How square should BMS angle be?

This topic has 8 replies, 5 voices, and was last updated 20 November 2011 at 05:21 by Fuzzy.

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19 November 2011 at 19:12 #78160
Fuzzy
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@fuzzy
I recently bought a piece of BMS angle 5mm x 32 x32 (square corners and roots). I assumed it would be square enough that it would need no machining. But when I put a square on the inside angle, there was a 12 thou gap at the upper edge.

Is this generally considered to be acceptable? Or should I be speaking to the vendor about replacement?

Grant
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19 November 2011 at 19:12 #5759
Fuzzy
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@fuzzy
19 November 2011 at 19:35 #78161
Fuzzy
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@fuzzy
I have just found a related thread, “BMS angle not square”, which answers my questions.
19 November 2011 at 19:44 #78163
Robert Dodds
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@robertdodds43397
Grant

the pdf below sets out the tolerances to expect and I suspect yours is within spec

http://www.parkersteel.co.uk/doc/BS/JPSBS0029.PDF

Bob D
19 November 2011 at 20:11 #78167
Sub Mandrel
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@submandrel
Making the cahssis for my shunter recently, I used the edge of a big slot drill to true up one side of the angle after riveting the other side to the stretchers. I had to shave a wedge about 10 thou thick at the top off. It didn’t take long.

Neil
19 November 2011 at 21:25 #78175
Springbok
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@springbok
If you are useing standard extruded steel expect to mill it to the tolerance

that you wish. To get a decent finish you will need to anyway

Bob
19 November 2011 at 22:00 #78177
Fuzzy
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@fuzzy
Thanks for the information, which I had looked for without success.

Using my “Tilt Box” inclinometer, the measured tilt of the outside arm is 1.2 degrees. (This device has a resolution of 0.05° (accurate to 0.2&#176).

The reading bounces between 1 and 1.2 while attached to the angle, giving an intermittent “error” message. It does not do this when attached to an angle plate, v-block, or 5″ machinist square; all measure at 0 deg.

According to the table you provided, the maximum deviation allowed for 35 mm angle is +/- .62 deg. Assuming my reasoning and observations are correct, the BMS angle I have is out of spec.

I suppose I could request another piece from the vendor, but I am in Canada and the shipping cost is three times the price of the angle and I don’t think it reasonable for the supplier to have to spend this to send another piece which might be marginally better but within spec, and take a month for the mail. As well, my measurements might be in error.

I have a machined piece of black mild steel angle which measures at 0 deg. It doesn’t look as good as the bright angle but it looks like the best solution.

Grant
19 November 2011 at 22:22 #78179
Terryd
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@terryd72465
Hi Fuzzy,

It appears that you read the table wrongly. The maximum angular error is + or – 1 degree. The deviation t is the maximum linear deviation, i.e. 0.62mm or approx 0.025″. As the deviation of your sample is 0.012″ it would appear to be well within the tolerance.

I may be wrong of course in my interpretation and would welcome clarification from the more worthy members of the forum who usually seem to be much better informed than me.

Best regards

Terry
20 November 2011 at 05:21 #78186
Fuzzy
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@fuzzy
Thanks, Terry, and thanks to all who replied.

Grant
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