Rough edges when milling steel

[Liljoebrshooter]

also some good quality end mills will make a huge difference.

 

[mikey]

I went up to a NEW 3/8" end mill. taking max .01 inch cut on what I assume is mild steel. There are so many variables to this hobby, it's making my head spin.
However, it's still making ragged edges at 1800 rpm or 850 rpm.
If I do the calculation using the chart from here: https://www.the-carbide-end-mill-store.com/Feeds-and-Speeds.html
420x3.82/.375 = 4277 RPM If this is true, then how do I machine steel with an 1800 rpm limit?

Let me back you up here. You are using a new end mill - is it carbide? If so, then 420 sfm might be okay but if its HSS then you should be using about 100 sfm for mild steel. Using the common formula, that gives us ~1,000 rpm for a 3/8" end mill. However, since we have to take different depths of cut both axially and radially, and we may be cutting either a slot or doing edge profiling, this alters our actual speeds and feeds so a better guide is the one from Niagara Cutter attached below.

For example, you are slot cutting so the entire width of the cutter is involved. Your depth of cut is called your Axial depth of cut and your speed will vary with this axial depth of cut. As you axial depth of cut increases you have to slow down so the flutes can cut. What Niagara has done for you in this chart is to give you different cutting speeds for the axial depth of cut you choose, and it applies to whatever size end mill you're using. Note that this chart is only for HSS end mills; carbide goes faster.

So, say you chose to go with a depth of cut of 1/8th the diameter of your 3/8" end mill, which works out to a bit more than 0.04" depth of cut. Your speed would be 1120 rpm.

Feeds can also be calculated but unless you have a CNC or NC mill or a DRO that tracks feed speed, this is not that useful. Most of us will manual feed. What I do is to feed so there is a slight positive resistance to the feed and the end mill cuts just fine.

Give this a try.

 

[Winegrower]

When you get the right end mill and work out the best feeds and speeds, there will still be issues. Check YouTube for a Joe Pie video on how to minimize burrs...he gives tips that may not be obvious when we are starting out.

 

[Aukai]

I used my Grizzly end mills ONCE.....

 

[matthewsx]

I leave my mill in 440 rpm ( i think) most of the time.View attachment 325085

I miss my mastermill, I barely got to use it....

John

 

[Lo-Fi]

A sensible and hobby machine friendly speeds and feeds calc I've used quite a bit:

Speeds & Feeds

The premier source of tooling, parts, and accessories for bench top machinists.

littlemachineshop.com

It tends to err on the conservative side, which is no bad thing when you're starting out.

 

[Janderso]

Get yourself some 12L14 steel, a quality sharp end mill, slow down and you will look like a pro.
Some steel just doesn't like to be machined.
Those Asian end mills aren't of the best quality. I learned my lesson on that score.
You only have about 8,000 choices for which end mill to buy.

 

[higgite]

First, a question for you more experienced folks. OP’s 2nd pic shows a 4 flute end mill. I was taught to use 2 flutes to aid in chip evacuation when slotting. Could that be contributing to the problem?

turningwheels,
1. Have you tried it with a 2 flute end mill to see if you get the same result?
2. In your OP, did you mean .002 deep or .02 deep?

Tom

 

[Cheeseking]

I have used ME Consultant a freeware feed and speed program for years. . Get’s you in the ballpark.
You can Google and download it.

1020 carbon steel (assumption)

1/4” dia 4 flute HSS end mill
Start with 100 SFPM
.050 DOC, .250 WOC (slotting)
RPM=1,528

For feed rate I’d try for .002 per tooth chip load = .008/rev
which is 12.2 IPM

The cheesy gold HSS end mill isn’t doing you any favors. Trust me. Spend $25 on a 4 flute carbide and your machining life will be transformed.

Use 4 flutes for steel in most cases.

Use air or a brush to keep the chips away from the cut and prevent recutting.

 

[turningwheels]

Loads of good info here. Thank you all. Now, if I were to buy some new end mills, what source do you use?