# What is causing these machining marks ?



## compact8 (Jan 6, 2022)

I am getting this irrespect of the material and depth of cut. In the photo ( picture 1 ) it's a piece of aluminium ( not sure what type but softer than 6061 ). The tool is a 10 mm carbide end mill and conventional cut was used.  The feeding was done manually and on the slow side. It's purely an aesthetical issue but I would like to know the reason. There was no chatter. Is it due to spindle runout ? or poor rigidity ? or other things ?

Update :

I subsequently did a cutting test under different settings and found that the relatively poor finish occurs only if the cutting is done along the Y axis. The only reason I can think of is the poorer rigidity of the head which is expected to flex / oscillate more along the X axis .

Details :

machine : Emco FB2 bench mill, weight about 300 lbs
workpiece material : 6061 aluminium
tool : Carbide end mill 10 mm diameter, run out measured next to the collet face = 0.01 mm TIR
spindle speed : 2000 rpm
feed speed : 65mm / min power feed ( along the X axis )  , about 80 mm / min manual feed ( along the Y axis )
depth of cut : 0.1 mm ( finishing )
length of cut : 9 mm
conventional cut
all axes with no motions including the quill locked
cutting fluid used ( Rocol )
set up shown in picture 2
surface finish comparison shown in picture 3.


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## T Bredehoft (Jan 6, 2022)

Is this cut done with the side of the cutter? (as opposed to the end?) What was the RPM of the cutter?


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## compact8 (Jan 6, 2022)

T Bredehoft said:


> Is this cut done with the side of the cutter? (as opposed to the end?) What was the RPM of the cutter?


Yes, it was done with the side of the tool. The RPM was 2000 which is the max the machine can do.


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## T Bredehoft (Jan 6, 2022)

I'd guess your tool was bouncing, dunno what to suggest .I'd use a heavier tool for that.

Was the spindle clamped? (Vertical Milling machine?)


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## JimDawson (Jan 6, 2022)

Hard to say what is happening, but it looks like chatter.  I would try increasing the feed speed.


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## higgite (Jan 6, 2022)

T Bredehoft said:


> I'd guess your tool was bouncing, dunno what to suggest .I'd use a heavier tool for that.
> 
> Was the spindle clamped? (Vertical Milling machine?)


And were the 2 axes that weren't in use for that cut locked?

Tom


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## macardoso (Jan 6, 2022)

How securely was the part clamped? was it hanging off the end of the vise a ways?


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## keeena (Jan 6, 2022)

Certainly looks like chatter. What size is that piece? I assume it wasn't hanging out too far from the vise? A pic of the setup might help.

What was the WoC? Do you have a powerfeed option? Hard to quantify "slow" as far as hand-feeding. 

Do you have an HSS EM you could try? Seems carbide wouldn't be the right choice here...


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## markba633csi (Jan 6, 2022)

I think the problem is all in the cutting tool.  Try a sharp HSS endmill and I bet your problem will disappear
-M


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## compact8 (Jan 6, 2022)

Thanks for all the replies. I will try again and report back with photos and other details mentioned.


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## Mitch Alsup (Jan 6, 2022)

compact8 said:


> Yes, it was done with the side of the tool. The RPM was 2000 which is the max the machine can do.



The pattern is from a resonance between each point of the end mill encountering the fresh aluminum and the rest of the machine bouncing back and forth in movements too small to see as chatter--but it is chatter nonetheless.

I would drop the speed a lot--I rarely venture north of 500 RPMs with my ½" end mill (12.4mm) in aluminum.

You said nothing about lubrication--put some WD-40 on it.


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## mmcmdl (Jan 6, 2022)

Linear knurling on a mill ?   All of the above posts are correct though , somethings not right there .


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## compact8 (Jan 6, 2022)

Mitch Alsup said:


> ...I rarely venture north of 500 RPMs with my ½" end mill (12.4mm) in aluminum.
> 
> You said nothing about lubrication...


