Round rod specification

The material used by RRP is ck55 [www.metalravne.com]. I as an electronics engineer know less than I would like about metals. Having taken advice from someone who knows more than me and before the RRP information became public I ordered some Ground and polished Silver steel now I am not sure if what I have ordered is suitable?

CHEMICAL ANALYSIS % C-1.15 Si-0.25 Mn-0.30 Cr-0.65 V=0.10
SUPPLIED CONDITION Annealed 180-240 BHN GROUND AND POLISHED AVAILABLE 1-2-3 METER LENGTHS
TOLERANCE
METRIC h8 (minus tolerance)
10mm-18mm +0 -0.027
HEAT TREATMENT (FOR GUIDENCE ONLY)
Heat slowly to 780-800 deg c quench in water to achieve 64rc, temper at 150 deg c for 62rc, 300 deg c for 58rc

Rory

Edited 2 time(s). Last edit at 01/04/2014 06:43AM by Rory166.

Silver steel is ke672 , it may have some other name applied to these days , but it's basically mid range tool steel , used for die bushes punches and a million other things
It can e used in the form it is in the omerod , but I'd usually polish it first , if you run your nail down it you'll see how rough it is ( in relative terms)
It should have hardened chrome plated rods fitted , maybe an upgrade for the future , as the steppers combined with budget bearings allied to the unplanted rods and general "loose " build will probably cause problems

Btw you'll find this plated rod on eBay for about a quid a foot

Have a look on the igus site for some other answers to this problem

Mike

Mike

The silver steel I have ordered is polished apparently. Both the ck55 and silver steel rods are hardened. I do not like the idea of plating much for a bearing surface. So far I can only find chrome plated linear motion rod from one US ebay supplier. Can you be specific about the Ebay source for your recommendation?

rory

Edited 1 time(s). Last edit at 01/04/2014 07:45AM by Rory166.

Plated bearing surfaces are commonplace in automation equipment
Any hydraulic / pneumatic cylinder shaft is plated most roller bearing rails also

Anyway the ck 55 is hardened , silver steel is supplied soft , so you can machine it then heat treat if needed


[www.igus.co.uk]

Try this for more info

The eBay seller was indeed the murican one you mentioned
Any local bearing supply shop should be able to help you
In fact rs used to sell it , don't see it listed now tho

Mike

Mike

Thanks for your help and advice. The silver steel I have ordered is bearing shaft supplied heat treated "Annealed 180-240 BHN" unfortunately I do not know what this means. I would assume that the polishing is done after heat treatment. I wonder if polishing the ck55 rods supplied with the kit would be advantageous, or would it reduce the diameter too much?

As I said I dont know much, the reason I dont like the idea of plating is if you wear through the plating then what?

Rory

I asked Adrian Bowyer - former professor of engineering at Bath University, instigator of the RepRap project, director of RepRapPro, and lead developer on the RepRapFirmware, for those that don't know - about the rods yesterday. It is his view that hardened ground rods, as we use on the Ormerod, are better than chromed rods. The surface is ground accurately to size, and certainly smooth enough for the linear bearings. Chrome plating can add inaccuracies, and it will be even worse on non-hardened and non-ground rods. So if you insist on chrome plated, check what you're buying. Chrome plating does give a smooth surface, but it's mostly for bushings or seals (as mikeemoto points out, hydraulic shafts use them, but they are subject to high pressure) and just unnecessary on RepRaps.

It is important that the rod is clean, and I need to add to the instructions that people should check their rods are clean before installation, but I would argue that this is common sense! In another thread, mikeemoto says there is rough running. However, the rough running and squealing problems are not to do with the rods; it's either the bearing on the Y and Z axis are not aligned - called 'racking' (easy fix - slacken bearing mounts, move axis back and forth, retighten) and X axis squealing is actually the bearing on the back of the x-carriage, if it's stopped from rotating (turn over the M3 washer).

Also see: [hydraraptor.blogspot.co.uk]
[www.zappautomation.co.uk] (sells hardened ground rails, not chromed, for linear applications)

Ian
RepRapPro tech support