View Full Version : Help, My Carbide is Solderophobic!

12-28-2008, 05:42 PM
I got a surface plate for christmas, so It;s time to try scraping. A while ago I broke a brazed carbide parting blade giving me a piece about 3/4 by 3/32 by 1/8. So I heated it up and pulled off the carbide piece. Then I tried to silver solder it onto a shank made from an old file. No success. The solder just balls up off of the carbide, using an HCL and zinc flux that came with a solder. I heated, cooled, and polished the carbide before soldering. Any idea how to solve this problem?

Also, the torch gave up the ghost in a rather scary way with fire coming out of places it shouldn't. Opinions on various bernzomatic style small torches?

12-28-2008, 05:46 PM
Carbide likes to form an oxide that's a pain to solder. Lightly hone the edge you're going to solder with a diamond hone so it's shiny and bright, and it will solder/braze just fine.

It also helps if you use black (carbide) flux, instead of the usual blue brazing flux.

12-28-2008, 05:49 PM
Hmm, OK. I was using soft sandpaper..

Flux is neither blue nor black, its a clear, runny liquid stuff that contains zinc dichromate and hydrochloric acid.

12-28-2008, 05:57 PM
Here's a link to an excellent thread about carbide brazing that explains some of the pitfalls you may encounter while brazing carbide.


12-28-2008, 06:03 PM
if you don't have diamond, sandpaper or rather emery will work, if its fine....the abrasive isn't going to cut through the carbide but the oxide is a lot softer

12-28-2008, 06:47 PM
Then I tried to silver solder it onto a shank made from an old file. No success. The solder just balls up off of the carbide, using an HCL and zinc flux that came with a solder. I heated, cooled, and polished the carbide before soldering. Any idea how to solve this problem?

What is the silver content? I use stuff up in the 44 - 56% range and black flux.


12-28-2008, 07:04 PM
A couple of things to consider with this. Aircosil brazing flux seems to work the best of any fluxes I have tried, a white and chalky paste, it adheres well to the parts where you want the silver solder to flow.

Heating the substrate is a little tricky. You want to heat it to about dark cherry red but not to bright orange. You have to adjust the torch so that it comes up to temp in a controlable manner, rather than overshooting the mark. If you overheat the flux it will not work and the silver solder will ball up and fall off.

I have always said that getting silver solder to flow correctly is "magic and JuJu." Some days you can do it and some days it just won't cooperate. :D

12-28-2008, 07:34 PM
Get your self to the welding store and buy some black are real dark brown silver solder flux. That will take care of the problem . The white and blue stuff is no good for this application.

12-28-2008, 07:38 PM
I have brazed carbide using the powder borax based flux with no problem. You first need to polish the carbide and you want to get you heat just right so as to not overheat the carbide. The only place I have used a liquid flux was for soldering sheet metal...

12-28-2008, 11:19 PM
Hmmm// I do not know the silver content, but will check. I think it came with this old Weller propane-canister torch that just blew up (almost singed my eyebrows there) and a tube (who puts liquid in a tube?) of clear flux. Torch does not really have much in the way of adjustments...

EDIT, no actualy I cannot find out the silver content, but it is a fairly soft solder, and it melts LONG before anything glows red hot. This is definitely soldering, not brazing, done with soft propane torch. The substrate is not a problem, the solder sticks to it fine. it balls up on carbide or if it does not, the carbide easily pops off with not a speck left on. Hopefully I can find this stuff...

12-28-2008, 11:31 PM
Deleted-accidental double post.

12-28-2008, 11:53 PM
Are you sure you have silver solder ?????

Is it pretty stiff to bend ?

Spin Doctor
12-28-2008, 11:54 PM
One reason why I like the Sandvik Coromant scraper with the replacable tips. Each blade has four cutting edges so you can sharpen all four and almost always have a spare edge on hand. It is also possible to have special blades for doing small areas and such. They also work well in the Biax power scapers

12-29-2008, 02:13 AM
Sounds like you have "Silver bearing solder", 1% or less, the rest likely Tin.

e-mail me an address and I will send you a bit of EZ Flow and some black flux, enough to do a few joints. You'll know what you need to buy. Someone just mentioned, elsewhere, that they were quoted 32 USD per ounce for true silver solder. Surely, that is not what you are using.

Also, when you have abraded the pieces to be soldered, blow them clean, do not rub the dust off. The oil from your skin will keep a bond from forming.



A Bernz-O-Matic SHOULD give you enough heat, though not ideal.

Forrest Addy
12-29-2008, 03:07 AM
Let me suggest to you the stuff I use. I use Harris Safety Silv 56 silver solder and Harris Stay Silv white flux. These are excellent products available from most welding supply shops. There are other good products on the matket. With the Harris stuff and most others there are clear instruction for its use. Needless to say you don't get much silver solde for $16; about 1 troy ounce. That's enough for me to make 60 scrapers. It goes quite a long way.

