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  1. #1
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    Question Copy mill surface finish

    I have tried every speed, feed, doc, and woc combination I can think of and I can't get a good finish on steel. I even removed all the cutters but one and got pretty good results but they still need to be better.

    EM https://www.amazon.com/Metaltech-Too.../dp/B00LEZMS14
    Insert RDMW0702M0 AH120

    No matter what I try the swirls won't go away. The head is as trammed as I can get it. I even tipped it on purpose a couple thousands and there was no change.

    Here is what I get will all the teeth.
    Shared album - Casey Cotter - Google Photos

    Here is the best I could get with one tooth, Shared album - Casey Cotter - Google Photos

    I have never used a copy mill before, am I missing something obvious? My next plan was to try a different insert but the limited option don't seem to have much of a different geometry. Search Page

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    That's bad...is the cutter out of round or not square? What rpm and feed are you running? What machine? That looks like one hell of a case of built up edge.

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    As already asked, what material and at what cutting speed are you running the cutter? Looks maybe like it may need more RPM. If you are running large radius inserts get that feed up also. If that vise indication of .005" is feed per tooth that's way low.

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    assuming the material is mild crap, your finish doesn't look too bad. But, why using such a small tool to face? At worst, try using a flycutter (cheaper is than cheaper does)

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    What is the machine? Round cutters have a lot of engagement and I have found they like a heavy cut = need a rigid machine and setup.

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    I second the fly cutter. Max RPM walking it as slow as you can

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    Copy mill? Let us see a picture of the machine.

    That cutter is not one I would use for anything, let alone a plain flat surface.

    I also get good results on wide flat surfaces with a flycutter using a brazed carbide tool bit. Google this to see examples.

    Grizzly Industrial H5935 - Fly Cutter Set w/Tool Bits 1/2"

    And steel likes to have a lubricant. This stuff is a stick of wax-like material that melts when the tool and/or work gets warm and works well without making a big mess.

    LPS 43200 Tapmatic Edge Lube Cutting Fluid

    Larry

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    Picture three is just full of chip weld problems. That is why you see deep scratches coming and going as the weld builds on the tool and then breaks off. The cutting edge did not stay clean.
    Picture 4 is better but the problem still there. Wonder the feed rate or spindle speed change on this cut.
    Carbide grade, spindle speed, tooth load, edge prep.
    The first thing I do here is go way up or way down with surface footage (spindle RPM).
    Lube or coolant also changes where this chip weld will occur in your cutting parameters.

    Due to the chip thinning underneath just in front of the finishing edge and the back feed per tooth cut round insert tools are the worse to deal with and should only be used when needed. They are very fussy.
    Die people have to live with and fight this, most of us don't.
    Round insets are always a problem.

    What is your surface footage or spindle speed and cutter dia. and what is the steel? Coolant or dry?
    Cut width per pass on your copy looks a bit large for the cutter dia. I know that means extra traces and that's not productive.
    Bob

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    First you do not mention the alloy, you just say steel. Some steels machine like a dream and others are almost impossible to get better than your photos with a milling cutter.

    You are using a cutter that is described as a contouring cutter to produce a flat surface. It is not one that I would have chosen fro that. And it has inserts, carbide I would assume. All inserts are not created equal. And most carbide inserts do not have the razor edge that can be had on a HSS tool.

    It does appear that you are getting some material from the chips welded to the cutting edge, causing it to produce those scratches.

    You do not say if you are using a cutting fluid or which one. One with good lubricating properties would probably help. I would apply it generously.

    Here is what I would try:

    First a different cutter and one with DEAD SHARP cutting edges on the inserts. If you can see the edge as other than a line with no width, under 10X magnification, then it is not dead sharp. Also your work piece seems to be around 2" wide. I would try a cutter that can do it in one pass, not three. A flycutter with a HSS tool bit could possible produce a better finish.

    A generous amount of an oil based cutting fluid. I know many will talk about the virtues of water based ones, but, IMHO, oil based fluids will have better lubrication properties and that is what you need: a film of oil on the cutting edges so the steel can not build up on them.

