On 02/12/14 2:28 AM, default wrote:> On 29 Nov 2014 21:31:05 GMT, Jasen Betts <jasen@xnet.co.nz> wrote: > >> 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. > > One hopes that it wouldn't be expected to run stalled for very long, > and the inrush/peak current of diodes is much higher than steady state > - since we see the same thing on linear power supplies with large > electrolytic capacitors. > > 1N4XXX series of diodes are good for 1 amp and can carry a surge > current of 30 amps. > >> >>> 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. > > > You might be correct with table saws where they use an induction motor > and keep a small sheave at the blade for that reason, but AC/DC motors > used in bench top table saws, hand held circular saws, miter chop > saws, etc. are direct drive (blade goes on the motor shaft - and > frequently the field and windings are offset a bit so the motor shaft > is not concentric with the housing, but of course, still concentric > with the field iron) >I used to repair such and I have never seen one that directly drove the blade, they all had reduction gears.
How to slow down RPM of miter saw?
Started by ●November 29, 2014
Reply by ●December 1, 20142014-12-01
Reply by ●December 1, 20142014-12-01
Rheilly Phoull <rheilly@bigslong.com> wrote:> default wrote: >> Jasen Betts <jasen@xnet.co.nz> 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. >>> >>> starting (stall) current could be 100A or more. >> >> One hopes that it wouldn't be expected to run stalled for very long, >> and the inrush/peak current of diodes is much higher than steady >> state - since we see the same thing on linear power supplies with >> large electrolytic capacitors. >> >> 1N4XXX series of diodes are good for 1 amp and can carry a surge >> current of 30 amps. >> >>> >>>> 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. >> >> >> You might be correct with table saws where they use an induction >> motor and keep a small sheave at the blade for that reason, but AC/DC >> motors used in bench top table saws, hand held circular saws, miter >> chop saws, etc. are direct drive (blade goes on the motor shaft - and >> frequently the field and windings are offset a bit so the motor shaft >> is not concentric with the housing, but of course, still concentric >> with the field iron) >> > I used to repair such and I have never seen one that directly drove > the blade, they all had reduction gears.Not that it matters, but the argument is lost... The original point was that the motor is spinning too fast to be an induction motor. Therefore, the 5500 RPM specification either applies to the motor or the motor is spinning faster than that. Talking about reduction gears doesn't help refute the fact that it's a brushed universal motor. But of course you may argue about whatever pointless thing you wish to argue about...
Reply by ●December 1, 20142014-12-01
>> > I used to repair such and I have never seen one that directly drove the > blade, they all had reduction gears.http://www.bing.com/images/search?q=direct+drive+saws&qpvt=direct+drive+saws&FORM=IGRE
Reply by ●December 1, 20142014-12-01
default wrote:> > 1N4XXX series of diodes are good for 1 amp and can carry a surge > current of 30 amps.** Errr, that rating is for one half cycle at 50/60 Hz. The time it takes to put a of charge in a filter electro. IOW way shorter than a motor's start up surge. .... Phil
Reply by ●December 1, 20142014-12-01
In article <enip7a17pheiant16dhullsb1hma9us1mq@4ax.com>, etpm@whidbey.com says...> > On Sat, 29 Nov 2014 19:18:57 +0000, Baron <baron@linuxmaniac.net> > wrote: > > >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. > Every power miter saw I have seen in the last 25 years had a universal > motor. They also have a circuit that dynamically brakes the motor when > the trigger is released. I wonder if that circuit would have any > negative effect on certain speed controllers. Probably not. In any > case universal motors have poor speed regulation. And lowering the > voltage or current significantly my make the speed regulation really > bad. As I recall from reading about it this is partly because the > brushes are located in the best place for the least amount of sparking > and changing the voltage or current will change this location. > EricIt would be interesting to how a series motor can be dynamically braked in a hand tool? Jamie
