# Back Purging



## jay_ntwr (Feb 15, 2008)

I did a search on "purge" and didn't see anything that looked like a dedicated thread, so I'm asking.

How many of you back purge? I assume that with a nice jig that this is a no brainer. But what about a guy like me that's welding a couple tubes and a time on a borrowed welder and can't do it? 

I did some searching and founds something called Solar Flux. Does anyone have experience with this? 

What happens if you don't back purge? How are guys with "sealed tubesets" back purging or are they?

What I do know is that a non purged back side doesn't look good in thin walled tubing.


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## Rody (Sep 10, 2005)

Jay,

The benefits of back purging are numerous, the downsides few.

Is back purging on steel necessary...no. It will help with prevention of backside oxidation and stability of the weld puddle in thin tubing, but much of the "ugliness" you are seeing is a result of poor heat control, due both to amperage and travel speed.

You do not need a fancy fixture, either a dedicated bottle, dual regulator, or a simple Y connection can be used with some creative tubing and a little aluminum foil to create simple stops/dams for your application.

Point is, for about 5-10 bucks per frame, it's hard not to justify a back purge.

cheers,

rody


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## TortugaTonta (Jun 14, 2004)

I can't add much to the above, but I will say this. . . . 

Don't, whatever you do, Don't! eat chocolate covered espresso beans and pick up a tig torch!

Ask me how I know. . . .


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## Walt (Jan 23, 2004)

*Tips*

Backpurging rules, and it doesn't cost much. In fact, if you account for the decreased wear and tear on your cutting tools (ie, reamers, taps) it probably saves you money.

For example, I am *still* (after ~300 frames) using a $99 set of "Icetoolz" BB taps. I've never even bothered to have them sharpened, because between the heat sinks and the backpurge, the bb threads pretty much always end up perfect. At this point, they're getting embarrassingly ratty, so I'm sure I'll eventually replace them, but that's still pretty ridiculous. Same story with my head tube reaming/facing tools and my $18 adjustable seat tube reamer.

So backpurging is worthwhile, IMO.

You can make yourself some purge plugs from brass or aluminum or whatever if you have a lathe and some free time, or you can buy them (made out of ti, no less!) from Paragon. They sell a relatively complete head tube/bb shell set of plugs that work with all-thread, and some nice tapered seat tube plugs (as well as odd sizes for smaller stuff).

A little OT, but if you look back at the "heat sinks" thread from a few months ago, PVD had a very nice seat tube collet/plug (which I copied and use myself now) that's excellent for preventing seat tube distortion.

-Walt



Rody said:


> Jay,
> 
> The benefits of back purging are numerous, the downsides few.
> 
> ...


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## scooter916 (Jan 2, 2006)

TortugaTonta said:


> I can't add much to the above, but I will say this. . . .
> 
> Don't, whatever you do, Don't! eat chocolate covered espresso beans and pick up a tig torch!
> 
> Ask me how I know. . . .


please tell


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## Pungbråck (Jan 18, 2009)

*Solar Flux*



jay_ntwr said:


> I did a search on "purge" and didn't see anything that looked like a dedicated thread, so I'm asking.
> 
> How many of you back purge? I assume that with a nice jig that this is a no brainer. But what about a guy like me that's welding a couple tubes and a time on a borrowed welder and can't do it?
> 
> ...


I use Solar flux for custom headers and exhaust in 304 stainless tubing, it works really well on stainless, have not used it in frame building yet, it might be worth a try.


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## TortugaTonta (Jun 14, 2004)

scooter916 said:


> please tell


Lets just say that I should have been mixing paint last night, not playing with the sparkle wrench.

I am just suprised that after having my heart rate at 200 for a couple hours the magic beans were still in my system. I guess what they say is true, your metabolism does slow down after 40.

But on a serious note, what flow rate do you guys use? Does it us a lot more argon to use a single tank setup as opposed to a dual tank setup? Is the Y a common fitting?


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## smdubovsky (Apr 27, 2007)

You can buy a CGA T at any welding supply place. Add a cheap ebay $20 2nd regulator and you have independent flow control over both on the same bottle for very little money. Prevents messing up the flow to the torch vs if you use only one regulator and a plastic T after.

Flow rate depends on your endcaps. If you can purge a tube and cap it off (sometimes as simple as pulling a rubber glove over the end or using a rubber stopper) you can turn the purge gas completely off. If you're welding something difficult/impossible to seal you have to leave the flow on.


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## zappa (May 12, 2004)

walt can you tell me/us where us got that $18 adjustable seattube reamer please.



Walt said:


> Backpurging rules, and it doesn't cost much. In fact, if you account for the decreased wear and tear on your cutting tools (ie, reamers, taps) it probably saves you money.
> 
> For example, I am *still* (after ~300 frames) using a $99 set of "Icetoolz" BB taps. I've never even bothered to have them sharpened, because between the heat sinks and the backpurge, the bb threads pretty much always end up perfect. At this point, they're getting embarrassingly ratty, so I'm sure I'll eventually replace them, but that's still pretty ridiculous. Same story with my head tube reaming/facing tools and my $18 adjustable seat tube reamer.


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## Walt (Jan 23, 2004)

*Msc*

Having recently purchased another one for use on 31.6mm seat tubes, the price has gone up considerably (or I'm misremembering what I paid 7 years ago): they're now about $35.

Still a steal, IMO.

-Walt



zappa said:


> walt can you tell me/us where us got that $18 adjustable seattube reamer please.
> 
> 
> 
> ...


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## smdubovsky (Apr 27, 2007)

They go on sale often @ enco (as does everything else.)


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## zappa (May 12, 2004)

Thanks walt!!!



Walt said:


> Having recently purchased another one for use on 31.6mm seat tubes, the price has gone up considerably (or I'm misremembering what I paid 7 years ago): they're now about $35.
> 
> Still a steal, IMO.
> 
> ...


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## unterhausen (Sep 28, 2008)

I missed where you get the adjustable reamers from, is the answer Enco?


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## zappa (May 12, 2004)

MSC direct


unterhausen said:


> I missed where you get the adjustable reamers from, is the answer Enco?


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## jay_ntwr (Feb 15, 2008)

Rody said:


> Jay,
> 
> The benefits of back purging are numerous, the downsides few.
> 
> ...


FWIW, I've installed a Y and another regulator, got the PMW BB heat sink and am purging now. The next frame will be 100% Ar purged whereas the one I just finished was only purged during the CS installation. How far I've come in just a year.

Thanks guys, Walt, I love the PMW sink. Dynamite!


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