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cnc roughing 6061... quickly

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Metal

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#1
So I'm trying to figure out optimally how to rough 6061 for parts, I get large quantities of 1" cutoffs and typically have to mill them way down to make parts, so I could use a good strategy to blow big chunks of those plates down to half or 3/8 of an inch thick in a reasonable amount of time.

so for right now:
-my rpm is locked in at around 1600, I think increasing it to the top speed for the machine (bridgeport, I "think" its the 1hp one) will reduce torque too much, it seems to not work as well either way. I'm using always-on air to cool right now but am open to coolant.

-I've tried 1/2" corncob 3 flute roughers, they dont seem to do the job, and end up melting down,seizing up, they are almost immediately covered in a coating of silver, I'm assuming the heat generated by cutting without coolant is enough to melt the tiny roughing chips but not the big "normal endmill" chips

-I've tried a 1" 2 flute indexible endmill, while I am only going about .1 per pass in my testing, they are huge wide passes and the thing just glides through the metal with a low hiss and not a typical milling noise as long as it isn't hitting an edge, so I think I'm on the right path, it doesn't center cut and with a mill that size ramps have to be huge, I'm open to just buying a better big indexable if it'll do the job.

-With a 1/2" HSS endmill I can get around 18ipm at .2 depth, any faster and the cutting gets noisy so I think thats about "right"

I've spotted some 3 flute 7/8" roughers for reasonably cheap I think I may try as well.

It seems to me that the most important thing at my RPM is to make big chips and have a lot of clearance for them (the smaller roughers just make powder and seem to rub/melt down. In my research a vast majority of the advice is either routers or really powerful machines.

Can anyone suggest a roughing strategy for a low-ish RPM machine like this?
 

mikey

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#2
I use a bandsaw to cut off the excess - saves my end mills.
 

jbolt

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#3
I would use a 3" or 4" 45 deg insert face mill.
 

Boswell

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#4
I agree with JBolt. I have 4" indexable face mill that is my goto tool for removing larges amounts of stock (when the band saw will not work as Mikey suggests) I have a couple of simple cnc programs that I use that use with the face mill where I can change the DOC and if it will 1 pass (4") or two passes (7.5") and what the depth increment will be. Just chuck up the blank and zero the mill to left of the part and hit start. It pauses for a couple of seconds after each pass to give me time to hit stop when I have removed enough. If you need to rough in a contour and not just overall then I just use the largest 3 flute cuter that will work. I bought a "roughing" cuter but like you, it did not work any better than a 3 flute. I use mist cooling so it clears the chips pretty well but I can always go faster than the chips will clear and that never ends well.
 

Metal

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#5
bandsawing a 6" X 1" plate standing on edge seems really dicey, hah

I have a 2.5" or so face mill already in the mail, how deep do you go with yours per pass as a starting point? I didnt think the stock BP spindle could withstand a 3 or 4 inch cutter.
 

JimDawson

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#6
-I've tried 1/2" corncob 3 flute roughers, they dont seem to do the job, and end up melting down,seizing up, they are almost immediately covered in a coating of silver, I'm assuming the heat generated by cutting without coolant is enough to melt the tiny roughing chips but not the big "normal endmill" chips
It seems to me that the most important thing at my RPM is to make big chips and have a lot of clearance for them (the smaller roughers just make powder and seem to rub/melt down. In my research a vast majority of the advice is either routers or really powerful machines.
Try using coolant, I use kerosene for aluminum, you will be amazed at the difference. WD-40 works good also, keep the tool wet. In aluminum you can cut full depth with a 1/2 inch aluminum rougher with your machine. Pretty sure you could go an inch deep with a 5/8 rougher also.

I have also taken 0.400 DOC with a 2.5 inch insert face mill, at about 40% stepover. But coolant is required in aluminum, the exception to this seems to be very high horsepower machines taking huge cuts. I have only seen videos of this.
 

wrat

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#7
If you want to move a lot of aluminum, your #1 priority is revs. The faster the better. 10,000rpm, if you can.
A 1/2" cutter moving at 10K is what we call "high speed machining" -- an irksome title as no one ever tried to do "low speed machining", but hype is hype.
It will move an astonishing volume of chips.
But then, if you're limited to 1800 revs... well.. probably one of the suggestions already given, then.
Oh, and Jim is spot on about the coolant. Literally anything. Water-based, Kero, Solvent, even Diesel... especially at those low revs and this time of cold. It's all good.. or at least better than none at all.

Wrat
 

Metal

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#8
Right, I have no desire to replace the upper half of the machine to support 10k rpm at this time

I'll start figuring out some way of containing coolant, thanks guys
 

JimDawson

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#9
Right, I have no desire to replace the upper half of the machine to support 10k rpm at this time

I'll start figuring out some way of containing coolant, thanks guys
Unless you are really OCD, you don't really need to contain the coolant. If you build a fogless coolant system you can use minimum coolant. I normally use about a quart in 8 hours of spindle time, about 1 to 2 drops per second or a bit more as needed.
 

Metal

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#10
Hey folks, a short update before I make a new thread

I seem to have accidentally figured out how to use roughers. Using fusion360 I'm now using adaptive toolpaths, which have always sucked for me.
However I'm using them conventionally, at full depths (almost an inch!) and relatively low engagement with my 7/8" rougher. Previously I was doing this wrong or adaptive took a really really long time, but it appears that once I hit half an inch or so adaptive becomes worth it since you can do it in one go.
Anyways, the quick passes of adaptive clearing keep the tool from building up melted aluminium and have been slowly turning up feed rates and non engagement rates to see how fast it can really go.
 

Metal

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#12
Sure, I have it on my facebook right now, it eats a lot of time "not cutting" which I'm looking at cutting down but overall removal rate is very high. I'll try and clip it here shortly

One other question probably for @JimDawson
Has anyone replaced the end screwmounts on their BP? (and/or have a cad of what they did?)

I don't use my old power feed since this is CNC converted, the damn thing gets in my way but I can't take it off due to supporting the longer leadscrew and it would be a universe easier to not have to keep taking it off to measure things then putting it back on to make the part!
 
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