Machinability of Drill-Rod

This might be more in the experience of someone from North America ....

On this (Canada) side of the pond, I can buy drill-rod in "air hardening", "oil hardening" or "water hardening" varieties. I never actually attempt to harden it - don't have the facilities - but I do use it as material stock. Usually I choose air hardening since it's somewhat less expensive than the others.

I did wonder whether there's any difference in machinability between the three grades and whether another grade might be a better choice.

Sorry, I mis-spoke above:

I usually choose water hardening since .....

A Google search on "drill rod" threw up this useful-looking reference as the first hit:

**LINK**

Perhaps you found it and it didn't answer your question, but it does at first sight seem to contain the details if you explore. Hint: click on the "Tool Steel Guide" link.

David

Edited By David Littlewood on 14/08/2012 19:11:37

Drill rod is what they call silver steel. So it will machine like any high carbon relativley high strength steel. Silver steel or gauge plate in the soft condition of course.

If you need to know precise details, then you'll need the ANSI spec for that grade which will only be a google search. If you don't know precisely which grade you have, then ask the supplier, and you can cross refence from there.

What were you going to use it for is the next question. Making tools - then probalby one ought to finish grind. If its for pegs and dowells any grade will do. If for driving pins, then case hardened mild will be an easier to machine and give a harder result.

I did of course check Google first. Unfortunately the information is mostly biased towards industry and their version of "good machinability" is not necessarily mine. I had hoped to pick up a few comments from people who had used it for ME purposes.

I had no particular use in mind, it's just something I use in any situation when I need a piece of accurate, straight bar without turning the maain OD.

Edited By Sid Herbage on 15/08/2012 04:12:27

Hello Sid, Here we have what is called 'Stubbs Steel' , high carbon which is centerless ground and is nearly always to size.

It does not machine well, the surface finish is a bit ragged when turning and the best method is grinding.

It is suitable when heat treated for punches and screwdrivers and locating pins. It will also make small 'D' drills and other shaped cutters.

It comes in all sizes and I have seen a diameter of 1". Usually I use a set diameter for whatever I am doing and do not machine it apart from cleaning up the ends and a chamfer. It is quite tough in the untreated state and suitable for most applications as its main attribute is its stated size/diameter.

Clive

Sid,

If you only need it because of its accurate sizing, then you should consider using PGMS (precision ground mild steel). It is, here at least, considerably cheaper than silver steel; the latter has no advantages unless you need to harden it. Like Graham, I have never found silver steel too difficult to turn, but it does need more care than MS.

People sometimes use silver steel for things like axles in preference to PGMS because they think it is stiffer, but in its unhardened state this is untrue, both have the same Young's modulus, though silver steel has a higher UTS (ultimate tensile strength). I'm not sure what the position is for hardened and tempered silver steel, but then that is a different beast altogether and much less suitable when resilience is required.

If you do need to produce a hardened component, then you need to take into account the slight expansion which takes place on hardening. It's slight, from memory a few tenths for say a 1/4" piece, but enough to turn a perfect fit into a no-go. Tempering will reverse the increase slightly but far from completely.

Sorry if the UK terminology is not entirely right for you; I think Graham must be right about the air hardening grade of drill rod, but it's simply not a terminology which we see over here.

David

Edited By David Littlewood on 15/08/2012 12:14:58

I have always assumed that the US water hardening steels are roughly equivalent to silver steel in the UK, ie, a plain high carbon steel. It generally turns and mills easily, with a slight tendency to tear when turning if conditions are not right. See here for an informal discussion,**LINK**.

Likewise I assume that the US oil hardening steels are roughly equivalent to gauge plate in the UK. I've never turned gauge plate, and have had limited success milling it with HSS cutters. It seems to cut ok and then suddenly it all goes wrong, and the cutter is completely badgered. I surmise that the material gets hot locally, hardens, which blunts the cutter, which heats the material more, and so on. I've had no trouble milling gauge plate with uncoated carbide cutters on both manual and CNC mills.

