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Post by Tim Bayliss on Mar 10, 2008 15:19:58 GMT
In a previous thread distortion was mentioned with regards to removing large chunks of metal from flat plate to make side frames and the like. Whereas it is always possible to get some degree of distortion when performing such an exercise the amount is generally small and not significant if the steel is being cold worked, and anyway it can often be 'made good'. If however an external heat source is applied much more distortion can occur.
The company I work with at present have 3 ways to cut steel, by flame cutting (oxy-acetylene), plasma-arc and water jet.
Flame cutting is hot and will allow the inherant stresses to bend a piece of 50mm plate like a banana. Plasma-arc is more localised heat and is less likely to allow great stesses to operate (laser cutting would be similar), although some distortion can occur. Water jet is classed as cold and we have not had any rejects from distortion in thin intricate shapes that would be a disaster if we tried to use a hot method.
The moral of this story is if you want to keep the possibility of distortion to a minimum the method of stock removal, ie. a cold method, is often a very important factor in the equation and it helps to keep heat sources to a minimum and localised.
Tim
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Post by rodwilson on Mar 10, 2008 17:09:23 GMT
Does anybody here normalize steel before they start work on a piece?
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russell
Statesman
Chain driven
Posts: 762
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Post by russell on Mar 10, 2008 20:20:19 GMT
The problem when cutting frames is not the heat of cutting but the stresses set up bu the cold rolling process used to make bright mild steel. If you cut a strip off one edge you remove the compressive stress on that edge and leave the stress whic was balancing it on the other. The result is a significant curve. The answer is to remove a bit off each edge, or better still normalise it first.
Even with thick sections such as for coupling rods you will see a curvature develop when milling one edge. When you mill the other side you will find the rod is thicker in the middle than at the ends.
Russell.
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Post by Shawki Shlemon on Mar 11, 2008 7:51:21 GMT
I only normalize steel for rods and works OK for me ,but I don't do that for frames as i don't have the space or heat to do it , but I use black steel for frames and is less prone to distortion than BMS .
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Post by ron on Mar 11, 2008 13:42:22 GMT
If the coupling rods curve slightly after milling there is a traditional tool which is excellent for straightening them out if expertly used.  Ron |
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Post by rodwilson on Mar 11, 2008 14:00:45 GMT
If the coupling rods curve slightly after milling there is a traditional tool which is excellent for straightening them out if expertly used. Ron I know I'm new here but I've worked that one out for myself  |
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Post by jamienwr on Mar 11, 2008 16:50:15 GMT
If the coupling rods curve slightly after milling there is a traditional tool which is excellent for straightening them out if expertly used. Ron Would this magic tool be a adjustable hammer? As I have had to use them on all gauge's from 4mm gauge to 1:1 gauge and they can be (in the right hands) be a very precise tool to get something to with 1mm tollerances. |
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paul
Member
Posts: 8
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Post by paul on Mar 11, 2008 18:12:16 GMT
If the coupling rods curve slightly after milling there is a traditional tool which is excellent for straightening them out if expertly used. Ron Would this magic tool be a adjustable hammer? As I have had to use them on all gauge's from 4mm gauge to 1:1 gauge and they can be (in the right hands) be a very precise tool to get something to with 1mm tollerances. No, he means a Birmingham Screwdriver. ;D |
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simonwass
Part of the e-furniture
Cecil Pagets 2-6-2 of 1908. Engine number 2299. Would make a fascinating model....
Posts: 472
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Post by simonwass on Mar 11, 2008 18:42:49 GMT
Does anybody here normalize steel before they start work on a piece? I did on my Seal engine crankshaft. Cut from a piece of steel bar so I normalised it, cut out waste to make rough shape then machined it. No distortion either during or long after machining. |
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Post by circlip on Mar 11, 2008 19:21:33 GMT
Phew Tim! and there was me thinking I was being an awkward b4stard for having the audacity to suggest that BMS could distort when machining it. Seems other people had had this experience too. I don't want you to think I'm being pedantic, or pendantic in mentioning to the forum that water jet cutting can also be used to cut ANY type of material, including armour plate, in ANY thickness up to 90mm. Or at least it could 15 years ago when I last used it. 40mm thick open cell foam gaskets and 2mm thick pieces of jigsaws cut from mirrors were customer illustrations.
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steam4ian
Elder Statesman
One good turn deserves another
Posts: 2,069
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Post by steam4ian on Mar 12, 2008 12:33:44 GMT
G'day all
As I recall from my time in the steel industry hot rolled structural and light sections were "straightened" after they had cooled. This was a cold rolling process which took the banana bend out of length of the section. A series of rollers were set to bend the product up then down in ever decreasing amounts; the finished product was straight to they eye. No doubt this would put some stress back.
Regards,
Ian
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Noddy
Statesman
Posts: 672
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Post by Noddy on Mar 12, 2008 12:49:27 GMT
Pretty much every material has stresses in it (just look at a perspex ruler or glass window through crossed polars)
Generally materials that have been heated or have cooled slowly since they were last distorted are less prone to this, e.g.black mild steel and cast Iron.
If SWMBO is amenable or, even better away, a few cycles of heating and cooling overnight in the domestic oven works wonders. Also roughing all over to allow the distortion to occur then shimming to prevent the clamps from re bending the work before the finishing cut works pretty well.
I've read that for v accurate machine parts, some steels are dimensionally unstable over the long term, although I doubt we'd ever notice.
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