Jackdawg Posted August 16, 2016 Share Posted August 16, 2016 So I have a piece of string how long is it? sort of one of those questions, so I will try and be as descriptive as possible. I am slowly building my forge. Fuel source will be charcoal. I have built the fire pot. usual inverted pyramid type shape. Bottom is about 5 inches square Depth is about 5 inches front and back, but sides are about 7 inches high (is designed to be 7 inches deep all round, but hedging my bets and going to see how it performs before adding the extra metal) airflow will be through the bottom, not sure of final opening, as I am thinking about building a drop in piece to go in to the opening, so it may end up smaller than the current 3 inch square tube, or then again I may just weld bars over the end of the tube, thinking about it. After doing some research and see what is available locally my choice is the good old hair dryer, or probably a boat bilge blower. Can get either for around the $30 - $40 mark. A Ducted bathroom exhaust fan starts at around $60, so being a cheapskate that immediately ruled that out So my question is how much air am I going to need for a charcoal fire? I have seen a few posts which indicate charcoal needs a "gentler" air flow, less air. No idea how much air a hair dryer puts out, been quite a few years since I have needed the services of a barber, or other hair grooming implement But the 3" boat bilge blowers (smallest size available) appear to produce somewhere between 90 and 135 cfm. They do not have a high air speed, relying more on aperture size than velocity. Now that sounds like a lot of air to me, but I have no idea. Obviously bleeding off air if you have to much is easily done, not so easy to fix if you dont have enough air.! So my my question is, would a 90cfm air delivery be enough? (Bearing in mind that rating would be an unrestricted flow rate, it would be less with the back pressure of having to push it through the pipe, bends and the bed of charcoal) Or is it so far over the top I should just raid the wife's side of the bathroom and make her hair dryer disappear? , Quote Link to comment Share on other sites More sharing options...
WL smith Posted August 17, 2016 Share Posted August 17, 2016 (edited) You won't need that much airflow make a method to bleed some off and test it until it works for your needs. Remember we all experiment until we find what works for our particular set up. Welcome to the fun!! Edited August 17, 2016 by WL smith Quote Link to comment Share on other sites More sharing options...
Jackdawg Posted August 17, 2016 Author Share Posted August 17, 2016 cheers for the advice, I will go with a bilge blower, knock up a bleed system for it, and just have a go!. Quote Link to comment Share on other sites More sharing options...
Jackdawg Posted August 27, 2016 Author Share Posted August 27, 2016 Well I did indeed go with the boat bilge blower, hit the hardware shop for the extra bits, put it all on the bench, had a think about it for a day or two, then put it together. Specs - The bilge blower as it came, 90cfm rated. 12 volt, rated for continuous operation, draws 3 amps, 75mm outlet. So using one of my smaller deep cycle batteries will give me a good day of blow before I have to worry about recharging. Use - Feeding my charcoal fire pot through a 75mm rhs bottom feed inlet. You will note the fire pot is designed to drop in to the frame of one of my steel cut off benches. Glued a 90mm T piece onto the blower, as the only flexi ducting pipe I could get at the local hardware was 100mm, (blower has a 75mm outlet). With the threaded end on the T piece, its external diameter makes it a near snug fit in the end of the flexi pipe. Just loose fitting the end plug in to the T piece at the moment. Also got a 100mm metal rain gutter fitting to act as the inlet for the bottom of the forge so the flexi pipe can connect it to and pretty much done. Used silastic to glue the various bits together, strong, takes good heat, flexible. Everything is pretty lose around the connections etc, including my air adjusting flap on the bottom of the forge, but when I fire up the blower there is plenty of air coming through the forge despite the leaks, so I reckon I will try it out just as it is. If I have to many leaks I will break out the duct tape, but if I can avoid using the tape, it will be much easier to assemble and take apart for storage. A few photo's. Quote Link to comment Share on other sites More sharing options...
Charles R. Stevens Posted August 27, 2016 Share Posted August 27, 2016 Charcoal likes low air velocity, and also has an affinity for side blast air Historically (Viking erra) 3/4 -1" tuyere were used (3/4" schedule 40 pipe is dang close to 7/8") Quote Link to comment Share on other sites More sharing options...
