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My nozzle has a lot of charred ABS on it. Is this normal? Some of it is flaking off and getting stuck in my prints.

If you clean your nozzle, how?

I've been designing a jig to align the MAX's towers. I posted an OpenSCAD drawing of a draft version several days ago.

Here is the fifth iteration. It clamps onto the extrusion (lightly). It has a hole for a 1/4-20 threaded rod. With nuts on both ends, I should (in theory) be able to precisely adjust the distance between any two towers.
Here it is attached to two towers.
Here's a closeup. There is a little tab that fits into the extrusion slot for alignment. You can see the two nuts that position it on the rod. The rod is pointed straight at the centerline of the extrusion.
The plan is to make a delta of these at the bottom, just above the table, and another delta at the top. Loosen the screws clamping the towers to the T-slot nuts, then carefully adjust the rods until the towers are exactly PRINTER_RADIUS (198.25 mm) from the center. Then I'll tighten the T-slot screws and remove these braces.

That is the plan. We know what happens to plans that contact the enemy.

Here are the OpenSCAD and .STL files.

kbob wrote:My nozzle has a lot of charred ABS on it. Is this normal? Some of it is flaking off and getting stuck in my prints.

If you clean your nozzle, how?

IMG_9797.JPG

I would use a small brass wire brush and lightly use it to clean the nozzle area. The softness of the brass should not damage the nozzle.
http://www.amazon.com/Forney-70489-Plas ... rass+brush

Acetone will also clean the nozzle quite well. Paper towel does wonders when wetted with acetone.

g.

Acetone, aaah acetone, how I do love thee. Aside from alcohol, my second favorite liquid. Water comes in a close third.

kbob wrote:I've been designing a jig to align the MAX's towers.

This is great. I was thinking of doing something similar last night.

The alignment quagmire grows.

Here are the constants in Configuration.h.
I've measured my arms. They are closer to 271 mm than 269.
I've measured the carriages' horizontal offset. Closer to 40 than 35.
Printer radius is also off. (Don't have the numbers handy.)
I have not measured the effector platform yet.

It's no wonder the firmware can't track the flat bed.

To be fair, I can print just fine in the center of the bed. The print height is only about 0.2 mm off at the edges of the bed. But the dimensions in the firmware aren't even close.

In other news, I calibrated the BSAC (link, link). It is off by about 0.15%, compared to my 150mm digital caliper and a steel ruler.

626Pilot wrote:

kbob wrote:I've been designing a jig to align the MAX's towers.

This is great. I was thinking of doing something similar last night.

You're welcome to start with my design. I made six clamps. I got some 1/4-20 threaded rod at Home Depot and cut it to 10" lengths. I haven't done the alignment yet because I found out I'll have to re-measure everything.

This is a great idea! Of course, you're also on track to building your own Rostock with those rods!!!

I was thinking that I might use a modified version of your bracket for the laser measuring device I've been working on. The general idea is to turn on an LED when the head passes the beam. That way, you get a very true vertical measurement on your axis' while calibrating. Hmmm... Thanks!

JohnStack wrote:This is a great idea! Of course, you're also on track to building your own Rostock with those rods!!!

I was thinking that I might use a modified version of your bracket for the laser measuring device I've been working on. The general idea is to turn on an LED when the head passes the beam. That way, you get a very true vertical measurement on your axis' while calibrating. Hmmm... Thanks!

Cool!

if this is going to become a generally useful thing, I'll mention that if you vary clamp_center_thickness, you can make the clamp's grip stronger or weaker. clamp_side_thickness has much less effect.

This post contains math. If you don't like math, look away now.

I mentioned a couple of days ago that some of the measurements on my Rostock MAX don't match the values in RepetierMAX's Configuration.h. I've spent several hours measuring, remeasuring, and calculating, and I have some numbers. Here is my report.

Methodology Notes

All calculated values are given with a precision of one micron. That's obviously bogus — my best caliper's precision is 10 microns. I just used high precision to avoid additional error from calculations. I'll list the approximate error magnitudes where I can; if it's not listed, assume it's better than the listed errors. (-:

I will not go into detail about how I got each measurement. I approached some of them obliquely. (-: (Distance from unmarked center of bed to center of extrusion?)

And I did calibrate the BSAC, as mentioned earlier.

The Parameters

Here are the original constants from RepetierMAX.
And here's the canonical diagram. Marlin's DELTA_EFFECTOR_OFFSET is Repetier's END_EFFECTOR_HORIZONTAL_OFFSET, and Marlin's DELTA_SMOOTH_ROD_OFFSET is our PRINTER_RADIUS.
The Measurements

I measured DELTA_DIAGONAL_ROD at 270.029 mm, +0.104 mm, -0.335 mm. One of my arms was ~0.4 mm shorter than the others. If you discard that arm, the other five are all within 0.1 mm of one another.