500 RPM ? I have been using 2000 because what I have read from the internet is that the appropriate speed for cutting aluminium is wayyyy.... higher.  Are they valid for super-rigid machines only ?

I do not use any lubrication because I sucked the chips away with a vaccum cleaner when cutting. The use of lubrication will result in the creation of a harmful mist that will be inhaled.


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## Watchwatch (Jan 6, 2022)

Buy some Anchor Lube if you are worried about fumes. Or use a respirator.

Don’t cut aluminum dry. It forms aluminum oxide.


Sent from my iPhone using Tapatalk


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## Mitch Alsup (Jan 6, 2022)

compact8 said:


> 500 RPM ? I have been using 2000 because what I have read from the internet is that the appropriate speed for cutting aluminium is wayyyy.... higher.  Are they valid for super-rigid machines only ?



Speeds and feeds are designed with the notion of high productivity of the machine (i.e., low production costs; even if it causes higher tool wear.)

When you have been cutting aluminum for several years, you, too, can use these higher speeds, but by then you will have found your machines weak spots and learned how to get around them.



> I do not use any lubrication because I sucked the chips away with a vaccum cleaner when cutting.



If you do not lubricate aluminum, the cutting edge (points) will get hot enough for aluminum to fuse to the cutting point. The points on your end mill might already have these little balls of aluminum stuck ferociously to them. Use an exacto knife point to gouge them off the tip.

WD-40 is kerosene without the nasal flavorings added to normal kerosene.



> The use of lubrication will result in the creation of a harmful mist that will be inhaled.



Perhaps machining is not really "in" your blood.............


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## mmcmdl (Jan 6, 2022)

Mitch Alsup said:


> Perhaps machining is not really "in" your blood.............


I remember MEK all too well . It worked great but was ALWAYS " in your blood " .


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## Mitch Alsup (Jan 6, 2022)

I started with DMSO and TriCloroethane, and I'm still around at 69 YO.


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## mikey (Jan 6, 2022)

Have to agree that it looks like chatter but that assumes a lot of things. 

That the spindle and tool holding system is accurate. What is your spindle run out?
That the end mill is *sharp* and not excessively long or used near the tip.
That there is no excessive play in the table/vise/gibs.
That the depth of cut was deep enough to bite instead of deflect.
Sorry to disagree but a spindle rpm of 2000 is not excessive for aluminum. I mill it at 2800 rpm all the time with both HSS and carbide. Calculated rpm for aluminum with a carbide end mill is in excess of 8K. 

If this is chatter then I would agree with Jim and *try increasing your feed rate* while also trying to increase your depth of cut. If a carbide end mill takes too shallow a cut it can deflect, especially if used up near the tip of a longish end mill; use the flutes as close to the shank as possible. I also agree with using some kind of lubricant. Relton A-9 works better than WD-40 but either will do and anything is better than nothing.


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## Ken226 (Jan 6, 2022)

I run 3/8" alu-power 3 flute end Mills @ 4500rpm, feeding between 30 and 45 inches per minute in 6061 and get good surface finishes.   

But, 6061 machines great.   Some mystery aluminum machines like bubble gum.  Try a known material first,  then  go through Mikey's bullet point list and check each of those items.   

I've had surface finishes very similar to yours with loose gibs, especially when the column/head gibs need snugged on the CNC.


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## compact8 (Jan 8, 2022)

Updates included in the first post. Will appreciate you guys' opinions.


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## tq60 (Jan 8, 2022)

For aluminum soapy water or anything slippery will work.

Atf really well.

For finishing cut climb mill, slower motion too and it should come out nice.

Very light cut until you determine what your mill can do..

Sent from my SM-G781V using Tapatalk


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## mikey (Jan 8, 2022)

Interesting. I would have expected there to be less rigidity in X, which makes me wonder if your Y-axis gib is adjusted well. You might want to re-evaluate those gibs and see if you can eliminate any play. 

