# Through slot in aluminum tube



## jwmelvin (May 4, 2020)

I have some 2x2, 3/16" wall, aluminum tube, in which I'd like to cut some 3/8" wide by ~8-12" long, longitudinal slots through both walls (to allow the tube to slide along its length and then be fixed in position by a bolt through the slot). I could mill the slots in two setups, working from each side;  I have a 2-flute cobalt end mill I could use. 

But I'm considering whether it's worth it to buy a long end mill and cut the slots in one go, reaching through the width of the tube to cut the far wall after cutting the close wall. This is a long stickout for the tool, but it would save a lot of time as compared to two setups with the associated effort to align the slots.

As potential end mills to use, I'm thinking of: YG1 JAG98911 (reduced shank for clearance as it reaches through); YG1 JAG97941 (straight 2" LOC); or Helical Solutions 46255 (similar to the first, reduced-shank YG1). 

I appreciate any thoughts or guidance you may have. These are just clearance slots for clamping bolts, so no precision to speak of. If I cut in two setups, I'd want the slots aligned to about 0.010" across their width, which seems reasonably easy with an edge finder.

My mill is a PM-30MV.

-jason


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## BGHansen (May 4, 2020)

You could use a long end mill or maybe spot drill and drill through holes at either end of the slots with a jobbers length drill bit.  Mill the slot in the top side, flip it, and use the drilled holes to locate the ends of the slots for the second side.

Bruce


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## Flyinfool (May 4, 2020)

IF the slots are centered on the tube and you set it up carefully for the first one with a stop to set the starting point, this will all be done in one setup. You will mill the slot flip the tube over and mill the other side and they will line up perfectly.


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## jwmelvin (May 4, 2020)

Yes the slots are centered so you are probably right it’s just better to save the $50 extra tool and use a stop to make flipping the tube an easy operation. 

I like the locating through-hole idea too, thanks.


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## RJSakowski (May 4, 2020)

I use an edge finder on both sides to center a piece of work.  If the tube dimensions are uniform, you can just flip for the second cut.  If not, you can just find the center as for the first side.


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## BGHansen (May 4, 2020)

If you were off-center, you could still flip it and still be very close.  Just keep the same side of the tubing to the fixed jaw when it's flipped.  Theoretically, you'd be spot on.  Yeah, takes time to flip the part, just a matter of spending the cash or spending the time.

Bruce


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## brino (May 4, 2020)

My only advise is to do it without a vise.
Nestle the tube in a t-slot directly in the table and clamp it down to the table.
This will avoid any pinching of the slot by a vise as you're cutting the slot.

Since your slot is 8-12" long you could put a temporary clamp (or two) in the middle and move them as you cut the slot.

-brino


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## jwmelvin (May 4, 2020)

I guess one of my questions is: if I _were_ to buy a long end mill, would that be a reasonable approach, or am I likely to have issues with chatter, etc. anyway such that the from-each-side approach would be better?


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## pontiac428 (May 4, 2020)

Long end mills flex, so I only use them when the job calls for it.  I'd indicate off of the stationary end of the vise, set the Y for the centerline of your work piece and lock the axis, set a work stop, then go go go paying attention only to x travel for slot length.


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## talvare (May 4, 2020)

jwmelvin said:


> I guess one of my questions is: if I _were_ to buy a long end mill, would that be a reasonable approach, or am I likely to have issues with chatter, etc. anyway such that the from-each-side approach would be better?



I have tried this before and I did experience serious chatter. Maybe I just wasn't doing something correctly, but this has been my experience.

Ted


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## mattthemuppet2 (May 4, 2020)

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.


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## MrWhoopee (May 5, 2020)

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.


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## Mitch Alsup (May 5, 2020)

MrWhoopee said:


> 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


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## jwmelvin (May 6, 2020)

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.


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