How often do HSS end mills need sharpening? SOLVED

[TomWS]

I'm sure this question been asked before, but I couldn't find it using search. So, I'm a beginner at metal milling and I was working on a project today and about midway through the project it seemed as if the cutting was struggling a bit more than it was in the beginning. It wasn't extreme, but did seem that it wasn't cutting as easily as earlier. This made me wonder how I know when it's time to get my end mill sharpened.

The specifics are:
Milling a recess in a block of 6061 aluminum, End Mill is a 3/4" 4 flute HSS end mill that I bought from LMS (my Mill is a mini 3990). They're coated with some kind of gold coating. Spindle RPM a little over 1000.

I have added power feed to the X axis and it's probably around 9-10 IPM. It doesn't have speed control. Most of the cuts were using power feed. I initially started cutting 0.020" deep per pass but that seemed too slow so I increased the depth to about 0.040" per pass. I used Tap Magic Aluminum as brush on lubricant. Most passes were about 6.5" long, 0.312" wide per pass. Overall I cut about 0.375" deep and about an inch wide. All passes were conventional cut, with a climb cut retrace back to the start.

Not sure what more you need...

 

[benmychree]

It is not how often sharpening is necessary, but it is a matter of how dull the end mill is and how that is effecting the cut, if you can see a bright spot on the cutting edge, it is time. It is strange that there is no speed control on the power feed, 9-10 inches per minute seems to be pretty fast.

 

[TomWS]

It is strange that there is no speed control on the power feed, 9-10 inches per minute seems to be pretty fast.

Well, I had a speed control on it but it was intermittent so I hooked it up directly to the DC power source. Still 9-10 is below the recommended Speeds and Feeds from LMS site. They recommend 15IPM for 4 flute 3/4 inch EM.

I'm not sure I know what you mean when you say 'bright spot' on the cutting edge. Can you explain?

 

[Aukai]

Are you using cutting fluid? I have read that aluminum does not like coated cutters, and may get weldment?

 

[TomWS]

Are you using cutting fluid? I have read that aluminum does not like coated cutters, and may get weldment?

I am using Tap Magic Aluminum. There is no sign of metal sticking to the cutter and chips look curly.

 

[benmychree]

Well, I had a speed control on it but it was intermittent so I hooked it up directly to the DC power source. Still 9-10 is below the recommended Speeds and Feeds from LMS site. They recommend 15IPM for 4 flute 3/4 inch EM.

I'm not sure I know what you mean when you say 'bright spot' on the cutting edge. Can you explain?

I guess that would be more obvious on uncoated cutters, it would indicate wear of the cutting edge.

 

[TomWS]

I looked at the end mill and, other than the very tip of one of the flutes, there doesn't seem to be any obvious wear.

Here is what I'm trying to machine. Overall size is 170mm x 38mm and the area that I'm milling is shown in blue. The total depth I'm milling is 10mm and is 21.61mm wide.

What I've been doing is taking 8mm wide slices about 1mm deep with each pass. I'm now thinking that I should use the edge of the end mill to go almost the full depth with each pass but only 1mm thin cuts. This will spread the heat along the length of the mill rather than just the tip. Is 10mm long x 1mm deep edge cut too aggressive for my mini Mill?

 

[TomWS]

Here is what I get with a 9.8mm height, 0.330mm cut. I don't think I should cut any deeper, it seems to be 'lugging' with this much depth...

 

[rabler]

My admittedly moronic approach to this question is to keep a new end mill on hand. If the new end mill cuts better, the old one needs help.

Then I get to ask what I did to dull the old end mill. That's where the thinking and learning begins.

 

[TomWS]

If the new end mill cuts better, the old one needs help.

LOL! Yeah, I guess that's pretty foolproof! Thanks!
I would like to get a sense if my speed and feed is reasonable for this task. Given that the LM3990 does not have a speed setting on the speed knob (other than 2500 max which is pretty useless) I have a feeling my 1000 RPM was closer to 1500. Unfortunately my POS handheld tachometer is equally useless.