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Suitability of hot rolled steel for machining

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Martin of Wick04/04/2019 22:05:15
82 forum posts
4 photos

I was wondering if there was any views on the suitability of using black hot rolled steel (HRS) as the basis for machining a slotted cross slide about 8 inches by 3 by1.

Cast iron would be preferable but always seems very expensive (>£50) rolled steel would be about £10. I am unable to heat treat so can't use BMS and I don't fancy fabricating a table, leaving HRS.

I would treat the rolled steel similar to cast iron, taking a deep cut with a carbide face mill all round to get rid of scale, then take approx. to size, then mill the slots and v-ways then mill the tees, then finish mill the surfaces (or grind on my Stent if I have to.

Is this sort of work feasible with this material? will it do as the 'poor mans' steel / iron and are there any common issues, risks or other things to be aware of when generally working with HRS?



Andrew Johnston04/04/2019 22:32:13
4722 forum posts
532 photos

I use a lot of hot rolled steel, both for my traction engines and for tooling. It has a number of characteristics, some good, some bad:

It is rather sticky and has a propensity to tear if speeds and feeds are incorrect. I use carbide tooling as a matter of course for turning and milling. Run fast and you'll get a good finish. It won't look like free cutting steel but is still fit for purpose

I don't worry about the scale, it's not like the hard surfaces on a casting

The material doesn't go banana shaped when you mill it

It doesn't seem to be prone to rust like free cutting steel. I get a great finish on EN1A, put it on the hall table and the next morning it shows signs of rusting. Hot rolled doesn't do that, it survives in the kitchen without rust, and the kitchen isn't exactly dry.

Hot rolled steel is good in tension and compression unlike cast iron.

This is part of press tool set I've just made from hot rolled steel:

press tool base.jpg


David George 104/04/2019 22:42:10
841 forum posts
292 photos

Hi Martin wear characteristics are better with cast iron than mild steel although it is cheaper than cast iron it depends on the use that the slide is put to and the amount of use. A mild steel slide would be stronger in certain circumstances T slots less likely to break but depends on thickness and load. The graphite in cast iron gives a better slide and will not pick up and smoother slide but may wear as all slides do to some extent. Just think cost versus usability.


John Reese05/04/2019 00:48:40
769 forum posts

I have an almost unlimited supply of 1" x 4" x 8" hot rolled bars. I use a lot of it. It is a little gummy to work and as Andrew said it does not distort and finishes well with the proper tools and speeds.

Justin Siemens05/04/2019 02:01:58
8 forum posts

Hot rolled is one of my go to materials in the shop as it is easy to source. I like machining it (it takes a bit to get adjusted as indicated above).

Just make sure you size your material to allow for cleanup. Most hot rolled sections aren't all that square so you have to remove a fair bit of material to clean it up. Obviously cold rolled doesn't suffer from this problem but it suffers from residual stresses.

For most home shop tools hot rolled works quite well.

Just be warned if you wish to scrape the slide in for fitting purposes, scraping steel can be miserable compared to cast iron. If you are going to scrape I would spend the extra money on the cast iron.

Thor05/04/2019 06:12:32
1102 forum posts
31 photos

I too use a lot of hot rolled steel, and use carbide tools to get rid of the scale. It works well for the things I make but it is a bit more difficult to get a nice finish like you get with a free cutting steel.


AdrianR05/04/2019 07:41:59
272 forum posts
20 photos

Do you have any links to suppliers please, looking around I can see bright and black.

Martin of Wick05/04/2019 09:34:56
82 forum posts
4 photos

Thanks to all that replied, very helpful and useful to know that this is material OK for general use, also useful to know that high speeds and low feeds are the way to go. I now feel emboldened to give the project a try. And if it all goes pear shaped, at least it wont break the bank!

As the project is only for home mini lathe use, the ultimate in high finish and durability is not really necessary. I hadn't thought about scraping issues but I wouldn't have thought it necessary for this application.

AdrianR - you ask an interesting question, I always thought in my ignorance that anything described as 'black steel' by stockholders was technically the same as hot rolled steel. Somebody please shout and tell me quickly if this is not the case!

I don't know of any helpful steel stockholders near to Weston that are willing to supply small quantities so was going to use M Machine Metals, but only because I have used them before (other stockholders are available).

Thanks to all,


David George 105/04/2019 09:38:46
841 forum posts
292 photos

Hi Adrian have you tried M machine metals they gave a great selection of materials and usually quick delivery.


Perko705/04/2019 12:21:04
275 forum posts
23 photos

I'm also a regular user of hot-rolled steel either in rod or bar form. Never had any issues with deformation after machining. It is sometimes difficult to get a good finish, but I find HSS tools better than carbide for this purpose. Usually machine dry but an occasional squirt with tapping compound will help when deep drilling. Main issue I find is inclusions, as occasionally I'll come across a hard bit that defies all attempts to get a smooth surface. Only option is to part off into the bin and start again.

larry phelan 106/04/2019 12:47:09
458 forum posts
11 photos

Might sound like a stupid question,but for turning jobs I assume it would be work for the four jaw chuck ?

