Need Help!- Trouble With Aluminium Feed

[Brenck]

Hi,

I recently finished my CNC mill/router, I use a Industrial Bosch Grinder as a spindle that has 300W and spin at 26krpm ( With no load of course )

Im milling 6531 aluminium ( Its what we get here its almost like 6061 that you guys get there )

Well I just dont know what cut speeds I use, I'm new to this milling thing and dont understand the cutting speeds at all, all the speed calculators I tried to calculate I didnt see any consideration about the depth step of the cut or the the side step of the endmill. I dunno the name for that i think its something like side movement % and vertical movement per pass... I think thoose calculators most of them consider a Industrial standard or some machine with a 10hp spindle, they dont know my spindle isnt strong enough to take 3mm deep each time

My step motors are strong so they dont loose steps even when I overload the machine with some set up that i cant run, basicaly the part jams the endmil on place but steppers keep runing and carry everything away, or break the endmill = (

Im using carbide end mill, most of them uncoated, I have ran tests on the speeds to see how fast i can go but it doesnt make sense like sometimes i get better finish with faster speeds, and somethimes dont, I can go like 80imp or 2000mm/min and cut just a little like 0,02depth / 0.6mm that it kinda cuts good and it barely heats the part, but when i start cutting things 1200mm/min ( 48ipm ) with deeper cuts like 1mm deep it doesnt cuts that good and it heats more... I tried lots of variations and sometimes a 1mm deep cut at 2000mm/min cuts better then a 1.5 deep with 1000mm/min ( all tests i just put some singer oil on the part and on the endmill, i tried dry too it tricks me anyways, finish using oil is way better of course )

Yesterday i cut 2 round pockets same set ups 1/4''endmill same depths and all, but one 1200mm/min and the other 700mm/min same amount of oil, the 1200mm had better finish and looked better ..... When i get a good result and i slow the speed most of the times i get a even better result with slow speeds, but not always

I think its something to do with the fact that the 300w spindle is not strong enough, but the biggest endmill i use is a 1/4''

Anyone have some tips or what set up I shoud use?
I mean i could just run ultra slow or ultrathin depths, but i wanted to make the parts as fast as my machine can, slowing about 30% after finding out how fast that is, of course just to avoid any surprises...

Sorry for the huge post
Thanks for anyone who hepls

[cutsall]

There are many sites that have calculators to help you decide on your feed speed depth of cut settings. You did not specifically describe your problem with finish. Aluminum is notorious for what I call "Weld Back" the heat generated by too slow feed and too high rpm without sufficient coolant causes it to pack the flutes of an end mill and poor finish and tool breakage is inevitable. If you are using a two flute carbide you are taking less than .002 inch per flute at 80 ipm and 26000 rpm. That is a light cut. If your spindle is too light you will have to stay with light cuts. The DOC Depth of cut and stepover amount will be dictated by the power and rigidity of your machine. With a more powerful setup a chip load per tooth of .01 per tooth resulting in a 400 ipm feedrate with adequate coolant is realistic. There are many variables involved in calculating metal removal rates and many resources available for calculatons. The best solution is to maximize you metal removal rate based on what your machine is capable of. Calculate cubic inches or cubic mm/cm/m that you are able to achieve with the depth of cut and feedrate you can produce. Climb cutting will reduce your spindle loading if you machine is rigid enough. You could also try a single flute cutter to reduce loading. They are used a lot in wood cutting on high rpm routers. An old rule for weak machines I have used is depth of cut not to exceed diameter of cutter and stepover no more tha one half diameter. You indicate that you are not even near that depth so I wold take light cuts and maximize my feedrate. What feedrate is your machine capable of accurately executing? Sometimes trial and error is the only way to maximize your machine capability.
Good Luck
Here is a link that has good info
http://www.americanmachinist.com/Cal...eedsFeeds.aspx

[Brenck]

Thanks cutsall

I can get 140in/m on rapid travel with accuracy, I can get even more but thats what I let as maximum velocity on my machine ( on Z i get a little less )

I dont think its possible to cut at 1 tool diameter depth on my machine, not in one step, I cutted a 1 inch part but it was with 0.1'' each step and a really light side cut and i actually got a good finish on that part

That link you posted its like all the other calculators i was talking about, it doesnt ask you about the depth of cut anywhere

Im using 4 flute endmills I dont have any 2 flute or 3 flute, i know 4 flute it suppose to hold more chips to the flute making the aluminium to weld on the tool and stopping my machine...

Do you think i try a bunch of speeds and depths and when i find one that looks good I calculate the SFM from the set up i had and use that to calculate for other tools? As far as I've tested here things look going a bit random...

[cutsall]

Please get your hands on a two flute mill you will be amazed at the difference. As I mentioned before look for a single flute router bit I believe this would be even better in your situation. A four flute has more surface in contact with the material creating more friction and heat and ultimately creating more load on your spindle. I guess the reason depth of cut is not included in most tables is that it depends on your spindle power, size of tool, and rigidity of machine and part. With a two flute cutter and a step over of half the diameter one cutting edge is leaving the cut as the other is entering so load is decreased a single flute cutter engages the part once per revolution and will travel one half a revolution with no load allowing your spindle to maintain its velocity. I normally wont use four flutes on aluminum I have had better results with two flutes. Hang in there it can be a steep learning curve.

[cutsall]

Originally Posted by Brenck Thanks cutsall I dont think its possible to cut at 1 tool diameter depth on my machine, not in one step, I cutted a 1 inch part but it was with 0.1'' each step and a really light side cut and i actually got a good finish on that part

Your 0.1" step is what I call Depth of Cut DOC Side cut I call step over distance. Ar you climb or conventional cutting? Climb cutting the cutting is to the right side of tool in direction of travel conventional is left of tool in direction of cut. Climb cutting often requires less power and leaves a better finish.

[Brenck]

If climb cutting its what you call ramp cutting yea I do that... Ive noticed that if i dont ramp my depth steps I'll be looking for a spindle overload or a broken endmill...

I can't teach anithing but I know that back in the days mill machining tactics was as deep as you can get but not as fast as you go and that with lots of coolant, and nowadays people noticed that is better not that deep but as fast as you can go due to several reasons like heating, endmill life, less coolant and all that... And basically what changed all that was the spindles that know can spin at amazing speeds. And I mean i dont have nothing special as a spindle but i have a motor that spins way faster then a cnc milling machine from the old days that most of them could get around 5000rpm and even good machine nowadays dont go more then 12krpm

Yes I could cut a lot deeper but cutting at maybe 10ipm but it wouldnt make sense due to my set up, like I said since I got a 26krpm spindle im suppose to adequate my ''machining tactic'' due to my spindle speed

Bringing up all thoose points looks like im runnig a production line or a huge machining company that take notes on each single costs and have to have all running on its best highest performance.... No I'm just gonna cut some parts for me and its a hobby... But well experience its never enough.

I dunno if i can get a 2flute endmill now, most of it its due to the fact that i will have to buy it from there and ship it here becase carbide endmills here they just sell thoose top quality sandvik seco and they end up 6 times more expansive then a other brand normal general prupose endmill. For me just worth buyng like 30 endmills from there and shipping here.

I need to run some tests here and try to find out where do i get the better finish, do you think I should run dry? With sense of course, but i mean run a few dry tests with shallow depths and see where do i get the best results and based from there I start pushing the depth down use coolant and get to my limit?

[Brenck]

If I mill aluminium lets say 1mm depth at 1000mm/min wil I get the same resulsts as 2mm depth and 500mm/min?

Thanks