Having troubles with aluminum

Mostly Printed CNC - MPCNC Troubleshooting
1

So I have made a couple of attempts at milling aluminum and I have to admit that I have absolutely no idea what I’m doing. Attached is a photo of my attempt at making a J-head mounting plate for a 3d printer. The pocket milling passes all seem to go very well, but cutting the perimeter is where it all goes wrong.

Settings:

1/8" Carbide 2-Flute end mill (this one was brand new)
Roughly 25,000 RPM (setting 4 on my Dewalt DWP-611)
0.3mm depth of cut
200mm/min plunge
300mm/min x/y feed rate
25% Step-over

I don’t think that any of the axes are missing steps, but I am curious about the thin layer of aluminum that has developed around the perimeter. Is this a result of over-heating?
Any guidance would be greatly appreciated!

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One more time, with a smaller image file.

IMAG001350pct.jpg
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I’m just a rookie at this, but I have had some success in my first few attempts at cutting aluminum. Maybe someone with a bit more experience can chime in if I’m not right in my assumptions. Your settings look the same as I have used and I used the same type bit. My RPM were roughly 13,000 RPM, about half the speed you used. I would suggest slow your RPMs down. You should be getting chips, or little curls of aluminum coming off the bit if your speed right. It almost looks like your melting the aluminum.

On the outside cuts, I have manually slowed down the feed rate with the slider in Repetier if it looked like it needed it. I also have an adjustable speed control that my router plugs into, so it’s easy to tweak the RPM while it’s cutting.

Have you tried the trochoidal settings in Estlcam? To find them, you need to turn them on in the Tool List window under View.

Dave

4

Here are some formulas machinist use
SFM= surface feet per minute. This depends on the type of cutter diameter of tool and type of material. I run between 150 and 200 on aluminum.
IPM= inches per minute feed rate
SFM=0.262 x dia of cutter x rpm
RPM= 3.82 x sfm / dia of cutter
use these formulas along with the recommended SFM above, a feed rate you are comfortable with and a RPM your machine can handle to get your speeds and feeds

5

How tall is your z axis? To mill aluminum you need the material to be as close to the gantry as you can possibly get it. Every time you half the length of the Z axis you at least double the rigidity. If you see my videos the aluminum is directly under the gantry and the setting I used are listed as well.

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Thanks all for your help so far. I have made another attempt at approximately 16,000 RPM and raised my X/Y feed rates to 700mm/min. I’m getting chips, as opposed to aluminum dust, but still not able to complete a cut through 1/4" plate. About half way through, the tool starts chattering and it’s all over. I’m sure it’s just a matter of rigidity, or the lack thereof. My Z-height is currently about 4" and I already have a 1" spoil-board under the work piece. I’ve got room to lift it another 3/4" or so, but that’s all I can do without re-mounting my tool holders to a higher point on the z-axis tubes.

With all of that in mind, I’m going to re-work the machine slightly. Does anyone have experience with the upgraded middle-z setup originally posted by “Camar0” (here)?

I have also been thinking about making the universal mount (here) and this would be the perfect time to add it to the machine. I’m somewhat worried that the universal mount itself will introduce more slop. Can anyone comment on this upgrade?

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1/8" 2 flute end mill, .3mm DOC, 5 mm/s, 2mm/s plunge. No coolant with the dealt at about 90% max speed.
My tool was way up but I could easily go another 1 1/4" higher. and cut faster or deeper.

A few things here. 4" z and you can only get a 1" block under the aluminum? Is your endmill all the way in the dewalt? How long is your bit? You speed is more than 2x’s mine I would slow down. The standard feeds and speeds do not really apply to us. We should not be using 2 flute bits We can not travel fast enough to keep the chip load high enough or slow the spindle down enough and retain torque. I used it because It was all I had at the time.

Before you modify things take a few more tries. It took me 3 tries to get it right but once I did the aluminum cuts just fine. Wood and plastic is very forgiving aluminum is at the edge of the machines capabilities, but it does work and when you set things right it works great.

