Cut 3D Finishing

I am having a problem in Cut 3D finishing. My parts have a lot of square edges that are being rounded off in the finishing pass. The roughing cuts are perfect. What's going on?

Possible from using CV mode?

Pictures talk... along with a file. How large is the model?

Thanks for the reply, the model is about 7" X 6". I have been looking for some buttons to push or knobs to turn to correct this problem. I have attached a pic, This one is in rough cut and has nice crisp edges. If I run the finish pass I'll get the rest of the details but loose those edges. This part attaches to other segments and needs to have a low visibility seam. I am not sure what is CV Mode?

Size (resolution) shouldn't be a problem... I can tell from the picture but is that all flat surface or is there some slope on this model. If there are no slope, then why is it made in 3D CAM rather than in 2D? You sure you tool is all tight and tidy, right?

Everything on the model is drafted except the bottom, that is flat. Tools are good.

Can you post the file (*.v3d)? Can you post pictures of the finishing toolpaths results?

I did some of these in plaster with a finish pass. I have attached two pics, one with and one without a finish. Notice that the edges have been rounded.

That's strange... I suggest you send your files (v3d and pictures) to Vectric support and explain them your problem.

What kind of machine and what control? CV= Constant Velocity.

I am also thinking he has CV mode on:(...May be his tool has some faults (wrong dia entered in Gcode).....just check the runout of tool too...

also check for close tolerance values set as '0'...
just a thought/guess...

GER21:)..If CV mode is on then he must get trouble in Rough pass too..But he is getting roundness in finish pass only...

I am using a cnc9000 with Mach 3 controls. CV Mode is checked. I'm not sure what that does but when I try to change it to hard stop it flashes an abnormal condition warning.

Abnormal condition just means you've made a change to your "normal" setup. It's not an error.

When using CV mode, corners can get rounded when changing directions. In order to try to maintain the constant velocity, one axis has to start moving before the other comes to a complete stop, which usually causes a rounded corner. You can turn off CV and run it like that, but it'll probably be quite jerky. Both increasing your acceleration and or lowering the feedrate will lessen the rounding. You can also try playing with the CV angle settings.

This will give yousome more info on CV.

http://www.machsupport.com/docs/Mach3_CVSettings_v2.pdf

Gerry, Thanks for the info, that makes sense. I'll run some parts tomorrow and play with the settings. I'll get back later with the results. Thanks.

Thanks to all who responded. I learned a lot from this problem. I changed Mach 3 to Exact Stop mode in the finishing pass. The roughing pass is fine in CV mode and much faster. I have enclosed a pic. Thanks again. HStinnett

This is what the forum meant for:)...
Cheers