[acannell]

okay the title is a little dramatic. according to the current reference of the spindle amp, it definitely SHOULD be stalling because its drawing way more current than its allowed to for continuous running..so the question really is, is this cut taking more power than it should, or does it seem about right?

here are the specs:

material: 6061-T6
cutter: 1/2" diameter cleveland L538 PM PLUS (course rougher "corn cob"..apparently has rave reviews as far as MRR)
axial doc: 0.2"
radial doc: 0.5" (full slot)
flood coolant: rust lick
rpm: 3600
feed: 27.6 IPM
current to motor: 17A
spindle amp max continuous current: 12.5A
power to spindle: not sure..the mill is rated at 2hp continuous, so i must be exceeding that

the cutter appears to be sharp but maybe its not? the top of the stock doesnt come out smooth, it leaves a ragged bur maybe 0.030" high along the top edges..maybe its dull..but i though it was brand new

it sounds okay cutting, just loud. but steady and healthy sounding.

[diamond.3211]

How much stickout? How many flutes? In Alum. you should be running 2 flutes, no more than 3 at most, especially when slotting. With the DOC's that you are running it is consuming between .5-1HP, try backing off of the Axial doc. to .05

[acannell]

How much stickout? How many flutes? In Alum. you should be running 2 flutes, no more than 3 at most, especially when slotting. With the DOC's that you are running it is consuming between .5-1HP, try backing off of the Axial doc. to .05

the stickout was the minimum i could make it, about 1.5". i dont think that would effect the power requirements of the cut though. not sure what you are talking about with the 2 flute recommendation, im using a very high performance aluminum rougher that has 3 flutes, and many aluminum roughers have 3 flutes.

it appears to be consuming considerably more than 1hp, thats the issue. the calculations show it around 0.7hp as a ballpark, but it seems to be well over 2hp.

Cleveland Twist Drill PM Plus Series 538 Speed and Feed Recommendations

im not sure if what that is saying is that wrought and cast aluminum that have more than 10% silicon are not recommended, or that wrought, cast, and aluminum with more than 10% silicon are not recommended. 6061 would fall under the "aircraft alloy with less than 10% silicon" wouldnt it? or would it be the wrought category that is not recommended? what a dumb table. at least include some common alloy numbers!

maybe im not running it hard enough, they say it may seriously degrade performance if the feed rate is too low.

[CRO-WD40]

The cut specs that you listed should require 1858W of power, that is 1858*1,36=2,526 HP
And that's with a new endmill no wonder your spindle is stalling.

Make yourself a excel spreadsheet from data of a endmill manufacturer like sandvik , that have all calculation formula's and material data in them.
And then reduce those parameters a bit, that should be a safe estimate.

reduce your axial DOC to 0.15 inch . Those parameters should require 1400W of power, or 1,9HP

[diamond.3211]

True the stickout doesn't effect the power requirements but it does have a lot to do with getting the right Feeds & Speeds. The longer the stickout the more the deflection grows exponentially, and leads to broken tools and bad finishes, at the numbers you were using you had .002 deflection with that stickout, you should never go above .001 deflection or tools will start breaking. As for the 2 flute, cutting Alum. requires larger chiploads which means there is a need for more chip clearance, the more flutes the less chip clearance, thus my recommendation of 2 flutes, at most 3 when cutting Alum.

The next thing, just because your mill says it is rated for max. 2HP does not mean that you should be trying to get anywhere near that. I would recommend that you stay below 1/4 HP cuts or you are going to wear out the machine quickly. For example, I have the benefit of working with 30HP machines on a daily basis, cutting Alum, 304 Stainless, Inconel, and Titanium, but if I were to try to force one of the machines to plow thru 304 with a cut that consumes 8HP I would most definitely stall the machine, or break something or someone.

Also, buying fancy endmills with high MRR ratings does not transform your 2HP mill into a real hogging machine, you are more than likely wasting your money because your mill cannot even remotely approach the Feeds & Speeds needed to make that MRR rating a reality.

I have attached a screenshot of what I would use for making the cut. Take a step back and slow down or you're going to hurt yourself or worse someone else.

