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The Newbies Arena Are you new to knife making? Here is all the help you will need.

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  #1  
Old 09-17-2018, 03:42 AM
Rasmus Kristens Rasmus Kristens is offline
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Cold working brass and a question about carbid burs

hi all

I was wondering, can I cold work smaller brass sections or do i need to heat it up?
The section size is about 0.25" x 0.25" I need to twist it and bend it a bit.

When using carbid burs, do i go with high or low rpm?
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  #2  
Old 09-17-2018, 04:58 AM
dtec1 dtec1 is offline
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low-ish I use about 1000 rpm
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  #3  
Old 09-17-2018, 05:23 AM
Rasmus Kristens Rasmus Kristens is offline
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Thanks dtec
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  #4  
Old 09-17-2018, 10:10 AM
jimmontg jimmontg is offline
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Do you mean a .25 thick square bar?

When you say it's .25x.25 section size I presume you mean a square bar? I am an expert on cold working various alloys of brass. First take a small section using either a tight fitting wrench or locking pliers and twist it, if it doesn't crack you are good to go, it isn't half hard brass.

Now that said, if it does crack or break I presume you have a method to heat it. A gas stove is actually sufficient to bend this alloy. Heat the whole section you want to work until a piece of pine wood smokes and turns black when rubbed against it. Let cool, you have temporarily softened it and you have 3 to 4 hours to work it before it goes hard again. Hope this helps you Rasmus.

By the way this also works for aluminum extrusions that crack when bent. What Dave said about the bur on brass, also it helps to smear a small amount of oil on the brass to keep from galling your bur.
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  #5  
Old 09-17-2018, 01:58 PM
Rasmus Kristens Rasmus Kristens is offline
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Amazing description jimmontg!
It is square stock.
Thank you very much, that sound simple enough to start with. Lets see if i can find a way to make it difficult for me anyway 😉
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  #6  
Old 09-17-2018, 08:21 PM
damon damon is offline
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carbides work well at high speeds/low torque. at lower speeds they can bite and skip across the work.
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  #7  
Old 09-17-2018, 09:43 PM
jimmontg jimmontg is offline
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Damon is more knowledgeable about using carbide burs than I. I usually, when carving metal, went about 1200 rpms and I always used a good cutting oil on the surface as I said before. But Damon is the expert on that aspect. So if you're only trying to make a Makers Mark I'd listen to Damon. If you're trying to shape and carve the brass that's a different story, but rule of thumb is the smaller the bur, the faster and vice versa.
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  #8  
Old 09-18-2018, 01:33 PM
epicfail48 epicfail48 is offline
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I run my carbide burrs in a pneumatic die grinder running about 35k rpm, never had an issue with them. This is a half inch cylinder burr as well, lasts me through a few dozen knives worth of shaping. Cant imagine why youd want to run them slow, after all most of them are made for die grinders.

Cold working brass can be done, once. Brass work hardened incredibly fast, so you can bend it once but after that it usually cracks if you try a second time. You might be able to get your project done in a single bend, but youll want to make sure you can anneal it just in case. Blow torch and a cup of water is all you need, heat it till it glows then quench it, same as hardening steel, only in this case itll make things soft
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  #9  
Old 09-19-2018, 05:22 AM
Rasmus Kristens Rasmus Kristens is offline
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But is it better just working with the brass hot then? Does that make it easier for me to bend it?
I'm not going to twist it anyways, just a few bends.
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  #10  
Old 09-19-2018, 11:01 AM
Rasmus Kristens Rasmus Kristens is offline
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Soo. I broke 2 pieces and the changed a few things. I changed the cross section som something more like 0.125x0.25 and annealed the area that i was going to bend ofte to try to a void it breakin.

It took som time, but Itwas a success! Thanks for the help, now to the next steps.
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  #11  
Old 09-19-2018, 05:21 PM
jimmontg jimmontg is offline
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Glad to see it worked for you Rasmus. Brass can be tricky to work. Once when I first started in sheet metal (the 70's), we got some brass sheet that cracked when bent. I had to use my TIG torch and fuse all the cracks back together. That's when we all learned that the zinc in brass vaporizes under an electric arc. All the parts were tossed into the scrap barrel because we didn't know anything about heat treating brass, or welding it either.

Epic, I used to have to bend brass tubing and the method I outlined above only temporarily anneals it and then it goes right back to a half hard condition, if he heats it like you said it will be permanently softened, just a heads up. By the way the water quench isn't necessary. Brass bar, rods and tubing are for the most part extruded just like aluminum, not rolled like steel. You are right about the burs, I used a slower bur when I was carving a brass pomegranate and too fast threw brass chips all over me and they were hot!

Same ht for T6 tempered aluminum, but a sheet of aluminum is almost impossible to anneal using my method because of heat transfer unless it's a small piece, but I used it whenever we got the 5150 aluminum extruded tubing that would always crack when bent.

I studied up on the heat treatment of nonferrous alloys and it gets weird, nothing like heat treating steel alloys. For aluminum and brass it is to take it up to 460+ degrees and let cool, it will stay soft for up to 4 hours, but only allow 3 hours as minor changes in the alloy can shorten the work time. But work hardening brass is always a danger even fully annealed, you're not going to re-bend a second 90 degree bend unless you anneal the part, indeed I doubt you could flatten it out without a little cracking. Bending metal always creates a weak spot btw.
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  #12  
Old 09-19-2018, 08:14 PM
epicfail48 epicfail48 is offline
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Quote:
Originally Posted by jimmontg View Post
Epic, I used to have to bend brass tubing and the method I outlined above only temporarily anneals it and then it goes right back to a half hard condition, if he heats it like you said it will be permanently softened, just a heads up. By the way the water quench isn't necessary. Brass bar, rods and tubing are for the most part extruded just like aluminum, not rolled like steel. You are right about the burs, I used a slower bur when I was carving a brass pomegranate and too fast threw brass chips all over me and they were hot!
Not permanently, brass still work hardens incredibly fast and will likely get back up to a half- to full-hard after a bend or two. I do agree that for some applications the half-anneal might be more desirable, like for a very slight bend.
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  #13  
Old 09-20-2018, 03:16 AM
Rasmus Kristens Rasmus Kristens is offline
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Hoper i can add a supplementary question when talking heat treating.
For my curent project, the fulltang is rather slim:


How do you get the toughest handle with the slim tang?
Is it best keeping it fully annealed?
Harden it and take it to spring temper,?
Harden it and take it to light straw colour like the blade?
Maybe something else?
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  #14  
Old 09-22-2018, 10:31 AM
jimmontg jimmontg is offline
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Rasmus, just harden, temper and draw it back with a torch to a spring temper will be strongest. Heat till it turns blue and make sure the heat doesn't travel into the blade area, I always used a wet rag in the vise holding it.
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  #15  
Old 09-22-2018, 02:44 PM
Rasmus Kristens Rasmus Kristens is offline
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Thanks, that what i Will do then
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