Test part repeatedly 0,3mm out of spec. < resolved >

[the_Swede]

Hi.
Been scratching my head for a while now.

When running a test part on my mill, just a 60x60x5mm rectangular square cut on top of a 70x70 aluminum stock, I get an extra 0,3mm in total width.
And it is repeatable.

Using cutter comp for such a big deviation does not feel like the proper way to resolve the issue.

No backlash on the machine worth mentioning.

Running the program a second time, a "complete" spring pass, the cutter never touches the material, so i can´t be because of ball screw load.
So basically, running it in the air, it still gives me the same measurements.

The X-axis has a glass scale DRO installed and when via G00 moving between 0 and 60mm, it hits the values just fine in both directions.
(Haven´t had time to install on Y and Z yet)

The part is programmed in Fusion 360, where I cant seem to find anything wrong either, no tolerances to adjust further- what I can see.

And ideas? Because I´m all out at this stage.

PS:
The machine is a complete DIY, so no make/model I can mention.
I have attached the Fusion file, reports from the Acorn and a picture och the 0,3mm that I don´t want .

[suntravel]

Fusion flile is ok.

Is the endmill exactly the diameter you use in fusion?

Will it cut if you repeat the finish pass?

Uwe

[the_Swede]

Fusion flile is ok.

Is the endmill exactly the diameter you use in fusion?

Will it cut if you repeat the finish pass?

Uwe

Yeah, the idea struck me but I kinda disregarded it. A new 12mm endmill should not be 0.15 under size. But heck, maybe its worth trying with another one.

// P-J

[suntravel]

Endmill too small, mill with too much flex, or turn ratio calibration wrong are the most common problems for this.

Uwe

[Houseman303]

An allowance for finishing of 0.15mm per side would be normal for me in the cam. You can use a test piece that is halved in size to check whether you get the same or a different measurement value. same material and same tools.

[Nigelo]

My money would be on incorrect calibration as you have all 3 axis set to exactly 5.00mm/rev which is highly unlikely. Carefully recalibrate each axis, resetting lash to zero before you start as that will need recalculating once fine calibration is completed

[ShawnM]

My money would be on incorrect calibration as you have all 3 axis set to exactly 5.00mm/rev which is highly unlikely. Carefully recalibrate each axis, resetting lash to zero before you start as that will need recalculating once fine calibration is completed

I agree and stop me if you've heard this before Nigel.........

There's no way the turns ratio will be EXACTLY 5 and no way they will all three be EXACTLY the same.

It's physically impossible if you want any sort of accuracy from your machine. Even the finest ball screws have tolerances. Then there's the rest of the drive train. Hence, your .04mm backlash.

I'd start with a fresh "fine DRO" adjustment using at least three 1-2-3 blocks. Or whatever you metric guys call them. The further you can precisely travel when calibrating the turns ratio the better. Then run your favorite backlash program and calculate the backlash again.

[ShawnM]

I forgot to mention, your report says you are running 4.64 which is VERY OLD and no longer supported. You should think about updating your software before you continue. Please follow the instructions for installing the latest version of CNC12 and do not "restore report".

[Nigelo]

My money would be on incorrect calibration as you have all 3 axis set to exactly 5.00mm/rev which is highly unlikely. Carefully recalibrate each axis, resetting lash to zero before you start as that will need recalculating once fine calibration is completed

I agree and stop me if you've heard this before Nigel.........

There's no way the turns ratio will be EXACTLY 5 and no way they will all three be EXACTLY the same.

It's physically impossible if you want any sort of accuracy from your machine. Even the finest ball screws have tolerances. Then there's the rest of the drive train. Hence, your .04mm backlash.

I'd start with a fresh "fine DRO" adjustment using at least three 1-2-3 blocks. Or whatever you metric guys call them. The further you can precisely travel when calibrating the turns ratio the better. Then run your favorite backlash program and calculate the backlash again.

Yep, I've lost count of the number of times we keep emphasizing this Shawn but always worth being repetitive

Even us "metric" guys often use imperial as I do (does that make me a metric Imperialist? ). FWIW, both my Mill and Router axes are set to 6 decimal places after substantial calibration and recalibration albeit with timing belt drive reduction.

[ShawnM]

Yep, I've lost count of the number of times we keep emphasizing this Shawn but always worth being repetitive

Even us "metric" guys often use imperial as I do (does that make me a metric Imperialist? ). FWIW, both my Mill and Router axes are set to 6 decimal places after substantial calibration and recalibration albeit with timing belt drive reduction.

Dear Metric Imperialist,

Can we trade measuring systems? I so wish the US had adopted the metric system way back when. I often use the metric system myself and I love it. It certainly makes more sense than 7/32 of an inch. Who the hell came up with this?

Two of my three machines have belt reduction and I love it. Mine are also carried out to at least 5 or more decimal places and yes this takes time and patience. But if you want accuracy this is how you get it.

And, after all that time to get the turns ratio dialed in then you have to move on to backlash. This is more time to dial it in but it makes a huge difference when you need precision.

I know I sound like a broken record but setting your turns ratio and backlash correctly and accurately make ALL the difference in the world.

Cutting wood on a router maybe 5 for you metric guys or 5.08 for us as a turns ratio may be good enough for some.

All joking aside, I hope the OP take the time to dial in the turns ratio better and solves his issue. Uwe had a good point also about the tool and it's diameter accuracy. I do know cutting aluminum with my router that even carbide tools do wear out over time.