[zoltan87]

Hi everyone!

I bought a chinese 6040 CNC machine and have been reading about feed rates, RPM, CPT (= IPT ?? ) and all these things trying to come to a conclusion, but before I go ahead and might destroy my machine / end mills I though it would be a good idea to quickly post a thread here, so you guys could give me a feedback if my logic is good and the numbers I came up with are more or less correct.

So, I am planning to cut 1.2mm - 3mm thick 6030 aluminium plates with a 3.17mm (1/8 inch) 2 flute end mill. The formula I used:

Feed = N x cpt x RPM

N: number of flutes
cpt: chip per tooth (I found a number of 0.05 for my kind of end mill)
RPM: spindle speed (rotation per minute) I read that between 18000 - 22000 is ideal (my machine has a water cooled spindle with a max 24000 RPM)

So here is my calculation for Feed:

Feed = 2 x 0.05 x 18000
Feed = 1800 mm / min

Does it look ok to you guys? Or am I off with some (all..) of these values? I just really don't want to damage anything on my first try. Thanks for all of you in advance, any suggestions are welcome.

[greggv]

Look at CNC Cookbook's feeds and speeds calculator. It'll save you hours of frustration.

[awerby]

It doesn't sound too far off, assuming your machine is rigid enough. You don't mention depth of cut; stick to half the diameter of your tool or less, so 1/16" DOC. Use plenty of lubricant, like WD-40, squirted into the cut so it blasts out most of the chips (you don't want to recut them).

[aarggh]

As Andrew pointed out, clearing the chips is critical to avoiding snapped bits and rough finishes, and the use of WD-40, while the fumes are not good for you, is invaluable for stopping the aluminium gumming up the cutters. Just a tiny spray every so often is enough to stop the cutter bogging down.

I also use lanolin spray as it's not harmful while machining, but on the smaller machines like 6040's, WD-40 probably works best.

cheers, Ian

[zoltan87]

Thanks for the suggestions guys. I haven't had the chance to try out my machine, hopefully tomorrow afternoon. In the meantime I decided that probably it will be better if I reduce my feed rate / RPM as I don't think this machine is strong enough for such speeds as I originally intended. Also I will use an air blower to clear the chips, I wasn't planning using any lubricant but might will do if you guys think it would make a huge difference. It's just after watching many videos on youtube I was under the impression that cutting dry is ok as long as the chips are cleared away from the end bit with a blower.

[awerby]

You need lubrication as well as cooling with aluminum. If you don't use it, the metal will stick to the end of the cutter - and then it breaks. I'm not sure you want to just blast the chips into the air, either. They are incredibly sharp and nasty; it's important to keep them contained, if you don't want to feel like a pin-cushion at the end of the day.

[zoltan87]

I guess I will go ahead with the wd40 idea then. Although I didn't mention, my cnc is in an enclosure so the chips won't be able to escape from there.

Attachment 290048

[InMesh]

I thought I had the wrong feed rate but I was climb milling so I ran a conventional cut and all was OK.

[Hytek]

As a rule of thumb, climb milling takes less power and gives the better finish as it clears the chips from the cut better. Also, for your lubricant try canola oil O.O yep. It's available in spray, cheap, no hazardous fumes and gives excellent finish on aluminum.

For what it's worth, that's my 2 cents

[zoltan87]

Well, today I made my first cut with the machine. Unfortunately it didn't turn out too well. I will attach the picture about the part I cut out...And please don't laugh, I know it's messed up, but as I said before I have never done anything like this before. I ended up breaking two end bits ( luckily the cheap ones, £1 each, but still annoying). The part is 50mm long and 10 mm wide, 1.2mm thick aluminium. I used a 2 flute 3.175mm end mill.

First time the feed rate was 1000mm/min and the spindle speed is 10 000 rpm. The bit break after like 1 second. Second time I changed the feed rate to 30% of the previous one in Mach3 and the spindle speed was 11 000 rpm. It almost cut around the part but with horrible quality as you can see the picture, and at the end before it could have finished it it break again.

So right now I am not sure what is wrong, with which parameter I am way off?? Following the "Feed = flute number x chip load x RPM" formula my first try should have worked but it failed miserably. And even though the second try I was way too slow according to the mentioned formula, I still managed to break the bit, and the quality of the cut was pretty much useless anyway. So I am seriously puzzled, what is wrong here? I will also mention that the depth of cut was 1.2 mm immediately, could that be the issue that it was too deep?

Attachment 290378

[mx270a]

When I cut aluminum with a 2-flute 1/8" bit, I run my router at 10K RPM and I use a feed rate of 9 inches per minute and a depth of 0.060" or less.

