Help! Cuts Wrong Size

[archcasings]

We have a warthog CNC router, but the manufacturer support is not helping us very well. We checked the backlash compensation and resolution.

The lines that parallel will be spaced improperly by as much as 1/16" if the cuts are in opposite directions. If the cuts are made in the same direction, then the space between them is correct.

Also, there is wandering when the cutter plunges and withdraws from the material. This leaves out of round marks that are very visible and need filing.
A straight line looks like this
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Any experienced help with this problem? My boss insists nothing is loose and the bearings should be okay

cnc@archcasings.com

[ger21]

It could be bit deflection, but it sounds like backlash. What size bits are you using, how fast, what material, depth of cut? The usual stuff.

[rustyolddo]

Sounds like mechanical backlash. you can't compensate for that in software, it's a hardware issue. Plunge into a piece of stock and push the motor left & right by hand & back & forth and see what you get. Or, you can use a dial indicator if you have one. Backlash can be a result of slop in the drive mechanism leadscrew & nut. or is can be slop in the guide system like the rails, or it could be something simple like the motor clamp being loose.

[Yossi]

What about tool compensation ?

[Unabiker]

A few things come to mind.
Depending on what sort of CAM software you are using, there may be an option on how the bit enters and exits the material. Make sure these options are set to plunge straight down, and not spiral or angle in or out.
Bits made a huge difference on my Warthog. I do lots of aluminum routing with mine and am very happy with Onsrud cutters.

[ger21]

Originally Posted by Unabiker Make sure these options are set to plunge straight down, and not spiral or angle in or out.

Plunging straight down will dramatically shorten tool life.

[Chris D]

1/16" is not backlash in a ball screw - if it is, that is the worse ball screw ever made!

With the machine unplugged, grab a hold of the spindle - not the tool.

Push and pull on it in different directions - you will see the deflection you are describing in your cut. If it is not visible with the naked eye, put a dial indicator on the spindle - you will see that it is moving, depending on how hard you push-pull, up to .100".

You will need to take out that slop if you can. Don't know what the machine looks like, but I do know that what you just described is slop in the machine.

Chris

[Unabiker]

Originally Posted by ger21 Plunging straight down will dramatically shorten tool life.

Agreed.
I should have qualified my earlier statement.
I do this straight down plunge using a single flute bit, cutting into .080" 6061-T4 sheet.
Before I switched to the single flute Onsrud bit, I was doing the same with a 2 flute carbide bit, and yes, tool life was less that good...like 4-5 hours.
With the single flute bit, I'm getting very good tool life. Good enough that I no longer bother to track it.

The Warthog uses a gear and track type system in place of a ball screw.
There is a drive belt connecting the servo/stepper motor to the driven gear. The alignment of this belt can have an effect on repeatability. You can tune the belts alignment by placing shims between the motor and it's mounting plate.

Another thing that I've encountered that may give similar results to what you describe is the workpiece not being held rigidly enough.
I'm not saying this is the case either, just trying to present some options.

I've had my Warthog since February and have been very happy with it.