[CYoung]

Hi Guys,
I am having an issue for quite some time now and finally decided to address it and hopefully get some help/guidance. I am profiling just simple shapes with my PRO4848 and I keep seeing the same thing. When the bit plunges and exits a cut, I get an indented line from the router bit along the wall of the work piece (see pic attached). In this case, I am cutting 3/4" Poplar with the following specs;

Passes = 6
Tool speed = 120 in/min
Router Speed=12K RPM (Dewalt)

The lines are when the bit rises up over a tab, then plunges again to continue with the cut. I have seen this with many types of wood and many different speed/RPM configurations. My first thought is the PRO4848 is flexing, but I dont know if this is true. These lines never show up on the simulations (BobCAM V24). Any thoughts on what is happening and better yet, how to eliminate this?

Thanks, Craig

[nlancaster]

I use vcarve pro and it has an option for 3d tabs. this causes a ramped move instead of retract and plunge move. See if bobcam has an option like that.

[CYoung]

I use vcarve pro and it has an option for 3d tabs. this causes a ramped move instead of retract and plunge move. See if bobcam has an option like that.

I can ramp in, but there is no option to ramp out. I get these vertical marks on both the entry and exit. I am wondering if it has something to do with the compensation (left, right, machine??), I really dont know.

[dgage]

I use vcarve pro and it has an option for 3d tabs. this causes a ramped move instead of retract and plunge move. See if bobcam has an option like that.

I agree. VCarve Pro has the 3D tabs which automatically ramp in and out making triangular shaped tabs. You might want to grab a demo and see if that helps any.

[gfacer]

This would be an issue of cut start and end ramping, nothing to do with tabs. Bobcad probably has what you need, probably called lead in and lead out.....ramping is good, but your issue isn't ramping related, exactly, probably mostly slightly lower machine rigidity than needed. Force of the z movement moves the spindle a bit. This would not always should up for the exit, so maybe a backlash issue or some other small problem. However, the lead in and lead out should make the marks go away even without solving the cause.

[CYoung]

This would be an issue of cut start and end ramping, nothing to do with tabs. Bobcad probably has what you need, probably called lead in and lead out.....ramping is good, but your issue isn't ramping related, exactly, probably mostly slightly lower machine rigidity than needed. Force of the z movement moves the spindle a bit. This would not always should up for the exit, so maybe a backlash issue or some other small problem. However, the lead in and lead out should make the marks go away even without solving the cause.

So should I slow down the z axis (up down) abit in addition to lead in and out?

[gfacer]

Nah, just use lead in and lead out and see if you can make the assembly tighter or more rigid....the slowing down might help, but probably not too much and might make the bits wear faster.

[CYoung]

Nah, just use lead in and lead out and see if you can make the assembly tighter or more rigid....the slowing down might help, but probably not too much and might make the bits wear faster.

Well, there really is no way to tighten up the assembly or make more rigid. At least none that I am aware of. I guess this is more of a general CNCROUTERPARTS question. Is this common with the PRO4848?

[gfacer]

No idea....but one question is what type of wood is it? Some are much more difficult than others.....I don't cut wood often, but tried Maple once, it was tricky!

[CYoung]

This particular example was Poplar, but I have the same issue with Maple, Cherry, Pine, etc. Maple is very tricky to mill, its the hardest I have worked with thus far.

[LeeWay]

How old is the router? Have you checked the runout in it?
It could be a little play in the Z axis. Have you trammed the Z axis?
I think you could tighten up the v bearings some if they are loose enough to be the cause of this. If they are tight already though, you would have to look elsewhere. I have the Pro 4824 sitting here, but it is not fully assembled yet. I know the Z axis came fully assembled, less the motor. Did you go over it after installation?

[dgage]

One there thought relates to material hold down. How do you hold down material and how secure is it?

[popspipes]

Hi Guys,
I am having an issue for quite some time now and finally decided to address it and hopefully get some help/guidance. I am profiling just simple shapes with my PRO4848 and I keep seeing the same thing. When the bit plunges and exits a cut, I get an indented line from the router bit along the wall of the work piece (see pic attached). In this case, I am cutting 3/4" Poplar with the following specs;

Passes = 6
Tool speed = 120 in/min
Router Speed=12K RPM (Dewalt)

The lines are when the bit rises up over a tab, then plunges again to continue with the cut. I have seen this with many types of wood and many different speed/RPM configurations. My first thought is the PRO4848 is flexing, but I dont know if this is true. These lines never show up on the simulations (BobCAM V24). Any thoughts on what is happening and better yet, how to eliminate this?

Thanks, Craig

The solution is to not stop cutter travel while its engaged in the cut, and still spinning, this will happen on any machine and any material that I am familiar with. Lead in, lead out, as suggested above is the only cure for it that I know.

[nlancaster]

The reason everyone keeps mentioning 3d or ramped tabs, is because you stated this is where the retraction and plunge happens when forming a tab. A ramped, or 3d, tab means that the router never stays in one spot but just keeps moving, this would result in zero retract and pluge moves. meaning no marks.

[CYoung]

The Router (Dewalt) is about 1 year old, I never even thought to check that! I trammed the Z-Axis when I build the machine about a year ago, but havent checked it since. I guess I should probably start there and verify the machine is square and tight.As far as I know, this entry/exit marking has always been a problem since day one. I am just now getting around to addressing it. I have worked around it by just finish sanding the edges of the machined wood, but I would like to solve this issue as I get more proficient with my machine.

[bhurts]

I would say 3d tabs if possible are your best solution. Lead in and out may help but it still requires a retract. I have been a machinist for a long time now and have used a range of cnc machines from cheap to very expensive. If you plunge right on the part wall and don't leave material for a clean-up pass you will see this even on very expensive machines. I make parts I'm not a scientist but here's what I think causes it. When you plunge with a flat endmill are pushing a flat face against a flat face with chips forming underneath the tool. The bit can't help but vibrate or oscillate a small amount. On higher end machines this is less pronounced especially with softer materials but still present. With harder materials it is just as bad or worse even on big vmc's. This is why we use lead in and out moves as well as 3d tabs.

Ben

[gfacer]

Now that I can post again, I agree with the 3d tabs, didn't read the OP well. Might have to use an onion skin and not tabs. or make a final light pass to final size at full depth. Does the same type of mark show on your cut retract and plunge.... If not, might be and acceleration or deceleration or even feedrate issue that is different for the tabs.

[Jon.N.CNC]

are you doing lead in and outs? i never get these marks doing this.. 2mm lead distance 4mm radius leads puts the bit 2mm away from the part before it retracts. only in very tight spot where a lead wont fit do i not use them. even 0.1mm lead is better than none tho.

[LeeWay]

Another consideration other than lead ins/outs might be direction of cut. Climb cutting or conventional.

[CYoung]

I added right angle lead in/out and that seems to have solved the problem. Not sure why I didnt think of this before? I guess I am still just a newbie as there is much more I don't know than I actually do know! Thanks everyone for the suggestions and support. Greatly appreciate all the help I get on this forum.