END_EFFECTOR_HORIZONTAL_OFFSET came to 31.638 mm, ± about 0.1 mm.

CARRiAGE_HORIZONTAL_OFFSET is 37.970 mm ± 0.1 mm.

PRINTER_RADIUS I measured just above the bed and also just below the top. The average of all measurements came to 200.823 mm. The minimum was 200.741, and the max was 200.972, a difference of 0.231 mm. (These measurements should be accurate to about ±0.04 mm.) I have not yet used my alignment jig to square the towers up, but I will, and PRINTER_RADIUS will change slightly.

Using these numbers, DELTA_RADIUS is calculated at 131.216.

The two numbers that are actually used by Repetier firmware are DELTA_RADIUS and DELTA_DIAGONAL_ROD. DELTA_RADIUS is off by ~0.97 mm. DELTA_DIAGONAL_ROD is off by 1.03 mm.

My best calibration efforts without changing the firmware constants left me with the hot end about 0.2 mm lower in the center of the bed than at the edges. I honestly don't know whether the errors I measured would account for that -- I find it hard to reason about how changes in rod length and printer radius affect the delta warp.

Anyway, that's where I am. Suggestions welcome.

(BTW, as a software guy, I'm fascinated and horrified at how hard it is to pin any of these measurements down. Pick up the caliper, put it right back down, and get a different reading. I did what I could to find repeatable ways to measure these things. Measuring the effector was hardest.)

Following up on myself... Early this morning I wrote up all the facts, but didn't summarize.

Conclusion

The dimensions in the firmware are all wrong. Not drastically wrong, but they're all a little bit off.

• Delta arm length: off by 1.0 mm.
• Effector offset: off by 1.4 mm.
• Carriage offset: off by 3.0 mm.
• Printer radius: off by 2.6 mm.

That bugs me -- it indicates that SeeMeCNC was just hacking at it until it appeared to work. Either that or there are deeper reasons not to use the actual dimensions that I don't understand yet. Or maybe some sizes changed between the kickstarter generation and my May, 2013 kit. But still. How can they all be off by that much? Bad data for one or two dimensions would be understandable. Not good, but understandable.

And there is good news. The good news is that the errors all more or less cancel each other out. Delta radius, which is derived from the last three, is only 1.0 mm. That's 0.7% undersize. And the delta arm length is also undersize by 0.3%. So the overall misalignment is, uh, something smallish less than half a percent. (I am not going to do the trig right now.)

Of course, if you're trying to get a thin layer of plastic to adhere to the whole bed, you need much better accuracy than that.

So when you used your measured values, how did the prints turn out?

When i measured the stock arms, they were spot on at 269mm.

ApacheXMD wrote:So when you used your measured values, how did the prints turn out?

When i measured the stock arms, they were spot on at 269mm.

You should ask that question in the future tense. (-:

I removed the effector and arms to measure them, and will probably not get another chance to work on the printer until next week.

I wonder if my arms are "special".

kbob wrote:
I wonder if my arms are "special".

HEHE they rode on the seemecnc short bus, we are all special in one way or another.

I believe the proper spelling is "speshul."

Could this issue have anything to do with heat cycles or stress causing the stock arms to "drift" in length over time?

CJGerard wrote:

kbob wrote:
I wonder if my arms are "special".

HEHE they rode on the seemecnc short bus, we are all special in one way or another.

Did they have to wear the helmet?

foshon wrote:

CJGerard wrote:

kbob wrote:
I wonder if my arms are "special".

HEHE they rode on the seemecnc short bus, we are all special in one way or another.

Did they have to wear the helmet?

All but one did, that's why it was ~0.4 mm shorter.

I have a cheap dial indicator. I got it at Horr'ble Fright last year for another project. http://www.harborfreight.com/1-inch-tra ... r-623.html

I designed this nifty little mount for it. I designed and printed it back in June, but didn't get a photo of it on the printer until tonight.
Here's the real thing.
I made the central hole a little undersized. The three slots around it let the hole stretch to make a nice friction fit around the indicator's shaft. I'm starting to figure out how to design for ABS.

You can also see the hair scrunchies that tension the delta arms. There are three more up by the CheapSkates.

Here is the OpenSCAD source file.
My printer is back together now. I aligned the towers using the alignment jigs, I've changed the printer dimensions in the firmware, and yes, I've used this dial indicator to see how well it's aligned. I haven't had a chance to print anything yet.

More on that later; right now I just want to tell you that using a dial indicator to adjust the limit switches is about 20 times faster than sliding a piece of paper under the nozzle.

