Hardening Rods

I am in the process of sourcing the parts to build a linear prusa mendel and trying to decide if I should buy my rods precut or cut them myself. The wiki says “each of the above parts are annealed, and are typically hardened prior to use. Which means, as they are delivered to you, they are soft, bendable, and machinable.” Just wondering how you guys go about hardening your rods? Also, just the smooth rods need to harden not the threaded rods, right?

That's rubbish I buy zinc threaded rod and stainless smooth rod from a local supplier for the Prusa's that I build and sell, the rods are cut by me to length and all I do is clean the ends up on a grinder to make sure there are no burrs and I make sure that the threaded rod accepts a nut. They certainly don't need hardening

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Experimenting in 3D in New Zealand

I kind of figured that, thanks. This is the wifi that I am using. [reprap.org]

Edited 1 time(s). Last edit at 12/19/2011 02:20PM by JRMN.

Unhardened rod should be fine for bushings. For LM8UU bearings, I'd want hardened rods. I haven't done this yet, but I would expect the balls in an LM8UU to eventually wear tracks in the rods.

Good point Dale, but that brings me back to my original question, how do I harden them?

That's why I use stainless its already a lot harder and the price difference for 8mm stainless is negligible

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Experimenting in 3D in New Zealand

JRMN Wrote:
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> Good point Dale, but that brings me back to my
> original question, how do I harden them?

I found interesting info here, A Woodworker’s Guide to Tool Steel and Heat Treating. Stainless for me, though, since it appears to be quite involved, particularly at the lengths we need.

Are you sure that stainless is harder? I didn't think that it was.

jbayless Wrote:
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> Are you sure that stainless is harder? I didn't
> think that it was.


Well it's a hell of a lot harder when cutting it and so far I have had no failures or rods getting grooves, yet when I used steel rods they would flats on them from bearings

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Experimenting in 3D in New Zealand

You can buy hardened ground rods cut to size. They are bit more expensive, but they have a much nicer surface for bushings than stainless steel. Having said that I have used stainless with LMUU bearings and not seen any wear.

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[www.hydraraptor.blogspot.com]

nophead Wrote:
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> You can buy hardened ground rods cut to size. They
> are bit more expensive, but they have a much nicer
> surface for bushings than stainless steel. Having
> said that I have used stainless with LMUU bearings
> and not seen any wear.

Well, you put more miles on your printers than anyone I've heard of. Can you tell us which class of stainless you've used? 316, 18-8, or...?

Nophead, I also would like to know because I've seen your name quite a few times in my research.

You can harden the smooth rod yourself.

BUT DO THIS AT YOUR OWN RISK:......The process is pretty straight forward but you need to be VERY careful. Do not do this indoors.

First you need to heat up the rod to point that it's no longer magnetic, then quench the rod (put the hot rod) in either motor oil, salt water or plain water.(best to worst)

Based on parts I have done over the years and tested, used motor oil will give you the best results and it's usually free...lol

I haven't paid much attention to the stainless steel grade. I got them from Farnell. I think I have used a mixture of 303 and 304 and some that was just described as stainless.

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[www.hydraraptor.blogspot.com]

Stainless tends to be harder than mild steel regardless of what grade you use and of course doesn't rust as quickly. You will know this if ever you have tried to drill a hole in stainless sheet as it readily burns out your drills.

I wouldn't worry too much about wear as the loads on a reprap are really quite low and LMUU bearings spread the load over a large enough number of balls. Hardened rods are sold, but are really for use in machine tools or CNC milling machines etc. where the loads are much higher.

I also wouldn't bother hardening as the bars may distort which gives you even more problems.

If you have a choice go for 303 its hardness is 262 Brinell . 304 is 201 Brinell. Mild steel is around 120 Brinell

I used www.metals4u.co.uk the softer stainless 304 and they run very smooth through LM8UU but cuts easily with a hacksaw.

Thanks, that's good to know because I can get my hands on some 303 annealed (unpolished finish, temper cold finished) smooth rod. Would that work and how hard would it be to cut with a hacksaw?

The stuff I use is fine for LMUU bearings but seems to wear out PLA and IGUS bushings in a few days. I get through about 2 hacksaw blades to cut enough for 1 machine. It is hard work cutting it by hand.

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[www.hydraraptor.blogspot.com]

Because I make and sell Prusa kits here in NZ I made a jig and do all of my cutting with a 4" grinder, my first couple of kits were with PLA bushings but I changed to LM8UU bearings very quickly and so far no more problems, I'm moving over to Aluminium gears in the new year too as I have decided I don't like selling my printed ones as they are not quite perfect.

I have used stainless from day one as it is really easy for me to get hold of from a steel reseller at the end of my street

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Experimenting in 3D in New Zealand

Several of you are mistaking toughness for hardness. Stainless is a fairly tough steel (much tougher than mild steel, and most regular steels as well). It is however not all that hard in the grand scheme of things. A quick google search will teach you the differences between the two.

If you are looking for accurately sized metal (extremely concentric, very accurate diameter) that is very hard, I would look into drill rod. I wouldn't recommend trying to cut it though if you don't have proper tooling. (i.e. carbide, ceramic, or diamond). Order it to length if at all possible.

[www.mcmaster.com]