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Lou L

My side blast forge design

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I'm not sure why but, after many months of reading and talking to blacksmiths I know I decided to make a side blast forge for my first forge.  I was going to make a propane forge out of an old propane canister but decided I wanted to go with coal because I wanted to go "old school" plus I wouldn't have to buy all the metal working tools up front (welder, grinder, etc..).  Well, I ended up having to buy all that stuff anyway.  You know what they say about the best laid plans...

I was able to scrounge most of the materials because I have access to the scraps from a fencing company (unfortunately most of his scraps are galvanized) so I only spent about $90 for materials on this forge.  I refuse to count the cost of the tools as cost for the forge...just because.

Anyway, here it is:image.jpeg

The base was a scrounged scrap storage rack from the fencing company as was the 1/8 plate steel that are only clamped on to the sides.  I wanted them removable just in case.  The design is based on what I have read from books and online but it was completely based upon the materials I was able to get.  I'd say the biggest limitation to the build was my ability (or really lack of ability) to stick weld.  I spent the $90 on the 1/8" plate steel for the bottom of the forge and the bosh in the back.

 

image.jpegThe tuyere is a 1 5/8" pipe jacketed by the 3/16" square tube seen here.  The biggest design flaw I have noticed so far is the size of the air outlet.  It is now about 3/4" but I think the size differential is causing a pressure drop and has made air a challenge.  Right now I have an old dirt devil vacuum that is way too strong (I use it to establish the size of the fire) and a bathroom vent fan that struggles to overcome the pressure drop (I use it to maintain the fire once it is strong).  Switching air sources is tedious and I'm looking for a quiet but stronger option.

image.jpegFrom this view you can see the bosh.  The pipe runs through and out the back.  Welding this up was a serious challenge and I ended up deciding to double down and use some high temp silicone sealant as insurance.  I had a few small leaks and didn't feel like chasing them with my welder for days.  According to everything I have read I should not have put the wall of the bosh right next to the fire but, so far I have run this thing for over six hours and not reached boiling temps with the water tank (it holds about 20 gallons I think).  The shape and size was totally based upon the materials I was able to get cheaply.  I could have paid to have plate steel cut to my dimensions but I'm too cheap.

 

image.jpegHere you can see the drain I installed along with copious amounts of insurance caulk!  The duct tape is for fitting the pipe with the pvc elbow I use as an adapter for my Frankenstein air system.  Please feel free to laugh at my welds.  I'm still learning how to use this thing efficiently but it sure can create a super hot fire.  Right now I can't get the control of the heat and have quiet at the same time.  I hate running the loud dirt devil vacuum and would love any ideas for a more quiet option.  Currently I'm using anthracite because it is the only thing available to me.  Plus, I live in suburbia in an uptight town and fear getting shut down if I produce too much smoke.  Problem is, anthracite is really picky about needing constant and consistent air.  After reading some here on IFI I'm thinking about using two fire bricks to shape my fire better but, aside from that, I would love more feedback and ideas on how to improve my setup.  Thanks in advance,

 

Lou

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Real chunk charcoal produces little smoke and take gentle air had is older than old school.  You would probably want to reshape the forge to use it more efficiently; but that can be done with dirt and a couple of metal plates to give it more of a trough shape.

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I had considered charcoal but the cost seemed high.  The only good stuff I can find is sold for grilling and is expensive.  I was putting serious thought into making my own charcoal retort but wanted to get forging first.

 

The forge is already lined with sand and ash so reshaping the fire "pot" wouldn't be too hard I think.  I chose this forge concept partly because it is supposed to be flexible with the fuels you use and then promptly forgot that ninjas other fuel options.  Thanks for getting me out of the box.

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I have a raised fire pit and burn wood in it and transfer hot coals to the forge as needed when I work with charcoal.