Did you miss me?

On July 17th, I took the delta arms off my printer. That started an odyssey of calibration, rebuilding, repairing, and upgrading that finally ended this morning at 12:15 AM when I successfully printed a calibration cube.

Here is the cube that I printed. It measures 20.00 mm across.
I typed in about four pages of text describing the ordeal in great detail. I edited it for two hours, then SeeMeCNC's web site threw the whole thing on the floor because I attached an oversized image. Bah. I'll repost parts of it someday. It's late now.

As a carpenter/furniture-builder guy, I dig the inlay. The print seems pretty good, too. Did you build the desk?

doctorgonzo wrote:As a carpenter/furniture-builder guy, I dig the inlay. The print seems pretty good, too. Did you build the desk?

My friend Jacque built the desk, but I "helped".

More desk photos here. http://www.perfect45degree.com/gallery/

So your measured geometry values worked out well I presume? That hollow cube looks pretty good!

ApacheXMD wrote:So your measured geometry values worked out well I presume? That hollow cube looks pretty good!

It looks like my last post about calibration was on July 18th. Between then and now, my printer has been inoperable most of the time for a bunch of reasons.

I measured the distance between each pair of towers both at the top and at the bottom. I picked the tower that was furthest away from the others as my reference. Then I squared that tower to the base. (It had been square once. But I've picked the printer up, transported it in the car, and generally manhandled it enough that it had gone out of square.)
Once that one was square, I locked it down and installed the triangular alignment jigs. One triangle went at the bottom and rested on the Onyx. The other triangle went at the top. It rested on some clothespin clamps, and the top assembly rested on it. The alignment jigs had to support the weight of the towers and the top piece, so I made sure they were clamped tightly enough.

Then I loosened the screws holding the other two towers (being careful that the alignment jigs prevented them moving vertically), and carefully adjusted the nuts on the threaded rod until all six triangle sides were exactly the same length, as measured using the above technique. Well, almost exactly. There is still 0.2 mm difference between the longest and shortest. Of course, re-tightening the screws changed the alignment, so there was a lot of trial and error.

Then I updated the dimensions in the firmware, installed the dial indicator and started testing. My dial indicator is not metric, so readings are in inches instead of mm. If I remember correctly, the first reading put the corners about 0.004" (0.1 mm) lower than the center. So after all this effort, I went back to tweaking PRINTER_RADIUS to find the value that works best. The best result was 0.675 mm less than the calculated value. With that done, I got the gauge to read the same number to within 0.0004 at all three corners and the center.


Here's a pro tip for bed calibrators.

The procedure in Gene's manual measures the corners 90 mm from the center. That was probably a good choice for the early adopters who had 8 inch square beds. But the Onyx is big enough to measure the actual corners. On my printer, the delta arms are vertical at 129 mm from the center. (129 ± 0.5. I wasn't real precise.) So I measured at X, Y = (0, +129), (+111.72, -64.5), and (-111.72, -64.5). Keeping the delta arms vertical improves resolution a little.


That's where I was on July 24th. Then stuff started breaking, and the printer did not run again until August 7th.

On the 7th, I set the absolute Z height. The dial indicator could only verify that the four points all had the same height, not that they were the right height for the hot end. I followed the usual procedure: heat the bed and hot end, move gradually down until a piece of paper drags, copy the calculated number into EEPROM.

Then I checked that the paper dragged at the corners. It was gratifying that the drag felt exactly the same in all four spots. I checked three times, partly to be sure, but partly to feel how nicely it repeated.

Then I printed a calibration cube. I'd switched to a new color of filament (Neon Purple from Toner), and needed to calibrate the extrusion rate. The second calibration cube is the one that measured 20.00 mm (+/- 0.02 mm) across. The walls are a tad thin on that one: 0.53-0.54 instead of 0.55. (photo)

Next, I printed the Rostock Onyx Bed Leveling Aid. It took a few tries to get a good glue layer on the board, but I eventually got a good print of it. The glass plate seems to be a little low halfway between the Y and Z posts (at 2 o'clock: you can see where the skirt came unstuck). I don't know how a glass plate can sag, nor how to compensate for it. Maybe it means I haven't finished calibrating. Or maybe the bed is cooler on that side. I don't know.
Then I printed another calibration cube -- er, brick. This one was 20 by 150 mm. After the bed cooled, it measured just slightly oversize, 0.3%. (After I peeled it off the bed, it was too flimsy to measure.)
So I'm happy. You can see that the printer is still not perfect, but it is a lot better than it was, and I bet it's better than the average working Rostock MAX.

Next: How I burnt out my RAMBo board.

Great post, trying it in a couple of weeks.