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Pcmaker

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#1
I have this block of mild steel that's 1.5 inches thick, 5 inches in length and 4 inches in width.

I have a PM25MV mill and using a 2" indexable fly cutter that has carbide inserts. My RPM is around 600.

I've been taking off .020 - .025 at a time and it's taking forever to get the workpiece to what I need.

What should my RPM be at and how much should I be taking off at each pass?


 

dtsh

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#2
It is my understanding that:

(CS X 4)/D
CS = Cutting Speed surface feet per minute of mild stell (350 with carbide, 100 with HSS)
D = diameter of the cutter in inches

So for your setup, I get 700RPM
(350 * 4)/2 = 700

That should get you in the ballpark.
 

JimDawson

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#3
Try 0.050 DOC and see if your machine likes it, then try 0.075. The cutter will take about 0.200 or better in steel, but your machine won't. @dtsh is correct, about 700 RPM is where I would start.
 

Pcmaker

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#4
I tried .050, but the cutting tool kept "seizing up" on the work piece. I have to take off this much and it's taking me forever to do so.

What's the best way to take off this much metal?

 

Al 1

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#5
PC, A band saw would be another solution. Finish off with mill. Al.
 

bill stupak

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#6
A roughing end mill will take material off pretty quickly
 

JimDawson

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#7
Sounds like you are just running out of horsepower. But that machine frame will only take so much. A 1/2 inch roughing end mill might be faster. You could go full depth in one pass with a reduced feed rate.

I just spent 2 hours shaving 1/2 inch off of a 1 1/4x4x9 chunk of 4150. I needed it to be 0.750 thick. Used a 1/2 rougher and did it in 2 passes but could have used a cutter like yours at about 0.050 DOC.

Since you have to take that whole piece out, start from the outside and step over about 40% of the cutter. I'll bet it will take 0.050 or more if you do that.
 
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mikey

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#8
I'm with Al 1. I would bandsaw the bulk of the material and finish off with an end mill or flycutter. Anytime you can debulk with a saw, you should.
 

lordbeezer

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#9
If no bandsaw drill all the holes you can..
 

Mitch Alsup

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#10
I tried .050, but the cutting tool kept "seizing up" on the work piece. I have to take off this much and it's taking me forever to do so.

What's the best way to take off this much metal?

Cutting fluid, or slow down in one dimension or another.
 

GunsOfNavarone

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#11
I have no idea what I'm talking about...here to learn. Could you a 1/2" HSS roughing tool? Seems like you could take bigger bites and feed faster and finish off with one light pass with the 2" carbide? I made myself a carriage lock and now i think i know it all!
 

tweinke

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#12
I made myself a carriage lock and now i think i know it all!
Just think if you would have stayed at a Holiday Inn Express last night...…………......:cower:
 

GunsOfNavarone

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#13
I was gonna say that but I figured no one would know WTH I was talking about! Good call though!
 

P. Waller

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#14
I would not use a triangular insert tool for roughing with a facemill.
Actually I would not use a triangle for roughing in any machine, finishing yes roughing no.
Seco makes excellent tools that are in the center of the roughing/finishing spectrum, I suspect that they will not do what you require however.
You will likely need 2 tools.
 

Pcmaker

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#15
Are 4 flute end mills considered roughing tools? Or do I need 2 fluted end mills for that?

I guess I'll try using my 1/2" 4 flute end mills tomorrow and see if that does a faster job.
 

GunsOfNavarone

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#16
I was thinking the 4 (or more) flute. I'm ordering additionally with the chip breakers, but i think that is more advantageous to side milling where it seems you are more so facing. Again, I'm here chime in and learn a thing or two. If your using 4 or more flute and taking some big bites, chip evacuation is key.
 

markba633csi

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#17
It's good to have a couple of roughing mills in your collection, cobalt preferred. They look like regular endmills but with a "corncob-ish" appearance.
m
 

JimDawson

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#18
Are 4 flute end mills considered roughing tools? Or do I need 2 fluted end mills for that?

I guess I'll try using my 1/2" 4 flute end mills tomorrow and see if that does a faster job.
No, a standard 4 flute is not a roughing end mill.

