Need help with rough cutting(backlash??)

[bd007]

I just completed my JGRO router but I am having problems cutting. When cutting with multiple passes each pass seems to be off ~1/16 to 1/32", x axis only, the y axis looks great. It has a stairstep effect. I am cutting 3/4" pine with a 1/4" spiral upcut, .25 per pass.

I used a dial indicator to move 1" then back to 0, it was off ~.002. If I try tighten the antibacklash nut anymore it starts to bind. I tried the backlash setting in turbocnc but didn't have any luck.

I am running turbocnc with 5/16 all thread.
Hobbycnc 127oz.

David

[ger21]

Is there any play in the machine other than the leadscrew? Perhaps your steps per inch setting is off a little bit. Screws can vary from their stated pitch a little bit. Maybe you need to fine tune the setting IN TCNC?

[bd007]

Thanks for the quick reply. I have a little flexing in the gantry. I tried drawing circles at a slower pace and still have the same results. When I configured the axis with the dial indicator I changed the Steps/Rev setting to 204 to get 1" of travel. Should this be set back to 200 and the adjustment be made on the tpi setting? Or will that be the same as adjusting the Step/Rev.

[Jason Marsha]

What is your plunge rate between passes?

There are several reasons for each pass being off

1. Plunge rate being too fast. Although I cut at 40"/min I plunge at 6"/min even
though my Z-axis is reinforced.

2. Your Z axis runners may not be tight against the pipe all through the plunge.

3. The bit should be sharp. Pine is a strange wood with those alternating hard
and soft bands which tend to show up any flexing in the JGRO when cutting it.

I an not sure about your TCNC settings as I use Mach3.

Jason

[bd007]

Originally Posted by Jason Marsha What is your plunge rate between passes? There are several reasons for each pass being off 1. Plunge rate being too fast. Although I cut at 40"/min I plunge at 6"/min even though my Z-axis is reinforced. 2. Your Z axis runners may not be tight against the pipe all through the plunge. 3. The bit should be sharp. Pine is a strange wood with those alternating hard and soft bands which tend to show up any flexing in the JGRO when cutting it. I an not sure about your TCNC settings as I use Mach3. Jason

1. I will try slowing down the plunge. I cut at about 20"/min but had the plunge set to 5 or 6 ( can't remember). I will try 3-4 tomorrow.
2. Looks tight.
3. Yes, I seen some flexing tonight. I agree pine is strange to cut. You can hear the router bogg down then speed up. I tried cutting circles with scrap MDF and still seen some flexing.

Thanks for the tips. I will try adjusting the plunge setting tomorrow.

Dave

[sgiese]

Did you make sure the z axis is square with the table? When I first got my router up and running I had this problem. Re-aligning my z axis to be square with my x-axis fixed the problem. You can chexk to see if this is the cause by cutting out a square. If one end is stepped but the opposite end is straight (in the x diirection) then it's not square.

scott

[Jason Marsha]

I agree the x and y axis runners must be at perpendicular to each other and the Z axis should be perpendicular to the cutting bed from the top to the bottom of the plunge.
To test, I slot cut a square and measured the diagonals.

Jason