Why are my slots stupid?

[Parlo]

Perhaps the clue is the description - slot drill.

 

[Firstram]

FF to today, I love to teach people what I know and challenge them. Unfortunately societal norms have shifted so much for the most part that even when a guy like me tries to help people and tones it way down, people still get their feelings hurt.

Extremely frustrating!

 

[jmkasunich]

Let me ask all you non 4 flute guys something.

How is a 4 flute crap while a 2 flute is good?

A 4 flute is just a 2 flute doubled up. There are always 2 flutes engaged. when the 2 flutes disengage another set of 2 flutes comes in and equalizes the cuts.

A 3 flute would be more prone to push off one side.

The more flutes you have the less vibration, less hysteresis.

You have a lower feed rate with more cutters because you are taking less off with each cut. A 2 flute can hog off more and has deeper flutes to clear chips with...

I think it's like a tablesaw with an 80 tooth blade, it cuts unbelievably slow, but with a glass like finish..
A 24 tooth blade is a fast cutting ripping saw, and will push through quickly but with a rough finish.

Same with metal removal.. more flutes smoother finish and slower feed, less flutes rougher finish and faster feed.

All bets are off with DULL cutters. I don't think a dull cutter will give you a clean even cut. There will be vibration and it will play havoc on the slot size.

Here's how I understand it. The picture below is a four-flute and two-flute endmill cutting a slot in a purple block.

The red arrow shows the cutting forces acting on flute #1, which is right in the middle of the slot taking the heaviest chip. The cutting force deflects the entire cutter to the left. The two-flute actually deflects more than the four-flute, since there is less "meat" in the core of the cutter.

But on the two-flute, the deflection doesn't hurt anything, since flute 2 is cutting air at that instant. Meanwhile, when the four-flute deflects to the left, flute 2 cuts deeper than it should into the left side wall of the slot, making the slot too wide.

With the two-flute, by the time flute 2 is starting to cut on the left wall of the slot, flute 1 is almost done on the right wall. The chip is very thin, so the cutting force is much lower and pointing up instead of left. Instead of deflecting a lot to the left and making the slot wider, the cutter deflects a little bit upwards which has no impact on how deep flute 2 cuts.

Hope this helps clarify things.

John

 

[toprecyler]

Here's how I understand it. The picture below is a four-flute and two-flute endmill cutting a slot in a purple block.
View attachment 464889
The red arrow shows the cutting forces acting on flute #1, which is right in the middle of the slot taking the heaviest chip. The cutting force deflects the entire cutter to the left. The two-flute actually deflects more than the four-flute, since there is less "meat" in the core of the cutter.

But on the two-flute, the deflection doesn't hurt anything, since flute 2 is cutting air at that instant. Meanwhile, when the four-flute deflects to the left, flute 2 cuts deeper than it should into the left side wall of the slot, making the slot too wide.

With the two-flute, by the time flute 2 is starting to cut on the left wall of the slot, flute 1 is almost done on the right wall. The chip is very thin, so the cutting force is much lower and pointing up instead of left. Instead of deflecting a lot to the left and making the slot wider, the cutter deflects a little bit upwards which has no impact on how deep flute 2 cuts.

Hope this helps clarify things.

John

Thanks for the picture. It is starting to make sense now, in my mind.

I just had the boss order me a couple endmills for the tool crib. I asked for 2 flute, mostly because they are easier for me to hand sharpen the tips, if I feel the need to.

I work manual machines, and I probably dull, chip end mills more due to human err than actually wearing them out in a cut. Either feeds and speeds not correct, or an careless movement of the hand wheel and feed the mill into the work too fast.

We try to keep a couple end mills in stock, but I have no problem doing a hand sharpen, or put a fresh cut on the end using the surface grinder. I like being able to finish the job, without having to wait a couple days for new end mills to come in.


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[woodchucker]

Thanks for the picture. It is starting to make sense now, in my mind.

I just had the boss order me a couple endmills for the tool crib. I asked for 2 flute, mostly because they are easier for me to hand sharpen the tips, if I feel the need to.

I work manual machines, and I probably dull, chip end mills more due to human err than actually wearing them out in a cut. Either feeds and speeds not correct, or an careless movement of the hand wheel and feed the mill into the work too fast.

We try to keep a couple end mills in stock, but I have no problem doing a hand sharpen, or put a fresh cut on the end using the surface grinder. I like being able to finish the job, without having to wait a couple days for new end mills to come in.


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are you using end mills with square corners, or radiused. I now prefer radiused, as they last longer, they don't chip the corner as easily.

 

[rwm]

John- that is a great graphic. Very helpful. Also I do find that purple metal is much more forgiving to machine...

 

[toprecyler]

are you using end mills with square corners, or radiused. I now prefer radiused, as they last longer, they don't chip the corner as easily.

Sharp corner. Half the time I actually need to use an end mill is to mill key ways in shafts.

