Worn out thread x vertical drive nut after 3 months?

After a little over 3 months of use, the thread on the vertical drive nut near the x motor was worn out. I was raising my the extruder today to see how high I can go at at some point it made a sound as if the motor was missing steps. Then I noticed that the left side of the x-axis was lower than the right side. At that point, I noticed that nothing is holding the left side up and I can move it up and down by hand. When I disassembled left x-axis assembly to expose the nut, I found that the threads were completely worn. Luckily, there are a lot of M8 nuts on the Mendel. So, I took one of the bolts on the bar supporting the z motor and swapped it with the vertical drive until I can get another nut. To be safe, I also swapped the drive nut on the right side with another nut from the frame. It wasn't as worn out, but I figured this would save me from having to level the z-axis again when it too wears out.

So, here's the question. How much service are people getting from the vertical drive nuts? This seems to be too soon. I even applied silicon grease (plumber's grease from Home Depot) to reduce wear. Perhaps the kit that I bought from Botmill came with the wrong type of nut for that purpose. Is there a particular nut that would be better?

i gotta admit, i have not given this issue much thought. i wonder if the nuts on the Z axis with the spring between them on the prusa would have this issue if not worse.

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[mike-mack.blogspot.com]

I use stainless studding for the leadscrew and BZP nuts. They have not worn out after near continuous use for a year. I did grease them initially and had to top up the grease recently as it started missing steps after a trip to Sheffield.

Stainless nuts would probably be better than BZP. Brass should give less friction and so might last longer despite being softer.

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[www.hydraraptor.blogspot.com]

The nuts in my vertical drive looks just like the 8mm frame nuts. Is there a way to tell if they're BZP (bright zinc plated) or BMS (bright mild steel)? I'm pretty sure that the lead screw is not stainless steel in my case. But it doesn't show any sign of wear even though the nut was so worn out that it slides along the lead screw. So that means that the nuts are made of softer metal than the lead screws.

I also had a problem with one of the smooth rods in the x-axis. The rear rod (the one with 120 degree bearings) was worn out where it made contact with the bearings. When I saw this the first time, I rotated the rod and made sure that there was very little or no tension on the bearings. After a few weeks, it was worn out again. Cdnreprap who was the Botmill supplier at the time I ordered the kit send me a pair of smooth rods for free. Thanks! I just installed it today and it looks much better than the first ones. It does look shinier and smoother than the ones it replaced and also the ones in the z-axis. I wonder if those bad rods were also BMS.

Even though Stainless steel is more expensive I use stainless steel threaded bar for the Z drive for these reasons:-

1/ Stainless steel threaded bar seems to have a better screw thread than zinc plated steel threaded bar.
2/ Stainless steel seems to always be straight compared to the zink plated threaded bar.

For the above reasons using Stainless steel seems to cut out Z wobble

As the zinc plated threaded bar is mainly used in the construction industry where its used as a mecanical tie maybe its not teated as carfully as the more expensive stainless steel threaded bar used more by the engineering industry.

Its a nice bonus if stainless steel threaded bar last longer..

I use a copper impregnated grease used to stop brake squeal on cars as thats the only grease I have in a can.

I also use stainless steel bar for the smooth bar it seems to be better than steel.. no idea why.

Edited 2 time(s). Last edit at 04/10/2011 08:16AM by BodgeIt.

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Bodge It [reprap.org]
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BIQ Sanguinololu SD LCD board	BIQ Stepcon	BIQ Opto Endstop
BIQ Heater Block PCB	BIQ Extruder Peek clamp replacement	BIQ Huxley Seedling
BIQ Sanguinololu mounting	BIQ standalone Sanguinololu or Ramps mounting	Print It Stick It Cut it

My rep strap: [repstrapbertha.blogspot.com]

Buy the bits from B&Q pipestrap [diyrepstrap.blogspot.com]
How to Build a Darwin without any Rep Rap Parts [repstrapdarwin.blogspot.com]
Web Site [www.takeaway3dtech.com]

One approach is to pick one of the two - studding or nut - to be sacrificed to the other. That is, use hard steel for the studding, and brass for the nut, then replace nuts as they wear out, or stainless nuts and brass studding and replace the studding.
Do not use stainless for both - even with careful and frequent greasing they will eventually gall and you'll have to replace both.

Zinc plating is like a built-in lubricant, but not for very long. It is thin and will wear off quickly.

If you want to replace these parts with parts that are designed for the task and will wear much longer, you need to move up to Acme screws (or similar). These are typically made from hardened steel and you can buy nuts for them made from brass with a high lead content to make them essentially self-lubricating. But you face problems with adapting them to a z-axis drive; the threads are much quicker, that is, the pitch is much longer, so fewer turns will produce more motion, which may require more torque or different pulleys, etc.

Good reasoning I've just switched over to brass nuts on my stainless bar..

I looked at using 10mm Trapezoidal Spindles for Z axis last year ~10mm was the smallest I could find in the UK.

It would mean a re-design of Z drive.
The Spindle is expensive & Trapezoidal nuts even more plus a need to change the bearings & gear / motor connection.

The Trapezoidal Spindle is about around a £1 per 100mm, Brass Trapezoidal nuts are about £7 each Steel Trapezoidal nuts are £3 each a motor connection £7 each 10mm to 6mm.

So a rough costing to make the change on a two motor Z axis would be :-

400mm Trapezoidal Spindle £4 > $6.4
2 Trapezoidal Brass nuts £14 > $22.4
2 Steel Trapezoidal nuts £7 > $11.2
2 Motor couplings £14 > $22.4
2 10mm bearings £4 > $6.4
Total £43.00 > $68.8
Vat @ 20% 8.60 ?? USA TAX
£51.60

I am asuming similar prices in USA my quick exchange rate at £= $1.6

However as with most things the USA always seems to be less expensive.. :-(

It may be better to design a Trapezoidal nut & Trapezoidal collars for the bearing, gear or motor connection then print it.

This could make it worth considering as an option maybe?

Or
Just design a 6mm nut to print fot the Z axis maybe a split nut so its grip can be adjusted as used on my 3 stage position mechanism 3 stage Bed

Edited 3 time(s). Last edit at 04/10/2011 03:51PM by BodgeIt.

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Bodge It [reprap.org]
=======================================

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BIQ Sanguinololu SD LCD board	BIQ Stepcon	BIQ Opto Endstop
BIQ Heater Block PCB	BIQ Extruder Peek clamp replacement	BIQ Huxley Seedling
BIQ Sanguinololu mounting	BIQ standalone Sanguinololu or Ramps mounting	Print It Stick It Cut it

My rep strap: [repstrapbertha.blogspot.com]

Buy the bits from B&Q pipestrap [diyrepstrap.blogspot.com]
How to Build a Darwin without any Rep Rap Parts [repstrapdarwin.blogspot.com]
Web Site [www.takeaway3dtech.com]

After reading this topic, (and luckily, before I installed the z-axis on my mendel), I decided to give the z-axis threaded rods a good cleaning.

I was amazed by how much black grit I was able to clean off the threads by chucking the rod in a cordless drill, and running dish soap down the threads with a wet paper towel.

If I ever assemble a second mendel, I think I'm going to run all the rods in the dishwasher, and re-grease them before assembling anything.