Reply by ●December 2, 20142014-12-02
On 2014-12-01, Tom Biasi <tombiasi@optonline.net> wrote:> >>> >> I used to repair such and I have never seen one that directly drove the >> blade, they all had reduction gears. > > http://www.bing.com/images/search?q=direct+drive+saws&qpvt=direct+drive+saws&FORM=IGREMany of those images are clearly gear driven saws. -- umop apisdn
Reply by ●December 2, 20142014-12-02
On 12/2/2014 12:23 AM, Jasen Betts wrote:> On 2014-12-01, Tom Biasi <tombiasi@optonline.net> wrote: >> >>>> >>> I used to repair such and I have never seen one that directly drove the >>> blade, they all had reduction gears. >> >> http://www.bing.com/images/search?q=direct+drive+saws&qpvt=direct+drive+saws&FORM=IGRE > > Many of those images are clearly gear driven saws. >I can't help that. Many are not. The statement was "I have never seen one that directly drove the blade"
Reply by ●December 2, 20142014-12-02
On Tue, 02 Dec 2014 05:29:09 +0800, Rheilly Phoull <rheilly@bigslong.com> wrote:>On 02/12/14 2:28 AM, default wrote: >> On 29 Nov 2014 21:31:05 GMT, Jasen Betts <jasen@xnet.co.nz> wrote: >> >>> 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. >> >> One hopes that it wouldn't be expected to run stalled for very long, >> and the inrush/peak current of diodes is much higher than steady state >> - since we see the same thing on linear power supplies with large >> electrolytic capacitors. >> >> 1N4XXX series of diodes are good for 1 amp and can carry a surge >> current of 30 amps. >> >>> >>>> 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. >> >> >> You might be correct with table saws where they use an induction motor >> and keep a small sheave at the blade for that reason, but AC/DC motors >> used in bench top table saws, hand held circular saws, miter chop >> saws, etc. are direct drive (blade goes on the motor shaft - and >> frequently the field and windings are offset a bit so the motor shaft >> is not concentric with the housing, but of course, still concentric >> with the field iron) >> >I used to repair such and I have never seen one that directly drove the >blade, they all had reduction gears.Some do some don't. How long ago was this? I have an old Skill Saw with a pair of gears, and a fairly old Sears and newer B&D that are direct drive, and depth of cut is nothing to brag about.
Reply by ●December 2, 20142014-12-02
On Mon, 1 Dec 2014 16:34:39 -0800 (PST), Phil Allison <pallison49@gmail.com> wrote:> default wrote: > >> >> 1N4XXX series of diodes are good for 1 amp and can carry a surge >> current of 30 amps. > > > ** Errr, that rating is for one half cycle at 50/60 Hz. > > The time it takes to put a of charge in a filter electro. > > IOW way shorter than a motor's start up surge. > > >.... PhilI know. I just looked up a 20 amp DO4 case diode and current surge is 400 amps. I couldn't find any definitive start-up specs for AC/DC motors just some comments like "double" or "several times" the rated current. When they say the motor is a 14 amp motor - they do mean it might pull 14 amps when cutting. My bench table saw has a universal motor in it and is rated at 15 amps. I've popped the 10 amp breaker on the power strip a half dozen times in 5+ years, and then cutting things like wet 4X4 wood with a dull blade. The power strip probably has a cheap thermal breaker on it, the 20 amp house circuit has never tripped. I can rip 8 foot 2X4's without tripping a breaker. I can't prove it, but would bet serious money it would work with a 20 amp diode.
Reply by ●December 2, 20142014-12-02
John Doe <always.look@message.header> wrote in news:m5d282$si5$1@dont- email.me:> 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. >I missed a part of the discussion due to the limitations of my news servers so I may tell no news. Nevertheless: This type of machines usually have universal motors. They can be slowed down by ordinary dimmer like controllers. This however is not very effective as lowering the voltage will make the speed very dependend of the load. The best way to control this type of motors is using DC and PWM. In my experience Al will not be cut very effective by an abrassive disk. The soft Al will smooth the disk by filling the spaces in it. I got the best results using a saw blade with hardened steel teeth as for hardwood, petrus bitbyter