By all accounts, the FB-2 is supposed to be a good machine. The Y-axis table is a big slab of cast iron and if Emco stayed true to form then they use gib screws along the length of the gib, not the crappy tapered gibs commonly found in Asian mills. If this is so then you should be able to dial out all play in that gib.


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## compact8 (Jan 8, 2022)

mikey said:


> If this is so then you should be able to dial out all play in that gib.


The Y axis gib has been adjusted before the test. Thats why I suspect that the poor finish is due to the vibration of the mill head.
In the past I didn’t notice the difference between the X and Y axes in this regard because all the side milling was done along the Y axis. I guess I will need to rotate the vise by 90 degrees so that side milling can be done along the X axis. But then the freedom in positioning the vise on the table will be reduced.


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## Ken226 (Jan 8, 2022)

compact8 said:


> The Y axis gib has been adjusted before the test. Thats why I suspect that the poor finish is due to the vibration of the mill head.
> In the past I didn’t notice the difference between the X and Y axes in this regard because all the side milling was done along the Y axis. I guess I will need to rotate the vise by 90 degrees so that side milling can be done along the X axis. But then the freedom in positioning the vise on the table will be reduced.



In my previous reply I mentioned that I see that type of finish when my head gibs are loose.  At the time, I didn't realize that you have a round column machine.

What does that type of machine use in place of gibs, to tighten the head? 

When my head gibs are loose, I see worse finishes along the Y axis than the X as well.


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## compact8 (Jan 8, 2022)

Ken226 said:


> What does that type of machine use in place of gibs, to tighten the head?


The rear end of the head is a steel block that slides along the round column. There is a vertical slot on the block that can be squeezed down by tightening a bolt.


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## Ken226 (Jan 8, 2022)

compact8 said:


> The rear end of the head is a steel block that slides along the round column. There is a vertical slot on the block that can be squeezed down by tightening a bolt.



Doesn't sound like there's much you'll be able to do to increase it's rigidity, assuming the bearings are good and the gibs are tight.

   A machine of that size and design is going to be limited in the feeds, speeds and depth of cut it's capable of.   

Perhaps try multiple passes along the side,  stepping down Z axis in smaller increments until you figure out what it can do.    Then perhaps some deeper z axis passes,  with less stepover depth.   

Is it possible that the mill is fine, and your just taking a bigger bite than the little machine can do?


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## compact8 (Jan 8, 2022)

Ken226 said:


> Is it possible that the mill is fine, and your just taking a bigger bite than the little machine can do?


The depth of cut is 0.1mm or 4 thous on 6061 aluminium so its already the lightest cut I think.


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## mikey (Jan 9, 2022)

I just don't buy it that an FB2 should chatter in Y with such baby cuts. Something is definitely wrong when a Sherline mill will outdo an Emco mill.

I strongly suggest you join the Model Engineer forum and post this issue there. There is a fellow named Graham Meeks there who is one of the gurus for Emco machines. He owns an FB2 and if anyone can sort this out, Gray will be the one.


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## Ken226 (Jan 9, 2022)

compact8 said:


> The depth of cut is 0.1mm or 4 thous on 6061 aluminium so its already the lightest cut I think.



Yea, there's definitely something weird going on.  A .004" cut is tiny,  and the chatter marks in your first pic look nearly as deep as your entire depth of cut.


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## compact8 (Jan 9, 2022)

Ken226 said:


> Yea, there's definitely something weird going on.  A .004" cut is tiny,  and the chatter marks in your first pic look nearly as deep as your depth of cut.


The chatter marks shown in the photo is kind of misleading because I intentionally adjust the lighting to maximize their visibility. The depth of the marks is definitely not that much.  I have tried to indicate the marks ( ball diameter of the indicator = 2 mm ), the TIR I get is about 0.003 mm or about one tenth.