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The easiest way to update your setting for variable air volume would be to use the Dirt Devil vacuum and modulate the output in one of three fashions:

  1. Put an outlet TEE, or cut a hole in the connecting pipe, that can dump out some of the air before it gets to the tuyere.  Use a movable cover on that outlet (dump gate) to increase the bypass air or the air fed to the tuyere as required.
  2. Add a butterfly damper to the supply side of the dirt devil vacuum (may be a problem with the fan motor as the extra resistance that cuts the air supply will force it to work harder)
  3. Put an adjustable shroud over the air inlet for the vacuum and open and close as required (mock this up in cardboard to see if it works.  some constant speed fan motors don't like getting starved).

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Thomas, do you prefer to use charcoal or, more specifically, do you think it would be a realistic option for long term, regular use?

 

Latticino, I rigged up an air diverted out of a pvc three way connector but haven't used it with the dirt devil because the connection between the two is a minor pain but mainly because I hate the loud whine of the thing.  My neighbors can hear it three houses down and I find it maddeningly loud.  Does everyone just learn to deal with the volume of their blowers?

My jury rigged air diverter:  I am thinking that maybe the air flow should be straight through and the release should be the angle.  I did it the way I did just for convenience because the smaller pipe section fits my tuyere pipe.  Thoughts?

image.jpeg

I have to take moving to charcoal seriously but I want the forge to be capable of using any fuel successfully.  Do you think increasing the diameter of the air inlet at the end of the pipe will help?  I would have to drain the bosh in order to drill it out with a unibit because making it any larger will compromise my welds.  So I'd also have to reweld it once I finish.  It's a bit of a pain to do but, if it would fix my air problems it would be worth it.  I guess this is what happens when a novice tries to build more forge than he needs!  I sure learned a lot in the doing though.

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I use a blower from the power vent of my last hot water heater.  It's not dead quiet, but it is not nearly as noisy as a Dirt Devil.  Others on here have posted that they use bathroom vent fans successfully, and I believe those would be significantly quieter as well.  They should be fairly inexpensive and available at pretty much any big box home improvement store.  Of course the often-used hair dryer is also an option, but they tend to be a bit noisy as well - and can get you in trouble with the spouse if you take hers without permission.

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1 hour ago, Lou Lestini said:

I had considered charcoal but the cost seemed high.  The only good stuff I can find is sold for grilling and is expensive.  I was putting serious thought into making my own charcoal retort but wanted to get forging first.

 

The forge is already lined with sand and ash so reshaping the fire "pot" wouldn't be too hard I think.  I chose this forge concept partly because it is supposed to be flexible with the fuels you use and then promptly forgot that ninjas other fuel options.  Thanks for getting me out of the box.

I just noticed that autocorrect changed "there were" to "ninjas".  My favorite typo yet!

 

Buzzkill, I already have a 100 CFM bathroom vent that is super quiet but can't push through the coal pile to maintain the fire well enough.  When I put work into the coals they move around and just one piece of coal can plug the air outlet such that the fire loses its mojo.  When I move that piece of coal two more fall into its place every time.  Raking coal is quite possibly the most frustrating thing about blacksmithing so far.  I swear the stuff is alive and actively trying to get itself where I don't want it!  What I'm trying to figure out is whether or not pressure drops in my air system (venting, air outlet diameter, etc..) are causing my problems or if it is an underpowered fan.  If others are succeeding with bathroom vent fans then it must be my air system.  If that's the case, I need to keep asking questions and seeking fixes.

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A typical bathroom exhaust fan has, at most, around 0.5" of external static pressure capacity at the lower of the airflow rates it is designed for.  A fan curve or chart will tell you more.  Your diverter appears to be designed backwards.  You can definitely use a Wye fitting, like you have, but the variable damper should be on the outlet side of the of the bypass (or release as you call it) side, not on the main inlet.  In this I assume the flex duct connects to your forge.   If it actually connects to your fan, and you don't have enough airflow, I suggest that you damper the bypass side and close up the slot you made.  As I said, exhaust fans don't develop much static, but you shouldn't need too much provided you keep your duct lengths short, avoid elbows and offsets, use smooth wall ducts and avoid rapid transitions in diameter (30 degree transition angle is a good rule of thumb).  A photo of the entire system, setup with the fan in place, would make it easier to diagnose.

