A question from a newbie

[spec]

Yes, that is my point. I am concerned because you do not understand the benefit that comes with isolation from a transformer when dealing with mains power.

Totally unsubstantiated. You have no idea what I understand and don't understand. Why are you isolating the motor anyway? Would you isolate an isolating transformer across the mains, and then another isolating transformer before that and so on? Or are you presuming that the OV of the motor is connected to its chassis? There are literally millions of motors connected directly across the mains, in the UK the mains is 230V too. In a typical washing machine, one of the most dangerous environments, because of the water hazard, there is at least three motors connected directly across the mains supply, not to mention various electromechanical valves and solenoids.

As for the commutation, listen to Audioguru - you will have lots of vibration if you commutation does not match the frequency of your 120Hz rectified AC.

Nonsense. What is the basis of that? I have already answered AGs post

 

[Tony Stewart]

A large flywheel can smoothen the vibration, but half-wave rectification of 120Vac is around 90Vdc avg.
An SCR can give variable speed with current handling for start surge.

The treadmill gives a flywheel effect. Vibration is not an issue there and this SCR control is all they use in old treadmills.

 

[shortbus=]

Why would a 1.25 HP motor be used for a brass tumbler anyway? Unless the tumbler is doing hundreds of pounds of cartridges at a time, that HP is way way overkill. Most hobby level brass tumblers use a shaded pole gearmotor for driving them. https://www.ebay.com/sch/i.html?_from=R40&_trksid=m570.l1313&_nkw=shaded+pole+gearmotor&_sacat=0

I made one years ago for a friend that we used a barbecue rotisserie motor for power.

 

[gophert]

The treadmill gives a flywheel effect. Vibration is not an issue there and this SCR control is all they use in old treadmills.

Vibration is an exaggeration but the word used by Audioguru. The hum is definitely present and intensity of the hum is noticeably different with small changes in speed and strain on the motor. The PWM versions of more modern and higher-end treadmills are definitely nicer and quieter.

 

[willeng]

Hi Everyone,
About 10 yrs ago I was in need for a small tumbler for Stainless Steel components & used a very low powered geared motor from a Microwave Oven, it must be only about 4W & just plugs into the mains supply. My wife used it continuously for years tumbling stones.
I have made many things from these including being used as the drive motor for a profile cutter etc & you can find hundreds of them at scrap yards for next to nothing.

This is the type I use, they are Japanese & they last forever, see picture below.

I'll probably get my head chewed off for saying this but I see there is a bit of an argument about the mains supply thing again.

It is far better in my opinion to EDUCATE people of any age about mains power dangers instead of ignoring or not answering there questions & try to help them rather than shove them aside.
People will play with mains power & millions all around the globe do it everyday, just look at the internet & you will see this.
You may think that forums such as this is not the place to be playing around with mains power but it is far better to teach rather than to ignore them as they will do it anyway?

What is worse, playing with 900W or buying a 17yr old a 450kW car to drive around in?
Forums such as this with the amount of expertise available should be the place that the inexperienced can turn to with confidence to be able to get an understanding & make things safe to handle.
Look at how many novices play with Valve amplifiers etc without knowing anything.

Professionals teach & there are many here that should do just that instead of being paranoid about something that 3 year olds plug into everyday all around the globe?