Fixing banding (z-wobble) with fine threaded z-rod (Page 3 of 4)

Completed this mod with M3 rod.  I drilled and tapped a 5/16-18 bolt to use for the new Z nut nut (1st pic.)  It just screws into the PEM nut in the aluminum bed which was the Z nut (note: Anneal the bolt with a torch prior to tapping if it is stainless - those buggers get work hardened during thread rolling and little taps are expensive).  No bed mods required (whoop).

I made a simple rigid coupling for the bottom out of scrap aluminum (2nd pic). 

The edge of the bed is now stable laterally within 0.0005 over a cm of vertical travel.

I realize not everybody has the tools for this stuff, but for those that do this mod is too simple and cheap not to do. Any hint of table induced banding is gone.  Now I am on a quest to figure out the last systematic goofyness in our prints (3rd pic).  This 45° banding is vexing.  It is worse with circles of large diameter (the pic is a 5in diameter test print).  I have tried Cura as a slicer (I like it by the way) and it is still there.  Belt hysteresis?

Other than that, things are OK.  We use the Doodle for making assembly fixtures that would be costly to fabricate otherwise (pics 4 and 5 - pre Z nut mod).  I am weighing spending more time on this machine vs. buying a higher precision unit.  Speed is of no concern to me.  I have been making use of RP (SLA SLS (nylon and SS) for over 25 years.  After using the Doodle,  it is weird to think that waiting a couple of days for an SLA is just too damn long.  What a world.

Sweet.  Thanks.  And thanks.

I've just installed an M5 rod, flexible coupler, and Lawsy's double slop nut. I am finding that I am getting 'blobbing' around the outside perimeters of each layers. I'm assuming this is because I haven't changed the z-steps per mm. I know where it is in EEPROM, I'm just not sure what value I need to use.

I am using an A2 M5 stainless rod. I don't know the thread pitch, and it also isn't listed on the eBay page where I bought it.

Does anyone know the steps per mm value I need please?

Just wanted to say, I made the m3 rod switch. It was bloody easy and the results are astounding. I had a slight wobble and now it's entirely gone from my prints. I have a solidoodle2 w wooden platform. To date this is the absolute easiest, cheapest, and best mod I have made to my printer.

The steps I took are as follows:

1. Printed off the http://www.thingiverse.com/thing:101308 Solidoodle "Slop Nut" by 2n2r5 . (pick the appropriate one from the customizer)

2. Unscrewed the z stepper motor from the assembly. Removed z-stop screw to allow the bed to move up to allow clearance for the 5/16" rod to come out. Make sure you do this. I almost forgot and thinking about it now it would have made a lot of problems had I broken the z-stop screw holder.

3. Used a small copper pipe , a washer and a 5/16" nut to remove the threaded rod from the stepper motor by putting the copper pipe all the way to the bottom of the stepper / 5/16" rod, then the washer, then the nut. Screw down until it pops the rod off of the nubbin (non-technical term) of the stepper motor. I heard a small crackle noise of the thread locker glue breaking away.

4. Purchased - http://www.ebay.ca/itm/370991384235 - Synergy M3 Nut Plain - E6/7
Purchased - http://www.ebay.ca/itm/300613019772 - Flexible Coupling Motor Shaft Coupler 3mm X 5mm
Purchased - http://www.ebay.ca/itm/300945669003 - M3 / 3MM A2 STAINLESS STEEL THREADED BAR ROD STUDDING - PACK OF 1 - 200MM LENGTH
note for m3 nuts- home depot (toronto, canada) only goes down to m4 , order online if you cant find in other stores.

5. After removing 5/16" rod, attached "Flexible Coupling Motor Shaft Coupler 3mm X 5mm" with an alan key (1.5 or 2.0 cant remember which)

6. reinstalled z-stepper, assembled, installed and greased the Solidoodle "Slop Nut" by 2n2r5

7. In repetier I set the eeprom z-steps per mm to 6400

8. added grease to everything else and ran the bed up and down a bunch, all the way down, all the way up in small 10mm increments to make sure that nothing catches. Be ready to pull the plug.

The very first print I tried crashed repetier, but the second time I ran it everything ran as smooth as butter and has been running smooth ever since.

I thank all of you for the inspiration, the knowledge, and the information on how to complete this mod. It is incredible.

side note: it sounds higher pitched now when the z-stepper runs, kinda scary at first, but whatever

This is going back a little while now, but as far as I can remember I think there was enough clearance as long as the z-stop screw assembly is removed.

I should also add I have one of the earliest solidoodle2's. The one with the particle board platform. Please let us know how it goes though and which version you have!

I had to pull the z rods out to take the bed out, seemed the least damaging way of doing it! Bed removal grob style:

(1) Unplug the bed heater, thermistor, z endstop switch and z motor from the board and pull the wires through
(2) Unscrew motor from bottom of case
(3) Loosen pipe clamps or shaft collars on z rods
(4) Push/wobble z rods out of top of case
(5) Watch motor, bed and everything topple out of front of case and onto workshop floor
(6) Unscrew motor by reconnecting everything to the board, powering up and pressing z-home while holding motor
(7) Prepare hammer drill and other gentle modification tools

etc.
No guarantees, please be careful, YMMV.

I didn't have an aluminum bed, but might it be easier to just carefully cut the old rod with a dremel if there isnt space?

Since an m3 is so much smaller than the original zrod if I were to do it again I would just keep the original nut in place but get a brass 5/16-18 bolt and drill and tap it with an m3 thread to make an adapter.  To install the new rod with enough clearance, the adapter would let you install the rod loose with the adapter screwed far onto the rod.  You'd only screw the adapter into the old nut at the end.

Good call on the threaded inserts! I was looking at those earlier but I want to go m3 upgrade and they don't have something compatible. Looks like I'm going to have to innovate!

...or just print a nut hugger from the forums.

Because nothing worth doings isn't worth overdoing, I decided to make my own nut by threading some delrin cut to spec to line up with the holes on my solidoodle 3. I will then drill some holes for alignment pins and cut the delrin in half , making two nuts of half thickness. I will then slightly pocket both of them for a spring. When I am done, I should have a wear resistant nut fitted to the bed with a spring spacer and another nut above it, using alignment pins to keep everything together. I will upload some drawings later if I get a chance.

My main reason for using delrin for this is that I don't have a piece of brass I would like to use and i keep thinking about the wear of using a steel nut on a steel screw. Nevermind that over the course of the printer's life it should never get worn enough to matter (thanks to the low weight it has to deal with), I just don't want to end up worrying about it.

Instead of delrin (which I have onhand) I might get a piece of MDS or oil-filled nylon. Having the nut be self lubricating might be nice.

Good luck with the upgrade tomorrow! Let us know how it turns out.

You are going to be so happy and amazed with the performance.  You had the worst case of z wobble I've seen in a very long time.

I have been swamped these last couple days, but i found a length of brass rod at work. I'm going to see if i can turn it down and cut some 5/16-18 threads on the outside and to make a coupler like the one you got, but for an M3 nut. My printer has been completely out of commission for half a year, so here's hoping I don't screw it up again as I upgrade it. I want it at least running before I start working on crazy anti-backlash ideas.