Do certain metals have grain? Milling question

cj133 · Apr 27, 2018

Hi all,

I've slowly been learning and getting the hang of things. Stuff is becoming more and more predictable which is nice.

However, I've noticed something and I wanted some input on it.

When milling 1/8" thick sheets of hot rolled steel it seemed like it milled fantastic in one direction, and poorly in the other.
Also, I milled a bunch of 1/2" thick 304 SS plates recently and in one direction they did great with conventional milling, and when I turned them 90 degrees I ended up with a horrible finish until I switched to climb milling which left a gorgeous finish.

It seems like this stuff has a grain, similar to wood.

Is this the case? Am I imagining it?

The 304 stainless really surprised me, and even more so when switching to climb milling left such a beautiful finish. Conventional milling left a terrible finish, rougher than cast iron while climb milling was smooth as can be. I've been climb milling more and more, but I would like to understand what's going on.

In the 304 situation I was using a 1/2" AlTiN coated carbide endmill with a mister, 1400 RPM, 7 IPS with 0.5" depth of cut and 0.125" radial cut.

Rbpercussion · Apr 27, 2018

Conventional milling will usually if not always leave a worse finish than climb milling since it's more so rubbing the material as it starts into the cut, whereas with climb milling the chip load starts large and then becomes smaller as the cutter rotates through the cut.

And I can't say with any authority but i imagine the answer to the question of whether metals have grain or not is yes because if you look at how stock is made, it's usually fed through a machine in one direction causing some sort of linear pattern. wheres something that was sintered, forged, or cast, would have an obscure type grain with almost no pattern at all.

azmachining · Apr 27, 2018

Forgings, extrusions, hot rolled have a grain structure as well as sintered materials like bronze, carbide end mills, etc.

azmachining · Apr 27, 2018

That's what makes forgings so strong is that it actually changes the grain structure and direction, and along with other effects the process has on the material.

Rob F. · Apr 27, 2018

Rbpercussion said:
And I can't say with any authority but i imagine the answer to the question of whether metals have grain or not is yes because if you look at how stock is made, it's usually fed through a machine in one direction causing some sort of linear pattern. wheres something that was sintered, forged, or cast, would have an obscure type grain with almost no pattern at all.

Think about why a drop forged tool is so much stronger than anything other method. The grain is forced to follow the shape of the tool. Also having large rings forged on a ring roller puts the grain arround the length of the ring instead of cutting the ring shape from plate stock.
Forging, Ring Rolling, Open-Die Forging, Hammer Forging-Kihlsteel.se - YouTube
I like this video in the link better than the one below. It shows the whole process.

dian · Apr 27, 2018

steels are composed of grains. i would doubt, however, that what you are seeing are the grains. there are specific procedures to make them visible under the microscope.

Hbjj · Apr 27, 2018

Grain direction is a key factor in forming
Not so much in milling...
Sound like something is wrong with your machine/process

cj133 · Apr 27, 2018

dian said:
steels are composed of grains. i would doubt, however, that what you are seeing are the grains. there are specific procedures to make them visible under the microscope.

I'm not seeing the grain, the way the endmill behaves, sounds, cuts etc seemed like I was going with the grain at times, and across it others.

With hot rolled steel it would cut much nicer in one direction, and then worse if I rotated the steel 90 degrees. It would then cut nicer again if I rotated it another 90 degrees (opposite side of first side).

It also seems audible if milling circles out as it changes direction, but maybe I'm imagining it.

Rbpercussion · Apr 27, 2018

cj133 said:
I'm not seeing the grain, the way the endmill behaves, sounds, cuts etc seemed like I was going with the grain at times, and across it others.

With hot rolled steel it would cut much nicer in one direction, and then worse if I rotated the steel 90 degrees. It would then cut nicer again if I rotated it another 90 degrees (opposite side of first side).

It also seems audible if milling circles out as it changes direction, but maybe I'm imagining it.

It's possible that it could be a problem of the machine, a lack of rigidity in one axis for example.

azmachining · Apr 27, 2018

Typically conventional milling on a loose machine will leave a better finish then climb milling. Climb milling is for finishing if you have a tight machine. Others with tight machines and actual back lash comp will climb mill.

azmachining · Apr 27, 2018

Your just seeing a surface finish resulting from cutting in the wrong direction on a loose machine.

cj133 · Apr 27, 2018

azmachining said:
Your just seeing a surface finish resulting from cutting in the wrong direction on a loose machine.

