Forums

How to slow down RPM of miter saw?

Started by John Doe November 29, 2014
The motor runs on standard USA 120 V 60 Hz, 14 A, at 5500 RPM. 

What's the easiest way to slow down the RPM? 

What about simply adding a diode in series on the power cord? 

Any advice, references, and links would be appreciated. 

Thanks.
On 11/29/2014 1:11 PM, John Doe wrote:
> The motor runs on standard USA 120 V 60 Hz, 14 A, at 5500 RPM. > > What's the easiest way to slow down the RPM? > > What about simply adding a diode in series on the power cord? > > Any advice, references, and links would be appreciated. > > Thanks. >
The saw is designed to run at a certain RPM and blade size. Changing either is not recommended. I know I didn't answer your question. My response was in the name of safety.
John Doe prodded the keyboard

> The motor runs on standard USA 120 V 60 Hz, 14 A, at 5500 RPM. > > What's the easiest way to slow down the RPM? > > What about simply adding a diode in series on the power cord? > > Any advice, references, and links would be appreciated. > > Thanks.
This would depend upon the type of motor ! If we assume a universal motor then a thyristor or triac phase controler that can handle the maximum current plus 100% could be used. An induction motor would need a variac (variable transformer) or one of the electronic devices used specifically for this purpose. But I would doubt that what you have uses an induction motor. -- Best Regards: Baron.
Have you ever even used a miter saw? 

More often the design of a common inexpensive tool takes into 
consideration the cheapness of its parts. A more expensive tool might 
run at a faster or slower RPM and be designed to do the same thing, only
better. Safety doesn't necessarily have anything to do with lowering the
RPM. If you want to go on a crusade for miter saw safety, you should 
talk about wearing eye protection and keeping your hands away from the 
cut. In fact, I am using it for aluminum. Obviously that's not what it's
designed for but that happens to be what many of us, including
professional metalworkers, use miter saws for. 

Miter saws are not for people who are overly concerned about safety. 
They are inherently hazardous. It also isn't for people who have no
basis for their understanding of safety. I've come across people who
don't really know what they're talking about that say you should use
gloves "in the name of safety", but that actually increases the risk. 

I'm trying to solve a problem that has to do with a potential hazard. 
And it requires a lower RPM. 

I think there is a safety consideration with lowering the RPM, but the 
reply author probably doesn't even know what that might be. If the idea 
were to increase the RPM, then there would be an obvious possible 
concern for safety that any Joe might recognize. 

I just bought a cheap abrasive cutoff disc made by a well-known
manufacturer that's supposed to cut metal. The thing doesn't cut
aluminum and therefore trying to do so is a safety hazard. 

Using a miter saw is not for the meek.


Tom Biasi <tombiasi@optonline.net> wrote in news:Lxoew.792810$1s.710374@fx05.iad:

> On 11/29/2014 1:11 PM, John Doe wrote: >> The motor runs on standard USA 120 V 60 Hz, 14 A, at 5500 RPM. >> >> What's the easiest way to slow down the RPM? >> >> What about simply adding a diode in series on the power cord? >> >> Any advice, references, and links would be appreciated. >> >> Thanks. >> > The saw is designed to run at a certain RPM and blade size. Changing > either is not recommended. > I know I didn't answer your question. My response was in the name of safety.
On Sat, 29 Nov 2014 18:11:14 +0000 (UTC), John Doe
<always.look@message.header> wrote:

>The motor runs on standard USA 120 V 60 Hz, 14 A, at 5500 RPM. > >What's the easiest way to slow down the RPM? > >What about simply adding a diode in series on the power cord? > >Any advice, references, and links would be appreciated. > >Thanks.
If the rotor is AC/DC (most inexpensive power tools like drills, circular saws, and miter saws) a diode is an excellent choice to just drop some voltage and slow it down. Since the thing can probably pull a few amps you want high current diode; 20+ amps would be my guess and whatever line voltage you run at. AC/DC motors are easily distinguished because they make lots more noise than induction motors. AND you are saying that you have 5500 RPM? That is too fast to be an induction motor on 50 or 60 cycles.
default <default@defaulter.net> wrote: 

