[MaCurless]

I have 2 Roland MDX-540 bench top mills and I can not seem to get any consistency out of the machines. They almost always come out to thin or to thick. Now I am not the cad operator I just run the machines. I do work closely with him and this is perplexing both of us. I also have about 6 months experience in cnc work I was promoted to R&D at my company. Other information neither I or the cad guy have had any training on these machines, just what we can figure out. Also what kind of base should these machines be sitting on, one of my theory is that the they are not secure enough to keep the machines from messing up. Any help would be greatly appreciated.

Matt

[roninB4]

Matt;
Not enough information to answer your questions. Define the thickness variation. Define the material and the cutting parameters. I can tell you that any machine will work better if it's secured to a solid base, even a bench grinder. Are you allowing a rough/finish cut or taking it all in one pass? What type of cutter are you using? Speeds/feed? How are you holding the workpiece? How far off over what distance? Are the cutters dull? Is the workpiece warping due to heat as you cut it?

There's a lot of variables to be accounted for, photos also help if you want others to chime in. More information generates a better reply most of the time.

[MaCurless]

OK hopefully this will help, on thickness variation we are shooting for .001-.005, but we keep getting .005-.01. The Material we use is Tivar, we use a roughing with these parameters Feed Rate of 4500 mm/min, Spindle rate of 12000 rpm's, Cutting in amount of .o850 inches, path interval of .0750 inches, and a finishing margin of .0080. The roughing uses a 1/4" ball end drill bit. The Finishing parameters are FR 3500, spindle 12000, cutting in .050, path interval of .0075, and a finishing margin of .0000. The finishing uses a 1/8" ball end drill bit. We secure the material to a phenolic board which is then screwed to an aluminum plate. The material is secured with two sided carpet tape and screws. Bits are all keep sharp and in good condition. I don't know how much heat plays into it, it does not seem to generate any heat at all, the piece is always room temperature and you can hold it and touch it as soon as it is taken off of the plates. The machines are placed atop a kitchen cabinet each, they are not secured to the ground or the wall. What would be a good thing to secure them to. I don't have any real experience with cnc well up till 6 months ago so all your help is much appreciated. I will try to give you any info I can if it will help you answer my question. the company I work for is kinda paranoid so I cant send pictures other wise I would. Again your help is much appreciated.

My most gracious thanks:
Matt

[eartaker]

My guess would have to be that it isn't the machine. I'm am guessing you are not getting an accurate 0 ref on your Z-Axis while indexing the endmills. That being said, how are you zeroing your z axis?

[MaCurless]

I zero the z axis using the z axis sensor that is attach to the machine. It is placed on the phenalic board next to the peice being cut, then using the mdx-540 control panel to detect the z axis, after that I remove the sensor and lower the bit to the now z origin, then I use the control panel to raise it to the z axis # that the drawing spits out of srp play.

[gd.marsh]

I think I would suspect the two sided carpet tape ..

I've seen various kinds & some seems pretty spongy to me ..

I also can't imagine ANY carpet tape would be consistent in thickness to the tolerances you're looking for .. based on what it's made for.

My $.02 ..

[roninB4]

The tolerance for the machines SHOULD be attainable (should being the operative phrase here). I would have to examine your set up to determine if you're:

1) Inducing distortion to your work piece using screws

2) Using tape that varies in thickness

3) Using some type/combination of parallel & vise that's not sitting flat

4) Something under the vise

5) The aluminum plate isn't flat and/or parallel

6) How are you holding the cutter?

7) When you re-zero, how much difference is there between pieces?


Those are the first questions that pop out of my head. I will say that taking an .085 cut in a workpiece that's held only with double sided tape would make me cringe a bit. I don't trust double sided tape for anything but light cuts. That's just me.