Face mill cuts one direction but not the other

[vmipacman]

I have a 4x8 table top we are facing. Inserts are a bit dull, just roughing it flat.
Cutting in the X+ direction, I’m removing material and all good, but cutter acts like it’s lifting after about midway. Then moving in the X- direction it cuts that side and acts like it’s lifting on the far side. Difference in the two cuts is about 30thou. On the end slats the cut difference disappears. You can kinda see how one slat to the left of center is cut full width and right of center no cut.
I have checked the rotary table and it does not seem to be moving at all.
Could it be the table twisting on the ways? But then why are the cuts on the extremities of the table flush and ok? Is that indicating anything?
Do dull inserts tend to grab and pull material in one direction vs changing the feed direction? I’ve kinda experienced this before but not this bad.
I put a mag base indicator on the angle plates to the table weldment and didn’t see anything immediately interesting.
Rpm is like 350, 15ipm.
Thoughts?
Thanks

 

[Gordon Heaton]

I'm no expert but that's a pretty long reach. Could there be a bit of one-sided slop in the quill?

 

[mach ramsey mn]

30 thou? .030”? Something is moving around. What is holding these “slats”? Something loose in the setup? Try cutting in the Y axis?

 

[Vancbiker]

If your head hangs off the side of the column, loose gibs/keeper plates can let the head “swing” which lets it cut one direction but push away in the other. The greater the quill extension the larger that effect will manifest.

 

[mach ramsey mn]

Vanc., I get what you’re saying but .030? That tool would have to go a long way…

 

[lobust]

30 thou.... something must be loose.

Pull all the way covers and put indicators between all the moving parts and the slides that they run on. You'll see any rock/shift very clearly as it happens.

 

[Vancbiker]

Vanc., I get what you’re saying but .030? That tool would have to go a long way…

I wasn’t paying attention to the.03”. Yes, a mile in machining.

 

[atex57]

Dull cutter makes a lot of heat and will make parts like that crawl around.

Ed.

 

[Garwood]

My kuraki table cocks on the ways. Mine is about .002" difference one way vs the other.

.03" sounds like the turcite fell out somewhere.

 

[Barbter]

If you change the cutter out for a plunger clock (I would normally say DTI, but "firfty fou" would be too much movement) and run the clock over the part, do you get the same "shape" (clock movement)?
I'm just wondering if it's quill or table and with no cutting force, this would eliminate the quill?

 

[Spruewell]

If you suspect an issue with thermal expansion, it looks like you might be able to put an indicator on the backside of the part and watch it for movement during a cut. However, you shouldn't be seeing heat transfer between the slats.

 

[MwTech Inc]

Wonky plates.......the two must be warped downwards in that spot.
So, what is the spec on flatness anyway??
Dull inserts, and you know they are dull...shame on you.

 

[Garwood]

Wonky plates.......the two must be warped downwards in that spot.
So, what is the spec on flatness anyway??
Dull inserts, and you know they are dull...shame on you.

The little tiny corner is like 5% of the insert.

You gotta look at it that way sometimes- That insert is still 95% good!

Cornerless carbide can still rough pretty good in mild steel, but it ain't gonna finish.

 

[MwTech Inc]

Yea agree, but VMI didn't say how dull....lol
also didn't give the depth of cut.... so in reality 20?-40? % of his Depth of cut could be grinding worn out inserts around......
Be different if the DOC was .250.
And with only 3 points of slat contact (am I right VMI?) slats could be moving......
Neg cutting head(?) worn inserts...just sayin.....

 

[Spruewell]

If the slats were moving the pattern would be more localized within each slat. not necessarily across the whole thing. Maybe check the quill and head to make sure there isn't something loose there. but then again, the pattern would be consistent within each slat as tool pressure changed between them and not across the whole part. If the table traverses in Z and rotates A, while the spindle traverses X and Y on a moving column, then that is where I would look. (since he has already checked to make sure there is no movement in the table)

 

[MwTech Inc]

Do we know if the machine can actually cut 8' and have a tight tolerance in that length?

 

[Mud]

What is the material being cut? Did I miss that?

 

[vmipacman]

What is the material being cut? Did I miss that?

A36 steel.
I was out looking at a job all day today. 11hrs in the car I’m beat.
Let me get on this tomorrow with some fresh inserts and indicator and see what I can see.
thanks for the ideas on possible causes

 

[eKretz]

Hmm. Pretty thin and long "planks" there, that fab doesn't look very rigid. Was that fabrication stress relieved after welding? Lots of reasons things could be moving, including stress relief as you remove material. If the machine normally cuts pretty straight, that's the direction where I'd be looking. And starting with fresh, sharp inserts on something that flimsy is always a good idea.

 

[lobust]

Hmm. Pretty thin and long "planks" there, that fab doesn't look very rigid. Was that fabrication stress relieved after welding? Lots of reasons things could be moving, including stress relief as you remove material. If the machine normally cuts pretty straight, that's the direction where I'd be looking.

The pattern looks way too consistent to be the part warping IMO.