Newbie with some brass and a MAPP torch - advice sought
I want to braze together a few small pieces of brass, and I've gotten a small sheet of medium silver solder, some flux to match, and some MAP gas. My total experience with joining metal is soldering electronics, a totally different animal. I'm looking for some pointers. I've done my fair share of Google, and I get the basics - heat the joint, not the silver. Clean with citric acid, before and after. Don't attempt to apply the silver until the flux is clear and runny. Polish facing surfaces to tight, close tolerances in advance. Zinc fumes are bad. Don't touch brass heated to 2000 degrees. Got all that.
My two big questions:
1. The pieces I need to join (for starters) are a 3", 1/4" thick brass disk, with a small, hollow hemisphere of brass (radius .75") lying "face down", centered on it. I've cut a rough, centered hole in the brass disk so I can get heat on both sides of the hemisphere. I don't care so much if the work looks like crap from inside the hemisphere, but I need the outside to be very clean and neat.
I'm thinking I need to enlarge the hole until it's just less than the diameter of the hemisphere, apply heat to the outside of the hemisphere and touch the silver, though the hole, to the inside of the join. I'm hoping that means most mess stays inside the hemisphere, and from the outside the join will be almost invisible. It also looks like an awkward way to apply the solder, so I'm asking if I'll do just as well to heat the inside, and apply the silver to the outside - easier to see what I'm doing. What's likely to be cleaner? I don't want to ruin a lot of brass finding out the hard way.
2. The other join I need to make involves the top of the same hemisphere, sanded flattened, with another hemisphere, also flattened at the top, turned upside down and "balanced" on top. Think hourglass shape. To make it more interesting, there needs to be a hole straight down through the join, again like an hourglass. The hole is going to be a good part of the diameter of the join (about 6mm hole in maybe 8-9mm diameter of flat surface, though I can enlarge the flat parts, and might if I get worried about join strength.)
My first instinct is to join them first and drill the hole afterwards - easier than trying to get two holes lined up exactly though the center of two separate hemispheres, and stay lines up doing soldering. My second thought is that my power drill isn't real happy boring through brass in the first place, and I don't know if boring though the brazed area is going to be harder (or weaken the joint badly.) What's better?
I need the finished, joined 3 parts to be fairly tough - if I drop them I want it to bounce, not separate.
Comments welcome. Be gentle, I'm a very casual hobbyist with a power drill, a dremel, and more ambition than sense.
Oh. Anyone got experience with high voltage and braised brass joints? There'll be 30kV (pulsed DC and AC, at very low amperage) running through these joins at times, and if a mixed metal joint is likely to misbehave, I'd like to know in advance so I can rig a separate copper pathway to handle it. Simple experiments have gone well, but they always do, right before the Big Failure.
Thanks in advance.
Perhaps your two/three different questions should be split up into three different posts? I never pile in topics, even with email. If I have multiple topics to ask one person, I create multiple emails with appropriate "get to the point" subject lines.
I do not squander a subject line or a title line, I get to the point.
That chunk of brass in your first question will require more than a couple of MAPP torches, if your idea of a MAPP torch is something found at Home Depot.
Which torch? How large of a tank?
A plumber's torch - originally my father's. Looks something like http://images.lowes.com/product/conv...42194654xl.jpg .
Originally Posted by S_W_Bausch
I didn't figure a small slab of 1/4" thick brass (the hemisphere is thinner-walled) would be that much of a challenge. Then again, I'm here because I don't know better. Youtube, that oracle of training videos, shows people doing pieces not much smaller, with related gear. Alright, what do I need to pull this off? Really don't want to get into oxygen assisted stuff - from the sounds of it, that's not amateur hour.
Thanks for the quick reply.
Since you have soldering experience just use flux paste and solder used for joining copper water tubing. The temperature required is much less than silver solder and if both pieces are tinned much like solding wire connections you will be surprised at the strength of the bond.
A Bernzomatic-type torch will be a bit small for brazing a big chunk of brass. I use a "real" plumber's torch of the Prestolite type (air-acetylene, B-tank). They come with different size tips so you can select a tip to match the size of the job.
Abrasive paper will clean the brass to prep it for soldering/brazing. Chemicals should not be needed unless the brass is oily.
