Milling flats on my curve?

[woodshopcnc]

Milling some exterior corbels for a house. For some reason my SB is milling a flat space at the bottom of the curves / arch. Have noticed this before but usually just sand them out. Only mills the flat at the bottom of the arc, not the top of any? see pic

Did a major cleanup on all machine rails, gears, etc before running this file.

My geometry is a smooth arc so I don't know why it is doing this, any suggestions?

running a PRS 48 x 96 with artcam pro, 1/2" ball mill with about a 10% stepover.

[Roy Harding]

A couple of quick thoughts:

Check the "cut depth" of the toolpath in your software.

Is your Z-axis "bottoming out" before reaching the full depth of the arc?

[woodshopcnc]

Roy,

The tool is not bottoming out. Also the cut depth is not the issue, it is following a 3d profile, extruded from a 2d vector. I do these all the time and it just started doing this within the past year. Even at various z heights, it still does the same thing, a flat at the bottom of the arc.

[myxpykalix]

Have you zoomed in on your vectors to make sure you don't have any straight vectors that have not been turned into bezier curves?:confused:

[woodshopcnc]

Jack,

There are no straight vectors. I draw any / all vectors in AutoCad as tangical arcs and import them into Artcam.

[myxpykalix]

Are you sure nothing gets changed during that transfer into artcam? I'd at least zoom in and look at my vectors because stranger things have happened.:eek:

Because when i look at your pictures those flat spots look more deliberate (not sure of a good term) as opposed to an errant messup by the machine as if it is programmed into the code as opposed to some mechanical problem with the machine...if that makes sense:confused:

[woodshopcnc]

Nothing gets changed during the transfer. Artcam imports the DWG directly and once in the software if I zoom in on the vector, they are perfect arcs (start point, center or point of arc, end point).

The kicker is, this has not always happened. Started about a year back and I just deal with it and sand more. These type shaped use to be a smooth curve. What is also strange, it is always the concave curves not the convex ones?

[gc3]

what pp you using in artcam

[woodshopcnc]

Gene,

What does pp mean? The machine output file is: Shopbot arcs(inch)(Speed)(*.sbp)

[Burkhardt]

Can you try outputting g-code and then import? Just to see if that makes a difference...

[gerryv]

I'd hazzard a guess that it might be the end geometry of your cutting tool. Could it be that it only happens with a certain combination of bit and vector radius?

[Brady Watson]

What does the simulation look like in ArtCAM (@ maximum resolution on sim) ? Do the flats show up there? If yes, then you'll have to investigate your settings in the software & pin point the problem. If no, then it is either a setting in SB3 that is off, you are cutting too aggressively or your bit isn't the same as what you told ArtCAM it was. What speeds did you use to cut this?

What do you have your tolerance setting set to in the 3D toolpath in ArtCAM? 0.0025" should be fine for this work.

-B

[myxpykalix]

Maybe you can send the file to someone else who can look at it in their program or do a simulation and see if it does the same thing for them.:confused:

[woodshopcnc]

B,

On high res or low simulation, the model machines correctly.

Tolerance is set a .001 (same setting I use on higher end carving as well).

I run a feed rate of 4.8 with an rpm of 16000. This is the lower scale on the chipload chart of this 52-360BL Onsrud bit. I run this same bit alot for the rougher carvings.

The more I think about it this may have started after I tried the new software then reverted back to the older version (machine would not run on the new) think more of my computer issues.

Some older setting in SB3 could have been cleared out. If you know what or where to alter settings for this type of curve, let me know.

[Brady Watson]

If you are rastering over the 'humps', I would pull the speed back, as that sounds very aggressive. Try running 2,1 or 3,2. Chipload numbers are for production machining where tool life is your primary concern. They pretty much mean squat on a ShopBot since it is a light machine...and even less with a 3D strategy. I'd try machining it slowly...just to sneak up on where the problem lays. You said 4.8 IPS, but I didn't see a Z number. Is this for all axes?

If you suspect the computer & SB3, be sure that the firmware matches the front end. So if running 3.6.46, make sure the firmware is loaded from 3.6.46 - and so on. The VR numbers are going to influence how your machine cuts over those curves. Slow Corner Speed has the most influence. You can read all about it here (http://www.shopbotblog.com/index.php/2008/03/a-ramping-the-vr-command-and-how-to-tune-your-tool-for-maximum-performance/).

-B

[Michaelodunk]

I was just watching an artcam tutorial and it was showing a arc like yours

it first showed a full arc and then he set a limit on the arch and it created the same arc with a flat bottom when he rendered it. the limit was set on the same screen that the arc was set on.

I don't know a thing about artcam but I just happened to look at that
video today