Jackdawg Posted August 28, 2016 Author Share Posted August 28, 2016 Well it is certainly plenty of air, actually seemed to run about right with the air bleed fully open, started it with it closed and the forge looked like the rear end of a jet fighter. Will look to put a rheostat in the 12 volt supply I think, make it more adjustable. Quote Link to comment Share on other sites More sharing options...
Frosty Posted August 28, 2016 Share Posted August 28, 2016 Use a reducer leading to the air grate to reduce the flow instead, Rheostats can be darned hard on motors, wiring and such. If the motor does NOT rely on the blower for cooling air you can make a gate on the intake side to control volume. I like a swing gate, one bolt or screw for the hinge and just swing it over the intake port. Closing the air off will reduce the strain on the motor, it's easier on the motor, no worries there. Frosty The Lucky. Quote Link to comment Share on other sites More sharing options...
Jackdawg Posted August 28, 2016 Author Share Posted August 28, 2016 cheers Frosty. Think a reducer might be the first thing I investigate. Don't want to restrict inflow side, as the air does cool the motor by the look of it. Quote Link to comment Share on other sites More sharing options...
Frosty Posted August 28, 2016 Share Posted August 28, 2016 If the blower draws the air through the motor you don't want it laying in the grass like that or it'll block the air vents on the motor's far end. Frosty The Lucky. Quote Link to comment Share on other sites More sharing options...
NoName Posted August 28, 2016 Share Posted August 28, 2016 Just thinking, one more pvc T. If you put the T between the motor and your supply tube, you could use a swing air gate on the open end to control air flow. Pat. N.N.F. Beautiful, Manchester, Michigan. USA Quote Link to comment Share on other sites More sharing options...
NoName Posted August 29, 2016 Share Posted August 29, 2016 On Saturday, August 27, 2016 at 6:06 PM, Jackdawg said: to Just took another look at your project. I am building a similar forge. You have the T, and its in the right place. Mount the blower where you can reach it. Just pop the cap off the T, and thats where the swinging air gate goes. N.N.F. Beautiful , Manchester, Michigan. USA Quote Link to comment Share on other sites More sharing options...
Jackdawg Posted September 6, 2016 Author Share Posted September 6, 2016 Well after a successful run playing with the forge the other day using charcoal as the fuel, I decided to have another go this morning using wood. Drilled 4 x 15mm holes in the end cap on the T piece as a quick way to reduce the air flow and it made it much better, ran the fire with the flap about half open and it went well. My son had scrounged the wood from an old fence his girl friends family had replaced.for use in his metal melting setup, but left it sitting in the yard for 6 months or so. So I decided to cut some of the hard wood palings off it and see how it went for fuel in the forge. Ended up using about half a bucket, would have been less if I had religiously remembered to turn off the blower when I took the metal out of the fire! Pretty good really. Made myself a little fire scraper / rake I had seen Andy McKenzie make on U Tube, went pretty well. Made it out of some 12mm reinforcing bar I had scrounged second hand for $5 per 6m length specifically to have a play with my forge with. Certainly happy enough with the result of my endeavours. Must say all the pen pushing in recent years instead of physical work has not helped in the stamina area, an hour of hammering and I was knackered. Quote Link to comment Share on other sites More sharing options...
ThomasPowers Posted September 6, 2016 Share Posted September 6, 2016 I know you don't need this warning; but for others: NEVER USE PRESSURE TREATED WOOD IN A FORGE! I like to convert my wood to charcoal in a different fire so I only have charcoal in my forge; make is nicer to work at. I built a shaker shovel to scoop up the coals and then a shake and the little stuff and ash drop out and just the good stuff gets poured into the forge. Also charcoal likes a deep fire so a few firebricks to make a wall of some sheet steel to make a fence with a hole in it for the stock will help. Charcoal has continuously been used for smithing since the beginning of smithing till now. Coal started being use for smithing in the high to late middle ages according to "Cathedral Forge and Waterwheel", Gies & Gies. Quote Link to comment Share on other sites More sharing options...
Charles R. Stevens Posted September 6, 2016 Share Posted September 6, 2016 I work wit charcoal and wood, depending on wich forge I use I either convert in the forge as you are doing, or use a separate forge like TP. I find that my side blasts don't do a good job of converting wood to embers, but they are more fuel effecent and controllable. Wile my V shaped bottom blast converts wood well. I tend to leave the air on with it as I am always adding raw wood and it cokes wile I work. This is my big ugly heat 2" stock forge. Quote Link to comment Share on other sites More sharing options...
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