Breaking saw tips

[Tom Walz]

In another thread the subject to breaking saw tips has arisen. Saw tips, used properly, are very, very hard to break. (We had a guy call all excited because Jackie sold him saw tips for mill saws that cut through 12 penny nails with no damage. Jackie was all excited and told us the story. Then she asked what a 12 penny nail was.)

The official test for carbide is a transverse rupture test where you support a rod on each end and put pressure in the middle. It typically takes 300,000 psi. to over 500,000 psi. to break the rod.

The easiest home test is to take a carbide saw tip, wrap it in a rag so the chips don’t fly and beat it with a steel hammer. It takes a really good blow to break a saw tip. You need to do this on a concrete floor or on the flat of a big vise.

When you braze carbide to steel they both grow with the heat but the steel grows about 2 to 3 times as much as the carbide. If you do it wrong you can leave the carbide stressed like a drawn bow. This can snap very easily.

The easiest test for this is to take a stick and beat the teeth on a saw blade to see what happens. The “official” stick is an 18” piece of red oak 2x2. An old chunk of 2x4 works just fine. This is one of those rule of thumb tests that works very well.

If you want to try breaking saw tips yourself let me know and I will put a couple in an envelope no charge. Just be careful because it takes a really good smack with steel hammer to break them and the chips can really fly.

Phone is 800 346-8274 toll free. (253) 476-1338
Sales@carbideprocessors.com (Sales@carbideprocessors.com)
jax@carbideprocessors.com (jax@carbideprocessors.com)

Technical articles are at www.carbideprocessors.com

Tom

[Jacob Reverb]

Yeah, but what about the brazed joint that holds them on? ;)

[Tom Walz]

Excellent question. Considering the tips without the brazing is much like considering tires off the car compared to tires on the car and running.

As with any other joint it can be good or bad.

If the surface are properly prepared then you create an intermetallic between the braze alloy and the carbide as well as the braze alloy and the steel. A braze joint gets stronger down to about 0.0005” but it provides more stress relief and impact protection as the joint gets thicker. A compromise is generally in the 0.003” to 0.005” range.

Having good fillets or shoulders can significantly add to the joint strength.

Chemistry is very important. The standard tool braze alloy (colloquially silver solder and technically braze filler metal) used to be 50% silver with Cadmium (as well as copper zinc and nickel.) When the government dramatically tightened restrictions on Cadmium exposure many tool makers went to a 50% silver braze alloy with no cadmium.

In test at Weyerhaeuser with SystiMatic we found that this braze alloy was about 30% weaker than the Cadmium alloy. If you use a braze alloy with manganese you get a much stronger bond.

There is also a difference between braze alloy as a wire or a trimetal sandwich of braze alloy.

Best practice now regards the whole assembly (carbide, braze alloy and steel body) as single entity much as plywood is various sheets of material with binder.

If you wish you can see more information on our web site about braze joints. I think the best is under braze failure analysis.

[Cliff Rohrabacher]

I've broke 'em. Plenty of 'em.