What is best way to machine large 4140 steel plate flat on 5 Axis CNC?

834MRN · Jan 26, 2019

We have a new Haas UMC750 5 Axis machine that we are milling a large plate (12” x 1.25” thick) with a 2” Kyocera face mill. Our finish pass going in the X direction, back and forth, left the surface with height variation from one mill pass to the next (we did allow for step over). You can feel it when you run your fingers over it slightly. Wondering what the best way to mill this plate flat would be? Is X axis the best direction, tool selection, teaming suggestions?

Appreciate all feedback!

DMF_TomB · Jan 26, 2019

834MRN said:
We have a new Haas UMC750 5 Axis machine that we are milling a large plate (12” x 1.25” thick) with a 2” Kyocera face mill. Our finish pass going in the X direction, back and forth, left the surface with height variation from one mill pass to the next (we did allow for step over). You can feel it when you run your fingers over it slightly. Wondering what the best way to mill this plate flat would be? Is X axis the best direction, tool selection, teaming suggestions?

Appreciate all feedback!

.
some call that lap or a height difference going across parallel mill passes.
many reasons for it

cameraman · Jan 26, 2019

Flycutter ?

On some 5 axis machines (depending on machine layout) the Y axis is straighter than the X (in ZY plane along Y axis.).

How wide is your part AND does the flat surface have to reference other surfaces and features in a precise/ accurate way (after positioning or 2nd ops clamping ? ).

How rigorously are you checking all your inserts etc. Assuming a CAT 40 machine here ?

Do you have ball bar plots + interferometry plots for your machine ? [Factory inspection report maybe hidden on the control in a sub directory as a PDF.].

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Random crap / stuff: There's the whole discussion of wiper inserts, + also the "Hack" of turning your face mill into a flycutter with a single insert... [Pinched that from New Mexico hatch green chile "Bob".]. Also if you are really up sh*t creek maybe consider a burnishing tool from Cogsdill (perhaps).

Have you mapped your machine out using a DTI and surface/ inspection plate ? Spindle has to be pretty straight in Z for every step over in Y ?

What form tolerance versus surface condition/ surface finish requirement---> IS this just first test cuts on a new machine ?

834MRN · Jan 26, 2019

Have not tried a fly cutter. Yes, CAT40. Inserts probably are dull, didn’t expect such a dramatic effect from inserts.

I will try an Y pass experiment.

Good question about the ball bar results. I will dig.

Have not used a fly cutter before, what is the technical advantage?

randella2020 · Jan 26, 2019

Try milling back and forth in Y axis. Sounds like the table isn't square to the spindle. Check machine for level and tram the spindle to the table

Sent from my XT1635-01 using Tapatalk

834MRN · Jan 26, 2019

End to End on the plate is not too bad, in the center of the part there are a couple of passes that were uneven.

cameraman · Jan 26, 2019

randella2020 said:
Try milling back and forth in Y axis. Sounds like the table isn't square to the spindle. Check machine for level and tram the spindle to the table

Sent from my XT1635-01 using Tapatalk

Maybe I'm being dumb here... Is it not the case with first clamping and putting an unreferenced piece of stock on the table that the machine should be able to cut a flat surface in the XY plane ?

Unless the machine is super unlevel... I think OP is running his/her finger nail over the surface and feeling tiny steps ?

But on the other hand as you say tramming the spindle THAT would be good to check ! Do a large sweep with an indicator ... Not sure how much jiggery pokery is needed to get that 5 axis table level in respect of spindle to tram ;-) That is kinda the $64,000 question lol Might have to end up with a separate inspection plate levelled on the table ? I'm just wondering how much a HAAS UMC 750 spindle (receptacle can be out of square ?) ---

So if the Z axis of the spindle is not square to the table then....

SO Inspection bar (300 mm long) in the spindle and running the spindle head up and down in Z with DTI in YZ plane and then again in XZ plane also to check squareness.

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* Caveat I'm on migraine drugs today so maybe I make even less sense than usual lol.

834MRN · Jan 26, 2019

It is a plate for a fixture. One of the first jobs for this machine, so first exposure to the symptom. Not grossly out of flat, just expected a better finish out of the gate. About 30 microns off on a couple of passes in the center.

cameraman · Jan 26, 2019

834MRN said:
Have not tried a fly cutter. Yes, CAT40. Inserts probably are dull, didn’t expect such a dramatic effect from inserts.

I will try an Y pass experiment.

Good question about the ball bar results. I will dig.

Have not used a fly cutter before, what is the technical advantage?

