I don't think so. Pretty common in my experience. Have you done a lot of work with fabs this size?
Face mill cuts one direction but not the other
- Thread starter vmipacman
- Start date
Yes, a lot and bigger too...
Look at the pattern, it's a perfect criss-cross in the middle of travel that blends perfectly at either end of travel.
Fabs warp of course, but they don't tend to be so neat about it...
Same here, and a lot of experience cutting large fabrications. I have seen them be very neat in their movement...it very much depends on the fab geometry and clamp arrangements. If the machine cuts straight otherwise and the job isn't moving on the table, I'd be very surprised if this was not movement due to stress relief.
Jashley73
Well-known member
Time to go over that machine with an indicator(s).
First, magnet on the part/table/base, and needle on the quill. Push/pull on the quill, up/down/left/right, a see what movement you get.
Next, do the reverse. Magnet on head/quill, needle on the part/table/base. Move left/right. Look for movement. Does the indicator's load change with left/right movement? Say over 1", while reversing directions?
Try putting a magnet on the table/base, and needle on the ways. Look for movement across the feed length. Try with the needle in the vertical, and horizontal directions.
I was also taught to put indicators on the table/part during machining. Magnet on table, needle on the part. On both ends, looking for the part to move back on the table. Maybe a 3rd, looking for the part to "slide" in the X-axis.
If none of that shows anything, try facing in the Y-negative direction. That will let gravity help with the feed force. If it acts wonky, that may indicate movement as well. Try facing Y-positive - gravity/feed-force will keep all of the sag in one direction.
In both +Y and -Y directions, put an indicator - magnet on head, needle on ways - to see if the head is moving/lifting off the ways.
First, magnet on the part/table/base, and needle on the quill. Push/pull on the quill, up/down/left/right, a see what movement you get.
Next, do the reverse. Magnet on head/quill, needle on the part/table/base. Move left/right. Look for movement. Does the indicator's load change with left/right movement? Say over 1", while reversing directions?
Try putting a magnet on the table/base, and needle on the ways. Look for movement across the feed length. Try with the needle in the vertical, and horizontal directions.
I was also taught to put indicators on the table/part during machining. Magnet on table, needle on the part. On both ends, looking for the part to move back on the table. Maybe a 3rd, looking for the part to "slide" in the X-axis.
If none of that shows anything, try facing in the Y-negative direction. That will let gravity help with the feed force. If it acts wonky, that may indicate movement as well. Try facing Y-positive - gravity/feed-force will keep all of the sag in one direction.
In both +Y and -Y directions, put an indicator - magnet on head, needle on ways - to see if the head is moving/lifting off the ways.
Jashley73
Well-known member
A36 doesn't keep a whole lot of stress internally, unlike 1018/cold-rolled steels. Any "stress" coming out of the part, would be from welds pulling on the pieces during welding.
Possible, but with any sense, kept to a minimum.
The surface-scale being cut in only one direction - and not the other - is a big clue that something within the machine itself is moving about.
Possible, but with any sense, kept to a minimum.
The surface-scale being cut in only one direction - and not the other - is a big clue that something within the machine itself is moving about.
I have found that not to be true with thin sections. Thicker ones, I agree. I am going on the assumption that he knows the machine well and this is an unusual occurrence. Machine geometry issues are usually not something that happens overnight.
Well idk what the root cause is. The machine is straight, best I can tell. I can’t get “any” movement with a 6’ crow bar. Checked table slop, rotation, head, etc
Sharp inserts made a big difference. But something is still moving a lot. I think it’s the slats but I just wouldn’t have expected it. Next time we will do a better job planning clamp arrangement. And make from durabar!?
thanks for all the ideas.
I’m really settling on this weldment being the problem.
Sharp inserts made a big difference. But something is still moving a lot. I think it’s the slats but I just wouldn’t have expected it. Next time we will do a better job planning clamp arrangement. And make from durabar!?
thanks for all the ideas.
I’m really settling on this weldment being the problem.
Happy to proven wrong on this one!
Herding Cats
Hardplates
I feel if you switch from a zig zag facing pattern to a unidirectional pattern that will tell a lot about if it is the machine or the work. If its the work I would expect to see the same pattern with both facing strategies. If it gets better with a unidirectional pattern then I would think it is machine related from cutting forces.
mach ramsey mn
Active member
Just think about this: take a piece of A36 3/4x6” 4’ long and put it in 3 6”vises. Using a 4” face mill try to cut it flat. What is going to happen?
The part is moving around like crazy.
The part is moving around like crazy.
True. This might be more like 3 vises but I get your point.
But actually... in that scenario I would have way under estimated its movement apparently.
I would have thought, "cutting it flat is possible! You just have to cut it in its relaxed position, sharp edges, and light finish pass." Ive dont it. Not to tenths, but a heck of a lot better than 30 thou.
That's why this business is so fun. Just when you think you have a few things figured out, something doesn't work the way you thought and you learn again.
MwTech Inc
Well-known member
You got that right........
mach ramsey mn
Active member
Doing a part like that I would have tacked an extra support down the middle of each side and had it thermal (if available) stress relieved. Probably tried the 4” face mill maybe went down to a 2-2.5” to lighten the tool pressure.
If the table is pitching on the ways and you cut in one direction only, it will look flat though
Herding Cats
Hardplates
That's my point. If it is "flatter" cutting in only one direction then the machine is suspect. If it maintains the same stepped pattern when cutting in only one direction then the work itself moving from stresses is suspect.
And that was more or less the goal. We are the customer and I've got some pretty low standards.
Herding Cats
Hardplates
IME diagnosing issues such as this require a systematic approach that begins at the fundamental level.
Knowing your machine, its condition and quirks eliminates some of the more basic checks. But if you perform these checks and do not find anything, it is far from wasted time. From there on forward you can operate with confidence in the machine tool itself.
I honestly did not read over every post in this thread, but I did not see a post stating "the machine is very accurate and has no problem producing a flat surface on a solid workpiece"
While I am not discounting the material moving, what I see in the photos appears to me to be a machine issue for a couple of reasons.
-the pattern is very consistent with every other pass which are in different directions
-the steps appear in the center of travel where you would expect to see the most wear
-the depth of cut appears to change in the middle in one direction and not the other (slop in the ways and a nut (ballnut) that is not in the center of the table could cause twisting of the table in one direction and not in the other)
-sharp insets helped which require less cutting force and are less likely to yaw the table (yes I know dull inserts introduce more stress in the material but they do that in all cutting directions)
Knowing your machine, its condition and quirks eliminates some of the more basic checks. But if you perform these checks and do not find anything, it is far from wasted time. From there on forward you can operate with confidence in the machine tool itself.
I honestly did not read over every post in this thread, but I did not see a post stating "the machine is very accurate and has no problem producing a flat surface on a solid workpiece"
While I am not discounting the material moving, what I see in the photos appears to me to be a machine issue for a couple of reasons.
-the pattern is very consistent with every other pass which are in different directions
-the steps appear in the center of travel where you would expect to see the most wear
-the depth of cut appears to change in the middle in one direction and not the other (slop in the ways and a nut (ballnut) that is not in the center of the table could cause twisting of the table in one direction and not in the other)
-sharp insets helped which require less cutting force and are less likely to yaw the table (yes I know dull inserts introduce more stress in the material but they do that in all cutting directions)
Mud
Well-known member
So what was learned about this? How did it come out?