Sheet silver solder can be clipped into small pieces and embedded in the flux between the two parts to be joined. But the joint you describe will require that the solder pieces be placed in the flux next to, not within, the joint. So the hole in the flat part should be smaller than the ID of the hemisphere, leaving a lip inside on which to place the solder. I would then lay the flat part on a fire brick with the second part on top of it. Aim the torch at the flat part, near the joint, so that the flat part gets more heat than the thinner hemisphere. When the joint is hot enough at one place to let the solder flow into the joint, you will see a little liquid silver flow through the joint, but capillary attraction will tend to keep it within the joint unless you hold the flame in one spot too long after the joint first flows. As soon as the first solder melts into the joint, you move the torch flame along the joint until all has flowed.
The trouble with a large part and a small torch is that the first part of the joint will solidify before you get the rest of the joint soldered. The job may still be possible, but a bigger torch, or a furnace, would make it easier.
For the second job, I would drill the hole in just the top part. Then flux the parts and place the solder in the hole. Aim the torch at the hole until the solder melts into the joint.
I think ordinary lead-tin electrical solder would be easily strong enough for the flat plate to hemisphere joint. Your torch will be plenty big enough to get the whole joint to flow at one time. Silver soldering the two hemispheres will be easy.
Thank you. This is exactly what I was looking for (and I feel like a fool for not coming up with "drill through one hemisphere, solder, cool, then finish drilling through.")
Originally Posted by L Vanice
I'm worried that the work will come apart if dropped, if I use standard tin solder - it's going to be abused and I want it to last for a very long time - but that's my fallback position if the silver fails.
I've always wanted an excuse to use acetylene. This may be it. Thanks again.
With your big disc +hemisphere job, I think that you need to contain the heat. Balance the disc on 4 small bolts (like table legs) with sheet metal under the heads of the bolts and a curved bit of metal over the top, allowing room for the hemisphere to be manipulated on top of it. I would flux up the top of the disc and the mating surface of of the hemisphere. Heat the disc until the flux runs, plonk on the hemisphere, the flux should run within seconds then apply the solder - cut it into thin strips, like wire and push it into the joint with a bit of steel wire.
For your hemisphere to hemisphere joint, I would drill both and put a rivet or a bit of thin walled tube through the hole and rivet the ends over to basically hold the parts.
Just my $.02s worth
It's grilling season, if you were to preheat the fit-up in/on your grill/bed of coals, you would be that much closer to the heat required.
My memory is the torch needs to declare MAPP gas compatibility, else the MAPP gas may not gain you anything.
A plumber's torch - originally my father's. Looks something like...
Alright, I'm rethinking my approach - having priced up MAPP gas, and having been warned that my old torch may not work with MAPP anyway. I've also priced acetylene, and that's not happening either. So now I'm looking at propane and oxygen.
Can someone suggest an appropriate torch? I do have a few pieces to braze, all about the size described originally, or smaller. Renting a torch doesn't seem to be an option in my area, so I need to buy. I don't expect to do a lot of this (but I've said that before, when tinkering with something.) What's reasonably priced and will take well to a propane/oyx mix? I've looked at the Smith Little Torch, but it's not cheap and I'm not sure it will put out enough volume of heat.
Thanks once again.
Put a Wanted ad on craigslist.
Don't tell your life story, whether you are disabled, doing this for a church, etc.
Just a simple Want To Buy: Torch ad
Buy the tanks, hopefully NOT in need of an inspection.
Personally, I am doing everything I can NOT to visit welding supply houses; tank rentals seem expensive to me, and then you have to drag them around.
Are you sure your need is a recurring need? Why not pay somebody to do it for you, and not have to trip over the hoses and the tanks?
Are you familiar with silver bearing solders? Same general fusion temperatures, as easy to use as soft solders too. No high heat, a simple propane torch is more than adequate for your fabrication. Much stronger that soft solders too, night and day comparison however they are not a strong as silver brazing alloys (what you are asking about). They're widely available and not expensive for the amount you'd require. Here's a link with information about a popular one.
You don't seem especially interested in life stories; but since you asked, the reason I haven't paid for someone to do it is because, this way, it will be me that has done it, just like every other part of the project - electronics, programming, wood caving, all the rest. I like learning to do things, and right now it's working with brass.
