Is a starter necessary?

[graham-xrf]

A beautiful design. I have seen several Rick Sparber spots, nice work all.

What I would comment on here is the particular switch used and its' limitations. First of all, that design switch is available in two pole for use on 240 Volts. In the UK and other 240 volt line countries however, a two pole switch isn't usually necessary. A phase to neutral connection is the norm.

Now, the down side to my remarks. The contacts in any "light" switch are not rated for motor use any larger than a pedestal fan. A "Dremel" is fine, a drill press isn't. A lathe or table saw is out of the question, don't even consider it.

Absolutely! About using domestic lighting switches, you said it all.

There is a reason why there are switches specifically intended for motors. Particularly, there are design features in contactors to make them suitable for switching inductive loads. A machine motor is an inductive load. In concept a contactor is just a "relay", but a special one. When the armature of the contactor pulls in it in effect makes short bars contact on both ends. Also, you are switching both the line, and the neutral return.

There is a whole class of contactor we hobby machinists don't need, known as "safety relays" where internally, all connections circuits go through two breaks in series, just in case one welds closed, and all normally open switches are internally two switches in parallel, just in case one stays open. All they do is switch other contactors or SSRs. Safety relay systems just for policing E-stops can get complicated, and very, very costly!

Like I said - we don't need them, but we do need to be realistic about how motor starting and stopping works, and use something up to the job. They need not be expensive. Most of us manage with motors less than 2HP.

I guess I have a bit of a bias, now that I no longer tangle with 150HP motors pumping jet fuel. Even for the "very small" motors that drive my lathes, I would never consider a domestic resistive load lighting switch. White things with rockers? No thanks!

 

[hman]

OK, you both make a good point. Back when I wrote the article in 2009, a Dremel was pretty much all I'd used the switch design for, so there wasn't a big issue.

It's also been pointed out to me that if the switch is left on and power fails, whatever is connected will start up by itself when power returns. Of course, that's also the case with any equipment (like a small lathe) that has a "sustained" power switch.

That said, I do have this switch on several of my motorized tools. I'm pretty sure I made it a point to buy 20 amp rated Decora switches, just because I was concerned about motor inrush loads. If needed, I could wire the switch to a suitable motor contactor for higher current or 230 volt loads.

Anyway, the following tools make use of the safety switch. Note the installation dates and motor horsepower info. None of the switches have given me ANY trouble since being installed.

Craftsnman-Parks 18" vertical wood bandsaw, horsepower unknown, installed 2013, used 1-2 times per week.
Harbor freight 14" wood bandsaw, 1 "Chinese" horsepower, installation date unknown, used 1-2 times per month.
Delta 1x42 belt/disk sander, ⅓ HP, installed 2013, used several times per day.
Grizzly G4000 9x20 lathe, ¾ "Chinese" horsepower, installed 2013, sold 2019, used 2-3 times per week when I owned it.

 

[projectnut]

I like your Sheldon lathe Projectnut!!
How come the chip pan is so clean?

Just to prove the machine does get used here are a couple pictures of it with the adaptor for putting marine antifreeze in the new pressure washer. Note there are a few chips in the pan. As for the adaptor it's another one of those protracted projects. What was supposed to take an hour is still sitting in the chuck a day later. With all my recent rearranging of the shop I put my short internal threading tools in a "special place". Now I have to find the special place to do some internal, and external threading. If this turns out like most "little projects" it'll take longer to find the tooling than it will to cut the threads.