Replacing the Z-Axis rods?

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BrainSlugs83
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Replacing the Z-Axis rods?

Postby BrainSlugs83 » Tue Aug 28, 2012 7:15 pm

Well, I derped up on assembling the Z-Axis rods -- one of them is a little bent -- didn't notice it at first -- but you can see it pretty visibly as the Z-axis rod spins while the carriage moves up and down. Strangely, nothing seems to wobble at all -- just makes a clicking noise if I set the Z-axis tensioner too tightly...

My question is, can I just replace it with any SAE .25"-20 rod that's at least ~10.5" in length? Or does it have to be special, like zinc plated or something -- what will give me the best results (aside from not derping up my replacement rod the same way)?

Edit: Might have found my answer here: http://tech.groups.yahoo.com/group/SeeM ... ssage/2969
"The standard threaded rods in the kit are ¼-20UNC, the UNC stands for Unified National Coarse, and they are straight(non-tapered) threads. This is a very common size." - Andy
and "It does NOT need to be stainless. Regular steel will work better with the stainless nuts." - Andy

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BrainSlugs83
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Re: Replacing the Z-Axis rods?

Postby BrainSlugs83 » Wed Aug 29, 2012 1:49 am

Well, this is lame. I picked up a couple of rods from Home-Depot for about a dollar each -- they were a little longer than needed -- 12" instead of 10.5".

Get them home -- one of the rods, a nut won't even thread all the way down -- it gets about half way and then gets stuck -- had to really apply some torque -- went back and fourth a few times, it hasn't really gotten any easier -- the other rod -- put it in -- and it's bent as well. -- Go back to the sticky rod -- not surprisingly, it's also bent. Damn! :x

Anybody know a good place online to buy these... preferably in pre-bent and threadable conditions? I don't want to order one from some random shop -- wait a week, and then find out it's bent too.

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Re: Replacing the Z-Axis rods?

Postby Eric » Wed Aug 29, 2012 6:25 am

It occurs to me that your cheap rods might be swappable for the original 12" rods used in the base. A subtle bend would be far less critical there, especially in the horizontal axis, and nuts are only used near the ends of those rods.

As for online sources, I'd ask Seemecnc first. I don't see it as a separate item in their store, but obviously they have exactly what you need. I bet they can help you if you ask.

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Re: Replacing the Z-Axis rods?

Postby BrainSlugs83 » Wed Aug 29, 2012 1:06 pm

It occurs to me that your cheap rods might be swappable for the original 12" rods used in the base. A subtle bend would be far less critical there, especially in the horizontal axis, and nuts are only used near the ends of those rods.

That's .... kind of genius! I wish I'd thought of that! *facepalm*

As for online sources, I'd ask Seemecnc first. I don't see it as a separate item in their store, but obviously they have exactly what you need. I bet they can help you if you ask.

Yeah, I didn't see it in their store either -- and I thought about asking them via email as a last resort, but didn't want to trouble them...

I figured I'd ask the community first, but it's so close to the three-day weekend that I jumped the gun last night and ordered some grade 2 titanium rods from amazon -- paid a little extra so it would get here in time. Hopefully it works, if not, I'll try your idea of swapping rods, or if I can't find one that works well, I'll contact the guys at SeeMeCNC. :D

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Re: Replacing the Z-Axis rods?

Postby stienman » Thu Aug 30, 2012 10:20 am

BrainSlugs83 wrote:I jumped the gun last night and ordered some grade 2 titanium rods from amazon


Nice, that ought to make the printer lighter as well. Now you just need to replace all the bars with that!

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Re: Replacing the Z-Axis rods?

Postby BrainSlugs83 » Thu Aug 30, 2012 5:27 pm

Nice, that ought to make the printer lighter as well. Now you just need to replace all the bars with that!

Ha! At $12/bar? I think I'll hold off for now! ;)

They just showed up from Amazon, by the way, packed in little tubes and everything! NICE. -- I'll let you guys know how they work out! :D

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Re: Replacing the Z-Axis rods?

Postby BrainSlugs83 » Sun Sep 02, 2012 1:36 am

Well, I hit a couple of issues:

First one -- whoever is cutting these bars for Amazon is fucking the ends up -- they're not threadable, from either side:
Image

So, I took a file and fixed them (I have the cheap metal file kit that home depot sells -- I found the small ones seem to work the best):
Image

Kinda sucks that it was required but oh well. Figured I'd put my full experience here, so that if someone else orders from Amazon, they know what they're in for.

