[Cruiser]

I think I'd run it again with no part, spindle, coolant, higher feed rate & watch the "z" values. probably would find a bogus or two.

[bill south]

Wildcat;
Just for grins, what were your machine settings regarding depth of cut, step over and feeds. Even though you are having dimension issues, the cut doesn't look that bad for a home brew!
Thanks.
Bill

[MetDetect]

Is it losing position on the Z axis towards the table? Attach a dial indicator to the head or spindle. Set indicator to zero off a vise or something stationary then make a number of 1 inch moves up and down on Z. If the Z axis is working properly after 10 or 20 or 30 moves the indicator will still read zero.

[holbieone]

About the curvature there was at least .005 and probably .050 on average. In the "flat" areas I would say the average was .100. I say "average" because of the nature of the roughing operation. Yes, only the ball was engaged with the material. I can assure you the drawbar was tight but given this problem is not uncommon to me I wonder if the collets are not great or the spindle does not have correct taper. The collets are Lyndex but I suppose even they can make a bad collet from time to time. I am considering getting a set of ER collets and a collet chuck and hopefully solving this problem.

if it only has a few points of contact in the holder then its possible it rocked its self down

it also can be a little bit of every thing combined

the more moving part the more places for error

for example most of the things i mill are in 5 axis and the error adds up
things we look for

worn tooling
tool run out
backlash in all axis (including the two rotary axis)
loose fixture
thermal growth in the machine as well as in the ball screw ,and the spindle(this will slowly change from the start of the part to the end of the part ,machine worm ups before milling helps)
machine not being level

[kentavv]

Wildcat;
Just for grins, what were your machine settings regarding depth of cut, step over and feeds. Even though you are having dimension issues, the cut doesn't look that bad for a home brew!

Thanks! With some polishing the problem areas would probably not be visible. I'm just trying to get a sense of what is reasonable with a home brew

Here are the numbers:
6ipm plunge, 10ipm feed, and 3200RPM for both roughing and finishing
.1 stepdown and .2 step over for roughing leaving at least .005 for finishing
1/2 degree steps while finishing (starts at the center and follows the curvature radially)

I currently go from 0 degrees to 360 degrees counterclockwise. I would like to try overlapping the start and end a bit and see if the "mark" that is being left could be blended a little.

[holbieone]

are you talking mm or inch for your step over

[holbieone]

going in the direction your cutting your conventional milling

climb milling would be better

[kentavv]

are you talking mm or inch for your step over

All measurements were in inches.

[kentavv]

going in the direction your cutting your conventional milling

climb milling would be better

I could be complete off base here, certainly happens frequently , but... During the finishing cut there is 50% conventional and 50% climb because of the radial zig-zag pattern from the center. While going downhill it conventional milling and while going uphill it is climbmilling. Going clockwise would only flip these around. I put up a picture a little earlier that tries to explain how the finishing pass ran. If you see a problem with that approach please let me know and I'll give it another go.

[holbieone]

OK your milling if by directional

that should work well

[Capteod]

The information you supplied as to feeds and speed, indicate that this is a very good roughing out of the part. Try to decrease the Stepdown and stepover to get a better finish. When we make a mold plug the feeds and stepover is always 0.25 times rates of feed used in roughing. The curvature at the bottom of the part is the ball radii of the cutter.

When we are finishing the parts for a mold, we use the smallest possible diameter ball cutter, and the use of a large diameter gives you a large kerf that must me polished out. Our parts will require no polishing and have a finish of 16 micro. If we need the square shoulder on the plug, we start the process with a regular end mill, removing the excess metal before cutting the profile of the part.

I think that the information in this thread is leading you on a false trail.

Thanks! With some polishing the problem areas would probably not be visible. I'm just trying to get a sense of what is reasonable with a home brew

Here are the numbers:
6ipm plunge, 10ipm feed, and 3200RPM for both roughing and finishing
.1 stepdown and .2 step over for roughing leaving at least .005 for finishing
1/2 degree steps while finishing (starts at the center and follows the curvature radially)

I currently go from 0 degrees to 360 degrees counterclockwise. I would like to try overlapping the start and end a bit and see if the "mark" that is being left could be blended a little.