CNC not making good hole cuts

Ok a bit of background first. I was thrown to the wolves a few months ago in our little acrylics shop and made head cnc operator. I have a strong background in machine maintenance but have no formal training with this machine. I've been doing all the machine maintenance since starting about 6 months ago and its in really good shape. What I am having issue with is really bad scalloping..I guess thats what you'd call it..when I cut holes or make a radius. If the radius or hole is large then its not too bad but at say .5" and up it gets really choppy. My bits are sharp and our material supplier has taught me much about chip load so Im fairly sure I have the speeds dialed in. I really need some advice on what to look for as out quality is going to hell rapidly and I need to get it under control. If you need any other info let me know and I'll do my best..oh and if this is in the wrong place please let me know where it goes and I'll put it there.
Thanks in advance,
Fred

Check you set-up to make sure your part is not vibrating or that the material is flexing away from the cutter or some other reason like that.

Thanks for the reply but its not moving parts. Being a new operator I tend to tape down my work probably more than needed but I dont want to ruin material. I can see the spindle chattering as it makes the cuts so I am thinking something mechanical but not sure how to go about testing the machine to see whats failing or whats out of alignment.

You say, "If the radius or hole is large then it’s not too bad," and then you go on to say, "at .5" and up it gets really choppy.". Did you mean to say, "at .5" or less"? If so, is it maybe acceleration values? You might be setting the feed rate to the proper number but if the acceleration is low it may never be getting to that feed rate on small holes. Just a thought...

i think would be better you understand feeds and speeds on an endmill and you can calculate yourself, than following some chiploads..

it is a little more than following one given number, or describing in a short topic..

if you have geometrical differences from programmed geometry then you you have 99 percent sure wrong feed or rpm applied.. for your given conditions..

with other words you cant set feed same value on a 1 inches shape, and a 3 feet sized straigt lines..

not to mention machines are different..

also a longer flute on an endmill will enforce you to slow down due to tool rigidity..
it just too many things to answering...



wont work...

Im trying to give everyone as much information as I can about something I know little about so bear with me while I try to muddle through this.
On holes .5 or smaller its less noticeable so thats why I stated it as I did. I'm running at 18k rpm and 150 IPM on materials in the .1875 to .750 using double fluted mills. Most of my operations are focused around a .1875 bit. Again..thanks for the help and please be patient Im a noob but want to learn and understand so I can do a good job.

Read up on the calculation of true feedrate during circular interpolation.
Here are several pages from the kennametal catalogue which explain it fairly well.
Have a read and see if you are calculating the correct feedrate.

It sounds to me like there is slop someplace; not really "Back-Lash", maybe look at the coupler and check the lead-screw.

If you grab the screw by hand and you can move it in either direction there is something wrong, it's kinds like a "Subduction Zone" (plate tectonics), where if the land locks, pressure builds up until it releases, once the stored energy is released you have a "spring" effect, (elastic).

Other than that, maybe try different CAM software. "Vectric Aspire" kicks but so far as I'm concerned.