View Full Version : Question about carving artifact

03-03-2015, 05:47 PM
I cut the following with a CNCRP 4824 Pro using a 1/32" bullnose spinning at 13100 and at a rate of 75 ipm. The wood is walnut. This is the first time I cut a recessed project and my question concerns the horizontal lines present throughout but most noticeable on the curved surface. The cutter swept in a raster pattern from L > R > L so I'm guessing there is something amiss in the Z axis. I tried different cut rates and a larger bit (125 and 50 ipm, a 1/16" bullnose) but the results are the same. I'm hard pressed to say I can actually feel them with my fingertip but obviously they are easily seen and will need to be sanded out. Any help as to where to look for the cause? Any other info I can provide?

I realize the lighting is horrible and the pic is upside down but the salient feature is seen.

03-03-2015, 06:49 PM
my question concerns the horizontal lines present throughout

I see vertical lines, not horizontal lines. I'd say it's a mechanical issue, causing a vibration or resonance.
Could be very tricky to track down.

03-03-2015, 07:29 PM
Yes, vertical in that picture. My bad. At least they can be seen.

As I think about it, maybe there's something about the x axis that is causing a periodic "bump" which is the translated into the z. Could this be an artifact of the R&P?

On my machine, the object to be cut is turned 90 degrees to the long axis of the table (in the pic provided the long axis of the oval is parallel to the short axis of the table) that's I wonder about the R&P.

03-03-2015, 08:04 PM
I don't know if it helps you

set federate about 80-90 ipm then try to raise acceleration so the router accelerate up on shorter distances..

I had this occurrence with mach 3... and this was what helped..

when I say raise accelerate it means raise as much it not jerking yet..
I also turned of the corner exact stops..in general config...

I also tried to put wood as grain was run along the table.. so gantry was ""steady"" and moved on passes end only..

03-03-2015, 11:43 PM
Are the lines going the same way your bit was rastering? If so is it possible you just have your stepover too high? I know lines start becoming visable at around 20%. i usually cut lithopanes and 3d rasters at 10%.

03-04-2015, 09:17 AM
Victorofga - appreciate the input, will give it a try.

Grubscrew - stepover was set at 9.9% and the lines are perpendicular to the rastering movement so I don't think that's it but thanks for the input.

03-04-2015, 11:45 AM
I had similar artifacts until I stiffened the base.

03-06-2015, 01:05 AM
I'm new to CNC routers, so take this idea for what it is worth (very little).

Create a program with the same parameters, cutting say a 12"x12" square, but cutting just a flat surface. Then use a dial test indicator in the spindle (spindle turned off obviously) as the machine moves it across a flat surface (like a piece of glass or a smooth piece of aluminum). I would think that if the issue is due to movement in any axis, it would be visible in the DTI. If your test shows that the movement is smooth, it would indicate that the issue is related to your router or router bit.

I'm amazed at how the lines are so perfect, from a newbies view it seems like it has to be caused by something that happens consistently through the movement of that axis. Could it be possible that your V wheels need to be tightened up, and that the R&P is causing vertical movement or rotation in the carriage? I would measure the distance from peak to peak on those striations and see if they coincide with the R&P dimensions.

Just some ideas, I only have limited experience with cnc routers, I have only been running a small benchtop cnc router for the last 6 months. But this is how I would go about testing the issue (at least till someone with more knowledge told me a better way to go about it).

Good luck! I'm interested to hear how it goes.

03-06-2015, 01:06 AM
I had similar artifacts until I stiffened the base.

How did you go about stiffening the base? Would you be willing to post some pics?


03-11-2015, 07:28 PM
Sorry for taking so long to get back to the list, had a small family crisis.

I more or less solved the problem for now by rotating the workpiece 90 degrees. Nearly all of the artifact is gone suggesting to me something is amiss with the x axis. Im planning on rechecking all bolts, rails, etc assoc'd to hopefully find the problem.

Thanks for all the help.

03-11-2015, 07:31 PM
I hope all is well.

It does indeed suggest a problem with the x axis. Let us know what you find out when you start trying to track down the problem.

03-11-2015, 08:40 PM
Have you trammed the machine?

03-12-2015, 01:03 AM
Tramming - I'm open to suggestions as to a good way to do this. I think I understand the process but not sure...

03-12-2015, 02:58 AM
since you used ball nose bit, the tramming wont help for this particular case..
even spindle misaligned, the ballnose just touching the surface on very small area..

using the gantry for the movement, will be better, because you get less ""flexing""