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BMS angle not 90 deg

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StirlingSingle07/09/2010 21:23:23
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40 forum posts
Hello,
 
Has anybody else noticed that some BMS angle is not 90 deg. I have just recieved a 2' length and when you put a square on it you see the error. I have enough problens making things square without this!
 
Incidently I got an old piece from the scrap box and this is square.
 
Food for thought.
John Haine07/09/2010 22:42:38
5563 forum posts
322 photos
This stuff is rolled.  Is "flat strip" flat, or straight?  It's made for fabricating frameworks where squareness isn't critical, if you need it dead square then either select a square bit or machine it.
Andrew Johnston07/09/2010 23:07:52
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7061 forum posts
719 photos
Well, you learn something new every day. I'd always assumed the bright MS angle was made by cold drawing through a die, obviously I was wrong.
 
John, can you tell us a bit more about how BMS angle is manufactured?
 
Either way, it doesn't surprise me that the angle isn't actually square. I seem to remember this being discussed back in the early 70's when I was a small kid (as opposed to today's big kid, with bigger toys) and was a member of the Bedford MES.
 
Regards,
 
Andrew
Ramon Wilson07/09/2010 23:47:27
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1655 forum posts
617 photos

I hate to say this Stirling but BMS angle can be a bit of a 'sod' to machine!  There are so many locked in stresses caused by the rolling process that the angle can exhibit a will of it's own when a skim is taken over it to square it up. I think it would be fair to say that on average to find a truly square bit would be an quite an occurance and its certainly a disapointment to find its not so square off the shelf as you think it will be.
Last time I machined some (at home) I was lucky enough to get it stress relieved in the oven at work which worked a treat but that's not really going to help you.  (Nor me either any more - the works is now in Slovakia )
 
If you do have to machine it take as light a cut as possible working from face to face on each cut which will help to equalise some of the stresses but not all. Preferably use a small cutter and try not to get it hot by the machining. Small pieces are easier - if you are making brackets do them singly rather than one long piece then cutting them up but if it's buffers then take your time and keep the cuts very light.
 
'Black' or hot rolled angle doesn't exhibit the same tendencies but the inside of the angle doesn't always have a parallel profile with the outer. Perhaps I should say didn't - it's been quite a while since I was involved with such
 
Good luck - if you get a 'good bit' you might get away with it easily but be prepared for a bit of frustration.
 
Hope that helps in some way and hasn't dampened the flame too much
 
Regards - Ramon
 
 
 
Nicholas Farr07/09/2010 23:59:14
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3988 forum posts
1799 photos
Hi, Ihave to agree with Andrew, BMS stands for bright mild steel which is cold processed in its final stage, it is normally fairly sqauare, but rarely exact. It would be quite pricey to use in general fabrication. Black, or hot rolled as it actually is, is used for fabrication perposes and very seldom square or truely flat. Regards Nick.
 

Edited By Nicholas Farr on 08/09/2010 00:12:36

Ian S C08/09/2010 00:16:49
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7468 forum posts
230 photos
Bms I think is also known as cold rolled, and is highly stressed, you could cut your short lengths and stress relieve it by heating and slow cooling ie in the ashes in the fireplace overnight. Better to use hot rolled, select a heavyer section and machine to size.I use a piece of 4"x 4"X1/2" angle as an angle plate on the mill, it has two bracing pieces welded on the back and 2slots on both faces, the outsides are machined square.
Another type here in NZ is called Duragal, this is rolled cold from from hot rolled strip, it has a round outside corner, its fairly springy, lighter than the same size hot rolled, and its galvanised, and not square. Ian S C 
Billy Mills08/09/2010 00:24:11
377 forum posts
  Was told some years back that  BMS is hot rolled that has been pickled ( acid dipped) , washed,  then cold rolled to "clean it up". Light oil stops it rusting too much before delivery.
Perhaps it is the cold rolling that puts the stresses in that make it tricky. 
 
Another machining nasty is hard drawn brass which will take the tip off small drills. The HD brass was some 5mm from a model shop that was open Saturday morning when I had a big rush job needing 100 1.0m holes straight through. I demolished many decent HSS drills and some very nice solid carbide drills before I realised the cause. Some CZ121 brass then drilled just as you would expect.  
 
Regards,
Alan.
Axel08/09/2010 06:52:01
126 forum posts
1 photos
BMS is called CRS in the USA, where I was trained.
Dusty08/09/2010 09:28:19
498 forum posts
9 photos
You could try putting your angle in the domestic oven (when the catering manageress is not looking) and leaving it there for a week or two. While the heat is not really high enough to give a complete stress relief the heating and cooling will have some effect. It is no good just heating it once. Do not be tempted to remove it from the oven while warm, allow to cool completely. Domestic godesses sometimes need bribing when attempting to use their appliances, it could be a small price to pay. If it works it will improve your language and you should be a better person to live with.
Gordon W08/09/2010 09:46:19
2011 forum posts
Will just agree with above. If you need accurate angle, use black steel and m/c square, cheaper as well.
KWIL08/09/2010 10:05:06
3681 forum posts
70 photos
As Ian SC says  COOK IT.  IF you want to machine BMS in anything other than a circular form from circular stock AND you need to minimise/eliminate distortion - post machining, there is only one way, that is to heat the material to RED heat and hold it there for 1hr per inch of thickness, then allow to cool slowly.(in the ashes overnight is a good way) or just cover with firebrick on the forge/hearth.   Machines beautifully after that.
 
As regards to BMS angle, same applies, it is not exactly 90 degrees, might be near at times.  Black iron has a near right angle externally, but the inside is definately tapered in the rolling process.
 
I have made my own angle from  heated stock when I have needed a precisely square item, tedious to mill, but there you are.

Edited By KWIL on 08/09/2010 10:05:40

John Stevenson08/09/2010 10:21:00
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5068 forum posts
3 photos
Slight aside to this but I have noticed a change in hot rolled bar over the last couple of years.
 
Normally hot rolled is a bitch to machine, gummy, tears and not great. Recently i had to price out some location pins in 90mm round.
As you would expect the material was pricey and the job they were doing wasn't critical.
I found out that for a 10' bar of 90mm bright drawn it was £140, hot rolled or just black came in 7 metre lengths, nearly 23' and was £166
 
Given the OD had to be machined I went for the black and ordered it cut into two lengths for handling. As it turned out it was delivered whole which caused some joy on the day, I can recommend Aldi's 9" angle grinder <g>
 
When machining this it turned out to machine very well, more like an EN8 steel with a very good surface finish.
Recently I have ordered smaller sizes and still getting good results, the cut off point seems to be around the 3/4" / 20mm mark, under this it's rubbish again, possibly because in the smaller sizes it cools quicker.
 
Anyway if you need larger diameters don't be put off by black hot rolled.
 
John S.

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