Shopsmith Forums

I know this is not really a wookworking tool question, but it could apply to really rough sanding of wood as well.

I have a Makita 7" angle grinder (GA7021) rated at 15 amps and single speed of 6600 RPM. I used it with a diamond cup grinding wheel to prep a concrete floor for a new thin cement topping. I gave the topping what I hoped would be a light broom finish, but it is rougher than I had hoped.

The diamond cup grinding wheel is too aggresive for trying to "smooth out" the cement topping (takes it all off in no time flat), so I am looking at using a 16 grit abrasive disk wheel on the grinder.
First experiment using the 16 grit disc was semi-successful ... it took off some material, but still spins too fast to be able to control it well.

My pad sander with 36 grit sandpaper (in oscillating mode) removed some material, but it was too slow. Dust was not too much of a problem with the pad sander (since it did remove material so slowly), but with the grinder a dust shroud would be used connected to a Shop Vac.

Looking at the HF Router Speed Control Dial https://www.harborfreight.com/router-sp ... 43060.html

it seems a lot of people use it for tools other than routers.

Has anyone used it with an angle grinder? How "slow" can it go? All thoughts and suggestions (other than buying a variable speed angle grinder) are welcome.

WORK - yes.

HOW LONG - ???

With a 6600 rated rpm it has to be a 'universal' motor(brushes).

With a rated current = to the max rating of the controller it is a bit of rolling the dice(think duty cycle).

At $20(- 25% tomorrow) it is to me worth a try!

I would try to find a way to adapt the head of a Harbor Freight 7 in. 10 Amp Variable Speed Polisher to support your abrasive pad (opposed to a polishing head with the flexible rubber backing pad) if I were attempting this.

The polisher runs slower than a grinder, and is already variable speed.

The threaded spindle on it is 5/8″ x 11 TPI

You need a head for your abrasive or a 5/8″ x 11 TPI adapter to something that fits it.

Everett

Thanks JPG and Everett for your thoughts and suggestions.

The grinder motor is "universal" (w/ brushes), so it should work with the router speed control, BUT, in reading more reviews and watching some YouTube videos, it appears the HF router speed control will not reduce the speed to as low as I want and need ... it may reduce the speed in half, but for my purposes that would still be too fast.

I will have to look again at maybe getting the polisher/sander (another tool for what is probably a one-time project), if I can adapt the abrasive disk to the spindle. The cheaper HF model polisher / sander does go as slow as 200 rpm, so that would be more my speed, and if I can get my dust shroud / vacuum attachment to work too, then I may just go that route ... and maybe I would use it for polishing a car now and then too.

Thanks again to both of you for your valuable advice.

could this be used on the shopsmith to slow it down?Larry

lalkie01 wrote:could this be used on the shopsmith to slow it down?Larry

No, I don't think so. All of the reviews I read said it would not work with motors with start capacitors or "soft-start" motors.

lalkie01 wrote:could this be used on the shopsmith to slow it down?Larry

NO!

would it work to reduce speed on shop fan? or air circulator, like vornado? they have speed controls, but slower speed will help to reduce the wind noise at times.

Greetings,
I have bought 3 of the Harbor Freight speed controllers (called Router Speed Control) to use with a 5" Makita angle grinder. It did slow the tool down (to reduce the amount of dust ejected when sanding tight spots on wood floors).

However, all 3 burned out the little fuse, even tho the grinder is much less than 15 amps. HF does not carry replacement fuses, they say they cannot even order it.

I meant to find a generic replacement, but Life got in the way.

Just noticed this old thread. The big problem using a simple voltage controller to slow tools with universal motors is that internal fans are running slower and unable to cool the tool sufficiently.

I've seen somewhere that running these motors at lower speeds produces more heat in the motor than running at full speed, that's a separate matter and I find paradoxical if true.