brazing bandsaw blades

[Jim Davenport]

I read a post about needing to get a bandsaw blade welded. I thought I'd post about how I braze my own blades for my metal bandsaw. The same process would work for wood blades. I buy my blade stock in bulk, 100' rolls.
First I milled a clamp jig on the Mill. I made the shelf for the blade .025" deep, and .450" side to brovide clearance for the teeth

[Jim Davenport]

I cut the blade stock to the desired length, twisted the blade so the teeth faced oposite directions, and clamped the ends together.

I then ground the ends to a slight angle and beveled both ends of the blade. Angles are not critical

I clamped the blade in my jig with a couple about .005"-.010" clearance between the bevels

I used my Harris torch with a # 0 tip

[Jim Davenport]

I brazed the first side.

I turned the blade over, reclamped and brazed the other side

I turned the blade over, reclamped and brazed the other side

I then used my Dremel tool to smooth out the braze joints.

I used an "AO" torch and brazed, but using a propane torch, and silver solder would work.

[Rick Lizek]

I've done a lot of silver brazing and there is no need to flip the blade over to braze the other side. What you ultimately want to do is have the braze flow between the ends of the blade. Directing the heat from below the solder will flow to the heat. You definitely don't want to get the blade red hot. Cadmium in the solder flows better and fills gaps better but is not safe from a toxic standpoint without proper ventilation. Solder with out cadmium is available so be sure you know which one you have. 1,200 to 1,500 degrees is all that's needed. One trick is to put a small snippet of silver solder on the joint and when the temperature is reached the solder will flow. Done right this will keep from over heating your blade. From your picture and description you are applying more solder than necessary. Just enough to go between the ends of the blade tips is plenty.

Just for clarification to other who don't understand the strength of silver brazing, this is how they put the carbide teeth on saw blades.

[Teri Lu]

Hi,

I would like to add that a suitable jig can be made from pieces of flat stock available at the local Borg and a file, just not as purdy as Jim's ;)

-- Teri

[Lincoln Myers]

Interesting Jim. Thanks for the post.

-Linc

[Dennis Peacock]

Jim,

So what you're saying is that it's just not that difficult to braze my BS blades? I have a MAPP gas torch and some solder I use for plumbing stuff. Will that work? or will I need to get a different type of solder? I have a couple of blades I sure would like to cut and shorten just a bit and resolder them. Let me know if I'm way off base here. This is one thing that I know nothing about, but really need to learn how to do.

[lou sansone]

Here is some technical information from a J W Harris who manufactures silver braze along with other brazes

"What is the tensile strength of a brazed joint?"

Joint strength depends on several factors: clearance between parts, base metal composition, service temperature and joint quality (low voids, good penetration). Joint design will also affect strength.The bulk tensile strength of silver braze alloys is 40,000-70,000 psi. When brazing copper-based alloys, failure will occur in the copper or brass. For copper this is usually the annealed strength of the copper alloy. When brazing steel or other ferrous metals, joint strength over 70,000 psi can be achieved under the right conditions.<O:pKeep in mind that braze joints are primarily lap type joints, so strength is a combination of tensile and shear. Joint strength is directly influenced by the above mentioned factors. The only way to accurately determine tensile or other values is to test the brazed assembly.


A couple of things do come to mind when I read this reply. If you are tensioning blades to 25000 psi, you have a safety factor of 3. For me, I would rather have my blades welded which should be basically as strong as the steel itself.

lou

[Bruce Wrenn]

Woodcraft carries a kit to braze blades, which includes holder, silver soider, and flux. Soider and flux can be bought seperately.

[Larry Norton]

Jim, Thanks so much for taking the time to show the process.

Larry

[Randy Meijer]

To eliminate any confusion, when most folks talk about silver soldering, they actually mean silver brazing. There is such a thing as silver soldering; but it is a different process. It is a relatively low temperature process that uses solder much like a plumber uses but has a little silver in it for extra strength. There are quite a variety of materials depending upon the application; but in very general terms, the two processes are as follows;

Silver Soldering.....Tin/Silver solder that melts around 500°F. Silver content is around 5%.

Silver Brazing.....Silver/Copper/Zinc rod that melts around 1400°F. Silver content is about 33%.

And for comparison, regular brazing uses a rod that is about equal parts of copper and zinc with tiny amounts of other metals to customise the rod for specific situations. Brazing is done at around 1600°F.

[Philip Duffy]

A fascinating discussion by all. Thanks for the info. Just one more thing that seems so difficult that is plain and simple when presented by guys who know what they are doing! BZ to all. Phil

[Don Henthorn Smithville, TX]

Woodworkers Supply (and others) sell a blade silver soldering kit. I paid $22.00 for mine but that was fifteen years ago or more. Very simple and inexpensive to do. Regular butane torch will do. I made a little jig clamp to hold both ends of the blade while I ground them to about a 5/32" or greater scarf joint. I then put the blade in the jig, added the flux and inserted a small piece of the silver solder ribbon between the ends and played the torch on it until the solder "ran". No need to turn the blade over. The solder will fill every place the blade ends touch. I kept a wet rag handy and cooled the blade immediately to take care of any annealing that might happen. Grind down any high spots on the sides and edge and you are ready to go. I soldered doxens of blades and never had a blade break at a joint. No need to throw out a good blade because of an unexpected break.

[Wallace Blackburn]

I know this thread is old as dirt, but in case anyone comes searching (like I did):

It is very important to leave a small gap between the blade ends! Mine kept breaking and kept breaking. I did it with a few thou gap as pointed out here and I've been resawing, etc. with no problem at all.

Thanks,
Wallace