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Gas forge wall thickness - 3mm mild steel okay?


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So my forge (purchased not self-built)... I started to repair it but soon realised I'd be happier rebuilding myself (current one was purchased - Liked it, but realised some tweaks I want to make). Jets seem okay (3 burner jet as per pic - uses mig welding tips as the jet tip?! Is that normal for gas forges? - Also it annoys me a bit that the jets are not straight! I'll be straightening with my build lol), so will use those and building a new forge, with ceramic wool and castable refractory then zircon paint...

 

Am about to order the steel. Current forge is 2mm, I'm thinking of going to 3mm, but wondered if that's still too thin, would 4mm be advisable?

It's a bit of a weigh off between... well, WEIGHT and longevity! Will be mobile with this forge sometimes and it's going to be about 500mm x 370mm x 270mm, so whilst not a huge weight, enough.

 

What do people think? Will 3mm suffice (with decent ceramic wool insulation, then refractory, then zircon paint coat ???

Last forge... got a bit hot on top (see the pic... EXCUSE the mess and position of the forge lol!). Partly this is likely due to the ceramic wool being a bit crappy, partly as had no refractory cement, but also I think IMO because the steel was a bit thin maybe??? (2mm).

 

Still getting used to gas forges... learned smithing on, and always used, a trad forge with back bosh & tue iron! haha.

 

20210726_160805.jpg

Edited by Mike Gracia
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3mm (11 gauge here in the states) is what I've used in mine with no issues.  Personally I think the insulation and refractory is far more important than the shell.  My next one will probably be built with something even thinner.

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Posted (edited)
6 minutes ago, Joël Mercier said:

3mm is plenty. A well made forge can get hot, but never red hot. 

 

 

 

5 minutes ago, Alex Middleton said:

3mm (11 gauge here in the states) is what I've used in mine with no issues.  Personally I think the insulation and refractory is far more important than the shell.  My next one will probably be built with something even thinner.

Thanks both! I've added a pic to the post now - adding here too... check the temp the steel got to! Deffo thick rebuilding from scratch will be best.

Quick additional Q if that's cool guys? The jets - you can see the pipes in the pic, essentially inside the cowl at the top, the pipe has been drilled & tapped, to allow mig tips to be screwed in (will check, either 0.6 or 0.8 tips), and this is the jet the gas comes through - Is this usual for self-made forges (I bought it). Will this suffice, do you think?

Cheers in advance for any replies - MUCH appreciated!

20210726_160805.jpg

Edited by Mike Gracia
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I'm not going to be much help on that I'm afraid.  I'm a blown burner guy.  I believe using MIG tips as gas jets is pretty standard though.

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If you want to make your own burners, there's a thread on this forum here. This is the one I built for my propane tank forge. It can forge weld and it is stable even when used outside with a light wind. 

 

 

 

 

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2 minutes ago, Joël Mercier said:

If you want to make your own burners, there's a thread on this forum here. This is the one I built for my propane tank forge. It can forge weld and it is stable even when used outside with a light wind. 

 

 

 

 

Cheers! Will prob stick with the current burners for now, but may change in the future, so this thread will be handy for sure!

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It is important to use tapered mig tips and Ward  black pipe fitting.  Ward is a brand name here in the US primarily used in sprinkler systems.  You might also check www.ZollerForge.com for Larry's Y fitting burner kit and his Ward burner kit.

 

The shell certainly should not get red at the burner attachments. I don't like square forges and prefer a round forge with the burner entering at a tangent to obtain a swirling flame and therefore avoiding hot spots and  more even heat.

 

Check out the Build a Gas Forge and the Ribbon Burner attachments on the Forge Supplies page at

www.WayneCoeArtistBlacksmith.com.

Let me know if I can help you.

About $100.00 plus the hose, regulator and burner using a 20# Propane tank.

 

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Just to add to the good responses:  Make sure you use enough wool.  2" (50mm) is the norm.  More is fine, less is a bad idea.  Your burners should have cones in the forge that you build into the refractory.  That should help keep the shell cool.  

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53 minutes ago, Jerrod Miller said:

Just to add to the good responses:  Make sure you use enough wool.  2" (50mm) is the norm.  More is fine, less is a bad idea.  Your burners should have cones in the forge that you build into the refractory.  That should help keep the shell cool.  

Interesting re: Cones... I can't find any info on. this & am trying to picture what you mean. Sorry to ask, but any more info? Cheers!

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The exit of the burner (in venturi burners, like yours) tend to burn better if it is in the form of a flare, just slightly wider at the tip.  The shape is about the shape of a paper disposable cup.  Some makers make them part of the burner tube, but you can form a flare shape in the last little bit of insulation oif the forge.

Just to add further to your confusion, there are also blown (fan driven) burner setups.  You can heat a case about the size of what you have with a single burner.  I use a single fan twin injector common rail system to heat a welding forge about twice the size of your forge.
 

Geoff

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1 hour ago, Geoff Keyes said:

The exit of the burner (in venturi burners, like yours) tend to burn better if it is in the form of a flare, just slightly wider at the tip. 

Flare!  That is the word I should have used.  Cone was the first thing to pop into my head and clearly should not have been.  Thanks Geoff!  

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And the taper of the flare shall be 1:12, and 1:12 shall be the taper.  Neither 1:10 nor 1:15, and 1:4 is right out...

 

Seriously though, about the same basic taper as a pint glass, wide end is the inner wall of the forge lining.  And if anyone tells you to use a bell reducer for that purpose, just say no.  

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23 hours ago, Alan Longmire said:

...And if anyone tells you to use a bell reducer for that purpose, just say no.  

Those bell reducers have a vicious streak a mile wide.  ;)

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As stated, the exterior shell doesn't matter too much.  I think the shell to my forge is something like 3/16.  It was a scrap of mild steel pipe 9in in diameter by 6 feet long.  I cut a 10in section off to build my first forge. My second one I've planned to be 7in in length but is going to be a design that Wayne Coe has on his site. 7in may seem very small, maybe piratically too small to do anything, but so far, I don't think I've ever been able to work 10 hot inches of steel all at once without a power hammer around.  For bending stuff yes, but general propose - almost never.  Wayne's design fits almost anything if you look at it right.  I went with a thicker shell just in case of something falling on it and causing some issues with breaking the lining.  That has never happened although I've planned for it. 

 

If you look though the pinned topics at the beginners page, you'll find a post with a collection of links about both; building forge bodies, and burners.  I suggest to look though them if you haven't already before you get started building.  There's some good do's and don't do's in there.  Don't fall into the trap of going with sub par materials or trying to substitute things with home improvement store finds. They never work as well.

Edited by Daniel W
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