finish pass

[jms]

I have made a few signs with raised letters and a raised border. use 1/4 bit to take out majority, then use 1/8 bit to get in tight pots and finish. Problem is no matter how I zero the 1/8 bit, using same feeler gauge, it mills a hair lower than the rest and its impossible to clean up with sandpaper. Do most of you just use the 1/8 bit  and don't bother using larger bit? thats the only way I can see how to eliminate this problem. even though it will take longer, it will look better.

Joe

[Bruce]

I usually us a 1.5mm or 1/16" (1.58mm) for the finish bit. I also use the probe function to zero the Z of the new tool. You may want to look into using it. I know what you're talking about and after I started using the probe for tool changes I found it makes a big difference.

[jms]

Thanks Bruce, yeah I gave up on probe tool after smashing a few bits. Maybe I will revisit that process.

Joe

[Bruce]

I use bCNC but I think the probe function is working in UGS. What are you using as the G-code sender?

[jms]

I use bcnc, it was you that helped me install that sender and I love it. Not sure if I used probe with bcnc yet, can't remember now. But when I did, I wrote my own macro for it, after smashing a few bits (which I believe was my mistake) and it worked. But I didn't see much need for it at the time, but in this situation it would come in handy.

Joe

[Bruce]

Here is a screen shot of the probe setup. Move the endmill to a range within the 20mm above the workpiece.  If you use aluminum tape clip the positive end of the probe to the tape.  If you have the router grounded to the same point as your control then you probably don't need to connect the negative probe side to the endmill itself.  You can check by starting the probe and then touch the positive end of the probe to the endmill. If it stops then you don't need the negative probe side connection. If it doesn't stop then connect the negative wire to the endmill.    
   
I also found a video that might be of help. 

 



Simple Touch Plate Probe Build using bCNC probe function.
 

[jeffm]

I second Bruce's comment, I wrote my own macros for 1/4 and 1/8 XYZ probing as well a a Z only macro, the only issue is when I forget to add connection to bit.

@bruce I have not been successful in getting continuity between the bit and any part of the dewalt611, is there any trick?
FYI I replaced power cord adding ground to outer case (and emi chokes) to dewalt611, I have added redundant grounds to all metallic parts, and measured no more than 3 ohms to earth at any point in machine and control module ground so well within engineering standards. But there is no continuity from bit to case or any other location, is there a trick to getting that continuity?

[Bruce]

Sept 30, 2020 15:28:13 GMT jeffm said:

I second Bruce's comment, I wrote my own macros for 1/4 and 1/8 XYZ probing as well a a Z only macro, the only issue is when I forget to add connection to bit.

@bruce I have not been successful in getting continuity between the bit and any part of the dewalt611, is there any trick?
FYI I replaced power cord adding ground to outer case (and emi chokes) to dewalt611, I have added redundant grounds to all metallic parts, and measured no more than 3 ohms to earth at any point in machine and control module ground so well within engineering standards. But there is no continuity from bit to case or any other location, is there a trick to getting that continuity?

I just plug the router into the same power strip as the control box. Make sure the probe is the red wire and ground is the black wire that is connected on the breakout board. And through the connector plug the red and black don't get crossed.
You can always clip the black one wire on the endmill and the red wire on the probe.

[petek]

Sept 20, 2020 18:49:14 GMT jms said:

I have made a few signs with raised letters and a raised border. use 1/4 bit to take out majority, then use 1/8 bit to get in tight pots and finish. Problem is no matter how I zero the 1/8 bit, using same feeler gauge, it mills a hair lower than the rest and its impossible to clean up with sandpaper. Do most of you just use the 1/8 bit  and don't bother using larger bit? thats the only way I can see how to eliminate this problem. even though it will take longer, it will look better.

Joe

Endmills typically have helixes that tend to try to pull material upwards (and the end mill into the material).  You can get downward cutting endmills, or straight cut end mills that can certainly help.  
Also - have you checked your router/spindle to see if there's axial play, with a dial indicator? 
Also - Are you sure you're stock isn't being pulled up off of the deck up into the end mill, by the upward forces from typical helix flutes?
Also - Did you check to see if the cutting edges of your 1/4" end mill aren't chipped? Obviously you'll need a optical loupe for this. I found 60x is a bit too much zoom.. 45x is a better.. a magnifying glass hanging around the house wouldn't do it (at least for me).

As a reference:
My Power Route's Dewalt 618 has something on the order of 0.0025" of axial play .. as I recall.  It's main bearing is a single row deep groove ball bearing.  I'm upgrading it to a pair of angular contact spindle bearings stacked back to back. 

I also measured the deflection of the Z-axis under 50 Newtons (5kg) of force in the z direction, which is probably unrealistically high, and I couldn't measure the deflection with a dial indicator (0.001" dial indicator resolution).