Something is off .02"

[eklug]

When I cut a simple 3" square with .25 diameter radius on the corners one side will be .02" larger than the other side. This happens whether it is a profile cut or an area clearance. Any help on what to look at first?

emily

[myxpykalix]

does this happen on the same side consistently? or different sides depending on type of cut?

[paco]

Is your tool well sit on the roller (carriage)?

Any play in the Z axis or something loose in this area?

Assuming your tool is in good shape and well set; what material? Solid wood can have this sort of behavior under heavy load (or when the tool is not firm on it's rails); the cutter has different bit in wood grain direction or cross grain... Only the first pass of an area clearance (pocket) is 100% tool bit wideness, the next passes are more than often less (generally 40%) thus much less load on the tool bit... not to mention that the stepdown of the pocketing might be different than the cut out (profiling)... same feed and RPM?...

Long story short, make sure the machine is solid on it's rails and nothing is loose. Next, make sure your comparing similar setting from different cutting strategies. In solid wood, to get a very accurate cut you may need a larger tool bit and a more delicate approach.

Keep us post.

[fleinbach]

Emily,

To narrow down the cause more information is needed. Mainly speed of cut and depth of cut. These factors will always make a differance in size of parts if they are to deep or to fast. Are you making your cuts using climb or conventional. Whichever one you where using make the cut using the other one. Did this make the part smaller instead of larger this time? If so your problem is with flex movement of the Y-car. As Paco said above make sure everything is as tight as possible but even then you will still have problems if your cuts are to deep or to fast.

[elcruisr]

Another factor can be tool diameter. .25 and smaller tools can flex during some cuts throwing things off.

[eklug]

Thanks

The tool is .5 downcut spiral. i am cutting .25 deep with a stepover of about 80%. Only one pass at 3 ips and its in mdf. Everything feels tight. and the tool is secure in the collet. its a columbo spindle. i can have maintainence check the axises. the profile was made using a climb cut and the area clearance was done with an offset cut. The area clearance cut is on an angle to the axises (it is diagonal to the x and y axis) the profile cut is square to the axises.
Im not sure if the same side is off on all parts.

any of this help?

[richards]

Emily,

Try running a simple test cut using the most basic commands:

SA
JZ,1.0
J2,5.0,5.0
JZ,0.05
M3,3.0,5.0,-0.25
MY,5.0
MX,5.0
MY,3.0
MX,3.0
MY,5.0
JZ,1.0
J2,0.0,0.0
END

That little program will ramp into a cut and then cut a 3" square 1/4" deep climb cut. Look at the corners and see if there is any overshoot. (There wasn't on my machine when I used a 3/8" cutter.)

My guess is that the ramp vs plunge is the culprit. Some of my cutters, especially spirals plunge very well, but sometimes a cutter's 'bottom' flute(s) are too dull or not designed for plunging and problems occur.

[fleinbach]

Emily,

On the profile cut you said you where using climb cut. Can you make a test cut using conentional and see if the problem reverses. In other words is the .02 descrepancy now smaller rather then larger as you described