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## Ken226 (Jan 9, 2022)

compact8 said:


> The chatter marks shown in the photo is kind of misleading because I intentionally adjust the lighting to maximize their visibility. The depth of the marks is definitely not that much.  I have tried to indicate the marks ( ball diameter of the indicator = 2 mm ), the TIR I get is about 0.003 mm or about one tenth.


 
Ok.  

I'm assuming you've checked your spindle to make sure it's clean inside,  no chips or burs, and tried different collets and different end Mills, just to factor out variables.   Perhaps try without the collet chuck as well, with an R8/mt collet, or end mill holder, depending on your spindle.  


Definitely ask on the model engineer forum.  Guys with alot of experience on your specific machine would be a great source of info.


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## mikey (Jan 9, 2022)

compact8 said:


> The chatter marks shown in the photo is kind of misleading because I intentionally adjust the lighting to maximize their visibility. The depth of the marks is definitely not that much.  I have tried to indicate the marks ( ball diameter of the indicator = 2 mm ), the TIR I get is about 0.003 mm or about one tenth.



A carbide end mill spinning at 2,000 rpm should shear cut the material at light depths of cut. Too light and the end mill will deflect but if is deep enough to bite, a sharp end mill will cut shavings light enough to float in air and produce a nice finish. I cannot see how the head of the mill could be the cause of this. Something is loose somewhere. 

Are you sure the is no slack in the Y-axis leadscrew?


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## compact8 (Jan 9, 2022)

mikey said:


> Are you sure the is no slack in the Y-axis leadscrew?


There is definitely some backlash, about 0.04 mm which should be normal.


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## mikey (Jan 9, 2022)

So, you're conventional milling this, right? That is, if the edge of the work is sticking out the right side of the vise, your end mill contacts the work piece at the front first as you pull the table towards you in Y.


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## compact8 (Jan 9, 2022)

mikey said:


> So, you're conventional milling this, right? That is, if the edge of the work is sticking out the right side of the vise, your end mill contacts the work piece at the front first as you pull the table towards you in Y.


Yes. I know climb cut is not for machines with backlash


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## mikey (Jan 9, 2022)

Okay, if the gibs are tight and there is no significant backlash and you're conventional cutting then I can't think of anything else. 

Try asking Graham Meeks and let us know what he says.


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## compact8 (Jan 9, 2022)

mikey said:


> Try asking Graham Meeks and let us know what he says.



Thanks for the referral. Graham Meeks replied to my post there and said that he also encountered the same problem on his Emco FB2. The problem can be alleviated / solved by changing the tool.

The thread :






						EMCO FB2 side milling issues | Model Engineer
					






					www.model-engineer.co.uk


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## mikey (Jan 9, 2022)

Huh. One is again reminded of the folly of assumptions and/or shallow thinking. I should have caught that.

Did you change the tool? What happened? 

For aluminum, high helix end mills work well. Niagara Cutter and Brubaker make good ones, as do others.


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## compact8 (Jan 9, 2022)

mikey said:


> Did you change the tool? What happened?


I meant Graham Meeks replied that the problem was solved or alleviated by changing the tool to those with larger rake angle. I have ordered this one which is supposed to be optimized for cutting aluminium. Will see what happen.


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## Ken226 (Jan 10, 2022)

compact8 said:


> I meant Graham Meeks replied that the problem was solved or alleviated by changing the tool to those with larger rake angle. I have ordered this one which is supposed to be optimized for cutting aluminium. Will see what happen.
> 
> View attachment 391595
> View attachment 391596




That looks like a Yg1 Alu-Power 3 flute?  If not, it's pretty much identical.

I used them with excellent results in 6061.  Be careful, the flutes will shave the hairs off your arm.  I've cut myself a few times handling them.


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## mikey (Jan 10, 2022)

Okay, a high helix end mill should work. I prefer HSS for aluminum but carbide will work. Just be sure to use the upper part of the end mill instead of the end to maximize rigidity whenever possible. Let us know how it works out.


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