> John Doe <always.look@message.header> wrote: > >>The motor runs on standard USA 120 V 60 Hz, 14 A, at 5500 RPM. >> >>What's the easiest way to slow down the RPM? >> >>What about simply adding a diode in series on the power cord? >> >>Any advice, references, and links would be appreciated.
> If the rotor is AC/DC (most inexpensive power tools like drills, > circular saws, and miter saws) a diode is an excellent choice to just > drop some voltage and slow it down. > > Since the thing can probably pull a few amps you want high current > diode; 20+ amps would be my guess and whatever line voltage you run > at. > > AC/DC motors are easily distinguished because they make lots more > noise than induction motors. AND you are saying that you have 5500 > RPM? That is too fast to be an induction motor on 50 or 60 cycles.
Yes, I'm sure it's an AC/DC motor. It's a cheap miter saw. So if it's an AC/DC motor, using a diode drops the voltage which in turn reduces the RPM? Using a diode won't just reduce the power? It's obviously the easiest possible attempt, that and providing a simple (properly rated) switch to change between the two power levels.
On 2014-11-29, John Doe <always.look@message.header> wrote:
> The motor runs on standard USA 120 V 60 Hz, 14 A, at 5500 RPM. > > What's the easiest way to slow down the RPM?
Unplug it! Do you see what lack of detail does to the quality of the answers you can expect.
> What about simply adding a diode in series on the power cord?
That will probably work, but this path (reducing supply voltage) is a good way to burn out the motor. if you follow this path your warranty is void.
> Any advice, references, and links would be appreciated.
If this is an important tool, replace it with one designed to run at the correct RPM. -- umop apisdn
On Sat, 29 Nov 2014 20:35:31 +0000 (UTC), John Doe
<always.look@message.header> wrote:

>default <default@defaulter.net> wrote: > >> John Doe <always.look@message.header> wrote: >> >>>The motor runs on standard USA 120 V 60 Hz, 14 A, at 5500 RPM. >>> >>>What's the easiest way to slow down the RPM? >>> >>>What about simply adding a diode in series on the power cord? >>> >>>Any advice, references, and links would be appreciated. > >> If the rotor is AC/DC (most inexpensive power tools like drills, >> circular saws, and miter saws) a diode is an excellent choice to just >> drop some voltage and slow it down. >> >> Since the thing can probably pull a few amps you want high current >> diode; 20+ amps would be my guess and whatever line voltage you run >> at. >> >> AC/DC motors are easily distinguished because they make lots more >> noise than induction motors. AND you are saying that you have 5500 >> RPM? That is too fast to be an induction motor on 50 or 60 cycles. > >Yes, I'm sure it's an AC/DC motor. It's a cheap miter saw. So if it's an >AC/DC motor, using a diode drops the voltage which in turn reduces the >RPM? Using a diode won't just reduce the power? >
Yes it will reduce the "power" since power is RPM versus torque. You will reduce the RPM to something less than half with less power (all things being equal) but the motor will still behave like an AC/DC motor and draw more current and produce more torque as the load tries to slow it down - something that won't happen with all simple lamp-dimmer triac/thyrister schemes to slow down a motor.
>It's obviously the easiest possible attempt, that and providing a simple >(properly rated) switch to change between the two power levels.
Yeah, single pole double throw center off toggle switch would be a good choice providing you can't accidentally bump it on. OR A diode and single pole single throw switch; a safer bet with the switch shorting the diode - shorted is full RPM, open half. I put a large size lamp dimmer in place of a powerstat (variable transformer) in a laboratory centrifuge with no problems - but a centrifuge has a constant load, unlike a saw. My substitution saved several hundred dollars and a week of downtime - and was still working 5 years later. With lamp dimmers and AC/DC motors you can slow the motor down well enough with the dimmer, but unless the dimmer is designed to handle inductive loads, the torque falls off as the load increases and so the motor slows down faster than the load increases. Undesirable in a saw...
On 2014-11-29, default <default@defaulter.net> wrote:
> On Sat, 29 Nov 2014 18:11:14 +0000 (UTC), John Doe ><always.look@message.header> wrote: > >>The motor runs on standard USA 120 V 60 Hz, 14 A, at 5500 RPM. >> >>What's the easiest way to slow down the RPM? >> >>What about simply adding a diode in series on the power cord? >> >>Any advice, references, and links would be appreciated. >> >>Thanks. > > If the rotor is AC/DC (most inexpensive power tools like drills, > circular saws, and miter saws) a diode is an excellent choice to just > drop some voltage and slow it down. > > Since the thing can probably pull a few amps you want high current > diode; 20+ amps would be my guess and whatever line voltage you run > at.
starting (stall) current could be 100A or more.
> AC/DC motors are easily distinguished because they make lots more > noise than induction motors. AND you are saying that you have 5500 > RPM? That is too fast to be an induction motor on 50 or 60 cycles.
Pretty-much all types of circular saws have some sort of gearchain or belt drive between the motor and the blade, the blade rarely runs at the same speed as the motor. One reason for this is to offset the bulk of the motor from the plane of the blade axle, allowing deeper cuts with a given size of blade. So, blade speed is not indicative of motor speed. -- umop apisdn
I don't know about New Zealand, but in United States English the 
expression "slow down" does not mean "stop". And in fact I am not asking 
for a specific RPM, therefore that specification is not needed, as the 
helpful replies already indicate. 

