PDA

View Full Version : Help with MAP gas



velosprinter
10-02-2010, 10:25 AM
I got one of those map gas torches that makes a nice blue 1 1/2 flame and after several minutes the join tube will get red but the base tube (not cut edge) does not seem to get red and I can't melt the brazing rod. What can I do? Are there hotter MAP torches? I really can't afford a Oxy/acc setup.

John Lewis
10-03-2010, 07:52 AM
Hi velosprinter

I don't know about MAPP gas torches but I brazed my first bike with a butane torch.
The trick was to get some bricks. Firebrick for preference. Then make up a little hearth arrangement to hold and reflect back the heat.
It was even better when I borrowed a second torch as I used one for general heating of the area and the other to do the brazing. That might be worthwhile and If you use a butane torch for general heating you will use less of the more expensive MAPP gas.

I know others on BROL have used MAPP successfully to build bikes.

John Lewis

ken will
10-03-2010, 08:51 AM
These kits work pretty good.

http://hand-tools.hardwarestore.com/69-407-torch-kits/cutting-604797.aspx

savarin
10-04-2010, 12:34 AM
I've had the same problem with map and have only successfully brazed small to small parts.
As John has stated a fire brick surround and two torches would give a better method of controlling the heat.
I will be experimenting with acetylene and compressed air and propane and compressed air in a welding torch soon and will report the results.

John Lewis
10-04-2010, 07:47 AM
I borrowed a big self blowing butane torch. I think its the kind plumbers use. It did a good job brazing except for two things.
First. The area heated was large so you didn't have fine control for fillets etc. It was OK though.
Second. And this was the killer. As the torch runs, the bottle gets cold and the pressure drops. By the third joint the flame wasn't hot enough. My cure was to stick the 25kg gas bottle in hot water.

In the old days of lugged bikes they put flux and bronze spelter (granulated bronze) in the lug and then heated the lot with a blow torch according to a chap I met who worked in a bike factory.

I read that in one factory in India. Hero I think. They spot weld the tubes to the lugs, flux it up and dip in a bath of molten bronze.

John

velosprinter
10-04-2010, 12:32 PM
It was a frustrating weekend for welding. I am on a seriously tight budget but really needed to transport 3 kids this week and the bus routes would take 2 hours compared to riding at 1 hour.

I went back to the store and got the bernzomatic ts8000 that their website claims is the hottest/fastest. Still just could not get those BB hot enough to take the brass. I added heat deflectors and bricks but and it is so close but not quite enough. The electric lighter did not work right out of the box so I took the ts8000 back. I figured I would just suck it up and wait until next weekend and buy a mini mig at HF for $100.
But on an end shelf walking out of the store I spotted the OX2550KC that uses Propylene and Oxygen $59. It says it will weld 1/8 plate. Firing it up it has the same flame feel of a real Oxy/acc torch but the "regulators" were very flaky. It still took quite a bit of time to get the BB up to temp but once there I was able to put in a nice fillet. Sadly the O2 was out in 15 minutes, box claimed 30-45... I got a second bottle 2.1oz that was a bit smaller $9 thinking maybe a low bottle in the kit. Nope smaller one lasted 10 minutes. You would think I could have gotten done in that time but I only made it 3/4 around the 3 joints. This is because it takes so long to get the BB hot even moving the flame for a few seconds to rotate.

The factors I think making this so hard are:
Chrome-molly
6500 ft elevation

I will be going mig or arc this coming weekend but the welds should hold fine this week, we will go easy.

If I was doing it over I would say the better setup short of a Oxy/acc would be a torch like the ts8000 w/ cheep fuel to get everything close to temp then weld quickly with the OX2550KC. However, in the long run I think the mig will be more value.

Please let me know if you have other thoughts/suggestions.


Here is the bike, all from parts we picked up for free.
http://lh3.ggpht.com/_thDShfGzeUg/TKko3u33XRI/AAAAAAAABvE/4hijte-Z0jM/s1024/IMAG0187.jpg

savarin
10-04-2010, 09:58 PM
I swear by the gas shield mig.
Having said that there are many time when I also want to be able to braze.
If money was no object I would have an ac/dc tig system so I could weld anything along with a small oxy/acetylene set for the small bit of brazing now and again.