Attachment 203384

I am sorry if this comes across as scathing, but milling is very dangerous when you push limits. Please be careful!!!

[acannell]

True the stickout doesn't effect the power requirements but it does have a lot to do with getting the right Feeds & Speeds. The longer the stickout the more the deflection grows exponentially, and leads to broken tools and bad finishes, at the numbers you were using you had .002 deflection with that stickout, you should never go above .001 deflection or tools will start breaking. As for the 2 flute, cutting Alum. requires larger chiploads which means there is a need for more chip clearance, the more flutes the less chip clearance, thus my recommendation of 2 flutes, at most 3 when cutting Alum.

The next thing, just because your mill says it is rated for max. 2HP does not mean that you should be trying to get anywhere near that. I would recommend that you stay below 1/4 HP cuts or you are going to wear out the machine quickly. For example, I have the benefit of working with 30HP machines on a daily basis, cutting Alum, 304 Stainless, Inconel, and Titanium, but if I were to try to force one of the machines to plow thru 304 with a cut that consumes 8HP I would most definitely stall the machine, or break something or someone.

Also, buying fancy endmills with high MRR ratings does not transform your 2HP mill into a real hogging machine, you are more than likely wasting your money because your mill cannot even remotely approach the Feeds & Speeds needed to make that MRR rating a reality.

I have attached a screenshot of what I would use for making the cut. Take a step back and slow down or you're going to hurt yourself or worse someone else.

Attachment 203384

I am sorry if this comes across as scathing, but milling is very dangerous when you push limits. Please be careful!!!

im surprised you didnt throw in a "my grandpa always told me..." somewhere in there. another machinist addicted to generalities and afraid of the machine they work on..dime a dozen arent they?..i wonder what that costs whoever you work for in lost productivity? limit cuts to 1/8th the rated continuous power of the machine? so everyone should be running their spindle at 12.5% according to you? hogging endmills are "fancy"? what does that even mean? where do you come up with this junk?

[acannell]

The cut specs that you listed should require 1858W of power, that is 1858*1,36=2,526 HP
And that's with a new endmill no wonder your spindle is stalling.

Make yourself a excel spreadsheet from data of a endmill manufacturer like sandvik , that have all calculation formula's and material data in them.
And then reduce those parameters a bit, that should be a safe estimate.

reduce your axial DOC to 0.15 inch . Those parameters should require 1400W of power, or 1,9HP

thanks for the info! could you tell me how you calculated the power? apparently i dont have a method that is accurate for this cut. ive been using ME consultant but it gave a much lower power estimate of only 0.7hp, which is clearly wrong.

heres some fun data i collected with this endmill:

all in 6061. the first 2 were without coolant. the cuts were only about 1 second long each, just long enough to get the current measurement.

it looks like your suggested feed would definitely fall under the 12.5A current limit.

this mill doesnt have a spindle load meter, so ive had to read the spindle amp current ref with a multimeter and do a little arithmetic to determine the current. im going to make a "load" meter using a $5 ebay 0-5V analog gauge hooked up to the current ref permanently, and make a new scale for the meter that is in percent. i think it will accurately reflect the spindle amp's current limit range, although im not sure it would accurately reflect how much power is being output. i.e. a very low rpm cut that draws more than 12.5A because of the high torque demand might actually be consuming much less than 2hp, right? but really on this mill, the spindle will only shut down if the current is exceeded (besides some other electrical failure), and the spindle motor is rated much higher than the spindle amp can deliver, so i think its still a reasonable way to check on whats happening.

DOC FEED RPM CURRENT
0.05 28 4200 5.1
0.1 20 4200 7.4
0.2 16 3600 12.3
0.2 20 3600 13.1
0.2 24 3600 14.4
0.2 28 3600 16.4 (stalled after ~2s)

[diamond.3211]

Lost productivity compared to your stalling the machine continuously, machine breaking down from pushing it too hard, and other costs associated such as broken tools, so how much productivity have you gained by pushing your machine to stall, if you don't want the advice, don't ask. Sorry I tried to help.