I doubt if the three jaw chuck would like it. Would this be correct ?

IanT06/04/2019 13:34:02
1279 forum posts
130 photos

Larry, not much 'raw' material is really round but I use my 3-jaw for holding all types of materials. However - you have to skim it true and then not remove it from the 3-jaw once trued (or it will not run true when replaced). A 4-jaw is useful when something that has already been 'trued' (by turning or grinding) needs to be set-up to run true (often for a second operation for instance).

If I have a piece of rod that I'm going to machine down - I'll generally just stick it in the 3-jaw, because it's quicker and simpler to do so. The 4-jaw generally gets used when I have something awkward to hold or where I need to set it to run true or (alternatively) have it run off-set (eccentrically).

So I think (and my apologies if I've misunderstood your question) the answer would be No - your 3-jaw chuck will normally be fine for hot-rolled rod.




Edited By IanT on 06/04/2019 13:38:56

John Reese07/04/2019 02:00:39
769 forum posts
Posted by AdrianR on 05/04/2019 07:41:59:

Do you have any links to suppliers please, looking around I can see bright and black.


I am not too familiar with UK terminology but I would assume that black refers to hot rolled steel and bright refers to cold finished. Some apparently bright sheet is actually hot rolled that has been pickled and oiled. In the US we are seeing supposedly cold rolled flats that are merely sheared from plate and the edges slightly rolled to remove shear marks.

not done it yet07/04/2019 06:51:06
3167 forum posts
11 photos

Are there any common steels, we would use as hobbyists, that are not rolled? Apart from nickel cast steels, I don’t thinkI have come across any. The specifications plastered over the internet show the differences - mainly in the strengths of the two types. Oh, and the corrosion resistance, to some extent.

One cannot ‘heat treat’ mild steel. Case harden, yes. Carbon content is too low. De-stressing by heating is a slightly different matter and the strength may well be compromised.

Andrew Johnston07/04/2019 08:04:53
4722 forum posts
532 photos
Posted by John Reese on 07/04/2019 02:00:39:
In the US we are seeing supposedly cold rolled flats that are merely sheared from plate and the edges slightly rolled to remove shear marks.

That's interesting. In the UK it's common for stainless steel flats to be sheared from plate, but not seen it for low carbon steels.


AdrianR07/04/2019 08:57:37
272 forum posts
20 photos

I think I was being dumb, of course black is hot rolled, haven't a clue why I thought different.

Nigel Graham 207/04/2019 11:51:40
351 forum posts

For the less pecunious of us, often using "pre-loved" metals, hot-rolled steel has the advantages of stability described above, and you are less likely to be caught out by some nice shiny stuff from the local scrap-yard being anything but free-cutting!

It is also usually readily welded, which is not recommended for leaded free-cutting steels. (EN1A will fuse, but the welds can be brittle.)

Recently I made a set of dovetail nuts to hold the magnetic read-out strip to my milling-machine table, using the slot that originally held the limit-stops. I saw this is the only practical way, on a Myford VMC mill not designed to take a DRO set. My stock was cut from old miniature-railway rail, flat-bar not profiled, scrapped as too worn and rusted for continued railway use. The worst corrosion pits were quite deep, but the nuts are sufficiently thinner than the stock to avoid them.

Years ago I worked as materials store-keeper for a manufacturer of industrial screen-printing machines, when it received a one-off order for special jigs to hold long surveying-poles for printing their rule scales (not ruler - I've read that thread!). The longest was at least 2m long, and after the miller had cut the requisite facings and channels along the BMS stock, it naturally warped. So it went off to a heat-treatment firm for normalising, but came back even more normally bent. I can't remember what they did eventually - might have used aluminium-alloy instead.

A further tip:

Those DRO nut's dovetail chamfers are at 45º. No suitable cutter, so I drilled and tapped all the holes regularly-spaced along the strip, then drilled matching holes along a piece of angle-steel, at the same settings. Screwed the nut-strip to the angle, clamped that to the mill table so it acted as an inside-out V-block; then kept the assembly together to hold in a vice for junior-hacksawing the nuts apart.

I marked the cuts first by tiny drill-spots during the drilling and tapping process: the nuts' ends do not need be more square than by eye, and a file soon tidied them.

Note: this process order will not work in all cases. What surprised me, when at the printing-machine manufacturers, was the number of times millers making extra T-nuts would drill and tap all the holes in a bar length then expect me to separate them on an auto-feed hacksawing-machine with a well-made but poorly-designed geared-roller vice. It was definitely not for such tasks and incapable of holding short bars anyway. I had to gently suggest to these apprentice-trained, skilled machinists that the repetition would be far easier and more reliable if I cut the embryo nuts from the stock bar before machining.

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