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This was with a flex shaft tool 1/4 the power, no rigid middle z, longer z axis, ball endmill 2 flute. This should not have worked at all but once you get the setting right it works fine. This was 3rd cut I ever made with the mpcnc I believe, maybe 4th.

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I should have been more clear about the z-height. The distance from the table to the bottom of the bit, which is inserted fully, is about 2.5". I have a 1" block under the aluminum and 1/4" thick material. That leaves me another 1.25" to come up, but then I have no room to clear clamps, etc., because I will be at my maximum z-height. The 4" is from the table to the bottom of the router body itself, when at maximum height.

I can certainly slow the speeds and try again, but I would like to make the machine as robust as possible so that I can cut some aluminum plate fairly routinely. I assume that I would be better off with a single flute bit?

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You should easily be able to mill aluminum with that setup. The videos I put up the machine in them has 5 full inches of Z that are usable. Yours sounds to be 2 inches shorter, much more rigid. Make sure your dewalt is 90 from the surface in both directions, maybe you are off at a slight angle and that is causing your problem. You can shim the top with a few wraps of tape.
Have you milled wood successfully yet? Can you snug up any of the center assembly a bit more? How big is your build in the x and Y direction? Can you cut more towards one corner instead of the center? How long is the part of your bit that sticks out when fully inserted?

I see people with 8" Z and of course they will have an issue, but yours should be fine. Before we had the rigid middle z part you could easily move the z-axis around and it still milled aluminum just fine, it is easily 4 times more rigid now if not more. Yes a more rigid machine is better but I’m not sure that is your problem.

Single flute will also help by taking more load per bite of the cutting edge. If you take too small of a bite you actually work harden the material and it gets worse.

The universal might not be the best addition yet, not for aluminum. I love that mount but it does reduce rigidity by moving the tool out a bit further and reducing the contact area with the z mounts. If you want to do aluminum you need to keep everything at a maximum.

As for camar0’s part. He took it down and removed all his accounts for some reason. Another user put it back on thingiverse, I can’t imagine he would be okay with that. The part itself, I have not tried it. It does increase the contact area with the rails, but it adds more rolling resistance and mass, and I’m not convinced of the geometery. I’m sure someone else will chime in on this but I really want to hear from someone that didn’t start with his parts and added them later. When it first came out I asked him and a few of the first people how much better it made the machine. None of them had tried it stock first, even Camar0, yet they all said it made it better. How could they know? I guess this one is a sore spot with me.

If you flex your z axis by pushing on the tip of your cutting tool, look closely at where the deflection happens. I have been working on a new center assembly to try and beef things up a bit but it is starting to come down to conduit flex.

If I make the roller motor mounts by milling them myself I plan on making a very small machine that is extremely short and just feed a strip of aluminum in and cut them 1 at a time as fast as possible.

11

So from what you’re saying, the z axis is the most important for rigidity? Would a 24"x21" work area with a short z axis be ok for milling aluminium?

Also would having a bit of “spare” z axis length cause any rigidity issues?

e.g. If you make the length of the z axis to allow for 6 or 7 inches of usable length but you made the legs short so that you only actually used 4 inches?
I’m considering doing something like that in case I want to use the extra length later on. I could just put longer legs on at that point and make use of the extra z length.

Looks like you’ve got everything setup great in that video with the DeWalt. What was the size of the work area on that machine?

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It should be okay. The one in the videos is 30"x24" OD a bit bigger than yours. Spare z should not be an issue as long as its not more than 6" extra. Is your dewalt mount flipped, like on the thingiverse page? Is there any reason you went so big, or can you cut it all down? If you want to do a lot of aluminum make it smaller for sure. Each time I make a new machine I make it smaller. I never do anything very big. The 3d printer parts that I want to release soon will easily be the biggest parts I will have made.

