Ray Rogers Handcrafted Knives
How to Build Your Own Forge Blower
One of the most expensive and mysterious parts of a forced air forge is the forge blower. Not just any blower will do the job and buying a professional forge blower is pretty expensive, especially for a beginner. To work properly on a good sized forge a blower should be rated at 100 to 150 cfm and from 32 to 40 ounces of static pressure. That last part is the killer because almost nobody puts the pressure rating on their blowers. Here's how you can build a forge blower for almost nothing that can exceed those specifications.
The above picture shows all the major components that you will need. First, you will need a motor. Mine was salvaged from a scrapped bench grinder and is rated 3450 rpm and 1/3 hp. A double shaft motor like this is handy because some blower wheels must turn clockwise and some must turn counter clockwise. With a double shaft you can use whichever blower wheel you can find because the two shafts turn in opposite directions.
My blower wheel came from eBay. They had literally hundreds of them and most were well under $20. You can use metal or plastic blower wheels. The ones you want will be 5" or more in diameter and must accept a shaft size that matches your motor. Usually, the bigger the shaft the bigger motor and the bigger the blower wheel. A 5" or 6" wheel is big enough but you should have at least a 1/3 hp or 1/2 hp motor. The rpm doesn't matter but it should match the rating for the wheel. My wheel was rated 1725 rpm but my motor is twice that so I'll likely burn out the motor after a while but I don't care. Blower wheels can be salvaged from old heating systems also. Remember, the blower wheel must be designed to turn in the same direction as your motor.
My motor shaft is 1/2" so I needed a blower that would accept that size. The blower wheel I found to match was about 10" in diameter. As it turns out, a 5 gallon plastic pail is just about perfect for a wheel that size. If your wheel is smaller, consider a paint can or a one or two gallon pail.
My motor has a face mount that consists of 3 screw holes. This was perfect for this project, all I needed was three holes in the bottom of the pail. Many motors are set up to accept a face mount but if yours doesn't, don't worry. Just mount the motor on a board and mount the pail on blocks in front of the motor (similar to how I mounted the battery powered mini-forge).
Next, I cut the pail down to match the width of the wheel plus about another inch. There is plenty of room in the pail for the wheel, this does not need to be a tight fit. You can see the scribe I made by taping a Sharpie pen to an old C clamp. I used this to draw a line around the pail where I wanted to cut it. Tin snips did the cutting.
The lid would no longer fit the pail after it was cut down so I cut the rim off the lid and flipped it over. Now it mates up nicely to the shortened pail. With a 4" hol;e in the center the lid will become the outside of the blower housing. BTW, the hole size isn't that critical either, just make it look somewhere near these same proportions.
Cut a hole for the blower outlet, make it kind of long so the the outlet tube can meet the blower body at a tangent (some of the later pictures show this angle better). You can simply stick the outlet in a 90 degrees if you want but it will cost you a good bit of your performance.
I used 2" PVC pipe for the outlet tube held in place with one screw and a bit of tape to cover the gaps. The whole thing is sealed up with good epoxy and it's solid as a rock.
Pay attention to the red arrow behind my photographic assistant. It shows the direction that the blower wheel will turn. The outlet tube must be mounted pointing in the direction of the wheel's rotation. If the tube points the other way you'll get very little output. Also, pay close attention to the way the tube meets the blower body. The closer you can get to this tangent the better the blower will work.
The finished blower. Final assembly consisted of mounting the blower body on the motor (3 screws), mounting the blower wheel on the shaft (one screw), and the mounting the lid onto the blower body (a few screws through the edges of the rim). Silicon caulk was used to seal up the air gaps around the lid, not critical but it helps.
Does it work? Oh, ya, sure, you betcha! First of all, it is very quiet. Second, I compared it to my commercial blower (160 cfm, 40 ounces static pressure) by simply holding my hand over the output tubes on both units. The new blower clearly has significantly more pressure behind it and appears to have more cfm as well. Next, I attached the new blower to my big double burner forge and observed that more air was moving throuh it (didn't light it yet).
A blower like this will easily operate your forced air forge. A large one like the one I made would also make a super air curtain....
A forge is not a toy and messing around with large quantites of flammable gas can be very dangerous! It is YOUR responsibility to exercise due caution and care if you chose to build a forge. Be sure to comply with all local regulations and restrictions. This web page is not intended as a guide for you to use when building a forge. It is merely intended as a record of what I did and as a way of illustrating the basic fundamentals of how a forge works. I am not responsible for what you choose to do with this information.
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Ray Rogers Handcrafted Knives