Spindle runout?

[Avalonnw]

Hello,
I'm an owner of one of the 3040 machines with 800W water-cooled spindle. I've been happy so fat until I got this problem.
I'm trying to expand a hole in a few aluminum pieces. I'm cutting with 6mm bit 1mm down 0.5mm thick, feedrate 1800mm/m at 12000rpm. The result was ok in the beginning but now the surface is wavy with sort of ridges. The bit is new.
Is it spindle runout or something else? I don't have a dial probe just yet (I intend to buy one) so I can't measure it really right now.
The spindle has only like 2 hours of runtime.

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[A_Camera]

I think 12k RPM is too slow. Try something like 18k. Is it a 1, 2, 3 or 4 flute cutter? I normally use 4 flute cutters on aluminium with the RPM and get very good results. I don't think your problem is spindle run out but can be caused by vibrations. I don't know how your machine looks like, how rigid and well made it is and so on, but to me looks like you have a vibration issue. Are you using any lubricants?

[NIC 77]

I don't understand your feeds.

You were cutting at 1mm down? So 1mm deep? and 0.5mm stepover?

Or 0.5mm deep with 1mm stepover?

Did it make alot of ghastly noise when you did this? This is called "chatter". This means that the machine and / or bit aren't stiff enough to cut that deep without vibrating like heck, or something else is wrong. Try 0.1mm deep with 50% stepover. (3mm for a 6mm bit) and see what happens. See what this sounds like. Then go up in depth slowly from there. Think fast but very very shallow cuts. And you need a very sharp bit, preferably carbide. Don't expect good or fast results from this machine in aluminum. Expect to use alot of sandpaper and to be continually annoyed.

It's simple to get an idea of how much runout you have without a proper indicator. Put something next to the tip of the bit, very close to it, then spin the spindle by hand being careful not to move the actual gantry or y axis. Get your eye in there real close. You will see what the runout is. You will actually see it wobble at the tip. Use a piece of paper to gauge the difference. It's about 0.003" thick. I don't believe that runout caused this to happen.

Is the spindle square to the table, both front and sideways? Can you adjust it? Use a square and have a look.

That's die cast aluminum. I've never tried to machine any, but I know it can be gummy, especially if care wasn't taken to treat it properly afterwards. Did you get any aluminum stuck to the tip of the bit? If so, that would be the major cause of your problem.

[Avalonnw]

I think 12k RPM is too slow. Try something like 18k. Is it a 1, 2, 3 or 4 flute cutter? I normally use 4 flute cutters on aluminium with the RPM and get very good results. I don't think your problem is spindle run out but can be caused by vibrations. I don't know how your machine looks like, how rigid and well made it is and so on, but to me looks like you have a vibration issue. Are you using any lubricants?

It's a 3 flute cutter. I tried 16000 rpm initially but the chips were more like dust and it was overheating I believe.
I know that spirit-based lubricant would be better for the job but I use WD-40

I don't understand your feeds.

You were cutting at 1mm down? So 1mm deep? and 0.5mm stepover?

Or 0.5mm deep with 1mm stepover?

Did it make alot of ghastly noise when you did this? This is called "chatter". This means that the machine and / or bit aren't stiff enough to cut that deep without vibrating like heck, or something else is wrong. Try 0.1mm deep with 50% stepover. (3mm for a 6mm bit) and see what happens. See what this sounds like. Then go up in depth slowly from there. Think fast but very very shallow cuts. And you need a very sharp bit, preferably carbide. Don't expect good or fast results from this machine in aluminum. Expect to use alot of sandpaper and to be continually annoyed.

It's simple to get an idea of how much runout you have without a proper indicator. Put something next to the tip of the bit, very close to it, then spin the spindle by hand being careful not to move the actual gantry or y axis. Get your eye in there real close. You will see what the runout is. You will actually see it wobble at the tip. Use a piece of paper to gauge the difference. It's about 0.003" thick. I don't believe that runout caused this to happen.

Is the spindle square to the table, both front and sideways? Can you adjust it? Use a square and have a look.

That's die cast aluminum. I've never tried to machine any, but I know it can be gummy, especially if care wasn't taken to treat it properly afterwards. Did you get any aluminum stuck to the tip of the bit? If so, that would be the major cause of your problem.

Sorry I was not clear enough. I'm trying to expand an existing hole on a part by 2mm. So, as I positioned the part on the table, I go along the side of the hole with Z stepping =1mm (multidepth cutting) and take 0.5mm at a time (is that stepover?)
There was no weird noises, no chatter, nothing bad as far as I can tell. Nothing was stuck to the bit. I use a lot of WD-40 and the bit is just a bit warm after cutting.
I actually have somewhat similar "stepping" on vertical walls if I do multiple depth even on MDF and wood, it's not THAT profound.

[Avalonnw]

I'll probably record a video and post it here.

[ger21]

Is there aluminum building up on the tool?

It may just be a gummy grade of aluminum.

