What type of threaded rod and nuts? (Quality, finish)

I'm more from the electronics side of life and don't know all to much about steel and mechanics, just some basic stuff i picked up a while ago during education.

So, i was trying to get some steel parts organized and checked out our local hardware stores online catalogues. Now, the problem i have is to decide what kind of threaded rod would be the best to use as spindle. I can have different quality ratings of 4.6 or 8.8 and there are some different types of surfaces like stainless steel, zinc coated (galvanized i think), INOX,...
There are even some with (from what i can tell) better thread tolerances (h6/h8).
All of the above for some "simple" threaded rods, amazing!

Maybe this question is totally stupid, but what is the best stuff to use? Price of the h6/h8 suff seems to be okay, but the 8.8 quality gets quite a bit more expensive than 4.6 quality, but would still be in my budget.
Is the better quality needed for a standard reprap sized machine? And what surface would be the best to have a pretty smooth and durable drivetrain in the end?

AFAIK the trapezoid spindles would be the best option, but there the price seems to go out of my budget, because i'd need the special nuts too to get some movement going.

Basically the same "problem" comes up when it gets to the nuts. A ton of material, quality and finish choices here too.
Would the machine benefit from a longer thread in the nuts on the spindle to reduce play (could order some 20mm long M8 nuts), or would the increased friction break to much and force more errors because of missed steps?

Any help is appreciated, i'm a bit clueless and overwhelmed from all the choices here...



(https://shop.bossard.com/us/ is the shop if you want to see the full list of parts i have access to in my local shop)

Here is a tip, that I can tell you from my work place, its better to go for stainless steel than zinc plated or galvanized, as when the parts are worked in, plated, and galv will jam and cause an absolute nightmare, where affordable, go stainless.

Aluminium, is also not a good idea, as it oxidises quickly, and may cause problems, least of which is trying to support a weight, aluminium rod will ben under the weight easily.

Go for stainless, all the way where possible

Okay, thanks. So i'll go stainless steel. Aluminium was never an option for me. I had a feeling the thread would get eaten up pretty fast and i'd end up with a lot of play.
What about the steel quality tho? Is the 8.8 steel a lot more durable in this application and recommended, or is it simply better in terms of bending and traction force it can endure and the 4.6 quality will do just fine in a reprap?

on the other hand... if you have to cut them by hand....
buy just ONE stainless steel an one galvanized first and give it a try

Don't get me wrong I love stainless steel (not only because it's beautiful too) but I hate to cut that by hand... that much that I'd never build a darwin with stainless steel without a perfect sized powertool to cut it

'sid

I have some powertools to cut and sand metal (angle grinder, jigsaw). Should not be that much of a problem to cut that stuff, and if it does not work, i'll find a friend or workshop who has the right tools...

Hey, a thread about rods!

I'll just add my Q too about this stuff: I'm having problems threading some regular steel rod (not sure about the quality, I found it at homedepot). This is for my own little reprap project, and I would rather thread these rods.

I only need an inch at each end threaded, so I'm essentially turning them into studs, 2 feet long with 1 inch at each end threaded, both are 3/8" and I'm threading for 3/8-16 (or 3/8-24, which would you recommend if I intend to tighten something to the rod so as to ensure it never wiggles loose?).

After around half an inch of threading the rod it gets stuck and rotates around in my vise. My dye set is very simple. I have tried using WD-40 to help the process. No matter what, I end up needing to exert so much force while threading that the rod rotates in the vice. Ideas on how I can fix that?

I am assuming your rods are mild steel. Stainless is very hard work.

Using a split die with three screws makes is easier. You tighten the middle screw, which has a cone shaped point that spreads the die, increasing the thread size. That allows you to do a shallower cut as a first pass and then close the die for the second pass.

I use Trefolex cutting compound which is green gunk resembling lard.

When tapping stainless I have to put flats on the rod to get it to grip in a chuck or vice.

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When you tap, using cutting compound, turn the die 1 turn to cut then reverse a half turn, and repeat, this makes it easier to cut long threads

On the wiki today (for Mendel), is mentioned that Zinc Plated is fine, though i'll still go for stainless steel for lead screws