Z-Axis accuracy

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willbrisco
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Joined: Fri Mar 07, 2014 10:35 pm

Z-Axis accuracy

Post by willbrisco » Wed Mar 26, 2014 11:33 pm

Hello there,

We are having some trouble with the accuracy of our z axis stepdowns. At times it appears to be very accurate with .1mm passes into our material to a target depth of 1mm. Other times the z axis would not lower anywhere close to the specified target depth, or in other cases, the drill would be brought down much too far. One example was cutting a piece of acrylic using a cut path made on MakerCam- using a 1/8th 2 flute endmill I set a target depth of -.9 and a stepdown of .9 (Feed Rate 800 Plunge Rate 400). The first time running this file it barely lowered into the acrylic at all. The second time the file was run our drill plunged through the entire acrylic sheet (about 3mm). We have made sure our starting points are consistent, it seems to be very sporadic. Any help would be great, thank you!

Will

WillAdams
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Re: Z-Axis accuracy

Post by WillAdams » Wed Mar 26, 2014 11:48 pm

400 is a rather fast plunge rate for a stock machine in a hard material such as acrylic --- I would slow that down --- note that on I.C.'s upgraded machine using a DW660 he used a 75mm plunge rate: http://www.shapeoko.com/wiki/index.php/ ... ls#Acrylic

You should also adjust the motor current per the wiki: http://www.shapeoko.com/wiki/index.php/ ... or_Current
Shapeoko 3XL #0006 w/Makita RT0701 Router w/0.125″ and ¼″ Elaire precision collets
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edwardrford
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Re: Z-Axis accuracy

Post by edwardrford » Thu Mar 27, 2014 2:52 am

Another thing to note with acrylic (or any hard-ish material) is a feature that makerCAM is lacking called ramping.

This is where the plunge is done at an angle into the material so as not to dive directly down (the hardest part for any machine) but instead to gradually work it's way down to the target depth for that pass.

Imagine the bit starting at Z0, and instructed to go down 2mm per pass.
- At 25% of the pass, the depth would be 0.5mm
- at 50% of the pass, the depth would be 0.1mm
- at 75% of the pass, the depth would be 1.5mm
at the beginning of the second pass, the depth would be 2mm.

If you are doing 2D work, you could always give cambam a free 30 day trial, and see if the ramping helps.

That doesn't really help you out with your situation, but I thought it was a relevant piece of information, given the topic.

-Edward
Shapeoko 1 #0 - a couple of upgrades.
Shapeoko 2 #0 - a couple of upgrades.
Shapeoko 3 #2 - Stock

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