Noob milling, speed and feed, technique mentors needed

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shorton

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I've had a RongFu RF31 mill for several years. Mostly used it for precision drilling (has a DRO). I have a power feed on X. But when it ocmes to actual milling, I'm a complete novice. I understand feeds and speeds, chipload, etc. How to calculate them anyway. I've looked to S&F calculators, like the Gwizard, but the results I get with it never seem right. It seems to be oriented toward max speed for production CNC environments, but it says if I don't go as fast as it says I'll suffer from rubbing and tool dulling.

My machine is listed as 500-3000 rpm. My power feed will probably go 20ipm full on if I remember right. But it would be good to know speeds I could turn by hand.

Can someone help me get up to speed no pun intended. I have a couple of examples I could use help with, I'll start with this one:

I figure at my lower speeds, cutting alu or plastic most of the time, HSS is better than carbide, and most of my tooling is HSS.

Say I want to mill a .125" slot in 6061 aluminum .125 deep. Normal flat bottom endmill.

For this setup, can someone help me arrive at a decent F&S that won't break the tool? Ideally get max depth of cut. And, forgot to say, what about # of flutes. I need to get some new smaller mills as I've broken the ones I have :) so what's best for my machine, 2, 3, 4 flute?
 
Often the small end mills break due to poor chip extraction or the aluminum melting to the cutter. Standard 2 flute end mills work fine if you do not push them too hard and use coolant. 2 flute high helix end-mills for aluminum work better since they get rid of the chips faster. Also check out 3 flute end mills. They have almost as good chip extraction as a 2, and they are actually stronger than a 4 flute. The 3 flue center cutting high helix end mills for aluminum are awesome .... crank the rpm's up as high as the machine will go and let er' eat.
 
Depth of cut? The GWizard tool puts it at 10thou max.

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jamie76x said:
Often the small end mills break due to poor chip extraction or the aluminum melting to the cutter. Standard 2 flute end mills work fine if you do not push them too hard and use coolant. 2 flute high helix end-mills for aluminum work better since they get rid of the chips faster. Also check out 3 flute end mills. They have almost as good chip extraction as a 2, and they are actually stronger than a 4 flute. The 3 flue center cutting high helix end mills for aluminum are awesome .... crank the rpm's up as high as the machine will go and let er' eat.
Click to expand...

I like the sound of 3 flute being stronger. But I thought the extra flute was going to require my feed speed to go up, too in order to maintain chipload per tooth.

What about in steel?
 
Yes, when going to the 3 flute you have advance your cutting speed and it also helps on machines that don't spin that fast... And they work excellent on steel and any other material due to the strength.
I have not looked at a feed/speed chart or calculator in years... Unless I am working with a material I am not used to working or a specialty insert that calls for specific speed/feed. Learning how to read your chips is better than any feed/speed chart or calculator.
 
shorton said:
Depth of cut? The GWizard tool puts it at 10thou max.

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I like the sound of 3 flute being stronger. But I thought the extra flute was going to require my feed speed to go up, too in order to maintain chipload per tooth.

What about in steel?
Click to expand...

Don't worry about maintaining the chip load, that is a maximum figure, it is perfectly acceptable to feed slower in soft materials like aluminum, mild steel etc., however, many tool steels do require a pretty heavy feed to keep the surface from work hardening.

In aluminum keep the tool wet and keep air on it to blow away the chips (unless you have a high pressure flood coolant system). A spray mist coolant is the best. For aluminum, WD-40 and/or kerosene is my choice of coolant. A 2 or 3 flute aluminum cutting end mill is the best for aluminum. For a 0.125 end mill I would use a 2 flute for greater chip clearance

The last major aluminum job I ran required a 0.250 slot, 0.375 deep, 8 inches long. I used a HSS, TiN coated, 2 flute, hi-helix aluminum cutting endmill with WD-40 mist spray, feed at 5 IPM, and 2800 RPM spindle speed. (Yes I know the spindle speed was too slow)

Made the cut in 1 pass. Used the same end mill for all 300 pieces.

In steel, use a water soluble coolant in a spray mist, adjust your spindle speed accordingly, start slow and ramp up the feed speed until it feels right.
 
Here's a few more things in-general...

You also need to consider the type of cut such as hill-climb or conventional. When cutting a slot the width of the bit, there is no difference but, if you're widening an existing slot or, taking a cut off the face-edge of a piece, you need to be aware of these types of cuts. A hill-climb is when the rotation of the bit engages the work and tries to pull the piece in the direction of table travel. On machines that have ACME screws to drive the table (even if it's a power-feed table) a hill climb will give you a good startle and likely break the bit. These cuts should be avoided with machines with conventional ACME screws. Conventional cuts (the kind where the workpiece needs to be forced into the opposite direction of the rotation) is the way to go. I'll bet dollars to donuts, your machine has ACME screws unless it was specifically converted-over to Ball-type screws.

Hill climb cuts can be used judiciously when trimming the side of a piece by limiting the depth of cut of material removed to just 1-2 thou. You can use the whole length (or much of it) of the cutting flutes -just don't push in deeply and take much material off. Those cuts will give you a very nice finish.

Also, with small diameter bits (in my book, anything under 3/8") you must consider the length of the endmill. They come in different lengths and longer bits will "bend" more. HSS and especially carbide tends not to bend but rather snap. Try to use the shortest length bits you can get away with for the particular job at and -and reduce cutting depths accordingly for longer bits.

I have never really seen any written text that clearly describes issues like chip load. I've seen some OK descriptions but, in general, the topic is vague and most examples I've seen start magically using chip load numbers like 0.00239 -with no description of where that number came from. I'm half tempted to write something -and it's on my very long list of things to do... but in all honesty, my milling parameters come from a mix of taking the recommended values from my CNC programs and tweaking them with many years of practical experience. -Must be doing something right because I rarely break a bit and when I do, it's because of a hurried/careless blunder not really related to feed or speed settings...

Ray
 
i found this u--tube video to be very useful. it answered a lot of the ques. i had bout ''feeds and speeds . the cool part is u can watch it over and over . i sure did. here's the link---http://thegeekgroup.org/2011/12/14/geek-group-cnc-5-sfm-surface-footage-per-minute/-----hope this helps u and others. re steve in mt.
 
As far as DOC is concerned, I usually start with the radius of the end mill and adjust from there. With a 1/8" endmill a .0625" DOC should be a good starting point and you can adjust your feed rate from there based on # of flutes and material. I pay close attention to the color of the chips and the sound of the machine. After a while the machine will talk to you and tell you what it likes and when you are pushing it too much.

Most of the speed/feed calculators and apps are more geared for CNC machines with much higher spindle speeds that what we have on our manual machines but some of them do offer recommended SFM rates that will give you a base for feed rates.
 
rmack898 said:
As far as DOC is concerned, I usually start with the radius of the end mill and adjust from there. With a 1/8" endmill a .0625" DOC should be a good starting point and you can adjust your feed rate from there based on # of flutes and material. I pay close attention to the color of the chips and the sound of the machine. After a while the machine will talk to you and tell you what it likes and when you are pushing it too much.

Most of the speed/feed calculators and apps are more geared for CNC machines with much higher spindle speeds that what we have on our manual machines but some of them do offer recommended SFM rates that will give you a base for feed rates.
Click to expand...

Does it make sense to think in terms of the cross-sectional area of the metal being removed? For example, if I can take a 1/16" deep full width cut with that 1/8" cutter, can I take a 1/8" deep cut if I am taking a 1/16" wide bite?
 
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