Son of Two Brick Forge

[ZDP-189]

I retired the first Two Brick Forge because I realised it had numerous fundamental shortcomings that couldn't be rectified.

For a start, the square cavity prevented efficient swirling of the burner flame and the so I got a huge hot spot where the flame hit and not a lot of flame elsewhere. Partly, this was also due to there being no way for hot gasses to pass out the back of the forge, so all the heat went towards the front. I suspect not having a rear port also gave me back-pressure problems and at the very least limited the size of forging I could do. My concept of having a small cavity was right, but trying to bottle up all the heat was wrong.

The other problem was structural. The forge really needed thicker walls for better insulation and a jacket to cushion it from impact and to hold it all together.

So considering the very low investment sunk into the project I decided to start from scratch. Hence, my second generation two brick forge.

Marking Out


I started by marking out as I had done before, but scribed around this lid to make the ends rounded.

Carving Out


This time, I carved the cavity with a home-made crook knife ground from a kitchen melon-carver. It cut nearly as fast as the router and was almost as accurate, but it left a neat little pile of sand instead of the horrendous covering of fine dust that the router left last time. I carved the ports with a junior hacksaw again though, because it seemed to work well.

In this version, I made an additional port at the back of the forge so that the knife blade could poke out the back and I could work on the ricasso. Last time, I could work the tip or the tang, but not much in between.

Making Fitting Depressions


The idea was to make holes that the mortar could bing into.

This was my first minor mistake. I drilled the holes too deep before I countersunk them and had to fill them later with refractory mortar. Ideally I should have only countersunk and not drilled, because the brick is really soft and a deep hole is not necessary anyway. Well, no big deal.

Flaring the Ports


You can see my second mistake here too. I forgot which way round the forge went and stuck a hole in the wrong place. I filled that with mortar too.

What this picture is intended to show is the way I flared the burner ports on the inside and flared the main port to allow better access with tongs or pliers.

You can also see that I sited the burner nozzle much closer to the front opening of the forge than before. If I even angle the flame I can get any part of the billet hot, all the way to the tongs.

I forgot to take pictures of the next step or two in the construction, because I got a bit carried away. I lined the forge cavity and ports with ITC-100 slurry and sealed the forge with refractory mortar.

Then I applied mortar to the sides and to the inside of a sheet of 1/2" kaowool, cut to fit the sides only (not the ends). Then I laid the kaowool on some fine mesh chicken wire, and wrapped the forge in that, with the wire on the outside and the kaowool sandwiched. Finally, I daubed a thick layer of refractory mortar over the kiln in two layers and left it to dry while I ran some errands.

The whole construction process, including parking my car, getting set up and doing it all took under two hours.

Initial Firing With Map-Torch


When I got back to the shop this evening, the shell was pretty dry, and although I really should have left it to dry out overnight, I went and gave it a quick firing to see how it would do and because it would dry quicker warm, anyway. Any bubbles in the refractory shell that I find later will be repaired.

You can see from the picture, when I ran the Map-Torch that I used with the first generation forge, I got a truly roaring flame that swirled all the way around the forge cavity. In fact, when the torch warmed up, and I opened the valve fully, flames were coming out the front and back at least 2-3". That torch really rocks, especially for something screwed on to the top of a gas bottle.

You can see that I needed to make the burner port a bit bigger, but I wanted to test out a new burner and hadn't yet decided the final size.

Map-Torch vs Bernzomatic


The Map is the one on the left. It has a big head and really pumps out those BTUs. A major problem though, is that the venturi induction holes are very close to the tip and that can lead to spluttering if hot combusted gases cycle back through the burner. I had the distinct impression that even when it wasn't spluttering, I wasn't getting the best burn out of my Mapp-gas.

Bernzomatic who make the Mapp-gas also make the torch on the right. The guys in the burner stores seem to reckon that I could get a few hundred more degrees out of this torch. However, on firing it, I found that the flame was only about a quarter to a third the size of the Map-Torch. So while the cone tip temperature might be higher, the forge temperature may not be.

Flame-On With the Bernzomatic


As you can see, the forge is not quite the same raging inferno that it was with the Map-Torch. That's not a big deal, because the Map was a bit monstrous and too much for the forge cavity, really. The cavity is the same size as the first generation forge, but temperature for a given torch power seems to go up a notch or two. Such is the importance of aerodynamics, I suppose.

I'm keen to use this torch, as it has a better regulator, allowing it to burn consistently even inverted; it has a really neat on-off-lock-on button and an automatic starter; not to mention the venturi holes are far away from the tip. It also has a really clever tip that swirls the flame.

As you can see from the picture above, it also gives a nice, even heat to the forge.