Originally Posted by S_W_Bausch
Your fit up is critical - you don't need much solder because it will move into the gap by capillary action. I'll say again you need a very small gap and not much solder. If the gap is too big, the solder slump and flow out onto the base, same if you add too much solder. You can contain minor over runs by drawing a containing band with a 2b lead pencil around the hemisphere. The graphite will resist the solder flow if you slightly over do it. There are also proprietary pastes for doing the same thing - check jewelery making suppliers.
The bbq grill idea sounds good. You might just need some top up heat from a torch.
One for everyone else - would you try to clamp the hemisphere or just have it resting on the base?
I have a wood gas stove - forced air through any burnable material, usually wood but it could be an oak chip/bbq charcoal mix. With the fan cranked, it puts out serious heat, and it's just big enough to hold the work in question. That's an interesting idea...
Originally Posted by technocrat
I agree with the idea of heat containment to improve the capacity of whatever torch you are using. I Use some fire bricks on jobs like this to build a "forge." I just put down a couple for a base and then stack a couple on their sides and a couple on top. Maybe one or part of one in back.
Originally Posted by chuckey
I have and would use silver solder ribbon that is about 5/8 wide and 10 thou thick or so. I would flux both parts. Cut some strips of ribbon and arrange them so that the hemisphere was sitting on a crude donut of foil. The whole assemblage would be placed into (or assembled in) the forge and then I would get out the Mapp gas (Home Depot) style to do the heating. I am confident the heat containment would make this doable. I have silver soldered (55% silver) hundreds of pieces using MAPP.
That said, some of the other methods--like the stove or grill idea would be helpful. Placing the parts on a grate above some ordinary charcoal briquets and blowing some air onto them with a hairdrier would get the assembly to red heat pretty quickly.
Oxy/Actylene would make this so very easy.
Let us know what you do.
Last edited by dgfoster; 07-12-2012 at 08:46 AM.
Reason: typos and clarification
Some of us not interested in life stories. We solve real problems for breakfast, lunch and dinner. Someone fixated on their chosen path no matter what isn't open to learning anything.
It's on the list to try if I can't get the hard silver to work out. I've experimented with the silver bearing stuff, but I was able to separate 2 pieces of brass joined that way. (In fairness to the solder, there were only a couple of square mm in the joint, and I hit it pretty hard. In fairness to the objection, the point where the two hemispheres meet isn't much more surface area, and if the piece falls, that's the point that's going to take the impact.)
Originally Posted by DaveE907
Looking forward to grilling some brass this Saturday.
You won't have any success with this project using silver solder (hard solder, that is) with
any of the following heat sources:
3) natural gas-air
4) any of the above combined with any kind of heat stove or preheat
I've never used propane oxygen so can't say
I've never used MAPP gas-air so can't say
My absolute choice for this if you HAVE to have silver solder is oxy-acetlyene, hands down.
If you want to soft solder it, 95 tin/5 silver solder has about three times the tensile
strength of lead/tin and just about the same melting temperature. Air-propane would do
fine for that.
If you hard solder, use borax flux. If soft soldering this, I would use plumber's flux, AKA
ZnCl in petroleum jelly.
I braze with oxy-propane, works fine. but i use that for cutting as well, if you do any amount of cutting, propane will save you some money. if you just want something you are only going to use very infrequently, oxy-acetylene is more versatile and you can normally find lots of used outfits on craigslist.
1. What is medium silver solder, please? It makes a huge difference. Do you have an AWS designation on the package or a supplier’s designation?
2. Is your flux compatible?
3. Why citric acid to clean. We use it for a polishing solution to remove very minor oxidation.
4. Make sure the parts are free of grease and oil. Oven cleaner, Dish soap, etc can work well for this.
5. See below for answers to some of your questions.
I am having trouble understanding all the points you wish to have addressed. I think that is what they mean by “life story”.
Brazing with Propane
Brazing with Propane and a Firebrick Oven
Choosing The Right Braze Alloy
Choosing the Right Brazing Alloy for a Specific Application can Increase the Quality, and Prevent Tip Breakage.
Brazing with Gases