[A_Camera]

It's a 3 flute cutter. I tried 16000 rpm initially but the chips were more like dust and it was overheating I believe.
I know that spirit-based lubricant would be better for the job but I use WD-40

With 3 flute you should definitely have higher rpm than 12000. If the cutter was overheated than you probably have too low feed rate also. I am not using any lubricant, but have a dust shoe, and when I mill aluminium the cutter is cool even after 15-20 minutes of cutting. This probably meant that I can go on longer also because after that time I think that the maximum temperature is reached. Never the less, I cut at higher speed, namely 18000 RPM, 2700mm/min and use a 4F 6mm cutter most of the time. Here is a video:



I don't think that generating aluminium dust is a good idea, because it can not transport the heat away from the machine. Make sure you cut at least thin chips, like I do in that video. I am not sure WD40 or any lubricant is necessary, but you have to find the optimal speeds and you must make sure your machine is rigid enough if you want to get good results. Of course, lubrication should not make things worse, but I think it is far more important to remove the chips than to lubricate. If your RPM is too low the cutter is not rotating fast enough to efficiently remove the chips, and lubrication can in fact make it worse, keeping the chips in the track and forcing you to mill the chips as well, creating more heat and uneven surface.

[Avalonnw]

I'm not sure I can run faster then 2000mm/m, I start getting missed steps. I thought to increase chipload I need to slow spindle down to allow more material into the flute. I'll do more tests then.

[NIC 77]

Sorry I was not clear enough. I'm trying to expand an existing hole on a part by 2mm.

What, that big hold in the middle?

Apologies, I thought you were talking about about the surfacing attempt in your photo that looks to be about an inch wide and looks like it was cut by a drunk sailor wielding an oxygen torch.

Oh, crud. Ha ha. Your picture looks like two different things depending oh how you look at it. Of course you wouldn't notice this because you already know what the shape is.

Were you climb cutting or the other one? Clockwise or counterclockwise? Try going the other way. That's a long bit then. Try a half inch bit.

The overall difference in hole diameter between top and bottom, that's because of runout. I hope you don't need a tight tolerance for that hole size.

The poor finish quality, I think that's mostly because of your machine's lack of stiffness, and the fact that this is die cast aluminum. You may be able to get better results by trying different feeds, definitely use a stouter, larger diameter bit, and seeing what the difference is between clockwise and counter clockwise as to your finish. Of course, runout could be a contributing factor, but I don't see it as the overall cause. Do you have more of these to do?

At the end of the day, it doesn't matter what you do (unless you want to spend more than you paid for the machine to try and make it better), you will never get a good finish on a milling operation of this kind from this machine. You may improve upon what you have, but it will never be a "good" finish. So grab yourself a six pack of beer and a 12 pack of sandpaper and have at it.

[Avalonnw]

What, that big hold in the middle?

Apologies, I thought you were talking about about the surfacing attempt in your photo that looks to be about an inch wide and looks like it was cut by a drunk sailor wielding an oxygen torch.

Oh, crud. Ha ha. Your picture looks like two different things depending oh how you look at it. Of course you wouldn't notice this because you already know what the shape is.

Were you climb cutting or the other one? Clockwise or counterclockwise? Try going the other way. That's a long bit then. Try a half inch bit.

The overall difference in hole diameter between top and bottom, that's because of runout. I hope you don't need a tight tolerance for that hole size.

The poor finish quality, I think that's mostly because of your machine's lack of stiffness, and the fact that this is die cast aluminum. You may be able to get better results by trying different feeds, definitely use a stouter, larger diameter bit, and seeing what the difference is between clockwise and counter clockwise as to your finish. Of course, runout could be a contributing factor, but I don't see it as the overall cause. Do you have more of these to do?

At the end of the day, it doesn't matter what you do (unless you want to spend more than you paid for the machine to try and make it better), you will never get a good finish on a milling operation of this kind from this machine. You may improve upon what you have, but it will never be a "good" finish. So grab yourself a six pack of beer and a 12 pack of sandpaper and have at it.

HAHA! Yeah, that surface in the middle is the one I'm asking about. It's a part of geodetic tripod (see attachment). On my initial photo it's upside down... sorta...
The hole is approximately 68mm dia, and 16mm tall, so I had to use rather long bit. I don't think it's a good idea to have endmill shank rubbing on material when cutting deep.
I do climbing milling, so I run CCW. (from inside the hole).
I'm not sure about the stiffness of the machine; it is a pretty standard Chinese 3040 with ball screws. It's pretty decent for the money (especially after reading these forums with lots of complaints).
I have quite a few more parts like that to cut, and, while tolerances are not critical I was hoping to play with this machine during this job to get a feel of it before trying to machine something with tighter tolerances.
Also, as I mentioned in the very first post, first couple of parts came out alright (there was still this "ribbing" but not that profound).
It's a steep learning curve and if I had a six-pack every time I get a problem I would be an alcoholic by now...

[rdnck68]

HAHA! Yeah, that surface in the middle is the one I'm asking about. It's a part of geodetic tripod (see attachment). On my initial photo it's upside down... sorta...
The hole is approximately 68mm dia, and 16mm tall, so I had to use rather long bit. I don't think it's a good idea to have endmill shank rubbing on material when cutting deep.
I do climbing milling, so I run CCW. (from inside the hole).
I'm not sure about the stiffness of the machine; it is a pretty standard Chinese 3040 with ball screws. It's pretty decent for the money (especially after reading these forums with lots of complaints).
I have quite a few more parts like that to cut, and, while tolerances are not critical I was hoping to play with this machine during this job to get a feel of it before trying to machine something with tighter tolerances.
Also, as I mentioned in the very first post, first couple of parts came out alright (there was still this "ribbing" but not that profound).
It's a steep learning curve and if I had a six-pack every time I get a problem I would be an alcoholic by now...

Just use an adj boring head with smallest rad. You can and a nice slow feed.... smaller the rad. Of tool the less chatter and better finish you will have in cast alum.

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