Flycutter---> Good surface finish and you can do a really wide pass. Rather than lots of narrow passes that may not be level (has a different look to it obviously) More of an advantage if you can straddle the whole part (Width wise) but, If your spindle is not square and you can't do the part (almost in one pass) then it's not so much of an advantage.). . Honestly it's more of manual machine technique but can work really well in CNC machines. There IS / are a quality of CNC machines where one does not need to resort to such methods/ techniques.

What do you estimate the difference in height you are getting ? A micron ? a tenth ? more ? And what is the distance on the surface between "Steps" in Z that you are picking up here / noticing ?

DMF_TomB · Jan 26, 2019

834MRN said:
It is a plate for a fixture. One of the first jobs for this machine, so first exposure to the symptom. Not grossly out of flat, just expected a better finish out of the gate. About 30 microns off on a couple of passes in the center.

30 micron = .0012" ? normally .0003" is a holdable lap tolerance
.
obviously factors that have an effect
1) depth of cut
2) feed rate
3) sfpm
4) coolant or dry (temp control)
5) servo's steady or oscillating ?
6) hydraulic pressure steady or oscillating
7) direction change often slides tilt and cutter position is effected
8) spindle warming up and heat cause cutter to grow longer as it warms
9) part growing as part warms
10) part deflection
11) wrong inserts throwing up a burr at edge pf pass indicates as narrow bump
12) bue or built up edge of part material sticking to cutter causing false cutting edge effect. if forming and breaking off thousands of times per minute when you stone surface you might see many shiny small high spots
13) dull inserts and some new inserts take 2 to 4 feet to wear in and cut stable
14) spindle tram error or spindle not in alignment and or leaning

cameraman · Jan 26, 2019

OK 30 micron

That's not trivial

(hmmm) :scratchchin:

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Will put thinking cap on.

My first "goto" would be an inspection bar (in the spindle) or Jerry (sp) rig one up (maybe) if you are good at that kind of thing.

The advantage of that is it doesn't matter what the orientation of the table is it's just the DTI measuring differences in Y and in X with the Spindle going up and down in Z … I.e. DTI tip touching on test bar in YZ plane with base of the indicator fixed to table and running the spindle head up and down in Z … Then do the same in XZ plane on test bar. [I'm sure you get what I mean.].

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Do you have specific example / reference for the Kyocera face mill ? (I am assuming relatively short tool length / common sense etc. ).

DMF_TomB · Jan 26, 2019

most professional shops do not use flycutters. when i got vibration problems i might take 3 of 6 inserts out but thats very rare
.
lap error is not normally number of inserts problem.
.
most inserts have very specific feed and speeds and depth and width of cut parameters. obviously look at what insert manufacturer recommends. not that they are always right but its best place to start

DMF_TomB · Jan 26, 2019

834MRN said:
We have a new Haas UMC750 5 Axis machine that we are milling a large plate (12” x 1.25” thick) with a 2” Kyocera face mill.
Appreciate all feedback!

.
large plate ?
.
it aint large til you need a crane to pick it up and set in vise and or fixture

cameraman · Jan 26, 2019

This is how they build their VF1...

If memory serves me right they don't use / show a test bar in the spindle receptacle…

They use a cylindrical square on the table a lot but that doesn't tell you how straight the angular orientation of the spindle AXIS and tool receptacle really is. That's fine for 3 axis but different test procedures and build setting are required for a 5 axis universal (beyond tramming a spindle to a table that moves in X and Y ).

---> With respect to a UMC 750 type machine Because the machine is a bridge style -ish universal (RAM-style) the XYZ movements are "Over head" and not with the table. So the spindle axis needs to be perpendicular to X and Y movements / axes and also parallel to the Z axis of movement/travel. (obviously).

^^^ This is where Nerdly found the calibration / test reports for his machine I assume it's the same on similar HAAS / vaguely contemporary controls.

cameraman · Jan 26, 2019

Just as a sanity check what's your DOC and speeds and feeds an' all that … (I assume you know what you are doing from other machines / work / similar cutting conditions... and how is it fixtured ? ---> All "hunk dory" I assume ? ).

You should be within 5 micron over 100 mm / roughly 4 inches, being super generous 10 micron over 100 mm

So you are still 3X to 6X out of tolerance…

The UMC 750 should be a lot better than that so something is definitely wrong / maybe alignment of spindle axis ? As the Y axis travels have to be a LOT straighter than that if YKWIM ?

Unless there is something bizarre with work holding/ tooling and approach to cutting/ machining ?

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