I am getting better at the speeds and feeds. I used to take passes about only .090- .125 “ deep, and do multiple passes, and realized this really dulls the end. Hence why I learned to hand sharpen the mills. I figure even if I get the flutes slightly uneven, I will just slow the feed down and treat the endmill like a boring bar tool, with only one flute doing the work.

Now I feel comfortable actually looking at the end mills to see if they are sharp, and hogging the key slot in one pass. Sometimes I may have to take a spring pass to get the keys to fit, but I am turning out better work than I was 5 years ago when I started full time machining.


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[Parlo]

Sharp corner. Half the time I actually need to use an end mill is to mill key ways in shafts.

I am getting better at the speeds and feeds. I used to take passes about only .090- .125 “ deep, and do multiple passes, and realized this really dulls the end. Hence why I learned to hand sharpen the mills. I figure even if I get the flutes slightly uneven, I will just slow the feed down and treat the endmill like a boring bar tool, with only one flute doing the work.

Now I feel comfortable actually looking at the end mills to see if they are sharp, and hogging the key slot in one pass. Sometimes I may have to take a spring pass to get the keys to fit, but I am turning out better work than I was 5 years ago when I started full time machining.


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Its common practice to have a small radius in internal corners with the mating part's external corners chamfered. In your case, the keyway can have small fillets in the bottom because standard key steel has external radii to clear them. So when grinding the ends of your slot drills, break the sharp corners. This will give extended tool life, a stronger shaft & a better finish on the bottom of the slot.

 

[verbotenwhisky]

Hi all,
Little background. I'm new to machining, milling in particular. Every time I try to make a slot it always ends up oversized. I just made a set of brackets for a friend and the original size was supposed to be a 7/16" slot. I drilled a hole at the beginning and ending of the slot hoping that would make it better. Nope, the slot still ended up oversized. My 7/16" end mill was quite dull which I'm sure didn't help, but its not the sole reason. In the pics I actually went back in with a smaller sharper end mill to clean it up because it looked terrible so now they're even more oversized. My setup is a Bridgeport J head I was probably running 500rpm with a dull 4 flute HSS cutter. I also had a coolant mister spraying the end mill.

I found this helpful...

 

[RaisedByWolves]

Let me ask all you non 4 flute guys something.

How is a 4 flute crap while a 2 flute is good?

A 4 flute is just a 2 flute doubled up. There are always 2 flutes engaged. when the 2 flutes disengage another set of 2 flutes comes in and equalizes the cuts.

A 3 flute would be more prone to push off one side.

The more flutes you have the less vibration, less hysteresis.

You have a lower feed rate with more cutters because you are taking less off with each cut. A 2 flute can hog off more and has deeper flutes to clear chips with...

I think it's like a tablesaw with an 80 tooth blade, it cuts unbelievably slow, but with a glass like finish..
A 24 tooth blade is a fast cutting ripping saw, and will push through quickly but with a rough finish.

Same with metal removal.. more flutes smoother finish and slower feed, less flutes rougher finish and faster feed.

All bets are off with DULL cutters. I don't think a dull cutter will give you a clean even cut. There will be vibration and it will play havoc on the slot size.

I use whatever I think works best. I have co workers who fall in line with certain lines of dogma, and I just tell them to look at my finished product and go find something else to do other than critique my methods.

As to the bold I disagree. A 3 flute will push off under heavy loads, but it will also make a smaller slot due to this and clean up taking a cleanup pass.

4 flutes wiggle and do all sorts of strange things as they have less web per flute to keep them stiff. If their cutting on both sides they set up a vibration and this does not have time to attenuate before the next flute starts to cut, so you get a bad finish and an oversize cut. 4 flutes=less web per flute.

You are also more likely to get a chip over the flute and have that push the endmill over making it cut bigger yet again.

In the pic above Im using a 4 flute on aluminum, some would call this idiotic. But if you take into account that I'm A: hogging and B: plunging 1/2 the diameter per stepover you would be foolish to try this with a 2 flute.

The reason you want a 2 flute in aluminum is that in general there is more clearance for chips and you can run faster with a higher feed rate, which is true. But there is no real reason to run full out on most jobs, so in taking the entirety of the job into view, I use what I feel works best.

Had a guy laugh at me for setting up and using a 4 flute 3/4" carbide taking a 5/8" deep cut. We needed to make 4 slots in a 1" plate for production as they were down. We lose roughly 10K per hour of profit at times like this.

I had the head turning 2500rpm and ran the feed as fast as it would go while spraying WD on it like a firehose. Carbide is very stiff, extremely sharp and slippery, mush slippery than HSS. So that coupled with the WD almost guaranteed it would not have chip weld issues.

My plates came out usable (Ie good enough but not brite shiny) and his came out perfect.

The difference? I knocked out 3 of the 4 plates needed in the time it took him to do one.

Not gonna lie, I made a hell of a lot of smoke and noise, but production does not care, they want things fixed.