Joint cleanliness is vital in silver brazing. It's not enough to wire brush off the crud and go to town. Both sides of the joint has to be abrasive scoured to clean bright grease free metal. A clean piece of enery cloth or a clean unused ScothcBrite pad works well.

Since carbide is so hard only diamond will abrade it. I suggest a diamond hand stone like a knife sharpener from a sporting good store. A couple of swipes from the stone will take off the oxide to clean carbide.

A good barrier to keep excess silver from drooling over the work is welder's soapstone. Mark the work with ruled soabstone lines. 1/16" away from the joint. The flux attacks the soapstone to a certain extent so this trick isn't fool proof.

Finally, use no lead or tin base solder products in connection with silver soldering. Silver soldering isn't really soldering anyway. It's more like low temperature brazing. The silver adds aggressive fluidity, as I understand. As soon as the joint is heated to the silver alloy's melting point it almost instantly slurps into the the crevices wetting the base metal and forming a surprizingly high strength bond.

12-29-2008, 04:41 AM
You have silver bearing solder, not silver solder just as George said.

Its pretty tough to silver solder with regular propane. Mapp will give you a bit more heat but you really want something that uses oxygen.

And be careful silver soldering. If you get it too hot you have to clean it up and start over.

12-29-2008, 12:05 PM
A Bernz-O-Matic SHOULD give you enough heat, though not ideal.

The biggest problem I've had with silver soldering/brazing with a Bernz-O-Matic is that I can't get the tip adjusted fine enough -- it just blasts the entire area, so it's hard to get the interface heated to the right temperature.

I use a torch with a number 0 tip, and it's perfect to heat just the bead-line on a scraper blade.

I also use the 56% Harris Silver that Forrest mentions, although the last time I went to Praxair they had "Wolverine" brand, which I've never heard of, but it brazes just the same as Harris. I do like the black carbide flux a lot better than the Harris Stay Silv for brazing carbide though. I've been using the "Sawfiler" brand -- the owner on PracticalMachinist was sending out 2 ounce samples.

12-29-2008, 02:42 PM
Oh. I see what is wrong......

I think my dad got that solder long before he ever thought he might solder anything else. I know it is some sort of silver solder, there are several feet of it. Not stiff at all.

"bearing solder"--- Odd I wonder what that is.

That solder might be older than me!

Buying a bit of carbide and clamping it was my backup plan- an indexable scraper sound cool- but that means I have to buy some, as opposed to this tiny piece which I have on hand. I probably will do that, later.

I guess i would be "my solder is carbideophobic" LOL

Liger Zero
12-29-2008, 02:54 PM
I'd invest in a simple oxy-mapp torch with interchangeable tips. Mine was sold as a "home welding kit" but I've never used it for that.

Done quite a bit of soldiering and brazing with it, haven't done anything more ambitious than joining pipes and the occasional oddball assembly for my neighbor... It's biggest use though is flame-polishing plastic widgets I make. Had the wife-unit freaking out the other day I put a part that required a decent finish in the lathe, spun it up to MAX and WHOOSH with the torch. Nice smooth surface, no hairs, strings, ridges anything. Looks like it was injection molded.

I'm looking at this thread with quite a bit of interest, I got tooling up one side and down the other including duplicates of stuff I know I won't use often... some of it may very well be sacrificed for "experiments." :D

Bruce Griffing
12-29-2008, 03:17 PM
What you have is a lead replaced (lead free) solder that contains silver. It is used for lead free plumbing applications. Real silver soldering is actually silver brazing. The material you are seeking is actually a little golden in color. Pretty expensive and not generally available at hardware stores. Try a welding supply place.

12-29-2008, 03:23 PM
Oh. I see what is wrong......

I think my dad got that solder long before he ever thought he might solder anything else. I know it is some sort of silver solder, there are several feet of it. Not stiff at all.

It may be that what you have was intended for soldering copper plumbing.

I recently bought a MAPP torch and small tank but have not had a chance to work with it yet. As Lazlo says, the flame is a bit unruly for fine work. I did see that Home Depot has oxygen/MAPP torches now but that oxygen looks rather spendy. I have an OA torch that seems always to be buried at the far end of my shop.