[aarggh]

Well, today I made my first cut with the machine. Unfortunately it didn't turn out too well. I will attach the picture about the part I cut out...And please don't laugh, I know it's messed up, but as I said before I have never done anything like this before. I ended up breaking two end bits ( luckily the cheap ones, £1 each, but still annoying). The part is 50mm long and 10 mm wide, 1.2mm thick aluminium. I used a 2 flute 3.175mm end mill.

First time the feed rate was 1000mm/min and the spindle speed is 10 000 rpm. The bit break after like 1 second. Second time I changed the feed rate to 30% of the previous one in Mach3 and the spindle speed was 11 000 rpm. It almost cut around the part but with horrible quality as you can see the picture, and at the end before it could have finished it it break again.

So right now I am not sure what is wrong, with which parameter I am way off?? Following the "Feed = flute number x chip load x RPM" formula my first try should have worked but it failed miserably. And even though the second try I was way too slow according to the mentioned formula, I still managed to break the bit, and the quality of the cut was pretty much useless anyway. So I am seriously puzzled, what is wrong here? I will also mention that the depth of cut was 1.2 mm immediately, could that be the issue that it was too deep?

You didn't say if you used any lubricant?

cheers, Ian

[zoltan87]

Hi Ian, no I didn't use any, I ordered a big 5 litre WD 40 bottle but it hadn't been arrived at that time. I have it now so next time when I will be cutting (probably Monday) I will definitely be using it. And also will go way slower, hopefully that will help.

[jfong]

You didn't mention what type of aluminum. Some are just really gummy and have a hard time milling cleanly. I pretty much only buy 6061, it mills nicely even without lube. Although I usually put a few drops of wd40 anyway.

[zoltan87]

You didn't mention what type of aluminum. Some are just really gummy and have a hard time milling cleanly. I pretty much only buy 6061, it mills nicely even without lube. Although I usually put a few drops of wd40 anyway.

I am not sure about it's quality, I bought it off eBay as normal aluminium plates, I would say the cheapest kind (5000 something ?). Maybe that's the issue? I also have a grade 6082 alu sheet but didn't want to use it until I figure out everything, I don't really want to ruin that sheet.

[InMesh]

I have been machining for a while conventional mills I know carbide is a great material but if you have access to high speed steel cutters try one of those I have found them to have a sharper edge ,just my 2 c also are you climb milling or conventional cutting .cheers John

[zoltan87]

I have been machining for a while conventional mills I know carbide is a great material but if you have access to high speed steel cutters try one of those I have found them to have a sharper edge ,just my 2 c also are you climb milling or conventional cutting .cheers John

I was climb milling. I will try to find out what was the material of my bit, I think it was carbide but I am not sure. Will try both of them next time.

[jfong]

Also another thing to consider is to check your spindle rotation. Makes sure it is spinning the right direction and not reversed. I've done that by mistake before.

I've bought some Home Depot aluminum plate as a last resort when nothing was open. I don't know what kind it was but nothing I did was able to get a clean cut. Looked just like your picture. Went out and got some 6061 plate and all was good. I try to use HSS end mills on my bench mill since it cuts better at the max 2500rpm spindle speed. On my gantry router, I use carbide since the spindle can run up to 24k. Usually I run it around 12k and 30-40ipm depending on depth of cut. Good end mills also make a large difference in cut quality. I get Onsrud when I can find them cheap on eBay.

[aarggh]

I asked about lube before as that picture looks fairly typical for a fast cutter without lube re-cutting the swarf as it's not being cleared, so the cutter just smashes it's way through while gumming up. It can be pretty hard cutting really thin sheet, as it will vibrate up and down if not held rigidly in place, but I find without some sort of lube to stop the cutters gumming up, it usually ends in a crappy finish, and/or broken cutters.

cheers, Ian

[zoltan87]

I asked about lube before as that picture looks fairly typical for a fast cutter without lube re-cutting the swarf as it's not being cleared, so the cutter just smashes it's way through while gumming up. It can be pretty hard cutting really thin sheet, as it will vibrate up and down if not held rigidly in place, but I find without some sort of lube to stop the cutters gumming up, it usually ends in a crappy finish, and/or broken cutters.

cheers, Ian

Yes I will definitely use some wd 40 next time. But now that you mentioned the vibration as a possible source of the problem i think probably that is the main issue. I don't think I attached it secure enough against any movement. I have a 6 mm thick small 6082 alu sheet, will try to machine tgat on Monday and will report back.