That’s why it seems like we are missing something. you machine should like its okay. How is it in wood? Fast and clean? The carving video I have it is killing it in that super hardwood. I could have easily gone full bit depth.

If you push on the tip of the cutting bit when it is all mounted up where does it move?

A few pics might really help here.

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I haven’t built it yet. In the process of doing it at the moment, so I’m trying to get a much info as possible to make a decision on the size. Definitely a lot of good information on this thread though.

The only reason for the bigger build size is for 1 project that I have in mind. It’s a bartop arcade machine and one of the panels will need that size. The only other things I might want a larger are for is quadcopter frames but I could shrink the size a bit for that. Do you think there would be a massive benefit from shrinking it down from the 24x21 area? How small would you recommend?
The router won’t be a DeWalt to start with at least, I’ve got a Bosch 300W router already that I want to try out first.

I saw you mentioned that 3d printer on your 1 year post. When will you be releasing more info on that? Really interested to see what you’ve come up with.

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Make sure your dewalt is 90 from the surface in both directions, maybe you are off at a slight angle and that is causing your problem. You can shim the top with a few wraps of tape.

Bingo! I investigated a little more this morning and this was it. Unfortunately, it’s a function of the weight of the tool. With the tool in its mount and a carpenter’s square lined up with the z-axis tubes, there is about 1/8" deflection over about a 9" span. With no tool in the mount, everything is perfectly square. This easily accounts for the problems that I’m having where shallow cuts start out fine, but I run into issues as they get deeper. I could shim it and fudge things, but I would rather solve the root problem.

Have you milled wood successfully yet?

Yes, tons of MDF, plywood, hardwood, and acrylic. They really are that much more forgiving.

Can you snug up any of the center assembly a bit more?

Just tried this. I tightened everything that I could get my wrenches on. Everything was perfectly snug, but each bolt got about another 1/4 turn. This had no effect on the deflection, which appears to be coming from the plastic pieces of the middle section itself.

How big is your build in the x and Y direction?

Usable area is about 18" x 20"

Can you cut more towards one corner instead of the center?

None of my cuts have been in the dead-center. If I move the toolhead all the way into a corner, there is seemingly no effect on rigidity which, again, points to the plastic parts of the middle section.

How long is the part of your bit that sticks out when fully inserted?

Just about 3/4"

As for camar0’s part. He took it down and removed all his accounts for some reason. Another user put it back on thingiverse, I can’t imagine he would be okay with that. The part itself, I have not tried it. It does increase the contact area with the rails, but it adds more rolling resistance and mass, and I’m not convinced of the geometery. I’m sure someone else will chime in on this but I really want to hear from someone that didn’t start with his parts and added them later. When it first came out I asked him and a few of the first people how much better it made the machine. None of them had tried it stock first, even Camar0, yet they all said it made it better. How could they know? I guess this one is a sore spot with me.

I agree that he took them down for a reason. I certainly would never be the one to re-post his work, but I may take advantage of it and give it a try. My machine may be a perfect candidate for this upgrade and, with the exception of a few bolts, I have all of the hardware and plenty of filament. It may do nothing for me, but I don’t think it will hurt to give it a try.

If that doesn’t do it (I too am a bit skeptical), I have considered a couple of alternatives. A counterweight might square things up a bit, but it would certainly be another detriment to rigidity and the added mass would probably just multiply any issues. The other thing that I was considering was installing a whole other set of cross-members with it’s own middle joiner and z-axis to box in the tool-head. I would either opt for the traditional dual-z motor setup like most 3d printers, or possibly slave the second z-axis threaded rod to the first using a belt and pulleys to maintain synchronicity. Thoughts anyone?

15

Thank you guys for your ideas. Do you guys think the nema 17s are going to be enough to move a dewalt 611 plus the weight of the welding head in 3d? I feel like I need the dewalt 611 and its variable speed for attempting steel.

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yup

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Try using peel pocketing and trochoidal paths for your cutout. Should really help.