Bandsaw blade welding

[awemawson]

When I use my blade welder, it can be a very frustrating operation, as despite annealing the blade is still very brittle, which I put down to the fact that the gap between electrodes is not huge, and the clamps are massive, and draw the heat from the glowing blade too quickly. I've now taken to annealing several times, each time sifting the blade left and right a bit.

Years back I made a jig on the lines of Tom's but rather less flashy, and silver soldered blades successfully. When I had a hard time at the welder a couple of weeks ago I went searching for it. But the gremlins had got there first and hidden it. Perhaps time to make another :)

[Dr Stan]

(12-19-2015, 10:37 AM)RobWilson. Wrote:

(12-19-2015, 09:44 AM)Dr Stan Wrote: I'll have to respectfully disagree as grinding the weld flush re-hardens the weld thus requiring a second round of annealing.

Here's a good YouTube on how to resistance weld a bandsaw blade including a 2nd tempering/annealing step. 

https://www.youtube.com/watch?v=GBwr3oPJHcs

With respect could you please explain how grinding the blade heats the blade up to a sufficient temperature that it becomes hardened ?

Rob

All one needs to do is watch the color change of the blade and then refer to a steel color/temp chart.  You'll quickly discover just how hot the blade becomes during grinding which in turn explains the re-hardening.

[Vinny]

(12-19-2015, 04:13 PM)awemawson Wrote: When I use my blade welder, it can be a very frustrating operation, as despite annealing the blade is still very brittle, which I put down to the fact that the gap between electrodes is not huge, and the clamps are massive, and draw the heat from the glowing blade too quickly. I've now taken to annealing several times, each time sifting the blade left and right a bit.

Dunno which blade welder you have, but on mine they tell you to move the blade out away from the back to anneal. What I found when doing it that way is only the back side got hot enough. What I do now is leave it all the way back and press the button for a count of 5, then release it for a count of 10. Then repeat for 4-8, 3-6, 2-4 and then 1 and let it set for a few seconds before removing it. Releasing the pressure and turning the width knob to 0 before all that, of course.

[RobWilson]

(12-19-2015, 04:32 PM)Dr Stan Wrote:

(12-19-2015, 10:37 AM)RobWilson. Wrote:

(12-19-2015, 09:44 AM)Dr Stan Wrote: I'll have to respectfully disagree as grinding the weld flush re-hardens the weld thus requiring a second round of annealing.

Here's a good YouTube on how to resistance weld a bandsaw blade including a 2nd tempering/annealing step. 

https://www.youtube.com/watch?v=GBwr3oPJHcs

With respect could you please explain how grinding the blade heats the blade up to a sufficient temperature that it becomes hardened ?

Rob

All one needs to do is watch the color change of the blade and then refer to a steel color/temp chart.  You'll quickly discover just how hot the blade becomes during grinding which in turn explains the re-hardening.

But if one watches the video you point to one can clearly see that  the blade is clean silver in color where it had been ground , showing that it had been no where near the RED heat required to harden the blade . 

Funny thing ALL my Starrett  bandsaw blades metal and wood show a silver weld grind , 

So do the ones on the Enco site , using USA site here .

http://www.use-enco.com/ProductImages/0902234-24.jpg


http://www.use-enco.com/ProductImages/0332208-23.jpg

Funny that   the Enco    blades are the same as mine and show no signs of a second heating    ,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,, maybe someone should inform Starrett that they are making their blades incorrectly ,maybe point them to the youtube video .




Rob

[awemawson]

But just heating the blade won't harden it anyway. It needs heating and quenching. Just heating will only anneal it unless I've misunderstood the metallurgy over the last 45 years ?

[TomG]

I have no idea how Starrett and Enco grind their blades. Perhaps they use coolant.

All I can say is that in my experience, tempering the blade after grinding results in a MUCH less brittle blade, and I am not alone in that assertion. DoAll recommends that a blade be annealed before and after welding. Here is a quote from one of their blade welder manuals:

"Imperial Bi-metal and narrow carbon saw bands require special treatment to protect a weld against accidental breakage. It is recommended that welds in these saw bands be annealed BEFORE removing for grinding and AFTER grinding as well."

(Their caps not mine)

And here is a commercial blade company (BandsawBladesDirect) that does a secondary anneal as well:

https://youtu.be/muqWF4UWUpc

The Lazy Machinist video (which I have never seen) is exactly the way I have welded blades all my life and will result in weld that is every bit as strong and flexible as the band itself.

In my opinion, I doubt that the grinding process is hardening the blade from heat. It is more likely a work hardening process from the action of the wheel on the thin cross section of the weld. Whatever the mechanism though, grinding definitely makes the weld harder than the surrounding blade.

Tom

[RobWilson]

(12-19-2015, 07:28 PM)TomG Wrote: All I can say is that in my experience, tempering the blade after grinding results in a MUCH less brittle blade, and I am not alone in that assertion. DoAll recommends that a blade be annealed before and after welding. 


Tom

Ok there is are different production methods . 

But my original question was "how can it be Temper the blade ? "    

 you have just pointed out with the quote from the DoAll manual  that it is Anneal the blade after welding . 

Quote:"Imperial Bi-metal and narrow carbon saw bands require special treatment to protect a weld against accidental breakage. It is recommended that welds in these saw bands be annealed BEFORE removing for grinding and AFTER grinding as well."


Tom

You even wrote ,

Quote:And here is a commercial blade company (BandsawBladesDirect) that does a secondary anneal as well:

Tom

There is a difference , Annealing and Tempering are two different things . 


Rob

[RobWilson]

(12-19-2015, 09:44 AM)Dr Stan Wrote: I'll have to respectfully disagree as grinding the weld flush re-hardens the weld thus requiring a second round of annealing.

Here's a good YouTube on how to resistance weld a bandsaw blade including a 2nd tempering/annealing step. 

So you are disagreeing with my question  " how could it be Tempering ? "  then say its Annealing , so you're agreeing with me ?   ,its not Tempering ?

then in your second line you say tempering /annealing make your mined up . 

 Apples /Oranges  


Rob

[TomG]

(12-20-2015, 04:44 AM)RobWilson. Wrote: There is a difference , Annealing and Tempering are two different things . 


Rob

Ah, so that's what this is all about, tempering vs. annealing. I have a difficult time following all the quote snippets that you use in your responses. The two terms are often used interchangeably, but you are correct that technically there is a difference. Annealing is heating the steel above critical temperature and slowly cooling it, tempering is heating the steel under critical temper. To clarify, I anneal the weld after welding to remove any hardness generated by the welding process and temper it after grinding to increase toughness. My point is, or was that a post heating process of some sort improves the durability of the weld on a bandsaw blade and whether annealing is better or tempering is better seems to be up for debate.

Tom

[RobWilson]

(12-20-2015, 09:55 AM)TomG Wrote: The two terms are often used interchangeably, 


Tom

Quote: technically there is a difference

Funny that , The American Society of Metals thinks there  is a big difference . Each has its own chapter . 



Oh well we live and learn 


Rob