here is my z wobble fix

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here is my z wobble fix

Postby Turbo442 » Thu Jan 24, 2013 5:58 am

Havent posted much lately but have been doing lots of testing.

Here is my z wobble fix. Other than keeping the lead screw perfectly true, the next most important thing is to keep the z motors rigid.
Attachments
118.JPG
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before and after
114.JPG
the fix CNC
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Re: here is my z wobble fix

Postby roberlin » Thu Jan 24, 2013 2:27 pm

I like your beefy brackets ;-)
What kind of couplers are those?

After switching to a totally rigid motor mount, I found I was still getting a little wobble no matter how much I fiddled with the alignment.
The last mile for me was swapping out my rigid coupler for a flexible one (simultaneously I ditched my mcmaster-carr ACME for precisiontech which may also have helped).

Since then I don't have perceivable (to me) wobble.

If I was approaching it today, I would try one of the versions of brnrd's wobble suppressor. But at this point I am hesitant to fix what ain't broke.
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Re: here is my z wobble fix

Postby orcinus » Thu Jan 24, 2013 2:59 pm

roberlin wrote:The last mile for me was swapping out my rigid coupler for a flexible one


That should've been the first mile.
There's no other adjustment that will have as much impact as switching from the stock couplers to flexible couplers or clamp-type rigid couplers. For the simple reason that all the set-screw designs unavoidably make the rod and shaft axes eccentric.
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Re: here is my z wobble fix

Postby flurin » Thu Jan 24, 2013 3:16 pm

removed. it was a mistake.
Last edited by flurin on Thu Jan 24, 2013 3:57 pm, edited 2 times in total.
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Re: here is my z wobble fix

Postby roberlin » Thu Jan 24, 2013 3:35 pm

orcinus wrote:
roberlin wrote:The last mile for me was swapping out my rigid coupler for a flexible one


That should've been the first mile.
There's no other adjustment that will have as much impact as switching from the stock couplers to flexible couplers or clamp-type rigid couplers. For the simple reason that all the set-screw designs unavoidably make the rod and shaft axes eccentric.


The couplers I had started with were actually premium clamp-type rigid couplers (From dumpstercnc. They even had threads to get the rod aligned perfectly, which I needed since my original rods weren't turned down at the end).
But I still had some wobble. So I switched to cheap chinese ebay clamp-type flexible couplers. Made a big difference (although as I mentioned maybe it was the rod?).
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Re: here is my z wobble fix

Postby Turbo442 » Thu Jan 24, 2013 6:08 pm

roberlin wrote:I like your beefy brackets ;-)
What kind of couplers are those?

After switching to a totally rigid motor mount, I found I was still getting a little wobble no matter how much I fiddled with the alignment.
The last mile for me was swapping out my rigid coupler for a flexible one (simultaneously I ditched my mcmaster-carr ACME for precisiontech which may also have helped).

Since then I don't have perceivable (to me) wobble.

If I was approaching it today, I would try one of the versions of brnrd's wobble suppressor. But at this point I am hesitant to fix what ain't broke.


I started out but spinning the lead screw on the lathe and tweaking it until I removed as much of the wobble as possible.
The couplers I machined on my 12x36 lathe out of 1/2 aluminum stock. I started by drilling and tapping a hole on one end for the lead screw. Threaded the coupler on the lead screw, then spun down the lock nut and tightened it. Flipped the assembly around and carefully clamped the lead screw threads in a 5c collet close to the coupler. Bored the motor hole and precision fit it to the motor shaft almost a press fit. Cross drilled the set screws 180 deg out on the Bridgeport.

Another option would be to get a slightly larger lead screw and bore the 5mm hole directly into the end of the lead screw.

I wanted to see how things worked with with the rigid couplers as an experiment. I have a set of 12mm x 300mm ball screws sitting here with couplers. I doubt that will yield much improvement. I really wouldn't mind finding a higher quality lead screw that runs true.

I am quite happy with the prints now. The photos are taken with an iPhone 5, which really seems to show off imperfections that you might not see when just holding the prints in your hand. I was at a printer party this weekend with about 10 printers. The best prints that we witnessed came off a replicator 2 and a ulitamaker. Both running PLA with a .4 nozzle and .15 layer height. I would say this ORD is as good as the best we saw this weekend.

I will be machining some different motor and pulley mounts next. I have to assume the original mounts are jumping around a bit during high speed motion changes.
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Re: here is my z wobble fix

Postby orcinus » Thu Jan 24, 2013 7:38 pm

roberlin wrote:The couplers I had started with were actually premium clamp-type rigid couplers (From dumpstercnc. They even had threads to get the rod aligned perfectly, which I needed since my original rods weren't turned down at the end).
But I still had some wobble. So I switched to cheap chinese ebay clamp-type flexible couplers. Made a big difference (although as I mentioned maybe it was the rod?).


Probably the rod, then. I had weird chinese flexible couplers for a while, that were clamp-type, but also had set screws (go figure).
So i've tested them both, using the set screws and using the clamp, then compared with fixed couplers with set screws.

Net result: fixed + set screw = flexible + set screw
But flexible + clamp = no wobble.

Also interesting - the diameter of the rod can have an effect as well. Thin rods can be less straight without producing wobble (the rest of the mechanics can constrain them easily), while thick ones are very unforgiving when not completely straight.
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Re: here is my z wobble fix

Postby cvoinescu » Thu Jan 24, 2013 10:14 pm

The Chinese flexible couplers with jaws and set screw aren't bad at all. The jaws tighten asymmetrically, one moving much more than the other relative to the body of the coupler. The set screw is on the jaw that moves less, so if you tighten the jaws about half way and finish the tightening with the set screw, you get the rod fairly well centered.
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Re: here is my z wobble fix

Postby orcinus » Fri Jan 25, 2013 12:18 am

Mine clamped symmetrically (or, rather, closed so that the hole ended up pretty much perfectly concentrically to the 5mm shaft hole).
Ironically, the 6.35mm to 5mm flexible couplers i've replaced them with *don't* have the set screws and aren't perfectly concentric :)
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Re: here is my z wobble fix

Postby blah_59 » Mon Sep 02, 2013 12:35 am

Maybe it's ADHD but in the middle of my Cerberus (Rostock derivative) build, I decided to look at the Z-Axis on my Hadron again. I've done the floating gantry mod already and that helped a lot but not a complete fix. I've also switched to purely even step increment layer heights, that I read in an article, to help with "banding" and it helped but still not a complete solution. So I just printed and installed these: http://www.thingiverse.com/thing:21071 and I think I'm finally there.

So I just wanted to remind anyone who is still having Z-Axis issues, and not using something like these, try them out.
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