Multiple Pass - Issues

[xoneeleven]

Hello All,
We have a CNC Shark HD3.
The software being used for design, is VCarve Pro 8.5
The software being used to carve, is the CNC Shark software.

The issue we are having occurs when multiple passes are used.
The passes are not seamless with each other.
Pass one works fine, and pass two appears to work.
However, upon inspection, there is a noticeable break where the two passes meet.
The passes should make a seamless cut, together. However, this is not the case.
Has someone seen this issue before, and what would the cause, and resolution be?

Thanks...
Mark

[bill z]

When this happens to me, the first thing I suspect is a static discharge. It doesn't take much to have the servos to skip a tick or two.

Have you grounded everything? I mean from your vacuum hose to your router mount and everything in-between.

Also, when I change my router bit, sometimes I move the router ever so little to loosen the old bit or tighten the new bit and that does it.

Check your clamps, If there is the slightest slip due to a so so clamp, that will do it.

Just some ideas for you.

[xoneeleven]

Hello Bill,
Thanks for the response.

Grounding:
We have not grounded everything together, but each has a grounding plug that should tie them altogether. We will try a separate grounding wire from the CNC, to the dust collection vacuum system.
We currently have the CNC plugged into an APC UPS. (could this be an issue?)

Router Bits: The bit does not change from pass to pass, so this would not be the issue source.

Clamps: All clamps are always locked down properly.

NOTE: This issue occurs on every job where we use multiple passes. The same result happens regardless of what bit we use (we use mostly Amana bits)

[jeb2cav]

When you say 'multiple passes' - is this multiple passes, but all coming from the same toolpath? Not that it should matter - but a potential problem if 2 separate toolpaths.

What toolpath speed are you using for these 2 passes? What is the bit and what is the per pass cutting depth?

I'd also try running this at 50% of the current speed. It could be that you're getting a slight shift while carving the first toolpath/pass, and when it goes to the second pass, it is now offset by a very small amount - but you get the result in your picture. If running this at 50% removes the defect, you can then start ramping up the toolpath speed until it creeps in again - and now you have a sense of the limit for that material/tool/depth/etc settings.

From the picture, you are getting some tearing/poor cutting/carving in some areas of the raised letters in the pocket. While you are cutting into wood, this can be addressed to some degree with a slower speed or sharp cutter (or both). If you're convinced the cutter is 'good', then this would be another reason to slow the toolpath execution. If a cutter is even slightly dull, the outcome can result as your picture is if the speed is high (high speed and even slightly dull cutter on cnc machine is a bad combination).

From the picture - you may want to double check if your router is square to the table in all directions. You can place a metal rod in the chuck and check this with a square, and then make adjustments as needed. It will not address the problem you raise, but it will cut down on the amount of sanding you'll have to do on the pocket surface.

I don't own an HD3 - however on my setup, you can remove any slight 'slop' in the axis action by loosening the set nut on the collar with the drive shaft, press firmly on the carriage in a direction opposite the motor, and with the pressure maintained, tighten the set screw on the coupler. You can do the same with the axis 'under' the table. While I think this is less likely given your picture and description of the work flow in this case, it can give a similar outcome.

As to the APC UPS - I suspect it is also a power conditioner, and in fact this is a very useful thing to have. It's not so much that you have to have everything grounded together, and it sounds like you do have everything grounded - most importantly is the dust collection system. I do agree with Bill's comment about losing a couple of tics from poor grounding and/or poor power (which if your APC/UPS also conditions the power is probably removed) as a possible candidate, and all of Bill's other ideas (for what it's worth). But some of the above ideas would also give the same result - in essence a couple of tics have been lost as the tool wasn't able to move as expected - and while it's really not much, it's enough to 'see' and also to have to address before final finishing.

[sharkcutup]

Although this is a minor result it does occur ---

Stresses being relieved within the wood!! I have actually witnessed this happening on several occasions after my clamps were tightened. I have also noticed variances (which is related to changes in the wood from previous tool path) in the virtual zero readings using same router bit on a different tool path for the same project job.

Everyone here has very informative input and I hope that you find and resolve your issue!!!

Have a GREAT DAY!!!

Be SAFE around those AWESOME machines!!!

[xoneeleven]

Thanks, sharkcutup and jeb2cav...

We are actually running quite slow (30in per minute feed rate at 1/8 depth using a 60-degree v-bit)
Although there are 8 or 9 tool paths, the passes are on a single tool path using the same tool. No changing of bits is done.

The wood we are using to prototype on is either pine or Tamarac.

We will look into these possible root causes and hopefully it will be an easy fix.

Mark

[Bob]

Also, measure the angle of your bit. Determine if it's exactly 60 degrees. Even a slight difference between what the program calculates and what the actual angle is, can make a difference in cut quality.
Bob

[tonydude]

Try using a different angle when carving. How does the preview look? I use a 315 dog angle when doing 3d work.

Tony