But you just said conventional milling on a loose machine will leave a better finish than climb milling.

I'm seeing a better, a lot better finish using climb milling.

Also, this is on two machines not just one. Could they both be loose? I suppose, but I need to know what to look for.

azmachining · Apr 27, 2018

What's the machine, that may help to know.

azmachining · Apr 27, 2018

Are you cutting with or against the direction the tool is spinning?

azmachining · Apr 27, 2018

Manual or cnc?
Are you taking a finishing cut?
What are your speed feeds doc woc?
What end mill are you using if using a em?

cj133 · Apr 27, 2018

azmachining said:
Manual or cnc?
Are you taking a finishing cut?
What are your speed feeds doc woc?
What end mill are you using if using a em?

Machines are a Prototrak SMX FHM7 and a much older Chavelier MX3
Both are CNC.

In the 304 situation I was using a 1/2" AlTiN coated carbide endmill with a mister, 1400 RPM, 7 IPS with 0.5" depth of cut and 0.125" radial cut.

thermite · Apr 27, 2018

cj133 said:
But you just said conventional milling on a loose machine will leave a better finish than climb milling.

I'm seeing a better, a lot better finish using climb milling.

Also, this is on two machines not just one. Could they both be loose? I suppose, but I need to know what to look for.

Climb / conventional attributes are only "absolutes" in theory.

Climb is VERY dependent on the capability of a given machine AND a particular alloy, cutter, and set up. All players have to be suited to it and working well together for the entire duration of the operation. CNC may be so "right out of the box". Manuals much less often. Be careful.

As has been pointed out - your machines simply appear to have one or more axis not as "stiff" as another.

Mostly, we all have that, some just worse than others.

Learn the condition and behaviour of each machine, put best features to advantage, minimize the effects of the weaker ones. You seem to be DOING that already, you just need to better understand the "why" of what works or does not.

If that required NO thought, learning, or planning?

Upper Level Management would have goldfish trained to do it to save freight costs to and from China..

..and we'd be out of work. Again.

magneticanomaly · Apr 27, 2018

Not enough info to be sure if "grain" is your problem, but most metals do have it. Unless you buy VAR or other extra clean or otherwise specially processed (see "Lukens Fineline steel")steel, you have metallic crystals with different orientations, and also non-metallic impurities like sulfides. These all get squished out or aligned by forming process, such as rollling or extrusion, until the structure is to some extent fibrous. If setup is rigid and tool sharp this is seldom a problem for cutting the metal, but often a problem with forming (material stretches fine in one direction but soon cracks in another), welding (weld sticks fine but a layer of the parent metal peels off with it) or fatigue loading.

thermite · Apr 27, 2018

magneticanomaly said:
Not enough info to be sure if "grain" is your problem, but most metals do have it. Unless you buy VAR or other extra clean or otherwise specially processed (see "Lukens Fineline steel")steel, you have metallic crystals with different orientations, and also non-metallic impurities like sulfides. These all get squished out or aligned by forming process, such as rollling or extrusion, until the structure is to some extent fibrous. If setup is rigid and tool sharp this is seldom a problem for cutting the metal, but often a problem with forming (material stretches fine in one direction but soon cracks in another), welding (weld sticks fine but a layer of the parent metal peels off with it) or fatigue loading.

I doubt "grain" is his issue, actually.

Even so, it is more accurate to say that ALL metals that we Chikn's are likely to work with have grain from their inherent "crystaline" structure, even if most metallic "crystals" more resemble the leaves of ferns or trees than those of diamonds or more-common table salt.

The special case exception, some few among PM may see and work with, but it is a rare one.

That of the "amorphous" alloys and "states" of alloys not so easily created, nor so easily maintained outside of temperature and stress limits - wherein there is no more grain than in a quart of Karo Corn syrup.

Amorphous metal - Wikipedia

As said "exceptions", not common, but nonetheless very useful ones for certain purposes, so we can expect to see more of it, going forward.

2CW

DMF_TomB · Apr 27, 2018

cold rolled metal can have a grain and differences in metal properties from the hard skin to the softer center. thats why parts warp. you will have less problems if metal is annealed or stress relieved
.
metal grain i see the most when bending metal. often you can bend 90 degree in long direction of rolling but if you try to bend 90 degree to the long rolling direction often the part will crack at the bend

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