How accurately ground is Silver Steel (aka drill rod)?

[awemawson]

What sort of tolerances would you expect on a run of the mill 3/8" ground Silver Steel, which I believe is called 'drill rod' over the pond ?

Andrew

[Brass_Machine]

I typically buy my drill rod from a company here called McMaster Carr. They list their O1 multipurpose tool steel as tight tolerance rods. +/- 0.0005

Not sure what other places list theirs as.

Eric

[philf]

Hi Andrew,

The only reference I could find was:

IMPERIAL SILVER STEEL TO BS1407
Tolerances: Up to 1.00" +/- 0.00025", Over 1.00" +/-0.0005"

METRIC SILVER STEEL TO BS 1407
Tolerances: Up to 25mm +0 /- 0.015mm, Over 25mm +0 /-0.025mm

From memory I thought that both imperial and metric had a +0 tolerance but it seems not.

 

Phil.

[awemawson]

Thanks Eric & Phil,

Within 1/4 thou will do nicely if that's what turns up!

I'm looking for a nice no wiggle sliding fit for a drag engraver  for the CNC machine. I've made one up that works  nicely from nominal 3/8" mild steel that finishes as 0.373" I'm sliding it in 3/8" sintered phosphor bronze bushes that are seemingly dead nuts on at 0.375". If the silver steel that turns up is on the high side of the tolerance I can easily lap the bushes down that much.

The mild steel one works ok but the slight 2 thou wiggle annoys me and must lose accuracy when the tool changes direction so small text would look distorted. 0.002 may not sound much but it shows.

As an aside I wanted a 'non rotating' tool on the CNC. The CAM program can output 0 RPM, but the TNC355 controller can't cope with that and errors. The CAM program insists on outputting an 'M03' spindle start. So as a work around I'm manually editing the  code so that any 'M03' is an 'M05' (spindle stop). I suppose I should edit the Featurecam post processor to do a bit of logic along the lines of 'if RPM = 0 then M03 = M05' !!!!

Andrew

[Pete W.]

Hi there, Andrew,

This might be an 'urban myth' but I was told in my formative years that silver steel, being centreless ground, can turn out to be tri-lobar (like a 50 pence piece but with three lobes rather than seven).  It was said to depend upon how well the centreless grinder is set up.  It'll apparently measure the same all round with a micrometer.

I've never actually tried to measure a piece but I've sometimes wondered just how I'd do it.           I guess it would self-centre in a collet and then a dial gauge would show the variations (if any) as the collet was turned.

I'm sure there are Mad Modders with experience of centreless grinding and I look forward to hearing their opinions.

[Fergus OMore]

Ordinary bright mild steel can come out at 3 thous down in diameter whereas precision ground bar is as it says.
However, the problem( for some) is machining silver steel/drill rod which may need something like Garia H or similar cutting fluid.

My niggle about BMS is that my Myford collets risk being cracked with stuff undersize and I've gone to these ER things - of Far Eastern Promise

Cheers

N

I ducked the three lobe issue- which is mentioned in GHT's books. Someone knew better in an earlier but similar question.

[Pete W.]

Hi there, again,

  but I just have to share this:

One division of a company I once worked for made relays - they sub-contracted actually making the contacts but free-issued the material.

One day, the sub-contractor phoned the purchasing department and said 'I just thought I'd better confirm the arrival of the latest material',  it was described on the paperwork as 'alloy XYZ978' or some similar cryptic identity.  The purchasing department guy asked why the sub contactor was being so particular only to be told 'you do realise alloy XYZ978 is a silver /platinum alloy?'.  The billet had been sent to the sub-contractor wrapped in newspaper and in a Jiffybag or something similar.
As is too common in some parts of industry, where activity is thought to be a substitute for action, there ensued the slamming of many stable doors!!!         

The reason I post this here is that one consequence, happily not permanent, was that all 'silver steel' was to be kept under lock & key and only issued against three signatures.