SOLVED: X axis movement has a change in Z from bed

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nabelrabel
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Joined: Sat Jun 20, 2015 10:38 am

SOLVED: X axis movement has a change in Z from bed

Post by nabelrabel » Sat Jun 20, 2015 11:08 am

SOLVED

Hello all!

This is my first post, so I'll go a combine intro and my first problem

Intro:
My names Nabelrabel. I live in Louisville KY. I bought a kittaz back in January and use it for work and play. I'm a mechanical engineer by school, and a gearbox designer by trade. I also dab in non mechanical creations with the my taz. It's been really fun getting in on the 3d printer fun.

Problem:
Something on my rig has a slight arc to it as I move the hot head along the X axis (CURA reference). I am moving the hot head to the center of the plate and zeroing out the Z. I increment it up 0.1 mm and test the gap with a 0.1 mm feeler gage so I know that the hot head isn't pressing against the table when zeroed. If I leave it at the 0.1mm increment and move the X axis to the right AND left the gap grows to 0.2mm (measured with feelers) I can move the X manually, or with the controls. I cannot for the life of me figure out what is causing this.

Here are the things I've tried.
-Hold a straight edge on the plate and see if there is any rocking. (seems flat)

-Hold a straight edge on the plate and pinch against one side and measure gap with feelers on the other (maybe .1mm, but I'm not 100% confident in this measure scheme

- hold straight edge against each horizontal rails and shine light through and against wall to see sliver of light.(no sliver of light on each)

-rotated rods 180 degrees to see if arc changes. (it stays the same)

-measure distance between Z axis bars, frames, and anything else that goes up and down at the top and bottom of the rig (as far as I can tell with a metal ruler marked on the 16ths, everything looks good)

This is a concern because every now and then when I print large surface area projects the far edges don't stick to the plate, and if I do adjust the setup so it does adhere the first layer in the middle is squeezed out and leaves a nasty lip. I understand that this is expected to a certain degree, but this looks REALLY bad. It is like a fingernail.

Any suggestions or tips would be greatly appreciated.
Last edited by nabelrabel on Sat Jun 20, 2015 6:41 pm, edited 1 time in total.

nopick
Posts: 1000
Joined: Mon Sep 09, 2013 11:14 am

Re: X axis movement has a change in Z from bed

Post by nopick » Sat Jun 20, 2015 4:19 pm

The X axis rods flex a little when the extruder assembly is in the middle of the bed. If you work with it a little you will find a happy ground where the gap in the center of the bed is a little smaller that it should be and the gap at the edges of the bed are a little more than they should be but everything will stick and work fine.

Just play around with your Z end stop screw. For reference, I set my Z0 with a 0.0015 inch feeler gauge in the center of the bed while the bed and hot end are at printing temps. That usually gets me close.

nabelrabel
Posts: 4
Joined: Sat Jun 20, 2015 10:38 am

Re: X axis movement has a change in Z from bed

Post by nabelrabel » Sat Jun 20, 2015 6:05 pm

nopick wrote:The X axis rods flex a little when the extruder assembly is in the middle of the bed.
Like the 10mm rods flex from the weight of the extruder and that is enough to displace them 0.1mm?

I guess I could do the math and see if that is really true.

Edit:

HOLY CRAP! :shock: The math checks out.

With a 725 gram extrude body and assuming 175 gram mounting piece (900 grams/2 rails = 450 grams or 4.41 N). Using 423 mm as the span length, 10 mm as the rod diameter and 211.5 as the load location. the max deflection is 0.0708mm!

I guess that solves my problem. Thanks nopick for reminding me about physics!

nopick
Posts: 1000
Joined: Mon Sep 09, 2013 11:14 am

Re: SOLVED: X axis movement has a change in Z from bed

Post by nopick » Sat Jun 20, 2015 7:27 pm

Yeah Science!

nopick
Posts: 1000
Joined: Mon Sep 09, 2013 11:14 am

Re: SOLVED: X axis movement has a change in Z from bed

Post by nopick » Sat Jun 20, 2015 7:31 pm

If you remove the extruder assembly and mount a dial indicator to the extruder mount plate, you will see almost no deflection in the center of the X axis.

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piercet
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Location: Battleground, WA
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Re: SOLVED: X axis movement has a change in Z from bed

Post by piercet » Sat Jun 20, 2015 8:08 pm

Take a look at the openrail conversion project in the development forum for a possible option with less deflection. Its still a work in progress but I think it may be promising to eliminate that droop

nabelrabel
Posts: 4
Joined: Sat Jun 20, 2015 10:38 am

Re: SOLVED: X axis movement has a change in Z from bed

Post by nabelrabel » Sat Jun 20, 2015 8:28 pm

Funny you mention that.

I just drew up my own alternative design using some 8020 and one their linear slide fixtures. Openrails works too.

RadRuss
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Joined: Mon Jan 26, 2015 8:08 am

Re: SOLVED: X axis movement has a change in Z from bed

Post by RadRuss » Mon Jul 06, 2015 6:08 pm

I'm just replying to high-five you, because I'm ALSO from Louisville, and I ALSO bought my KITTAZ in January! Nice!

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