Others might be able to comment on the size of your coal.  The last workshop I went to we made an effort to screen out all the "fines" leaving us with only the larger size pieces (these were still in the 3/4" -2" minor diameter size though, not huge fist sized chunks.  This worked extremely well for the upblast style forges we used, but I'm not that familiar with a side blast, so don't know what kind of pressure and airflow are needed.  All I can say is that the conventional hand cranked or electric forge blowers I've seen all are more of the low airflow/high pressure style (radial paddles) instead of the high airflow/low pressure style (squirrel cage centrifugal) like your bathroom exhaust fan.  The former most likely develop 4 times the pressure yours does, for the same airflow.  If nothing else see if your exhaust fan has a backdraft damper built in.  Remove that.

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Lou,

I am just starting to put together plans for a forge myself.  I have seen pics of an "in-line" fan with what appeared to be 190CFM VEN-Tech 4" used on a bottom air Forge.  I was able to find what appeared to be that unit on Amazon for about $70.  A little searching and I was able to find another brand with mounting bracket and speed controller for about $60.  They are typically used for horticulture or ducting and appear to be suitable for static pressure use.  

Dave with Fiery Furnace Forge was the one making the forges, saw the fan on his facebook page.  I don't know if he's still selling that unit or not, but he responds very quickly to facebook messages.

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In my case it's a bottom blast forge, and I don't know if the others using a bathroom fan were side or bottom blast so that could be a difference as well.  I was burning anthracite rice coal from TSC and had no problem ruining the blade I was working on due to overheating.  Since I have no experience with a side blast system I'll let others handle further suggestions.

I was wondering what that "ninja" thing was all about.  Thanks for explaining!

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Oh man, I'm back to laughing about the "ninja" thing.  It had me seriously gut laughing for some reason.  You all are saints for patiently ignoring nonsense like that!

 

Thanks so much for the input all!

Latticino, I can't help but think you are right.  The flexible hose was connected to the vent fan.  I made my decisions for convenience and I think I set myself back.  I was also concerned about coal size.  Small pieces of coal have kinda gotten wedged into the tuyere outlet and large ones have redirected the air flow causing me to have two separate fires on the side rather than one in the middle.  The dirt devil vacuum powers right through it Åland the air always diffuses right where I want it.

I was working under the assumption that the side blast would have less problem with air pressure.  I'm going to rework my knuckleheaded air ductwork, remove the backdraft damper from the fan and have another go at it.

Currently I'm using nut coal but I'm going to pick up some pea and rice sized and do some comparisons.

Bcrosby71, I've seen a bit on inline fans.  I was trying to figure out which might work.  They make them for boating ventilation that run on 12v and others for home heating systems.  I'll check out your sources, thanks.

 

I'm still looking for any other insights into the design of the forge.  Everything about it is educated guesswork.  I used videos from Joshua Delisle on YouTube as my most useful bit of insight.  http://youtu.be/ypahcig1KQw

I'd love to hear any suggestions or ideas, even if it is just guessing.  This forge is a work in progress for sure and it's about time more than one mind work on it.

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Did some researching on inline fans for possible forge use.  Thanks for the heads-up Bcrosby71.  Here is what I found:

The Ventech fans that Fiery Furnace Forge used are strong but have some negative reviews for bad bearings and terrible customer support.  They are still a good option.  For about the same price ($68) you can get one made by Active Air that has good reviews.  

There are speed controllers for brushless motors that are pretty expensive but I dug around and learned that you can apparently use a router speed controller designed for brush type motors 15 amp and under.  These can be had for $20 at HF if you are willing to be seen there!

So, for about $88 I could have fully controllable high volumes of air without even needing my terribly designed air gate.

That would be $2 less than I paid for the materials to build my forge and I'm cheap...but I'm tempted to try the experiment.

Im still going to try to make my current system more efficient per Latticino's suggestions and see if that works first.

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