    You will always have some marks from the cutter. It can not be completely avoided. But I have found that a feed rate that is more constant than what I can ever accomplish with manual use of the hand wheels will yield a far better surface finish. A constant feed rate can be produced with the use of larger diameter hand wheels or a very long crank handle (4" to 6") added to the hand wheels or by using power feed. I have proven this with experiments. The improvement in the appearance of the surface was quite dramatic.



    The top edges of these two aluminum parts were milled in my SB lathe with a fly cutter. The one on the right was done with hand feed via the OEM, rather small hand wheel. The one on the left was done with the exact same set up and tooling, but with a larger hand crank added to that small hand wheel. That larger radius crank allowed my hand to move a lot more uniformly as I cranked across the cut. You can see the difference.

    The tool was HSS and it was dead sharp. It was an aluminum part so I used WD-40 for the cutting fluid. I am sure that power feed would have produced the same or even better results but that lathe was not so equipped.

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    As previously mentioned, that tool is not for facing, hence the name "copy milling" Moldmakers use those for many years roughing out 3d surfaces. You may improve your surface finish but it will take a bunch of trial and error. I personally would start with more rpm's and air oil mist lube, but even then you will tear once and a while. Get yourself a face mill.

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    The machine is PM30MV that I converted to CNC.

    I am running at 3000RPM and I dropped down to 1500 in 250 increments, 2250 worked the best. My DOC I tried 0.005 to 0.015. Feed has been everything from 2ipm to 30ipm. I tried with coolant, without coolant, and just air. It is definitely a lot better with coolant (It is TRIM something).

    I understand that this is not the best tool for facing and I have SuperFly but when I am doing a pocket I would like the finish too be good enough that I don't have to clean it up. That is just a piece of scrap I had, A36.

    I bought the tool as an all purpose rougher knowing this little machine can handle a lot more axial load then radial. I really want to try some plunge milling with it and see how high of a MRR I can get. But first I have to get a decent finish with this tool or get a different one. Would a 45 degree cutter have the same issues?

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    That's an issue with your machine. It can't handle the engagement.

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    What do you mean by engagement? I am not married to this tool I just want it to be better With only one cutter at 0.005 depth and 10ipm there is not a lot of engagement. What type of cutter would you recommend?

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    Quote Originally Posted by sundewzer View Post
    What type of cutter would you recommend?
    are you deaf?

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    By engagement, I mean the amount of contact the tool makes with the part. As said those full radius inserts have a lot of surface engagement and take some rigidity to run. As previously said a fly cutter should give you better results.

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    Quote Originally Posted by sundewzer View Post
    The machine is PM30MV that I converted to CNC.
    That's a hobby machine, and as such is against the rules to discuss here. That said, either use a flycutter or take multiple passes with a much smaller solid carbide cutter.

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    Quote Originally Posted by sundewzer View Post
    The machine is PM30MV that I converted to CNC.

    I am running at 3000RPM and I dropped down to 1500 in 250 increments, 2250 worked the best. My DOC I tried 0.005 to 0.015. Feed has been everything from 2ipm to 30ipm. I tried with coolant, without coolant, and just air. It is definitely a lot better with coolant (It is TRIM something).

    I understand that this is not the best tool for facing and I have SuperFly but when I am doing a pocket I would like the finish too be good enough that I don't have to clean it up. That is just a piece of scrap I had, A36.

    I bought the tool as an all purpose rougher knowing this little machine can handle a lot more axial load then radial. I really want to try some plunge milling with it and see how high of a MRR I can get. But first I have to get a decent finish with this tool or get a different one. Would a 45 degree cutter have the same issues?
    With that machine id go with a 1" 3 insert 45° face mill...

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    Just do everything with a 1/4" endmill and a flycutter. Your limiting factors are going to be hp and rigidity. You can play with all the tooling you want but at the end of the day 1 hp = about 1 cubic inch of steel per minute. 2 haaspower = 1 cubic inch a min

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    Quote Originally Posted by Hardplates View Post
    Just do everything with a 1/4" endmill and a flycutter. Your limiting factors are going to be hp and rigidity. You can play with all the tooling you want but at the end of the day 1 hp = about 1 cubic inch of steel per minute.
    1 hp and a rigid machine, not a glorified drill press.

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    Quote Originally Posted by plastikdreams View Post
    1 hp and a rigid machine, not a glorified drill press.
    A drill would likely give the highest MRR


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