How to slow down RPM of miter saw?

I have no problem cutting aluminum. The problem I have is better
discussed in an appropriate USENET group.

I would suggest that you cruise on over to the metalworking group
to discuss your theories. It's a big group with lots of participants.
But hardly anyone on USENET appreciates unformatted Google Groups posts...



jurb6006@gmail.com wrote in news:e8b36fa1-96a4-43f9-b69c-203513237d14@googlegroups.com:

I jumped through here to tell you, it is improper to reduce the RPM in this case. what you need is the proper blade. In most cases a bandsaw will do what you eant better, again, with the right blade. however sionce you posted it I am going to assume you have a eason to use the chop saw, which is what some of us call lower end miter saws. (or maybe you are cuting a compound angle, whatever reason)

A miter saw is NOT a lathe where you calculate cutting speed in SFM. the first thing you need is a many toothed carbide tipped blade. What's more, when you cut, you FEED it, donot babyu it or the aluminum will clog up the blade teeth.

Keep the RPM up and the feed slow, very slow. If you need to cut really fast, there are blades made for that.

With a half decent carbide tipped blade I can cut muffler pipes and shit, bumpers, all kinds of things. The problem is that it is so easy to overload the blade and fuck it all up. AND LOWERING THE RPMS WIL NOT REDUCE THE CHANCES OF THIS.

And the LAST thing you want is for that blade to stall in aluminum. and there is almost no way without a servo circuit, to make sure it does not stall under an underpower condition, which you must create to lower the RPMs. If youy REALLY have to lower the RPMs, do it with gears. That is my advice. Lowering the motor RPMs electronically is a bad move, a wrong move, and will make a mess.

Of course some will try it anyway, if you do, just make sure you are ready for that torque and shit when the thing stalls.
Click to expand...
 
John Doe wrote:

DROK AC 110V 3000W SCR

http://www.amazon.com/DROK-Electronic-controller-Governor-
Thermostat/dp/B00BXUCWQG/ref=cm_cr_pr_product_top

Will that work?
Click to expand...

** Possibly it might do.

> Will it increase the current when the load increases?

** Doing that requires back emf sensing as found on SCR speed controllers for drills, food mixers etc. These are very good at maintaining full torque down to a few hundred rpms but are not made for large motors.

The above unit appears to be triac based (since it can de used as a dimmer) as are nearly all speed controls fitted into mains powers hand drills.

The sort speed control YOU are asking for is specialised, designed expressly for high powered AC motors (like routers) with back emf sensing and includes a soft start feature - like the one on this page:

http://www.mlcswoodworking.com/shopsite_sc/store/html/smarthtml/pages/speed_control.html

The 20Amp model looks worth a try.


..... Phil





One comment said that it chops the AC signal amplitude and that it's
hard on motors. Is that a concern about increased current when the load
is too much?

If it works, 20 bucks is very attractive.

--






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?
Click to expand...
 
On the subject of safety...

Here you have a major retailer Lowe's hardware showing a guy wearing
gloves while using a miter saw...

http://www.lowes.com/

Hover your pointer over "Ideas and How-tos".

In fact, as the vast majority of professionals will tell you, wearing
gloves while using such a power tool is a bad thing.

Stuff unnecessarily amputated...

https://www.osha.gov/pls/imis/accidentsearch.accident_detail?id=200651750

At approximately 11:30 a.m. on July 8, 2010, Employee #1 was operating a
CTD model M25R chop saw (powered miter box type saw) and cutting aluminum I
beams. She was wearing gloves when the saw blade caught the gloves and
pulled her fingers into the blade. The blade amputated her left thumb, and
index, middle and ring finger at the distal interphalangeal joint.
Additionally, the company had rules about not wearing gloves while
operating the chop saw. After the accident, she was transported to a
medical center where she received treatment and was hospitalized.
 
etpm@whidbey.com wrote:

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.

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.
Click to expand...

I'm probably going to try the diode method first. There are some
ultracheap 1000 V 10 amp diodes available. I might put some of them in
parallel. I doubt that has the same problem. And then it can be used for
any other appropriate brushed universal motor device.
 
Baron <baron@linuxmaniac.net> wrote in news:m5ik9q$rf5$1@dont-email.me:

John Doe prodded the keyboard

etpm@whidbey.com wrote:

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.

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.

I'm probably going to try the diode method first. There are some
ultracheap 1000 V 10 amp diodes available. I might put some of them
in parallel. I doubt that has the same problem. And then it can be
used for any other appropriate brushed universal motor device.

I suspect that it will not achive the desired effect !
Click to expand...

What effect do you suspect it will have?!

--



Recall that a universal motor will happily run on ac or dc, the motor
brush gear simply chops up a dc supply to create an alternating field.
Click to expand...
 
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.
Click to expand...

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...
 
On Tue, 2 Dec 2014 16:22:14 -0500, "Maynard A. Philbrook Jr."
<jamie_ka1lpa@charter.net> wrote:

In article <bh3s7ah06br8cdtal7q8dmuggna2rchq16@4ax.com>,
etpm@whidbey.com says...

On Mon, 1 Dec 2014 21:06:34 -0500, "Maynard A. Philbrook Jr."
jamie_ka1lpa@charter.net> wrote:

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.
Eric

It would be interesting to how a series motor can be dynamically braked
in a hand tool?

Jamie
An induction motor can be dynamically braked by connecting DC to the
windings. This can be done with a capacitor and a diode. I think that
if the brushes are shorted and DC is connected to the windings this
would work like an induction motor. See this link:
http://www.google.com/patents/US3548276
It is from 1970.
Eric

The key is DC current... where does one get that from a device that
only has an off/on switch to a series motor with no magnets for self
generation?

You can dynamically brake a series motor but it's not as simple as
just connecting the A1 and A2 together.

Jamie


Jamie
Click to expand...
I know it is not that simple. Please follow the link or just search
for the patent number. It describes a system that supplies the DC.
Eric
 
In article <n2nu7aljnn5728uo23vupuleuhrb3r19a8@4ax.com>,
etpm@whidbey.com says...
You can dynamically brake a series motor but it's not as simple as
just connecting the A1 and A2 together.

Jamie


Jamie
I know it is not that simple. Please follow the link or just search
for the patent number. It describes a system that supplies the DC.
Eric
Click to expand...

I guess you missed the point, oh well.


Jamie
 
On Wed, 3 Dec 2014 17:00:30 -0500, "Maynard A. Philbrook Jr."
<jamie_ka1lpa@charter.net> wrote:

In article <n2nu7aljnn5728uo23vupuleuhrb3r19a8@4ax.com>,
etpm@whidbey.com says...

You can dynamically brake a series motor but it's not as simple as
just connecting the A1 and A2 together.

Jamie


Jamie
I know it is not that simple. Please follow the link or just search
for the patent number. It describes a system that supplies the DC.
Eric



I guess you missed the point, oh well.


Jamie
Click to expand...
Greetings Jamie,
I guess I did miss the point. Would you please explain it to me?
Seriously.
Thanks,
Eric
 
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