As for "voiding the warranty". I can void a warranty before even touching 
a product...


-- 
Jasen Betts <jasen xnet.co.nz> wrote in news:m5dd6r$c6d$2 gonzo.reversiblemaps.ath.cx:

> Path: eternal-september.org!mx02.eternal-september.org!feeder.eternal-september.org!news.glorb.com!news.astraweb.com!border5.newsrouter.astraweb.com!not-for-mail > From: Jasen Betts <jasen xnet.co.nz> > Newsgroups: sci.electronics.basics > Subject: Re: How to slow down RPM of miter saw? > Date: 29 Nov 2014 21:18:19 GMT > Organization: JJ's own news server > Message-ID: <m5dd6r$c6d$2 gonzo.reversiblemaps.ath.cx> > References: <m5d282$si5$1 dont-email.me> > X-Face: ?)Aw4rXwN5u0~$nqKj`xPz>xHCwgi^q+^?Ri*+R(&uv2=E1Q0Zk(>h!~o2ID 6{uf8s;a +M[5[U[QT7xFN%^gR"=tuJw%TXXR'Fp~W;(T"1(739R%m0Yyyv*gkGoPA.$b,D.w:z+<'"=-lVT?6 {T?=R^:W5g|E2#EhjKCa+nt":4b}dU7GYB*HBxn&Td$ f%.kl^:7X8rQWd[NTc"P"u6nkisze/Q;8 "9Z{peQF,w)7UjV$c|RO/mQW/NMgWfr5*$-Z%u46"/00mx-,\R'fLPe.)^ > User-Agent: slrn/pre1.0.0-18 (Linux) > Lines: 22 > NNTP-Posting-Host: c4b94cb6.news.astraweb.com > X-Trace: DXC=X?i4J4aj=24UH[0COH:iH0L?0kYOcDh :S5oH5G9TkZ=Q4`Yco4[6E:l9B_G1R=S=7]YVTRZ:Ha`7T2B9638eA]6]c1WZ_ml=I8K<_C1=h8Ji; > Xref: mx02.eternal-september.org sci.electronics.basics:44163 > > On 2014-11-29, John Doe <always.look message.header> wrote: >> The motor runs on standard USA 120 V 60 Hz, 14 A, at 5500 RPM. >> >> What's the easiest way to slow down the RPM? > > Unplug it! Do you see what lack of detail does to the quality of the > answers you can expect. > >> What about simply adding a diode in series on the power cord? > > That will probably work, but this path (reducing supply voltage) > is a good way to burn out the motor. if you follow this path your > warranty is void. > >> Any advice, references, and links would be appreciated. > > If this is an important tool, replace it with one designed to run at > the correct RPM. > > -- > umop apisdn > > >