Roughing end mill..... this one happens to be a 6 flute, but they come in 3 or more flutes. Most common in a 1/2 inch is a 4 flute

1536295766792.png
 

NortonDommi

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#19
350 fpm is way too low for Carbide. I run a 2" 4 insert cutter at 960 rpm and 1 mm DOC and have no problems,(RF-45 clone),up to 1640 rpm,(max), and .25 mm DOC for finishing in MS.
Little Machine Shop has a handy calculator: https://littlemachineshop.com/Reference/CuttingSpeeds.php
I use the Turning speed for Carbide for the Mill calculator and never had a problem.
 

Janderso

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#20
You beat me to it Mr. Dawson.
 

ericc

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#21
Weak mill and wrong inserts. A bandsaw, even a small one, is more appropriate.
 

homebrewed

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#22
For my own education, I've got a question about the use of a roughing end mill in this situation. The end of the mill doesn't appear to be shaped any differently than a standard end mill. So I wouldn't expect it to be any faster than a standard mill (with the same number of flutes) if doing facing work. Am I wrong? If so, why?

Thanks

-Mark
 

Pcmaker

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#23
I think roughing end mills are meant to attack from the side
 

JimDawson

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#24
End mills in general are designed to cut both on the end and side. Roughers due to their design reduce the power requirement and machine/chip loading. The chips come off of them as small chunks rather than a long spiral chip as with a normal end mill. You can many times use a rougher to make a full depth cut, but you may have to slow down the feed rate a bit depending on the material and your machine.

Many times when I wear out the first 1/4 inch or so of the end of any end mill, I'll use the upper part of the end mill for side cutting.
 

Pcmaker

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#25
Broke my 1/2" HSS 4 flute regular end mill trying to use it as a roughing end mill. The mill kept on "jumping," too.
 

P. Waller

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#26
The grooves on the cutting edges are chip breakers, as mentioned they produce very small manageable chips but will not provide a hobby shop friendly finish. This greatly reduces the cutting power needed.

They will bang out some heavy roughing however so are invaluable.

They are often available in coarse and fine grinds, choose what works best for the job at hand.
 

JimDawson

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#27
Broke my 1/2" HSS 4 flute regular end mill trying to use it as a roughing end mill. The mill kept on "jumping," too.
Might be time to head to Harbor Freight and pick up their end mill set. https://www.harborfreight.com/20-piece-titanium-nitrade-coated-end-mill-set-5947.html I use them around here for utility work, and they're cheap so when you break one or burn it up you're not out much. It really sucks when you take a new $35 end mill out of the package and instantly break it. I have quite a collection of really expensive end mill shanks. :rolleyes:

''Jumping'' might indicate that you were making a climb cut rather than conventional cut, is this possible? Did you lock the axis that you were not using? On your machine with a 1/2 inch standard end mill, I might start out at about 0.200 DOC and not more than 30% cut width (about 0.150), and around 600 RPM. Your machine is capable of doing very nice work, but it's just not heavy enough to really hog off material.

 

Mitch Alsup

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#28
Broke my 1/2" HSS 4 flute regular end mill trying to use it as a roughing end mill. The mill kept on "jumping," too.
Too much DoC (depth of Cut) and probably too high a feed rate.
 

tcarrington

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#29
Having a PM25 also, I will attest that in most situations you won't be able to climb cut to remove a lot of material. (I usually limit climb cutting to aluminum and then with 0.010 max DOC and less than standard feed. Climb cutting on my machine is used for finish, the last cut and mostly either a spring cut or 0.002.

With conventional milling, correct RPM and feed, you can be limited by the spindle horsepower. All the advise given above should lead you to a good solution. I tend to use 4 flute more often than the folks on larger and stiffer machines. As long as the chips clear, keeping more flute contact helps, IMHO. The mild steel I have cut stays lubricated with regular cutting oil (I like the way it smells, too). I use the smoke as an indicator in regard to how fast to hand feed. Slow, no smoke and you can speed up the feed. Go too fast and you drive all the lubricant off. If you hear your spindle slowing down, slow the feed. That might help with such a mill as you have.

The only thing I will add is check your jibs and make sure they are as tight as can be allowed. Lock the axis you are NOT feeding. Our machines are light and will not just stay in place.
 

Downunder Bob

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#30
Broke my 1/2" HSS 4 flute regular end mill trying to use it as a roughing end mill. The mill kept on "jumping," too.
If the mill kept jumping, were you by chance climb milling? NEVER climb mill when roughing, only ever for a light finishing cut, especially with lightweight hobby machines
 
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