Preferred tool for milling flat surfaces

dsela · Jan 6, 2016

Hello,

This is a general newbie question regarding milling.
I need to mill a thick 200mm * 200mm Aluminum 6061-T6 plate with a flatness requirement of 0.02mm and best surface finish that can be obtained by milling.
What is the best tool for these requirements? Face mill or end mill? Preferred diameter? High or low speed and feed rate?
Are there other parameters that are important for flatness?

Thanks!

Conrad Hoffman · Jan 6, 2016

Face mill with sharp inserts made for aluminum, probably running as fast as your machine will go. You'll need to pay special attention to tramming the mill so the surface is flat.

Mtndew · Jan 6, 2016

Conrad Hoffman said:
Face mill with sharp inserts made for aluminum, probably running as fast as your machine will go. You'll need to pay special attention to tramming the mill so the surface is flat.

Pretty much this.
I tend to like Mitsubishi Carbide for their aluminum inserts and facemills,but you can find alum specific cutters anywhere.

DMF_TomB · Jan 6, 2016

dsela said:
Hello,

This is a general newbie question regarding milling.
I need to mill a thick 200mm * 200mm Aluminum 6061-T6 plate with a flatness requirement of 0.02mm and best surface finish that can be obtained by milling.
What is the best tool for these requirements? Face mill or end mill? Preferred diameter? High or low speed and feed rate?
Are there other parameters that are important for flatness?

Thanks!

.
larger diameter cutter can have more error from machine alignment tram error and cutting forces deflecting part. often part in a vise will bend just from vise pressure so final cutting is done at lower vise pressure. sometimes smaller diameter cutter work better if thin part is vibrating when using a larger diameter cutter

dsela · Jan 7, 2016

Thanks for the answers.
So my next question is when cutting the surface with a face mill, I can see the different passes the machine made. When I run my finger across the surface I can actually feel a bump between the different passes. Is there a way to eliminate this?
I need to get a flat surface in order to get a good seal between two surfaces..

Mike1974 · Jan 7, 2016

If there is a 'bump' between the passes it is one of two thing.
A) your head is out of tram
B) you are not overlapping the cutter enough between passes

Are you using a manual machine or cnc? Manual machine, like a bridgeport, is easy to check the tram of head. Attach an indicator to the spindle and sweep the table (or vise if that is what you are using), this will tell you if your head is square to the table. If it is a cnc and you have the mismatch between passes (and the tool is overlapping) you have a much bigger problem IMO.

crossthread · Jan 7, 2016

The first thing I would use in this situation would be a fly cutter. If you use a cutting tool in the fly cutter with a large radius and very sharp you should be able to get an excellent finish. I think you would have a better chance of meeting your flatness requirement as well due to the large sweeping cut.

stephen thomas · Jan 7, 2016

Manual machine, like a bridgeport, is easy to check the tram of head. Attach an indicator to the spindle and sweep the table (or vise if that is what you are using), this will tell you if your head is square to the table.

He's looking for (approximately) 8" x 8" piece with flatness within 8 tenths (.0008) Parallel tolerance not stated.

On a 9" travel BP type with some wear, tramming the table may only be 1/2 way to parallel with the ways. He should first tram the table surface Y travel to verify surface is still parallel to the ways. Then tram the mill head to the table with that info. (may have to kick up at one end or other of travel, if he looking for stepless pass under .001" total tolerance)

If there is a good 12" or larger lathe available, it may be a better option for step-less finish.

I'd put it on the surface grinder first. Second option, planer. I'd even consider a (larger) shaper over a BP.

smt

rons · Jan 7, 2016

dsela said:
So my next question is when cutting the surface with a face mill, I can see the different passes the machine made. When I run my finger across the surface I can actually feel a bump between the different passes. Is there a way to eliminate this?

Even if you do all you can to tram the mill it will not be enough. With a large fly cutter it might take 2 to 3 passes.
The discontinuities will be there. If I were you I would use a 4 jaw chuck on a lathe.

trevj · Jan 7, 2016

dsela said:
Thanks for the answers.
So my next question is when cutting the surface with a face mill, I can see the different passes the machine made. When I run my finger across the surface I can actually feel a bump between the different passes. Is there a way to eliminate this?
I need to get a flat surface in order to get a good seal between two surfaces..

In a nutshell, no you cannot eliminate this. At some level, you will always have some roughness, and you will always have some variation between passes, esp with a manual machine.

Things you can do include getting the head in to tram, as has been suggested, and learning to use the slightly out of perfect alignment in order to get the best results. Typically this means feeding the cutter across the surface for the finish cut, so that the deepest portion of the cut is at the trailing edge of the cutter, which usually leaves a nicer surface finish. You then rinse and repeat, offsetting each pass across the part by an amount that the resulting scallops cut by the cutter, blend together and result in a surface that meets tolerance for roughness.

