ok so I have replaced my bed and lead screw myself, I have even fabricated my own stepper and lead screw setup and that is not the problem.

no one wants to do the math

Nope - most of us regulars have all been there, and whilst it helps, its not the only issue. But top stuff if its sorted your problem for you.

And FYI - the calculator is right here; http://calculator.josefprusa.cz/

this is the problem with 90% of the banding.

the firmware is incorrect where is say "default steps per unit". furthermore when you slice you stl file in whatever program you're using you're probably making your layer height to .3 or something to this effect. the issue with putting a nice rounded number like .3 is your stepper motor would need to take 42.523033309709426 steps to give you exactly a .3 layer height, but your stepper cannot do this. So you need to slice at a layer height optimum for your lead screw and your stepper motor. this will rid you of banding.

for example a layer height of .13 should actually be set to 0.1270 for an exact number of steps at 18 so now every time your motor steps to a 0.1270 layer height it ends at a full step. see the stepper will end at a full step anyway leaving you with more or less layer height every so many layers giving you a consistent banding making you think its the screw.

no one wants to do the math

314159, check out eBay, pack of ten for 2.79

For the Well nuts? What search term are you using? "5/16 well nut" doesn't give anything under £14.19 ($21.53) with postage.
"5/16 backlash" gives me no hits at all.

Since the idea is to pre-load the thread, maybe a spring washer would work. Just screw the spring washer down with the nut, then fit something to the nut that stops it rotating by fixing it to the M3 screw holes.

I've heard ABS anti-backlash designs have too much flexibility, but I have some metal sheeting, so perhaps I could cut something suitable out of that...

I think the anti backlash mod is the one to try, but if I'm spending that much, I may as well look for a proper 5/16" anti-backlash nut. If anyone sees a site that ships to the UK, please let me know, as I'm still looking!

If your lead screw is bent, I'd be looking at using a felxible coupling between the motor and shaft....and while your at it...just get rid of that screw and get a metric one... 1" long brass standoff can be used for the nut

+1 on a new lead screw, but just switching to a metric one of a similar size won't do much; the trick is to use one with a finer thread pitch like an M3, M4, or M5 rod.  Since the banding width matches the thread pitch of your rod, going to a fine pitch will always eliminate the visible banding.  You'll need to make an adapter for a smaller nut and change the steps-per-mm value in your firmware (which you can do via gcode commands).

I am in the US so my shipping was just $5 but there you can have the Well Nuts (well 12 of them) for about $5 US and $16 shipping. Still not cheap.

I think these are the right ones, I can let you know in a few days lol

I think I need to keep shopping around.

http://www.soliforum.com/topic/2341/poo … -required/

Before you go out and spend some real money on a anti-backlash nut, you should give this a try.  It's simple, doesn't require any modification or disassembly of the printer, and it costs less than $2.

It really helped my printer and apparently it helped others that had similar problems.

Good luck