The Siren Board

Okay, so I've decided I'm going to give a shot at making a homemade siren. I'm going to use an 8 inch, 3650RPM 1/2HP bench grinder as the motor, plywood for the chopper and stator, and a jigsaw to cut the plywood. I'm going to make an 8 port siren. I'm getting the building materials tomorrow, so stay tuned to this thread for a build log!

Good luck!! If plywood doesn't work, try using some sheet metal, but be warned: sheet metal has some very sharp edges. Hope to see some pics soon.

Good luck! I tried making one with a bench grinder.. but I just couldn't because the wood was thin,a nd I was using drill bits to cut out the base for the chopper.. so it was too small. Good luck, I hope you do it!

Valtonus wrote:Good luck! I tried making one with a bench grinder.. but I just couldn't because the wood was thin,a nd I was using drill bits to cut out the base for the chopper.. so it was too small. Good luck, I hope you do it!

Thank you! I have one question, though... Because I'm measuring an 8-inch circle, how long do the ports have to be to get an even amount of ports and make them even on the chopper? Half an inch?

GreenblottF wrote:

Valtonus wrote:Good luck! I tried making one with a bench grinder.. but I just couldn't because the wood was thin,a nd I was using drill bits to cut out the base for the chopper.. so it was too small. Good luck, I hope you do it!

Thank you! I have one question, though... Because I'm measuring an 8-inch circle, how long do the ports have to be to get an even amount of ports and make them even on the chopper? Half an inch?

Sorry, I don't know that... I bet Cal's Engineering could help you (I don't know his ARS username though...)

Valtonus wrote:

GreenblottF wrote:

Valtonus wrote:Good luck! I tried making one with a bench grinder.. but I just couldn't because the wood was thin,a nd I was using drill bits to cut out the base for the chopper.. so it was too small. Good luck, I hope you do it!

Thank you! I have one question, though... Because I'm measuring an 8-inch circle, how long do the ports have to be to get an even amount of ports and make them even on the chopper? Half an inch?

Sorry, I don't know that... I bet Cal's Engineering could help you (I don't know his ARS username though...)

What you do is measure the circumference of the circle, than divide it by 16. Let's say the circumference is 20in. You divide 20in by 16, which gives you 1.25. You make a mark on the circle every 1.25 inches, than you place a chopper blade every other marking.

Synther wrote:

Valtonus wrote:

GreenblottF wrote:
Thank you! I have one question, though... Because I'm measuring an 8-inch circle, how long do the ports have to be to get an even amount of ports and make them even on the chopper? Half an inch?

Sorry, I don't know that... I bet Cal's Engineering could help you (I don't know his ARS username though...)

What you do is measure the circumference of the circle, than divide it by 16. Let's say the circumference is 20in. You divide 20in by 16, which gives you 1.25. You make a mark on the circle every 1.25 inches, than you place a chopper blade every other marking.

Thanks! I did some calculations, and the circumference of an 8-inch circle is 25.1 inches. 25.1 divided by 16 is 1.56875; I'll round that to 1.6... So the chopper blades have to be 1.6 inches apart. Thanks so much!

Be careful that the chopper is solid and well balanced before you spin it up. One way to balance the chopper is by placing a marble in the hole in the centre of the chopper and drilling out material from whichever side has a tendency to lean. Also make sure that the chopper is completely round before you spin it up, and make sure your tolerances are decently tight. If the siren runs smoothly, there is a decently low chance of it blowing up, but always stand away from the sides of the chopper while it is spinning. I have made plywood sirens before and they can actually be pretty loud, considering that they are homemade. Good luck with your project!

clm 10 12 wrote:Be careful that the chopper is solid and well balanced before you spin it up. One way to balance the chopper is by placing a marble in the hole in the centre of the chopper and drilling out material from whichever side has a tendency to lean. Also make sure that the chopper is completely round before you spin it up, and make sure your tolerances are decently tight. If the siren runs smoothly, there is a decently low chance of it blowing up, but always stand away from the sides of the chopper while it is spinning. I have made plywood sirens before and they can actually be pretty loud, considering that they are homemade. Good luck with your project!

Thank you! I have an angle grinder and a jigsaw with a circle-cutting jig so I will make sure the chopper is perfectly round. Also, I know about the marble trick, so I just drill small holes wherever it tends to lean to until it's well-balanced. I ordered the bench grinder off of e-bay; it should be here by Monday.

Isn't the maximum 60Hz induction motor speed 3600RPM, since 60hz (revs per sec) x 60 seconds is 3600 RPM?