I have no practical experience of the air hardening grades, and I hesitate to disagree with Gray, but I don't think that air hardening steels are classified as HSS. Unlike HSS it should be easy enough to harden the air grades in the home workshop. I suspect that these grades are unlikely to available from the normal ME suppliers, but are available from specialist steel stockists, see here **LINK**.

Best Regards,

Andrew

I'v had mixed success turning silver steel, I used it when I first started making Stirling Engines for crankshafts, I found the sometimes if I turned a bit of 1/4" rod down to a smaller dia, it would have made a passable file if hardened, maybe the tool was blunt, don't know, I use lower grade steels now. Ian S C

Silver steel machines well and takes a good quality thread when screwcut. Correct insert grade and speed is all that is required. Some coolant.

When I first started machining silver steel I used to get a rough finish but now can get a good finish. I don't know what I'm doing differently - just practise I guess. I use a sharp HSS tool, a bit of suds brushed on, andspeed slightly slower than for MS.

Russell.

Sid - you have a private message. JD

I worry that if you are not hardening the material, you may be either wasting money or not using the best material for the job.

My understanding is that drill rod and silver steel differeing in that the letter includes a little chromium.

I understand they are both poor choices for anything that is not going to be hardened - my recollection is that in terms of wear resistance silver stel is little or no better than mild steel, and that for the price one pays one should choose from:

Precision Ground Mild Steel - for axles and spindles where an accurate diameter is essential.

Bright Drawn Mild Steel - for general work where good unmachinmed (but not accurately sized) surfaces or a good turned/machined finish is more important than absolute strength.

Leaded or free turning versions of the above where easy machining and excellent turned finish matter.

Black mild steel - hot rolled or drawn, for parts to be machined all over where lack of distortion matters.

Then there are many alloy steels of greater hardeness, strength and toughness than mild steel that will generally machinme better than silver steel and not require additional hardening for most purposes.

Silver steel is really just for tools, locating dowels and the odd part that needs to be hardened.

Finally, fear not, if water hardened drill rod is hardened in the same way as silver steel, it's an easy task using no more than a standard blowtorch.

Neil

Graham,

Very nice, but why? If it isn't hardened, is there any value in using silver steel? I think for such a job, if mild steel was not considered good enough, I would have used EN24T (817M40 in new money). Machines quite well, and is very, very strong.

David

Edited By David Littlewood on 22/08/2012 14:23:37

I have used silver steel extensively over the years, even when unhardened it offers

far better qualities than mild steel if it is to be used as a moving part.

There is far less likleyhood of silversteel 'picking-up' if used as a rotating part without bearings.

Because of it's toughness, it resists cutting, and as mentioned a well ground hss tool will give

excellent results. In my opinion, leaded free - cutting mild steel should only be used to reduce machining time comercially, unless the part is not doing any work I would try not to use it. The value of the parts, when hand made, is largely your labour, and you won't thank yourself for saving a couple of quid if three or four hours hard work ends up a big disapointment!

Just an aside

If I remember correctly; there is [or was] an occasional problem with Silver Steel being Trochoidal in section, not circular. Reuleaux_triangle    Something to do with centerless grinding, I think.

This shape [usually three-lobed in this context], has a constant "diameter" but varying "radius".

... The UK 50p and 20p coins have the same characteristic.

Thinks: Perhaps that explains the varying results that people have when using Silver Steel for axles.

MichaelG.

Edited By Michael Gilligan on 25/09/2012 11:25:45

'Lobate'

Neil

True ... but that's a rather broad description.    Lobate

It reminds me of the comment that all Crows are black birds,

but not all black birds are Crows.

.

MichaelG.

Edited By Michael Gilligan on 26/09/2012 23:15:41

Edited By Michael Gilligan on 26/09/2012 23:16:48

Michael,

That in turn reminds me of the three prodessional men who travelled up to Scotland together for the first time. On crossing the border they saw several fields containing numbers of black sheep.

"Look" said the historian "it seems all the sheep in Scotland are black"

"No" said the engineer, "it only proves that some of the sheep in Scotland are black".

"Well, said the logician, " if we wish to state the position precisely, it only proves that not all the sheep in Scotland are [not black] on both sides".

David

Edited By David Littlewood on 27/09/2012 01:04:29