# Very basic milling question about depth of cut



## Pcmaker

I have a Precision Matthews PM25MV mill and I have a general beginner question.

When it comes to milling mild steel, around how much is my max depth of cut should be when using my machine and using 3/8 or 1/2 end mill? I've just been taking around .005 DOC in fear of breaking my end mill or to prevent the mill from vibrating.


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## 4ssss

You can take off plenty if your speeds and feeds are right.


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## Cadillac

I usually won’t go more than half the diameter of cutter. Also plunge cut would be less than a side cut.


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## T Bredehoft

I've been taking.050  with both HSS and carbide, but watch your RPM, take it easy, don't expect CNC speeds. A half inch tool probably runs best in the 3 to 400 range, if that. I  only use   as large as 3/8 with carbide, the PM25 doesnt' like slow speeds. (below 350 or so)


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## macardoso

There are many ways to skin a cat. When I first started machining, I would take light depths of cut using the full width of the cutter. Now I will typically use the full length of the cutter with small radial stepover (depends on the feature being cut of course). This way you make nice long chips and use all of the flute length of your cutter.


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## Pcmaker

Do you guys doless depth of cut when climb milling or you don't do climb milling at all. From what I've been told, climb milling is suitable for doing small finishing passes.

Also, in general, large DOC means very slow feeds? I have zero clue how fast my feeds are. The graduation is .50 per rotation of the handle


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## macardoso

A Large DOC and small WOC results in a phenomena called chip thinning. Unintuitively this mean you can use a faster feed than if you were using the full width of the cutter. 

Climb cutting produces better surfaces than conventional, however it generates forces which tend to want to pull the work forward (rather than push it backward). In machines which backlash (such as manual machines) this can cause the work to pull into the cutter whatever distance you have slop in your screws and can damage work and cutter, hence the recommendation to use only for finishing cuts where forces are low.


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## JimDawson

Pcmaker said:


> Also, in general, large DOC means very slow feeds? I have zero clue how fast my feeds are.



Feed to what your mill will take, it will let you know when you are going too fast.  I have rarely broken an endmill by feeding too fast, normally caused by rapiding into the work.

The endmill will cut as fast as you can turn the handle. The limitations are spindle speed, horsepower, and machine rigidity.  A 1/2 endmill will take at least 1 inch DOC and 30-40% width of cut in steel.

Without ball screws, you can only take very light climb cuts due to backlash.  You can cut full depth, but maybe only 0.005 on the width.


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## Pcmaker

I was confusing WOC with DOC. WOC was what I meant. Like milling off the side of a piece of mild steel


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## mikey

Hopefully this will help to clarify this for you, Pcmaker. I am attaching some pdf files here because I can't download them to the downloads section for some reason. 

Several things to note:

The data assumes you have a full sized industrial mill, which you do not. Therefore, I suggest you reduce the recommended speeds and feeds by about 20% or so.
The process you're using matters. You can do Profiling or Perimeter cuts or Slotting cuts. The amount of the end mill's diameter or length you choose to engage affect the speed. 
The max depth you should use in a slot cut is the diameter of the end mill, so for a 1/4" OD end mill, you can cut 1/4" deep at a time. If you need to go deeper then make multiple passes.
The max axial depth of cut, meaning the max amount of the end mill that is touching the work when doing profiling cuts, is 1-1/2 the diameter of the end mill. So, for a 1/4" end mill doing an edge cut you can engage up to 3/16" of its length max. This has to do with deflection of the end mill more than anything else. Carbide can take more but staying with this guideline works for most of the end mills you will use.
The cutting speed varies with the amount of radial depth of cut when profiling and axial depth of cut when slotting. The deeper you go, the slower you need to go.
Cutting speeds also vary with the end mill type - roughing end mills can go about 20% faster and feed about 20% faster.
Feeds are for NC or CNC mills. For those of us with manual machines, feed per tooth means little. The best approach that I've found is to feel the end mill cut. At the right speed and depth of cut, feed so there is a slight resistance to the feed. That is, feed until you feel a slight resistance to the amount of force you apply to the wheel. This applies to all materials and you will quickly be able to feel and adapt to the cut.
When in doubt, slow down your speed and feed. Do not just use the end of your end mills to take baby cuts; this just wears the cutter faster. 

When profiling/peripheral cutting, more flutes is better. When slotting, fewer flutes is better for chip clearance. Learn about high helix end mills for aluminum and use them.

Please, please buy some roughing end mills to do the bulk of your milling. Save your finishing end mills for finishing cuts. Roughers outlast finishers by a big margin and will cut faster and save you time and effort.

These are just general guidelines. If you have a specific application, contact the end mill maker and discuss your needs. Take notes on how you made a cut, what worked and what didn't work. Over time, you will have enough data and experience to feel comfortable with milling. 

Also, do not be afraid to make mistakes; that is how we learn. Well, at least that's how I learn.


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## wildo

Mikey- can you make one addendum to your very useful post above- can you recommend a high helix roughing end mill for aluminum? I haven't been able to locate a ZrN coated, high helix, roughing end mill.

