jack bacon
Well-known member
Can I use a variable speed control on my DeWalt 3400 RPM 6" grinder? I want to get the speed down to around 2000 to 2500 rpm.
Thanks
Thanks
Bench grinder speed control
- Thread starter jack bacon
- Start date
neophyte
Well-known member
If this is to run an accessory requiring a lower speed than your grinder is rated for, I would not recommend it.
Generally, you should never run accessories on a tool with a higher maximum speed than the accessory is rated for, if the tool uses electronic speed controls.
When the electronic speed controls fail, the grinders can speed up to maximum, creating the possibility of the accessory exploding, dangerously.
Generally, you should never run accessories on a tool with a higher maximum speed than the accessory is rated for, if the tool uses electronic speed controls.
When the electronic speed controls fail, the grinders can speed up to maximum, creating the possibility of the accessory exploding, dangerously.
seber
Well-known member
You would need a VFD to do that. The cost would exceed that of a variable speed grinder. In addition, motors should be rated for the purpose to avoid overheating due to lack of ventilation when run slowly. I suspect a non fan motor like a grinder would be OK, but I wouldn't count on it.
Those are only good for brushed ac motors... if grinder is AC cap start, you can still use them but have to start it with dial on maximum then lower no more than 1/3 of its speed. actually have that controller from HF more than 10 years ago.. works well on routers, or grinders but those are bushed ac motors.Never tried it but HF sells a speed controller for $18 rated 120v 8A or lower.
seber
Well-known member
Using that control on an induction motor will burn the windings in short order.
WWheeler
Well-known member
Definitely listen to this. The speed for an induction motor can only be controlled by using a variable frequency drive (VFD), which will cost more than the grinder. A simple pot like they sell for universal motors like routers, like cgrutt posted, will definitely make for a bad day for your Dewalt.
Your best bet would be to find a variable speed grinder to start with.
8 in. Variable-Speed Bench Grinder with LED Work Light
Amazing deals on this 8In Variable Speed Bench Grinder With Light at Harbor Freight. Quality tools & low prices.
www.harborfreight.com
You may be able to find a good deal on a used one like these examples near you on Craigslist or Marketplace.
Definitely listen to this. The speed for an induction motor can only be controlled by using a variable frequency drive (VFD), which will cost more than the grinder. A simple pot like they sell for universal motors like routers, like cgrutt posted, will definitely make for a bad day for your Dewalt.
Your best bet would be to find a variable speed grinder to start with.
8 in. Variable-Speed Bench Grinder with LED Work Light
Amazing deals on this 8In Variable Speed Bench Grinder With Light at Harbor Freight. Quality tools & low prices.
You may be able to find a good deal on a used one like these examples near you on Craigslist or Marketplace.
Not doubting you but curious why the variable speed grinder that you suggested appears to be a capacitor (9) start induction motor that uses a simple potentiometer (24) (and not a solid state variable frequency drive) for speed control.
Old Man Roger
Well-known member
I got a porta cable adjustable speed 8 inch bench grinder on sale from lowes for like 89 bucks? Been using it for years with no issues.
I have a 3600 RPM bench grinder and never thought I had a need to slow it down- for the purpose of grinding steel. I do love my variable speed Metabo 4.5" right angle grinders though, but I primarily use them with a flap wheel for lighter work.
It’s not a start capacitor, it’s a run cap sort of, a split phase motor I think that is called. and the potentiometer is connected to the circuit board., not directly to the motorNot doubting you but curious why the variable speed grinder that you suggested appears to be a capacitor (9) start induction motor that uses a simple potentiometer (24) (and not a solid state variable frequency drive) for speed control.
Yeah missed the circuit board but still not a VFD. The pot on the "router" speed controller is also connected to a circuit board BTW. I don't know enough about this but wouldn't a split phase motor also have a centrifugal switch to cut out the start winding? I don't see the switch on parts diagram. There is an optical coupler but assuming that is so it can sense how fast motor is turning. Anyway, as I said I'm not doubting the HF speed controller is a bad idea just trying to understand how it works.
seber
Well-known member
That is a triac speed controller in the base of the grinder. It chops the input cycle to the motor. That has the effect of lowering the current without dropping the voltage. It is a cheap and effective method of speed control for an induction motor. If you could find such a circuit for sale and know how to wire it, you could use that system. Washing machines also commonly use that method but unfortunately they normally only use 1/3 hp motors. Worse, you would need to know a fair bit about electronics to adapt the wiring.