[acannell]

Lost productivity compared to your stalling the machine continuously, machine breaking down from pushing it too hard, and other costs associated such as broken tools, so how much productivity have you gained by pushing your machine to stall, if you don't want the advice, don't ask. Sorry I tried to help.

again youre just making stuff up. i stalled the machine a couple times and then tried to figure out what was wrong. now i can run the machine much closer to its limits than i could before, because i know where the limit is, and ive learned that the way i was calculating power was incorrect. so to answer your questions, ive gained about 720% productivity because now i can run the machine at 90% of its capability instead of the 12.5% you were suggesting. no tools were broken or even damaged.

theres a knob on your mill that lets you run the program at a slower feedrate than the program calls for. maybe its a "button" on your mill. similiar idea. one turns, the other is pushed. so when i first ran the program, i set the feedrate to 50% to be conservative. the mill stalled. so now im figuring out why. thats why they have those knobs (or buttons, see above explanation), to play it safe when its appropriate. thats when it pays off by letting you adjust things to work right.

NOTE: LEAVING THE KNOB AT 12.5% YOUR WHOLE CAREER MAY CAUSE LOST PRODUCTIVITY

[CRO-WD40]

thanks for the info! could you tell me how you calculated the power? apparently i dont have a method that is accurate for this cut. ive been using ME consultant but it gave a much lower power estimate of only 0.7hp, which is clearly wrong.

heres some fun data i collected with this endmill:

all in 6061. the first 2 were without coolant. the cuts were only about 1 second long each, just long enough to get the current measurement.

it looks like your suggested feed would definitely fall under the 12.5A current limit.

this mill doesnt have a spindle load meter, so ive had to read the spindle amp current ref with a multimeter and do a little arithmetic to determine the current. im going to make a "load" meter using a $5 ebay 0-5V analog gauge hooked up to the current ref permanently, and make a new scale for the meter that is in percent. i think it will accurately reflect the spindle amp's current limit range, although im not sure it would accurately reflect how much power is being output. i.e. a very low rpm cut that draws more than 12.5A because of the high torque demand might actually be consuming much less than 2hp, right? but really on this mill, the spindle will only shut down if the current is exceeded (besides some other electrical failure), and the spindle motor is rated much higher than the spindle amp can deliver, so i think its still a reasonable way to check on whats happening.

DOC FEED RPM CURRENT
0.05 28 4200 5.1
0.1 20 4200 7.4
0.2 16 3600 12.3
0.2 20 3600 13.1
0.2 24 3600 14.4
0.2 28 3600 16.4 (stalled after ~2s)

Every endmill manufacturer has calculation formulas on their site or in catalogue.

just one example
Formulas

You need to calculate required power prior to machining or you are just going to ruin your machine.
Amp gauge ( power delivered to the spindle) is just used to check if your calculations are correct, or if the tool is wearing out.

[diamond.3211]

No you're calculations are correct. Those specs from your first post result in .8 HP requirement, where you are going wrong is that you are assuming your machine is 100% efficient. But if it is stalling on a .8HP cut and should be able to handle 2HP then your machine is only about 30-40% effeicient. Which is what I was getting at with keeping the HP down. The bur and loud nosie you mentioned in the first post is probably being caused by tool deflection that is why I asked about stickout and how many flutes.

HP=(axialDOC)(radialDOC)(Feedrate)(Material Constant) and times that by (Machine Eff%) and you get the true HP consumed by the machine to make the cut.The Alum. material constant ranges from .25 to .32 depending where you look. So I'll use the approx. middle.

HP=(.2)(.5)(27.6)(.29)= .8004 so if that is stalling your machine then .8004HP/2HP= .4 or 40% Machine Efficiency. So I'll give you that, that I was a under that with my 1/4HP but still I wouldn't go above a 1/2HP cut for normal practice, push beyond every once in a while and no problem, but on a consistent basis you're going to mess up your mill. That knob that you mention, I prefer to start low and use it increase to test rather than start high and back off. You might find it is a much more efficient way to find the max.