[EDIT]- I probably should have googled better. I found this one which looks quite nice (a 1.5 LOC version is also available)





						ZrN Coated 1/2 dia 3 Flute High Helix Carbide Rougher X 2.0 loc MariTool
					






					www.maritool.com
				




[EDIT x2]- I'll create a separate thread. See here.


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## mikey

Hey Wildo. I use a 3-flute coarse pitch roughing end mill, Niagara Cutter N75201 , for aluminum. This is a cobalt cutter with a 36 degree helix angle so it works good for both slotting and profiling in aluminum. They come in various diameters and flute lengths. I usually go for a 3/4" flute length to keep deflection down unless I need to deep; then I have to use a longer one. My most used one is a 3/8" diameter and it will HOG! Imagine a Sherline mill taking 3/8" depth of cut in a pocket. Chips all over the place!

I prefer coarse pitch roughers in aluminum. Makes a mess but the chips are bigger and easier to clear with a vacuum or blast of low pressure air. Fine pitch is okay but the chips tend to pack up at the feeds and speeds I can use so I use these mostly for  steel and other harder non-ferrous stuff.

Hope that helps.


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## JimDawson

Here is a video of what a 1/2 inch endmill will actually take..... If you have enough machine to drive it.  Most of us are not going to be able to run a machine this hard, but it really shows how strong a quality endmill actually is.  It also helps to have a ~15,000 lb machine with a 30HP spindle


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## wildo

That was really incredible. And they doubled the RDOC on today's video:


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## Cadillac

wildo said:


> That was really incredible. And they doubled the RDOC on today's video:



That was chattering the whole time. I do not no anything about the cnc world and watching the video was amazing to see material getting mowed off but left me a lot of questions.
 Why sparks when plunging the holes? No sparks on any of the other movements.
Why are they climb milling on all movements?  All movement was in clockwise rotation. 
Wouldn't you conventional while hogging out then go to a climb on your finish passes?
Why not use a 3/4 or 1" and go even bigger cuts?
Like said idk about cnc so I'm curious as to their mindset.


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## wildo

Cadillac said:


> That was chattering the whole time. I do not no anything about the cnc world and watching the video was amazing to see material getting mowed off but left me a lot of questions.
> Why sparks when plunging the holes? No sparks on any of the other movements.
> Why are they climb milling on all movements?  All movement was in clockwise rotation.
> Wouldn't you conventional while hogging out then go to a climb on your finish passes?
> Why not use a 3/4 or 1" and go even bigger cuts?
> Like said idk about cnc so I'm curious as to their mindset.



I am certainly no expert, and I also wondered about the sparks.

For the rest of it though, here are my guesses:
-I have read that for roughing end mills, they can be more effective in a climb pattern since the swarf is shot out of the way. In conventional milling, the swarf is pushed ahead of the tool and recut. Plus they have a rigid machine unlike old clapped out mills.
-In HEM, I think that they don't have a need (well... a regular need) for large end mills like in manual shops. They use very, very high feed rates with smaller cuts in order to achieve significantly faster MMRs.
-I suspect that the surface finish could have been improved with coolant, but then we wouldn't have gotten to see anything in the video. Not to mention that the video was more about testing the end mill to capacity. Then again, I think it's fair to make the claim that perhaps surface finish doesn't matter as much with your rougher, and you'll come in with a finishing tool to address the surface finish.


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## JimDawson

Cadillac said:


> That was chattering the whole time. I do not no anything about the cnc world and watching the video was amazing to see material getting mowed off but left me a lot of questions.



The chatter would be no problem for a roughing pass.  It's all about removing material as fast as possible.  I think the MRR was a bit high in the last video, but this was just a test of the endmill.



> Why sparks when plunging the holes? No sparks on any of the other movements.



Good question, and the only thing I can think of is that when plunging the cut depth/tooth (chip size) was smaller than the side milling and thus putting more power into a smaller mass.



> Why are they climb milling on all movements?  All movement was in clockwise rotation.
> Wouldn't you conventional while hogging out then go to a climb on your finish passes?



Normally on a CNC you climb cut for everything because you normally have little to no backlash because of the ball screws.  When climb cutting the endmill is actually taking a nice big bite of the material as the tooth enters the material then the chip thins out as the tooth continues around.  Less rubbing and more cutting, much better heat transfer.  You can't do this on a manual machine with acme screws because the cutter is being pulled into the work, and the backlash in the system causes the cutter to grab too much material and you can't control it.



> Why not use a 3/4 or 1" and go even bigger cuts?
> Like said idk about cnc so I'm curious as to their mindset.



In this case they were testing the end mill, but yes, they could have used a bigger cutter.  At some point you run out of horsepower driving a larger end mill.  In another video they actually stalled that 30 HP spindle with a large (3 inch?) face cutter.[/QUOTE]


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## Cadillac

Thank you Jim for the responses. Specific to this scale of machine. As for climb milling wouldn’t conventional be able to chew through the material easier because the EM helix is directed into to material. Idk if that makes sense? The chip would still shoot just in a different direction. Idk


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## JimDawson

It's a bit counter intuitive, but climb milling produces less cutting forces than conventional so it's a bit easier on the equipment and tooling.  You can take a much bigger bite climb cutting, but does require a rigid machine and minimal backlash else it will try to bite off more than it can chew.


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