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.

 

[4ssss]

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

 

[Cadillac]

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

 

[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)

 

[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.

 

[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

 

[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.

 

[JimDawson]

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.

 

[Pcmaker]

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

 

[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.