12-29-2008, 03:31 PM

As far as torches-- The old one was a slowly rusting propane-only torch. After we switched the torch head a while ago, it started having fire come out of the wrong places, but that stopped. Until yesterday, I was heating up my carbide it preperation for non-silver silver soldering and FWOOSH!.:eek:

Jets of flame come out the sides of the torch. Stare at the thing for second, there is a flame 6 inches long coming out the side, almost burned my face, Turned it off and tossed the torch- no longer safec. :(

I heard MAPP burns cooler than propane-is it more directed or something? Propane/Mapp torches are inexpensive and common, can burn upside down (a boon). Then there are the other types. My main thing is going to be heat treating- Can I heat up something 2 inches long and varying between 5/8 and 3/8--- As most of my tools will be that size. :)

I have made a little box for heat treat out of ceramic- a heat proof box to reflect the heat, but never tried anything big. :cool:

12-29-2008, 03:48 PM
Mapp is hotter than Propane, perhaps relative to each temperature one transfers heat better than the other?

If you're going to Home Depot, get the Mapp/propane torch that's adjustable, not the one-sized-flames-all model.
I use it for heat treating of similarly sized objects, but usually just the cutting end tip.
Turn it up all the way to bring it up to temperature, then turn it down to a smaller flame to hold it there for awhile.
Not sure if that would be good for brazing, I haven't done any of that, perhaps a finer tip/flame is needed.

P.S. - Teenage Machinist, you seem like a smart kid. Keep up you enthusiastic curiosity and you'll be an expert before you know it!


Liger Zero
12-29-2008, 04:10 PM
P.S. - Teenage Machinist, you seem like a smart kid. Keep up you enthusiastic curiosity and you'll be an expert before you know it!


I thought he already was. :D

12-29-2008, 08:13 PM
Long time to go, many pieces scrap to make

Also, I looked in McMaster Carr, and you can get oxy-propane torches very cheap compared to the self-lighting mapp/propane torches. You mentioned cutting, Ryobiguy where are you talking about an oxy-something torch and where about just a propane or mapp?

Edit: Email sent.

12-29-2008, 08:32 PM
Teen, Home Depot is closing out their BernzOMatic torches: I bought their top-of-the-line TS8000 torch that comes with a 14 oz bottle of MAP/Pro on clearance for $37.

This is the solid aluminum torch head with auto ignition and adjustable flame control. I haven't opened it up out of the plastic yet, but the torch head alone weighs more than the old Bernzomatic torch head plus a bottle of propane :)

12-29-2008, 08:33 PM
Is that a self lighting one?

12-29-2008, 08:34 PM
Auto-ignition :) It's a big yellow trigger button that you can push one-handed.

12-29-2008, 08:39 PM
Those are nice as they save gas. Safer too. Other option is an oxypropane torch which is very cheap on McMaster Carr, which is a first for mcmaster. I wonder if this is in all places.

12-29-2008, 10:34 PM
Three notes.

1. Mapp and Mapp-pro are only compatible with a torch if its specifically marked as for mapp gas or propane and mapp gas.

2. I had a bernzomatic torch of the non self lighting type and I was having trouble soldering plumbing. Not very hot. I got frustrated and I really wanted a self lighting one since the work was going so badly. I got a Lenox that is good for both mapp and propane. It's amazing how two torches that look very similar have radically different heat outputs.

The lenox tourch put out so much more heat with propane than the pesky bernzomatic from home depot that I didn't end up needing MAPP gas to complete the plumbing job. You do get what you pay for in torches.

3. They've stopped manufacturing MAPP gas in north america and so most of what you find new will be mapp-pro which is actually mostly propylene and some other witches brew rather than methyl Acetylene Propane-diene (MAPP). MAPP-Pro is said to be even better than MAPP gas but I haven't tried the new cyllinder of it yet I got during a recent silver soldering fiasco which ended in milling a new part out of solid 1 inch plate. . .

12-30-2008, 12:20 AM
Hm, the "swirl" heads are better?

I looked at 3 side by side in a catalog. Very different BTU output and soldering ratings for nigh-identical torches.

12-30-2008, 12:26 AM
I do almost all silver soldering (and heat treating) with propane and air - run on a 10lb cylinder; about 1/2 size as what you use for a bbq - you could just as easily use a bbq 20 lb cylinder. They last almost forever and are refillable.

If the work has a lot of mass I'll use O/A being careful to heat indirectly, but propane is so easy, safe and cheap I prefer it - heck refills are at the gas station; O/A is the welding store which is a lot further away and not open on weekends :(

12-30-2008, 02:22 AM
I have several rolls of "silver" solder here. They are all very soft and I dont think they are for brazed type stuff. Actually dont know what they are used for. The containers say "Conductaloy" "super-set" solder.. What should I use that on???

Then I have three round containers with some very stiff wire that says "Safety-Silv 45T". Its really hard, no way a propane torch will melt it. What do I use that for??? So confusing..

