Don't get those Delta Arm Blues!

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mhackney
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Don't get those Delta Arm Blues!

Postby mhackney » Wed Mar 27, 2013 7:57 pm

This sticky is copied from my from the post called Don't get those Delta Arm Blues! in my build thread. It describes how stiff Delta Arm joints can cause problems with gaps in your prints. There is more information in my build thread along with the Z Calibration Thing STL file. The file can be found here: Z Calibration Thing

Following up on my post yesterday on the controlled experiment to determine why I am getting gaps in the infill on my prints. Here are the 3 test prints laid out to show how they were printed.

Image

Note that I oriented the fill to go from the center of the build plate to the tower. You can read the details in the earlier post.

I know how this story ends so hang in there!

First, look at the part at the Z tower. It actually looks pretty reasonable and is the best infill I've had to date. At this position, there is very little movement along the axis (from the tower to the center of the table) and a lot from left to right.

Now look at the part at X. It may be hard to see but I have gaps at the arrows. This is what I typically have seen and the problem I'm trying to fix.

Then look at the part at Y, it's the worse one of the three. Gaps along multiple sides.

After thinking on this overnight, I hypothesized that one side of the Z delta arm U joints may be stiff or have backlash. I couldn't predict which side but it just seemed like Z was the culprit. I disassembled the delta arms from the Z carriage and immediately discovered that the delta arm on the X axis side was very stiff compared to the others. I took it apart and found 2 problems: 1) I had used a small screwdriver to install the arm on the aluminum bearing - BAD IDEA. I had several gouges in the face of the bearing that had burrs large enough to create a lot of friction. I also discovered that I had not "defuzzed" the delta arm U joint when I rounded the top. The fuzz had caught between the arm and joint, again adding friction. I cleaned all of this up, regreased with lithium grease, reinstalled and prepared for a test print to see if I found the problem. And here is the result - this piece was printed at the Y position so it was in the same spot as the worst of the three prints in the photo above:

Image

This part is very nice! No infill gaps and nicely filled overall.
So I am ready to proclaim that stiff delta rod U joints can lead to odd printing behavior! Given the number of folks with infill gap issues, I think re-investigating the U joint fit will eliminate those Delta Arm Blues!

Now I can go on to more fun things!

Cheers,
Michael

EDIT: some more info on fitting the joints.

I used 400 grit silicon carbide sandpaper on a small metal sanding block to sand the inner sides of the U joints on the arms. This takes off very little material so you have lots of control to minimize the possibility of overdoing it. Once I had the joints fitting well (constantly reassembling and testing) I moved on to cleaning up the holes in the U joints. These were tight and contributed to a lot of the stiffness. I used a new XActo knife blade (a #1) and carefully scraped the interior of the hole with a twisting motion. Then chamfer the edges slightly with the knife. This takes off very little material and is easy to control. It is a SCRAPING motion not a CUTTING. If you scrape you will be able to close in on a great fit in a few attempts. I used a little white lithium grease after fitting too, that helped a lot.

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Re: Don't get those Delta Arm Blues!

Postby MorbidSlowBurn » Wed Mar 27, 2013 8:28 pm

Exactly what I was thinking about the standalone post. Between this and polygonhell's extruder calibration post the site is on a great start to a FAQ.

Next thing needed is a sticky addressing firmwares. E.g. EEPROM and how to use. And locations of the various firmwares.

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Re: Don't get those Delta Arm Blues!

Postby cassetti » Thu Mar 28, 2013 9:57 am

Is there any easy way to find 1 specific sticky arm (or narrow it down to a specific axis) - your post makes it sound like I can check if it's a Z issue or if it's An X/Y issue. Is there a way to know for sure - yes this is an X axis related issue? I'm afraid to start pulling off all my arms and ruining what I've got so far

From my prints, it looks like I did a fine job sanding the first time, except maybe 1 arm that may need a little sanding (or deburring)
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Re: Don't get those Delta Arm Blues!

Postby xnaron » Fri Mar 29, 2013 4:55 pm

Good post. I had major stiffness even after sanding the insides of the arms where the attach to the aluminum ujoints. I lubed them and it was better but still not perfect. I am assuming you still have the loop/solid infill gap setting set to 1.0 in KISS slicer? On my cartesian I get no gaps with a setting of 0.75.
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Re: Don't get those Delta Arm Blues!

Postby mhackney » Fri Mar 29, 2013 7:03 pm

Yes, I have it set to 1.

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Re: Don't get those Delta Arm Blues!

Postby xnaron » Wed Apr 03, 2013 3:55 pm

I have a slight gap on my test. See attached picture. (sorry for quality black is hard to photo). Anyhow my issue with the gap seems to be with the outside loop being too far away. It measures 10.26mm wide at the place of the gap and 10.01mm wide where there is no gap.

I've sanded and lubed all my arms but I still have a bit of stiffness in them. I bought extra arms when I bought the kit. I sanded one arm too much as the top and bottom inside were not even touching the u-joint and it was still stiff. I think this is because of the hole the the nipple on the u-joint pops in being a little small. I figured this will loosen up with time.
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Re: Don't get those Delta Arm Blues!

Postby mhackney » Wed Apr 03, 2013 4:02 pm

That is glass filled nylon and really is not going to wear in easily. Best to chamfer and fit these before installing.

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Re: Don't get those Delta Arm Blues!