Second issue -- and this one's the kicker -- new rods have the same exact wobble as every other rod I've tried in that slot... -- either I'm slightly bending rods by accident (which is completely possible :lol: -- though less likely with the titanium ones... -- and somehow I got lucky with the other side!) -- OR -- it's the fucking 1/4" x 5/8" bearing that's warped! :x

I pulled the bearing out and just tried spinning the rod on just it... I'm really starting to think it's the bearing. So, I'm gonna head to the hobby shop tomorrow, and I just fucking hope they have one in stock! :D

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Re: Replacing the Z-Axis rods?

Postby BrainSlugs83 » Sun Sep 02, 2012 8:02 pm

Well... crap. I'm at my wit's end here.

I've now tried four different rods, and three different bearings...! :x

No matter what I do, it always wobbles... -- I wish this thing had more than one Z-axis support! I guess, for now, I'll just assemble it, and see how it prints, and maybe build a second z-axis support at the top, eventually. :cry:

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Re: Replacing the Z-Axis rods?

Postby bvandiepenbos » Sun Sep 02, 2012 10:38 pm

you might want to replace the nuts that clamp against each side of the bearing. If the face of nut is crooked that can make the z-rod wobble.
I have had that issue.
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Re: Replacing the Z-Axis rods?

Postby BrainSlugs83 » Mon Sep 03, 2012 5:32 am

you might want to replace the nuts that clamp against each side of the bearing. If the face of nut is crooked that can make the z-rod wobble.
I have had that issue.

Well, I don't have any other 1/4"-20 lock nuts laying around (derp) -- so I took the narrow end and filed it as flat as I could get it and put it on backwards of what the directions say (narrow end down instead of up.)

Still got the wobble issue -- and decided fuck it -- started reassembling the axis...

Got the X axis caddy thingy reattached and the top all bolted back together ... low and behold -- no more wobble. -- At least I thought -- get it closer to the bottom and a little bit of wobble creeps back in... -- At least the wobble is a lot better now. -- I wonder if the caddy sitting on the original rod for six months put a bend in the original one? * dep / facepalm * :roll: (the two caddys were not connected at all with the bars, since the instructions for that part weren't published when I mothballed this project.)

Anyway, So far, it has a new rod (titanium), a new bearing ($10! WTF!?), and a filed lock nut...

I think I will head down to the hardware store and grab some new lock nuts tomorrow and see if they help any. ;)

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Re: Replacing the Z-Axis rods?

Postby tom10122 » Sat Sep 22, 2012 10:23 pm

There isn't a homedepot anywhere nearby? I got mine from there, threaded a nut, then cut and un threaded it which fixes the messed up threads

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Re: Replacing the Z-Axis rods?

Postby BrainSlugs83 » Wed Sep 26, 2012 7:57 pm

As I said, Home Depot is where I bought the first replacement rods that were all janky, though, cutting the nut while they're on the rod sounds like a *great* idea! How did you cut it? I've got a miter box, but I think I'd need a really strong saw to cut through them.

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Re: Replacing the Z-Axis rods?

Postby Polygonhell » Thu Sep 27, 2012 2:44 pm

Most of the threaded rods can IME be cut with a hacksaw pretty easilly, but if you're lazy use a dremel with a cutoff disk or better still an Angle grinder if you have one.

I was just reading this thread, and to some extent the threaded rod doesn't need to be perfectly straight as long as the smooth vertical guide rods are stiff enough to constrain the vertical motion.

Bent screws causing ZWobble is very common on printers, and the usual suggested solution is to not constrain the ends at the top of the motion (The H1 doesn't), and to use smaller screws (on a mendel it's 6mm instead of 8mm the H1 is already using 1/4 inch), the goal being to let the screw wobble but not have the screw constrained in such a way that wobble translates to X/Y motion of the X carriage.

My H1 has two relatively straight screws, and doesn't displat any significant ZWobble.

In my experience on my mendel max which had some marginal ZWobble, I tried 8mm, 1/4inch, 10-32 and precision 1/4 inch acme lead screws, every one wobbled, and I finally fixed the ZWobble I was seeing not by changing the screws, but by changing the XEnds to use bronze bushings instead of the self aligning igus bushings it came with, this allowed the smooth rods to actually do their job and isolate the vertical motion.

Short version is I'd put it together with the straightest screw you've got and see if there is an issue when you start printing.

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Re: Replacing the Z-Axis rods?

Postby tom10122 » Sun Sep 30, 2012 8:00 pm

Yup ^^^^ Used a hack saw


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