For small concentrated heat I have a lil torch called "the little torch" of course,, made by Smith equipment. I have it Tee-ed into my Oxy-Act rig. Lil green and red hoses. The thing is tiny... And some of the tips actually have a lil piece of red stone looking stuff at the tip, like a jew. But it can give a pretty hot flame, just not meant for large stuff, the flame is so small. It might work for brazing on some carbide tips, but maybe not, to heat up the shank would mean alot of heat.

I also have this neat lil flame thrower put out by radio shack LOL Yeah, I know. But it has a nice hot flame, and again, prolly too small. Its called Micronox. Whatever that is. Its a two part bottle, tiny, but its more for electrical stuff I guess.

And I have the Benzo setup with a couple bottles of Mapp left... Its kinda hot.. Still reach for the Oxy-Act rig though when I want a nice hot flame.

Oh, or the plasma when I want a really hot flame.. Oh!!! And dont rule out the TIG torch when you want some heat. I have used it (just outta convenience, its always ready to go) to warm up some steel. It doesnt always need to make a pin point heat source. Hold that baby away at four or three inches and it keeps a nice flame of heat. Dont know If its screwin up my high freq side, I dont let it ride on the HF when doing that, its all peddle.. Is that bad for the unit???

I gotta try some brazing of the carbide. I really liked Forrest's post. He would be the one to know about them scraper tips.. JR

12-30-2008, 03:43 AM
I am no expert, but, Home Shop/Small Shop, Oxy Propane is probably the choice.

As mentioned, Wal-Mart will swap you a full one at 4 Am Sunday night. Acetylene, you wait till Monday morn when the weld supplier opens.


"Silver bearing" does not mean it is for bearings. I don't know if that was the question you posed. Sorry, "bearing solder", as I see from scanning back.

It "bears" silver, from a miniscule percentage to 55% or more.

"Lead Free", as in the new "code" for plumbing, from what I have read off the spools in HD, are about 99.3% Tin and .7% Copper.

Teenage, you gave me an address, but not a name to send to, and you deny e-mail.

Gimme a name to add to your Dad's address.



12-30-2008, 07:07 AM
Oxy Propane is good for heating, soldering, light brazing and cutting. For gas welding you need Oxy-Acet. Propane dosnt have the heat capacity needed for welding. Oxy Acet is the second hottest flame you can have. There is one compound that burns hotter but is highly toxic.

True silver solder like you have, JRouche, is great stuff. You need the proper flux and if you do much of it oxy-acet is really nice, especially if it is a larger piece. Its strong, and you can even braze stainless with it. It is also NSF approved for food handling equipment. Whats neat about silver solder, as it has been mentioned before, is that wicks into cracks and crevices. It has low surface tension when melted and capillary effect draws it into the joint. You can put a dab on part of the joint and it will follow the flame as you go around the joint.

The Smith Micro torch is a neat little torch. Primarily aimed at jewelers and modelers who need pin point flames. The tiny tips have either ruby or sapphire orifices swedged in the ends.

I have one of those little micronox torches. They are neat but I really have never used it for much. It uses butane as the fuel and nitrous oxide as the oxidizer.

Doubt if you can get 3 or 4 inches from a tig arc. Maybe two. Shouldnt hurt the machine. The longer the arc the higher the voltage since its a constant current power supply. It will lower the duty cycle rating though.

12-30-2008, 03:24 PM
" TIG arc torch"?

My dad has a good tig welder, so that may be an option. What do you use as the ground, a tungsten?

How do you do it?

12-30-2008, 07:09 PM
No such thing as a tig arc torch. Closest thing would be a Atomic Hydrogen Welding setup.

You might be able to use some silicon bronze rod and braze the carbide on with the tig. Maybe even use the tig with true silver solder.

12-30-2008, 07:35 PM
I've had bad luck trying to silver solder with a Tig torch although lazlo and others say they have done it. It requires some practice which I don't have and I didn't get when I realized I started the failed project with 25psi of argon. . .

12-30-2008, 10:29 PM
I've done TIG and MIG brazing with bronze wire, which works fantastic, but I've not tried silver "soldering" (brazing) with TIG. I'm assuming there's no such thing as a spool of silver MIG wire, or if it does exist, only the military could afford it :D

Silicon bronze melts at 2100 F. I just checked the Harris Safety Silv 45 datasheet, and it melts at 1370 F. Silver conducts a heck of a lot better too, so it'd probably take some tweaking...

12-31-2008, 01:21 PM
What would you think is better if one only gets one- Small (disposable cylinders) oxypropane/oxymapp torch or just a good mapp torch? Do not plan do do much brazing.

01-02-2009, 02:18 PM
Update: New Mapp torch works way better than the old propane one. It does not look much bigger but was able to heat up my home-made form relieved dovetail cutter very quickly.