Heating a Billet


Considering that the gas flow through the Bernzomatic is much more economical, I was a little surprised to see the billet come up to temperature quicker and reach a hotter maximum temperature. I could have left it in longer, but I'll probably not reach a welding heat and pushing it further would waste gas and the carbon in my steel.

Compare this with the pictures from the first generation forge and you can see a substantial difference.

A more Even Heat


The last forge was really disappointing in its ability to get a large billet up to an even heat. It's not surprising, really, if you remember how concentrated the heat was and how poor the circulation was.

This time, I stuck the whole 5160 test billet in and gave it a minute to come up. You can imagine how happy I was to see the whole billet get like this. I reckon that with a bit of fine tuning of the burner, I can get a nice even heat that would be nice to forge.

...


PS/ Before you ask, yes, I did consider pluging both torches in and/or making a longer, stacked forge. Instead, I found that I could blow the Map-Torch in the front port with only a bit of spluttering. The stacked modular forge is also a possibility, but it would need to take into account the curvature of such a blade, and seeing as I have a good 6" of hot-burning forge cavity, that should provide me with enough hot steel to pound, especially if I play the blade in and out of the forge.

PPS/ I found that the Map-Torch on it own could bring a billet up to a dull red and that's good enough to hammer, so if you can buy one and a Mapp cylinder, you can get started right away while you shop around for fire bricks. The first generation forge was a big step up above this and the second generation forge was half again as big a step in temperature.

PPPS/ What's next? Well, I plan to use this forge for heat treating and for forging small stuff around the shop when I can't be arsed with going up to the roof. I can see a third generation eventually, but I believe I have squeezed most of the performance out of the medium. A bit better insulation would be advantageous, but after all my testing, I could still place my hand on the forge shell without burning myself. I believe the biggest single improvement in forges designed for a Mapp burner the would be to make a standardised hard refractory lining and stick in in a metal shell with plenty of insulation. I have seen pictures of linings like this on the web, but costing hundreds of dollars and am looking into the possibility of home casting high-alumina inner shells.

Any comments or questions?

[mloc]

do you use the small canisters of gas


or do you use the large re-fillable bottles with hoses and valves


or do you use a piped in gas main

[Sunraven]

Great info ZDP

I am hoping to advance to having a try at making a blade myself and this is a simple and cost effective forge I could do. Now I just need to move so I have somewhere I can set one up hehe

[ZDP-189]

do you use the small canisters of gas <Mapp Gas>

or do you use the large re-fillable bottles with hoses and valves <LPG>

or do you use a piped in gas main <LPG/ natural gas>

These two brick forges are designed to be easy to source materials and burners for, be quick and cheap to build and run, and to be readily portable in a backpack, etc.

Therefore, I am running small torches available in most DIY stores. Both these torches use Mapp Gas in the small yellow bottles that you pictured above.

I also have a number of other burners around the workshop. I have an LPG+compressed air burner, a butane cigar lighter, a white spirits+bellows burner, and an oxy-acetylene (actually Maxy Gas) porta pack.

All these gases would work as long as the flame is large enough, because they all burn well in excess of the forging temperature of steel. Of these gasses and gas mixtures, I'd be reluctant to use oxy-acetylene, because it burns so hot that it'd be easy to damage the blade.

Mapp Gas is my top choice because of power and portability.

LPG (calor gas) and air would work and be pretty economical too.

[ZDP-189]

Great info ZDP

I am hoping to advance to having a try at making a blade myself and this is a simple and cost effective forge I could do.

I'm glad you like it and I hope it brings you closer to forging.

Don't worry if you can't get all the parts I used from your local DIY shop. Firebricks, wire or wire mesh and the burners should be readily available, but the other parts I used may be more of a challenge.

Kaowool is not totally necessary, and I use it as much as a bump-protector as anything. It probably doesn't add much to the performance, as long as the bricks are not stood on a burnable surface. You might even get away with a lower temperature-rated insulator, because it is not in direct contact with the flame.

The same goes for refractory mortar, though if you need any, send me an email and I'll pop you a small packet in the post for no charge.

ITC-100 is more tricky. It's more costly and harder to get. Rex Price at hybridburners.com can sell you some cheaply and a pint will line maybe a dozen or more of these forges. I can't say definatively, but I feel that there is a noticeable difference in performance between a lined and unlined small forge. If however, you can't get it, it shouldn't hold you up, just start work with your forge without it. A Mapp Gas burner should easily get you up to a cherry red without a lining, and almost certainly high enough for an oil-quench.

