Z wobble something

Everyone,

A little help here. My Hadron Ord Bot is producing the dreaded z wobble, but it is not the standard wobble where everything shifts one way or another. Instead, I am getting an accordion effect, where the each layer is slightly wider or thinner around the entire outside and inside of the part. My gut here is that the z axis is moving at slightly different amounts per layer, but I can't verify it. The offending layers do line up with the threads of the screw.

Any ideas. How do I resolve this?

Thank you in advance for your ideas.

It looks like your Z-rods isn't straight.

If your Z-rods isn't straight, they will enter the nuts at an angle, when the rod rotates the point of contact between the rod and the nut will move around in circles inside the nut, this leadd to non linear movement of the Z axis, compressing some layers and expanding other.

Flexible Z couplers may get rid of some of the ripple effect, but number one is to straigthen the rods, or find some that are straight.

That is absolutely a possibility. I have used just about every strategy out there to eliminate it, but I have not replaced the z rods. Is there a really good source for 8mmx300mm threaded rods?

If you don't want to go for trapezoidal rods, the best bet is probably the local hardware store, where you can touch, feel and see, before you buy.

Trapezoidal rods are usually a higher standard, since they are typically used for linear motion, so a random supplier on eBay will probably be just fine, but they are also more pricy. Remember to get the nuts as well if you go down that route.

Flexible couplings serve two purposes

1) allow bent rods to move slightly - you can actually have visibly bent rods and no z wobble if your couplings are appropriately flexible.

2) account for any angular and axial misalignment between the motor axis and the z nut trap.

With #1 straight rods will solve. But reason #2 necessitates a coupling which can cope with misalignment. Pretty much all machines with long shafts have a flexible coupling - so a home made 3D printer definitely should!

Whatever you do, do not place a bearing to hold the top of the Z threaded rods still. This is pretty much the worst thing you can do to try and solve z wobble, it will make it worse!

Edited 2 time(s). Last edit at 07/02/2014 12:36PM by konwiddak.

Flexible couplers and These. is what I have on my hadron.