Simple metal threaded rod repalcement

Simple metal threaded rod repalcement

Postby Metatron111 » 2014-May-Mon-03-May

Hi there,

I'm looking for a replacement for the z-axis threaded rod on my printrbot simple metal.
Can someone tell me the exact dimensions of the rod, in the bill of material from printrbot it just says "ACME rod" but with just that its hard to find the right part.
Could you substitute the ACME rod for say an M8 rod, since its probably very difficult to get a hold of an ACME rod where I live.

Thanks for your help!
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Simple metal threaded rod repalcement

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Re: Simple metal threaded rod repalcement

Postby RetireeJay » 2014-May-Mon-06-May

If you replace the threaded rod with a different type, you have two other parts to be concerned about: (1) the coupling from the motor to the threaded rod and (2) the coupling from the threaded rod to the carriage that moves up and down. If you have a way to make all three parts compatible, then you have a great deal of flexibility in what you choose.

Why do you want to replace it? Was the original damaged? Or are you expanding the Z axis?

Printrbots were made originally with US "Imperial" dimensioned threaded rods. But those rods really are manufactured as fasteners. Your metric threaded rods (like M8) also are made for fastening things together. Acme rods are manufactured specifically for the purpose of motion control; they have a different thread profile and more precise dimensions. But the reality is that good-quality Imperial or Metric threaded rods will be satisfactory for all but the most extremely precise requirements. If you don't use Acme, then people tend to recommend using brass Imperial or Metric rod as it seems to be manufactured to higher quality standards and it doesn't have rough plating on top of the base material.
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Re: Simple metal threaded rod repalcement

Postby Mach-Chris » 2014-May-Mon-07-May

Mcmaster-carr has lots of linear motion solutions. Though they are usually the more expensive route. Still, their online database makes it very easy to browse through possible solutions and then source the parts elsewhere. As jay said, unless you go with the same acme thread, you will have more than just the rod to replace.
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Re: Simple metal threaded rod repalcement

Postby Metatron111 » 2014-May-Mon-08-May

I wanted to extend my z-axis to get a bit more flexibility in the z-direction, however it is very difficult to get acme rods where I live (Germany) because hardly anyone sells them.
However, I still need to know the dimensions of the standard printrbot acme rod, I suspect its 1/4'' or 3/8'' can anyone confirm this?
Do I need Right-Hand Threads or Left-Hand Threads? Does it matter?

Thanks for your help
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Re: Simple metal threaded rod repalcement

Postby Mach-Chris » 2014-May-Mon-08-May

It is 1/4-16 acme RH,

In theory You could replace it with 1/4-20 precision lead screw, without changing the coupler, but you would then have to change the nut. Made of delrin, I would make a new one out of brass.
one relatively simple work around would be to drill out the delrin to 3/8 and press in a brass nut, something like a "keensert" or even a STI (steel threaded insert, like helicoil), that's only if you have enough material in the delrin to do so.

the added advantage to the finer pitch being higher resolution on the z axis, (more turns per unit traveled)

You weren't kidding, I'm having a hard time finding an acme supplier that will ship to Germany.

Hope this helps
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Re: Simple metal threaded rod repalcement

Postby KDog » 2014-May-Mon-08-May

The metric equivalent of ACME threads are Trapezoidal threads. You will find them across Europe designated as TR followed by the diameter in mm.

Cheers,

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