Now I just need to move so I have somewhere I can set one up hehe

With equipment this small, space is not a consideration, but ventilation definately is. As a general guide, don't use these things anywhere you wouldn't use a BBQ/hibachi. You need a balcony at least, or an extractor and a really, really good through draft. If you start too feel a headache, dizziness, tingling on the face or any of the other symptoms of carbon monoxide poisoning, stop the burner immediately, ventilate the space and get some fresh air, fast.

[Danzo]

That's a great tutorial Zed, easy to follow but very informative. Will you post a tutorial talking us through the process of using it, from start to finish? I fancy building one of those in the garden.



Danzo

[CPShines]

This is great, Z. Thanks for documenting all these steps, particularly around how to place the burner and shaping the forge for even heating. It's fantastic information for someone like me who is thinking of building a small forge and hasn't yet started. I'm bookmarking this thread so I can refer to it when I need to.

Thanks again.

[Mr_Yarrow]

I'm not going to make one (atm), but if I ever want to, I will digging this out asap.

Once again a great thread by a commited bunch of guys for the beterment of all etc etc etc - keep up the good work chaps

[Sunraven]

At the moment I am in a flat so the only place I could do it would be in the carpark outside. Should be moving soon though so will be able to do it outside in the back yard. Got 4 knife handles to do as well now, 2 for a friend of mine and 2 for a friend of my mothers who neither of us knew liked knives though we have known her for years. She saw the knife I had done and wanted one as well as a bowie.

Once I have those done I want to try my hand at making a knife fully from scratch so a forge like that would be ideal.

[Iron_Heinie]

Awsome tutorial there ZPD! I may just be able to set up a forge afterall! This will especialy be a good introduction before I put down the big bucks for a large forge.

thanks man,

[Martyn]

Dan, thanks for posting this. Your experiments will save me going through the same. Hopefully I can cut to the chase and go straight to the point you're at. I'm gonna try making one tomorrow.

great stuff.
Thanks!

[ZDP-189]

Ooh, it's good to see that this one has had som much positive feedback. My intent was to demistify the basic forge and show what you can do with a simple DIY gas torch, a couple of bricks and a sharpened spoon.

I suppose it has become a bit of a tutorial, even though my technique was imperfect. I'll move it to the right place, where someone looking for ideas might go to find it.

If anyone gets stuck making a forge like this or needs further advice before starting, post here or PM me.

[Martyn]

The Map is the one on the left. It has a big head and really pumps out those BTUs. A major problem though, is that the venturi induction holes are very close to the tip and that can lead to spluttering if hot combusted gases cycle back through the burner. I had the distinct impression that even when it wasn't spluttering, I wasn't getting the best burn out of my Mapp-gas.

Bernzomatic who make the Mapp-gas also make the torch on the right. The guys in the burner stores seem to reckon that I could get a few hundred more degrees out of this torch. However, on firing it, I found that the flame was only about a quarter to a third the size of the Map-Torch. So while the cone tip temperature might be higher, the forge temperature may not be.

Dan, I have the same bernzomatic torch (the peitzo one) and am thinking of using that for my forge too, though I agree, the cone is smaller and although this is a better built torch than the cheapo one I've been using I would think the forge wont be as hot with it.

However, the brass nozzle unscrews. I was wondering if it's possible to fit the nozzle off the other torch onto the peitzo torch to give a bigger, broader cone?

[ZDP-189]

Dan, I have the same bernzomatic torch (the peitzo one) and am thinking of using that for my forge too, though I agree, the cone is smaller and although this is a better built torch than the cheapo one I've been using I would think the forge wont be as hot with it.

However, the brass nozzle unscrews. I was wondering if it's possible to fit the nozzle off the other torch onto the peitzo torch to give a bigger, broader cone?

I was told by the burner specialist shop that I get my stuff from that the tip is the biggest determinant of flame heat in a burner. However...

This model is not designed to be altered this way. The burner's air intake is located close to the body and you'd have to retune the ports to match your flame mix. The bigger problem is you need to regulate the gas flow to dump more into the bigger nozzle. Also, the igniter might not work. So, if you need more flame, you should get a different burner altogether.

But it may not matter. The propane torch you were using will put out more BTUs, even though the flame temperature may be a few hundred degrees lower. But given that the propane flame is way over welding temperature anyway, the additional flame volume will outweigh the lower flame temperature and get more of your forge hotter, quicker, and cheaper.

If you do go back to your propane torch, you will also have a really capable back-up in the bernzomatic that has numerous outher uses around the knifemaking shop, like silver soldering, brazing and caramelising the missus' desserts.

[Martyn]

Benzomatic do make alternate tips for the ts7000. I just tried another tip of another torch and it produces a bigger flame and seems to work fine, still not nearly as hot as my cheapo with a 3/4" nozzle though. It just doesnt get the forge as hot, regardless of how hot the cone of the flame may be.