3/8" slot width you'll need to use a smaller than 3/8" end mill, as endmills tend to cut slots over dimension. You see it when cutting in the other direction in solid as it'll take a little more out of one wall than the other. 2" on a 5/16" endmill is really long. Maybe carbide would work.

What I'd do - bolt it to the table as mentioned above or your vise will squeeze the slot shut, then chain drill with a 5/16 or so drill through both sides. Mill one side, being careful of backlash in the screws as you clean up both edges of the slot with a 5/16" end mill (or whatever you can find that's a bit smaller than 3/8). Then flip over, rezero to the same edge you zeroed to before and repeat. Should come out plenty close enough.

 

[MrWhoopee]

Drill holes through at both ends of slot. Mill the slot through one side, flip the part END FOR END to keep the same surface against the fixed jaw and mill the other side. If you're trying to hold the slot width, rough first with a 5/16 to eliminate cutter deflection on the finish pass.

 

[Mitch Alsup]

Drill holes through at both ends of slot. Mill the slot through one side, flip the part END FOR END to keep the same surface against the fixed jaw and mill the other side. If you're trying to hold the slot width, rough first with a 5/16 to eliminate cutter deflection on the finish pass.

This! End-for-End

 

[jwmelvin]

Thank to the advice above, I had a go at this tonight. It worked pretty well. I’m sure some things could be improved but this was my setup, with three stops on the table and two clamps:

I used the x-axis travel stops to make the slot length repeatable and flipped the part end for end to cut the other side. Since the slot is just a clearance for an M8 bolt, the 3/8” end mill was just about right.

The setup took a while to get something I was happy with but once I did, I was able to cut slots in the four pieces I had to do without much trouble.

I’ll have to use similar setups for some other slots in this project too so I’m happy to have learned a bit. Thank you for the help.