Path: ...!weretis.net!feeder9.news.weretis.net!panix!usenet.blueworldhosting.com!diablo1.usenet.blueworldhosting.com!nnrp.usenet.blueworldhosting.com!.POSTED!not-for-mail From: Richard Smith Newsgroups: rec.crafts.metalworking Subject: Re: rod-mill project - "mains" electric motor advice Date: Tue, 22 Apr 2025 08:44:18 +0100 Organization: BWH Usenet Archive (https://usenet.blueworldhosting.com) Message-ID: References: MIME-Version: 1.0 Content-Type: text/plain Injection-Info: nnrp.usenet.blueworldhosting.com; logging-data="87196"; mail-complaints-to="usenet@blueworldhosting.com" User-Agent: Gnus/5.13 (Gnus v5.13) Cancel-Lock: sha1:Rl9ifzODKlYNmSeIoVFXHJT4n7Q= sha1:NZBK5fiOkc9prgOAkScyhPK07ek= sha256:1XtGAIY6OI/QBuGC1WOyAU/IsJ+DTiQigkiJa+6Q0o8= sha1:axv0P/QQ8su019krC9d4Zz+1GlE= sha256:ep7ZGP/ZvNvHmf3z5EnoH7qHrNcacOi5e1pqfO3KWeo= Bytes: 4599 Lines: 82 "Jim Wilkins" writes: > "Richard Smith" wrote in message news:m1wmbd29er.fsf@void.com... > > Hi everyone > I have been shown how to do this with power-electronics and > "off-the-shelf" gearbox, etc. With all speed-control needed. > A friend had made a small welding positioner. Hence adapted it: > * VFD - 1ph-to-3ph > v > * 3ph induction motor > v > * worm-drive gearbox > You turn a knob setting the output Hz. Adequate speed range. > > Having seen this - that it works and does everything wanted - will > simply do it this way. > Have friend's equipment on "unspecified loan' in my car to take home and > play with more. > > ----------------------------------------- > > That is an excellent way to learn what works. The potential problems > are cost and custom machining. In that instance I'd look up and save > the components' data sheets and see how their max power ratings > compare to what was needed and what you intend to do. I've been burned > by guessing that something was good enough, my sawmill left a trail of > broken ball bearing innards until I switched to a more reputable and > expensive brand for the blade guides. > > I hardly ever find the same device twice as second hand and must > decide on the spot if what I found is suitable, which may depend on > its power rating. People dispose of what they can't use, typically > because they are either inadequate or broken. > I tested that contactor for pull-in voltage and contact resistance. I will go with "off the shelf". Now seen what's needed. Time si too valuable. * have the thing working (hopefully!) and making inroads here in Cornwall * free to get on with other things I have to do - would cost me more in what I have not done than I could save not "placing orders" for what is spec'd for the job. One "blessing". Gearbox must for sure have a torque rating. Derive torque. Found it's gloriously simple - relation of power, torque and revs. P=tau.omega P=power (Watts) tau = torque (Newton.metres) omega = rotation-rate (radians/s) Latter makes total sense - well it does for me :-) Radian is where a radius is wrapped around the circumference. Very often gives vast simplifications (compared to working in angular Degrees or Revs Per Minute, etc.). Prompted that way, I can easily see from first principles how "P=tau.omega" can be derived, giving total satisfaction in applying it. So I can look through spec.sheets for "off-the-shelf" gearboxes. I have a 30:1 gearbox on loan. However, reckon 7:1 would make the drive "synchronous" (if ran motor at mains frequency, would give the right drive speed). Of course you need speed adjustment to make the mill(s) work exactly right - but what you are asking is very achievable - say +-25% - which an induction motor can do no problem. [welding positioner - is so low power draw for small parts that eg. 10% of the mains synchronous speed it is designed for is not a problem] So going to have to get a 7:1 ish gearbox for mill. Speed control should be wide enough to run rod-mills and ball-mills on the same rollers-on-a-frame, no mechanical changes needed. I calculated for the "metallurgical" part of the rod-mill - everything which is and is within the "shell" ("drum"): * 65RPM of shell rotation rate * 127W of power draw