knots Posted February 21, 2020 Share Posted February 21, 2020 Every now and then I will purchase plate drops from my local metal supplier. On acouple of occasions I have encountered hardened edges. In a couple of cases the edges were hard enough to destroy the usefulness of a band saw blade. Is this a comon problem ? Just wondering how the best way to test for hardness before starting to cut and how deep to expect the hardening to extend away from the edge. Quote Link to comment Share on other sites More sharing options...
JHCC Posted February 21, 2020 Share Posted February 21, 2020 Leaving aside the causes of the phenomenon, you could try scratching with the corner of a file before you start cutting to see if it's hardened. You could also try grinding off any slag before taking it to the bandsaw. Quote Link to comment Share on other sites More sharing options...
Kozzy Posted February 21, 2020 Share Posted February 21, 2020 Laser isn't usually quite as bad but with plasma there will virtually always be a hard heat affected zone. Most plasma systems use dry air as their cutting method so are actually burning material and that can cause both hard oxides as well as plain old carbon-hardening at the edges. With laser, they tend to use nitrogen and blow the kerf rather than burning the kerf so you don't get quite the same HAZ..but there is still some. Rarely, plasma will also use nitrogen and blow the kerf but that's pretty expensive for basic plasma cutting. SOP for machining such things is 1) grind the entry point through the HAZ so you start cutting in "fresh" material and 2) when machining (most often profiling), you make sure your depth of cut is plenty to always be cutting in fresh material--and always conventional cut rather than climb cut so the endmill isn't diving into the hardened surface...it's always coming out of the softer material to remove that HAZ. Sawing basically the same although most people are lazy and only grind the infeed point. Best on the blade if you also grind the HAZ off the exit point too. Quote Link to comment Share on other sites More sharing options...
knots Posted February 21, 2020 Author Share Posted February 21, 2020 JHCC thanks for the reply. Well, yes I did do a file test, and the cuts are clean with no slag. Basically, at least from this source I will need to assume increased hardness from this supplier and start and finish the cuts with abrasives. I tried to anneal the metal in my oven without success so it could be an alloy . I called the supplier - they were clueless. Thanks Kozzy. Yeah I guess I just need to accept the hardness and grind finish and start to accomoate a good source of materials. Quote Link to comment Share on other sites More sharing options...
Recommended Posts
Join the conversation
You can post now and register later. If you have an account, sign in now to post with your account.