You need to provide better information to get better answers. What machinery have you to use? Manual or CNC? Cutters? Static seal, or does it move? Seal have an O-ring or gasket? What does it need to seal against? Vacuum, pressure, keep mice out of the flour bin, etc?

Is this homework? Or are you actually making something?

Cheers
Trev

Tyrone Shoelaces · Jan 7, 2016

stephen thomas said:
He's looking for (approximately) 8" x 8" piece with flatness within 8 tenths (.0008) Parallel tolerance not stated.

On a 9" travel BP type with some wear, tramming the table may only be 1/2 way to parallel with the ways. He should first tram the table surface Y travel to verify surface is still parallel to the ways. Then tram the mill head to the table with that info. (may have to kick up at one end or other of travel, if he looking for stepless pass under .001" total tolerance)

If there is a good 12" or larger lathe available, it may be a better option for step-less finish.

I'd put it on the surface grinder first. Second option, planer. I'd even consider a (larger) shaper over a BP.

smt

I'm not mad about grinding Aluminium. Last place I worked at did lots of Ally. Most of the time they used to fly cut it.

Regards Tyrone.

rogertoolmaker · Jan 7, 2016

6061-T6 is not the best alloy for machining.

dsela said:
Hello,

This is a general newbie question regarding milling.
I need to mill a thick 200mm * 200mm Aluminum 6061-T6 plate with a flatness requirement of 0.02mm and best surface finish that can be obtained by milling.
What is the best tool for these requirements? Face mill or end mill? Preferred diameter? High or low speed and feed rate?
Are there other parameters that are important for flatness?

Thanks!

6061-T6 is normally used for extrusions and is not the best for machining. A aluminum alloy in the 2000 series would be much better. A face mill is a best choice.

Rogertoolmaker

Mtndew · Jan 7, 2016

rogertoolmaker said:
6061-T6 is normally used for extrusions and is not the best for machining. A aluminum alloy in the 2000 series would be much better. A face mill is a best choice.

Rogertoolmaker

Eh?
Anytime I've ever had to make anything out of aluminum for any of my customers in the last 30 years, it's been 6061 T6, unless on the rare occasion it's been 7075.
6061 is very easy to machine, not sure where you're getting that info from.

Mike1974 · Jan 7, 2016

rogertoolmaker said:
6061-T6 is normally used for extrusions and is not the best for machining. A aluminum alloy in the 2000 series would be much better. A face mill is a best choice.

Rogertoolmaker

I'm with mtndew. 6061 is the preferred aluminum in my humble experience. Often specced out (in plate form, not extruded) for lots and lots of applications...

JNieman · Jan 7, 2016

rogertoolmaker said:
6061-T6 is normally used for extrusions and is not the best for machining. A aluminum alloy in the 2000 series would be much better. A face mill is a best choice.

Rogertoolmaker

What kind of tools are YOU in the business of making?

6061 is not -the best- (as in #1 undisputed) for machining but it's sure damn easy!

6061 is common for extrusions and rolled shapes. Hell, it's Aircraft Grade!

ETA: And this includes holding tolerances like the OP is asking about.

Co2 mech · Jan 7, 2016

Mount it on a faceplate and turn on a lathe.
Regards

stephen thomas · Jan 7, 2016

I'm not mad about grinding Aluminium. Last place I worked at did lots of Ally. Most of the time they used to fly cut it.

Regards Tyrone.

Tyrone,

all due respect and personal preferences certainly depend on tools (machines) available. Got all those listed my first post except the 12+" swing lathe; and throwing it on the surface grinder with a couple hold downs would be about fastest to the best finish, for me. 46 I or J, full flood & induced through the wheel. I know oil is recommended for Al, but don't have that option.

If there is a great pile of to do instead of one piece, i'd conisder stringing them up on the planer....

If the mill will swing an 8" flycutter, no objections.

Then again, OP has not clarified what his real sealing requirements are.

smt

onecut · Jan 7, 2016

Think I agree with most of the posts.Tram the head for peace of mind.You could buy a face mill specially designed for alluminium get the reccomended tips that go with the cutter for the material being cut-you could buy a one that has a large enough diameter to do each face in one pass.One of those that size will cost a pretty penny.So maybe a 4ins diameter face mill and do it in 2 passes if any trouble with the step over-leave a millimeter on and make a fly cutter large enough to cover the face and skim both faces with the fly cutter to size.

Laverda · Jan 7, 2016

Get a metal shaper. None of the issues you get with a mill. I had to make some steel plates as flat and best surface finish as possible a few months ago. The metal shaper laughed at the surface finish the Bridgeport could only do.

Bruce

dian · Jan 7, 2016

why does a fly cutter produce a better finish than a good facemill?

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