Z Lead screw 4 start Upgrade

[New Passion]

I was just on Printrbots website, and I noticed they have a new Z lead screw update, https://printrbot.com/shop/z-lead-screw ... t-upgrade/ . I have a Printrbot simple metal, If I order this and put it on my printer, will I have to change something in the firmware, like Z steps/mm , or is this just a simple upgrade, swap out the old for the new.

They also have the new G2 Printrboard https://printrbot.com/shop/printrboard- ... evelopers/

Mark

[Mooselake]

You'll definitely need to change the Z steps/mm. I upgraded the Z screws on my plus to 4 start TR8-8 (what PB used) some time back. In addition to the steps/mm you might want to do some testing and increase the maximum Z speed (mine went from 3.5 to 20+ mm/sec) and tweak the acceleration and jerk. I believe I posted about my upgrade, search is your friend.

Definitely worth it. You can buy the parts for $30 or less (that's two 300mm screws) from the usual far-eastern suspects if you don't want to pay the PB tax. Mine came from AliExpress. I also changed out the couplers for what we call Lovejoy couplers here, but they call them Plum couplers there. No springy thingies needed.

Kirk

[New Passion]

Thanks Kirk,

EDIT: I just found everything I need from Reddit.

[IB3D]

Perhaps you could post a Reddit link as I searched the other evening for the thread mentioned by kirk without success.

[Mooselake]

I'll see if I can look it up when I fire up a real computer.

Not a lot of setup; calculate the steps/mm, then test with increasing speeds and acceleration. Your bot is unique, more so after modding. Ignore other people's speed/acel/jerk settings except maybe as starting points that might, maybe, possibly be somewhere around yours. Test before and after; not every mod is an improvement and hard numbers are more reliable than opinions and hopes

Kirk

[Mooselake]

Brief discussion of my settings here, and a discussion of somebody else's install here. While the steps/mm depend on commercially machined parts that are more accurate than most of us can measure, and your values should be the same as mine assuming 200 step/rev motors and 16x microsteppings. Speed and acceleration depend on differences in printer design (your simple is lots different than my tweaked plywood plus), the quality and amount of wear on your bearings, and on the stepper motors installed, their current settings, etc. Yours will be different than mine.

The steps/mm setting is (200 steps/rev * 16 microsteps/step) / (8mm/rev) or 3200/8. A big change from the original allthread's 2000+ (2260 irrc, notebook not handy)

Kirk

[YellowGTO]

Wow, what an awesome mod. Ordered. Are the antibacklash nuts worth it? and do I just cut it with an angle grinder? 300mm is too tall for me.

[Mooselake]

I'd be interested if somebody could compare the quarter inch acme and TR8-8 screws. They should be pretty close. The only real advantage is the larger pitch (travel per turn), which is a mixed blessing, assuming PB used reasonable quality acme screws. If you aren't going to increase the max z speed then the power off drifting might offset any improvement.

I have a gcode generator to test z speed, if anybody wants either the program or some pre-genned gcode

Kirk

[Dr_Radium]

Moose lake said :" If you aren't going to increase the max z speed then the power off drifting might offset any improvement."

And the power off drifting is brutal. At least it was for me. Granted I am using a modified printhead with a E3D chimera, but there is not a lot of extra weight given everything is aluminum and I built specifically to limit extra weight. we are talking a few extra grams, not a huge amount. If this was the problem, there is no way the Z 4 start lead screw upgrade will work for anyone with significant extra weight at the end of the Y arm. For a unit which is supposed to be user mod friendly, such a thin margin of error for the Z level not holding due to weight seems a poor engineering choice.

In any case, when I would jog up, I would loose from 3-15mm of Z height at the end of the jog due to drifting down. In theory, provided auto leveling is used, the Z stepper motor is supposed to be on all the time while printing, but it isn't. I would have periodic movement failure on the Z arm. This was so bad, I seriously scratched my print bed trying to troubleshoot the drift as suggested by PB tech services. Ended up trying a lot of things including replacing the Z stepper motor and all it did was improve things enough that rather than have the print head crash into my bed, I just had everything print poorly at about 3/4 of the height it was supposed to be. I went back to the 1/4" lead screw wiser if slightly less rich. I was thinking about posting a request for ideas and to see if anyone else had this problem and was able to solve it. Came across this tread doing pre-post searches and figured I should say something here before posting a new thread. If anyone has this upgrade and had similar problems, or if someone with extra weight on the Y arm installed the kit without problems, I 'd like to hear about it. Especially if you had problems and solved it.

Regardless, I'd advise being very cautious about getting this upgrade if you have any increased weight on the Y arm, even a tiny amount.

And if anyone wants to see what I am talking about and what the print results were, I have photos and video available if requested.

Mike

[RetireeJay]

If you compile your own firmware, you can exercise an option in Configuration.h to keep the Z motor on continuously. My only caution is to check the motor temperature after 10 or 15 minutes to make sure it's not getting too hot to touch. If that happens, decrease the drive to the motor (manual potentiometer on Rev D board; "digipot" on Rev F boards)

[Mooselake]

There's two kinds of power off drifting. The motor shutoff while printing, and the motor shutoff while powered down.

When i first installed the screws about all I could print, other than small objects, was pancakes since the printing vibration made it drift down. After rebuilding/reflashing that went away. My motors were cool before, and cool after, didn't notice any change. That probably means my motor current could be higher, but 20+ mm/sec (and boosted accel/jerk) is fine with me.

The drift while the bot's sitting powered off and reflecting on whatever bots think about is more nefarious. About all you can do is a quick relevel (if you're not of the alien probing persuasion. A few seconds and a piece of paper when you first power it up will allow you to level left to right. I tweaked the bed adjusters so it matched up with how the steps work out on both size. No idea if that's a real full step, or just where the microstepping ended up after the first home cycle. I've thought about facing off the ends of a short aluminum rod and using that, frame to carriage, on both sides but haven't gotten to it yet. Gotta do something with the minilathe and aluminum stockpile.



Kirk

[Dr_Radium]

Just in case anyone has the same problem with z drift I did, I ended up solving it with a simple mechanical solution. I moved the deldrin nut provided with the upgrade kit to the upper set of screws instead of the lower ones that it normally used. The spacers then moving to the lower set of screws. I then put a nylon anti-backlash nut on top of the deldrin nut. This increased the friction with the new lead screw enough that I no longer had z drift problems.

[Mooselake]

Where did you get a TR8-8 anti-backlash nut?

Kirk

[Dr_Radium]

Where did you get a TR8-8 anti-backlash nut?

Kirk

Off eBay actually. From zyltech (who was also the seller), a deldrin model. Cost about $11. Just go to eBay and search “anti backlash nut tr8-8”
It came up as tr8x8 but it was the same thing.

Sorry for the extreme delay but I didn’t realize anyone had responded to my post. I hope this helps someone. This problem frustrated the [expletive redacted] out of me until I figured this out.

[Dr_Radium]

I should also mention that this work around has held up despite adding more weight to the y arm in the form of an aluminum plate designed to extend the y axis from 6” to 10”. I haven’t made the change in the build plate yet but I wanted to test the weight addition before I took the full plunge. So far so good.

Also, oddly enough after all my trials with PB tech services, I got the idea that actually worked while conversing with Brook over YouTube comments! Go figure.