Postby xnaron » Wed Apr 03, 2013 4:15 pm

mhackney wrote:That is glass filled nylon and really is not going to wear in easily. Best to chamfer and fit these before installing.


I was reluctant to do anything to the holes for fear of making them too big and introducing play. Did you do anything to fit the holes to the nipples on the u-joints on yours?
The Xnaron Project http://xnaron.com find me also on youtube http://youtube.com/xnaron

3D Printers: Behemoth, Xnaron Prusa Bumblebee, Xnaron Prusa, Jolly Roger, MG Prusa, Rostock Max

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Re: Don't get those Delta Arm Blues!

Postby mhackney » Wed Apr 03, 2013 4:23 pm

Yes, I described the process in my build thread - basically I used a new XActo knife blade (a #1) and carefully scraped the interior of the hole with a twisting motion. Then chamfer the edge slightly with the knife. THis takes off very little material and is easy to control. It is a SCRAPING motion not a CUTTING. If you scrape you will be able to close in on a great fit in a few attempts. I used a little white lithium grease after fitting too, that helped a lot.

Sublime Layers - my blog on Musings and Experiments in 3D Printing Technology and Art

Start Here:
A Strategy for Successful (and Great) Prints

Strategies for Resolving Print Artifacts

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Re: Don't get those Delta Arm Blues!

Postby MorbidSlowBurn » Wed Apr 03, 2013 5:00 pm

@mhackney- I reccomend you add an edit to the first post to address that the holes in the arms need to be fitted also and repeat your info on the scrapping not cutting this will save people from searching the thread.

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Re: Don't get those Delta Arm Blues!

Postby mhackney » Wed Apr 03, 2013 5:12 pm

Done!

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Re: Don't get those Delta Arm Blues!

Postby cassetti » Tue Apr 09, 2013 3:44 pm

What about when you sand too much! I've got at least 2 arms with side-to-side play that I can see is causing some issues in my prints.

I am looking for some ultra thin Delrin (Acetal) washers. Right now it looks like the thinnest I can get is 0.5mm thick which is way too much (I'll need to sand more!).
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Re: Don't get those Delta Arm Blues!

Postby mhackney » Tue Apr 09, 2013 3:55 pm

You can shim those with soda can washers (i.e. make them from aluminum soda cans) or buy commercially made shimming washers .001" thick. McMaster carries them and shim stock. Plastic, bronze or steel are fine.

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Re: Don't get those Delta Arm Blues!

Postby JohnStack » Tue Apr 09, 2013 3:58 pm

During the build event, a couple of us wrapped a single layer of carbide sanding paper around the axle and shoved it into the hole and just spun it around. That might reduce potential problems with using an exacto knife...
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Re: Don't get those Delta Arm Blues!

Postby cassetti » Tue Apr 09, 2013 3:59 pm

mhackney wrote:You can shim those with soda can washers (i.e. make them from aluminum soda cans) or buy commercially made shimming washers .001" thick. McMaster carries them and shim stock. Plastic, bronze or steel are fine.


Thanks! I'll check out the plastic shims - do you think they'll hold up to the wear of the machine?
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Re: Don't get those Delta Arm Blues!

Postby mhackney » Tue Apr 09, 2013 4:01 pm

Are you talking about the 1/8" diameter axle?

The key to using an Xacto knife is to SCRAPE not cut. Scraping removes very little material and is very controllable.

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Re: Don't get those Delta Arm Blues!

Postby mhackney » Tue Apr 09, 2013 4:02 pm

They have virtually no forces acting on them so they should last as long as you do!

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Re: Don't get those Delta Arm Blues!

Postby cassetti » Tue Apr 09, 2013 6:01 pm

mhackney wrote:Are you talking about the 1/8" diameter axle?

The key to using an Xacto knife is to SCRAPE not cut. Scraping removes very little material and is very controllable.


I'm talking about the bracket mounted to the cheapskate where the bearing/axel assembly sits. This is one of the worst, it has probably 0.5mm of side to side "play". Fortunately there is only 2, maybe 3 with too much play, and none of them are on the same arm (so movements are still good enough for decent test prints as seen).

I'll pick up some really thin 0.001" shimming washers (I'm sure I'll have PLENTY left over, if anyone needs a few).

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Re: Don't get those Delta Arm Blues!

Postby cassetti » Tue Apr 09, 2013 6:44 pm

Oh, forgot to mention before, for anyone who's concerned about removing your delta arms, I found this tool works perfect for the job. The rubber pads keep the arm snug while you give it a twist, pops off with little trouble.

It's a Kobalt "Magnum grip" (heh...) 404862 0812 - http://www.amazon.com/Kobalt-2-Piece-Magnum-Grip-Pliers/dp/B00A0KVY46
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Re: Don't get those Delta Arm Blues!

Postby JohnStack » Tue Apr 09, 2013 7:40 pm

mhackney wrote:Are you talking about the 1/8" diameter axle?

The key to using an Xacto knife is to SCRAPE not cut. Scraping removes very little material and is very controllable.


Yup. The 1/8 diameter axle. My Xacto skills are not so Xacto.
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Re: Don't get those Delta Arm Blues!

Postby mhackney » Tue Apr 09, 2013 9:02 pm

JohnStack wrote:My Xacto skills are not so Xacto.


Good one!

Sublime Layers - my blog on Musings and Experiments in 3D Printing Technology and Art

Start Here:
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Strategies for Resolving Print Artifacts

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