I had one such "need" for an invention recently. I guess it's not so much an invention really, but a DIY version of something that is currently available on the market, just for more money than I am willing/able to pay. What I needed was a commercial blower unit to suck blown in insulation out of attics. They are available for purchase, at a price point somewhere around $5000. So I figured, I'm a smart dude, I went to engineering school, this is my jam. So I got to it, and what follows is my method.
Step 1: Design
I went with a 14 inch impeller, backwards curved blades, mostly determined by what raw materials I already had available to me for the impeller. I went with five blades, also just because. The impeller works in counter-clockwise rotation, based on the shaft rotation of the motor I was going to use.
I will try and add some Inventor screen caps later on.
I am in the process of a redesign right now. Instead of a direct drive, it will be a belt drive with a centrifugal clutch. This has many advantages over the original design, and all of this will be explained after I complete the project, again. I should be done the project by the end of the week, and the updated instructable will follow shortly.
Step 2: Parts, Materials and Tools
Horizontal gas motor (6HP)
Assorted nuts and bolts, 1/4" & 5/16"
Threaded ready rod & nuts
9" plastic water pipe
1/8" aluminum plate
3/16" aluminum plate
1/4" steel plate
16 Ga steel sheet
Assorted steel tube (for cart)
Metal cut off saw
Sockets and wrenches
There are also various other small hand tools you will need throughout the job. Best to be able to do this in a well stocked shop.
Step 3: Impeller Part 1
I started with the back plate of the impeller. I used 3/16" aluminum plate (this could bring up problems, more later) to keep the impeller as light as I could, while keeping it strong. I cut the aluminum plate into a circle using a jigsaw with a metal blade. To lay out the blades around centre I used a pentagon with a center hole to match the centre hole of the back plate. The aluminum pentagon in the first picture was later replaced with steel pieces to provide a better bearing point for the drive shaft keyway.
The blades are were cut out of 9" water pipe. The pipe was first cut into quarters on the table saw, then cut into sections for the blades. After layout, keeping in mind which way the drive shaft spins, the inside corners of the blades need to be cut off at a 45 degree angle.
The pentagon hub was cut out of three pieces of 1/4" steel plate, with a hole drilled in each corner of the pentagon. The impeller back plate is sandwiched between the steel hubs, one on the back side, two on the front side.
Finally, there is a ring on the face of the hub, cut out of 1/8" aluminum, again using a jig saw. Using a retaining ring on the face of the impeller allows you to spin the impeller faster and create additional airflow.
Step 4: Impeller Part 2
Now that all the impeller pieces have been made, it's time to put them all together.
The three impeller hubs, the pentagon pieces, are bolted through the front two pieces, and threaded into the back side hub, this avoids the need for nuts on the backside of the impeller which would impede clearance. The hubs are also all glued with super glue (more on this below).
The blades are arrayed around the hub, aligned with the leading edge on the corner. The blades are also bolted and glued (see below) onto the back plate. The two inside holes are threaded to receive 1/4" bolts, and the outside hole is bolted through the top ring to hold it on.
The centre hole is drilled out to 3/4" to accept my shaft, that is, the shaft on the motor I was using. The keyway is easily the hardest part of this little operation, it is very important to make sure it is the right size, not too big or there will be backlash in the shaft and that would inevitably result in the key failing.
The different parts of the impeller assembly are all glued together as well. I needed to find out which adhesive would work best, so I did a simple test using four adhesives to see which one worked best for my application. I tested Lepage PL Premium Fast Grip, Gorilla Glue, Gorilla Super Glue, and Krazy Glue. The best result was achieved from the Gorilla Super Glue, so I used that for all the glued parts of the assembly.
Step 5: Blower Housing
The housing is made from 16 Ga steel sheet, welded into form. I wanted to make the housing so that it could be removed easily to have access to the impeller, for maintenance reasons.
I cut out the flat pieces with a grinder and rolled the sides of the housing to make an approximate curve. the sides are welded onto the front and the back flange is welded on to the sides. The back flange is a thin strip, so that it will fit past the impeller when the housing is being removed.
The back of the housing is made from 5/8" plywood, cut out with a jigsaw. The important part of the plywood back piece is the holes lining up with the shaft and mounting holes on the motor. This is the point where you really need the motor to continue with the project, up until this point it could all be done without having the motor on hand.
I also made a part that attaches to the housing for the inlet hose to attach to. It looks like a top hat without a top.
After the housing was all welded, I primed and painted it to keep it from rusting, and to make it look nice.
Step 6: Mounting the Blower
One thing that I neglected to do but would be a good idea is to use thread locker on the bolts used to mount the housing to the motor.
Once the back plate is on you can attach the impeller to the shaft. Slide the impeller onto the shaft and then insert the key into the keyway. It shouldn't be easy, but if you have to smash it with a hammer to the point of deforming the key then it's time to stop and fix your keyway. When the key is in, put the bolt into the end of the shaft with an appropriate washer to hold the impeller on. This bolt needs to have thread locker on it, the strongest stuff available.
Now you can put the blower housing back on the plywood, mine is screwed onto the plywood.
Step 7: Cart
Step 8: Finished Product
Step 9: Revision
Step 10: Redesign
To eliminate any possible issues of starting with a heavy flywheel I changed the drive to a belt drive with a centrifugal clutch. The clutch is mounted on the engine drive shaft, and a belt in turn runs the blower, which has it's own shaft with a drive pulley. The blower housing is mounted on a sled which is in turn mounted on to the cart.
The belt drive starts with a centrifugal clutch mounted on the engine drive shaft, this is the easiest part of the drive system. Just mount the clutch and put the belt on it.
In this new version I welded the drive axle directly to the impeller. This has the draw back of not being serviceable, but I didn't want to deal with a keyway on the impeller. The impeller shaft is mounted to the sled in two pillow block bearings. The drive pulley is mounted between the bearings, but I had to weld this on to the shaft as well. This was not my intention, but the keyway in my drive shaft was not the right size, so instead of messing around with it I just welded it on. If I need to service or change the pulley I will just have to cut the shaft out.
I hacked up and remade the cart in a configuration that works for the new drive arrangement. It is now longer and the motor mounts sideways from the way it did before.
The new design seems to work a lot better than it did before. There are new pictures here, there will be a couple more and ideally a video soon. Thanks.