Replies

1. 
   nikkiwood | Aug 19, 2004 04:29pm | #1

   I am no electrician, and I don't know what a "variac" is -- but I do know there are specific devices offered in many tool catalogs to allow your router to work at variable speeds.

   However, if you are working with a medium sized router (1 1/2 - 2 1/4 HP), slowing down the speed is rarely necessary.

   Using the 1" roundover bit you mention is a case in point; if you make multiple passes, and don't hog off too much material in a single pass, your router will do fine at full speed.

2. 
   JohnWW | Aug 19, 2004 04:41pm | #2

   Dave,

   A Variac is an adjustable transformer, it will simply lower the voltage to the tool.  This will cut the speed but it will also significantly reduce the power, which will make it easy to bog the router down or stall it completely.  You can use it, but you'll have to take lighter passes to keep the speed up to a useful level.

   The modern electronic speed controls reduce the speed but preserve most of the power so they are more useful for motor speed control.  You can buy a plug in electronic speed control from a number of woodworking suppliers for under $40.00.

   John W. 

1. 
   BarryR | Aug 19, 2004 07:04pm | #3

   John is correct, but since this is a roundover bit, you can take small cuts & lower the bit as you go.  That will take care of the power issue.  BTW, did the bit come with a max speed recommendation?

1. 
   davd | Aug 20, 2004 12:17am | #4

   Thank you for the help.  The bit did not come with a speed reccomendation, looking at the size of the bit it just seemed like something awful big to have spinning at 20,000+RPM.  Iwill look into speed controlers, I know that I could get away with running full speed, but I still feel hesitant, and would be more comfortable with a slower speed.

   Thank you,

   DAVE

1. 
   cudavid | Aug 21, 2004 02:10am | #5

   Hi, I have a large old PC router , 1 speed, I have used a variac for years, NO problems, works great w/ BIG bits!

3. 
   user-277699 | Aug 23, 2004 02:20am | #6

   Dave,

   I have both a Variac and an Electronic Router Speed control.  A variac (variable autotransformer) works great for dimming lights or reducing output from electric heating devices (like soldering irons), but shouldn't be used with motors. 

   Electronic Router Speed controls have their shortcomings.  They are intended only for use with "Universal" (brush-type) motors.  They will not work properly with induction motors.  If you use them with motors that have any built-in electronic circuitry such as speed control, feedback circuitry to maintain power under load, or "soft start" circuitry, you risk damaging that circuitry.  Also, you have no easy way to gauge how much speed reduction you really get.  I tried using one such speed control with my Milwaukee 5680 2-Hp router once.  As I dialed the speed down it SOUNDED as if it was really slowing a lot.  Later, I borrowed an optical non-contact photo-tachometer and actually measured the speed reduction.  Full speed of the 5680 exceeds 26,000 RPM.  With the speed control in circuit, the router's motor stalled at 22,000 RPM!  This was still 4,000 RPM faster than the 18,000 RPM which was a manufacturer's recommended maximum for the bit I was using.  After much searching for other speed controls I ended up purchasing a DeWalt DW618 Router to use when I need speeds less than "full throttle."

   Musician42

   PS - An autotransformer is a type of transformer where the primary (input) winding and the secondary (output) winding have portions in common.  There is NOT electrical isolation between the input and output windings.

1. 
   BarryR | Aug 23, 2004 09:26pm | #7

   I'm not sure why you say you shouldn't use an autotransformer with motors.  Just as with an electronic control, you can only use them with universal motors; induction motor speed cannot be controlled by varying the voltage.  I have been using a small Variac on my single speed Dremel Moto Tool for twenty years without any problems.  As for electronic controls, my PC690 will run at less than 5000 RPM with my electronic control.  While your router may stall at 22000 RPM it's more likely the tach was misreading the speed - a common problem with optical tachs.  I own a strobe/tach so I know how easy it is to get a wrong reading from these devices.

   My advice: if you already own a Variac that can handle the motor current, give it a try.  You won't hurt anything & may find it suits your needs perfectly.  If not, you can buy an electronic control for as little as $20.  The only problem with the really cheap ones is that the speed may vary - "hunt" - when the router's not under load, but they'll hold a steady speed once you start to cut.

1. 
   Ram22 | Dec 11, 2006 06:23pm | #8

   I am trying to make cabinet doors.  I have a brush type single speed 3hp (so the plate says) router rated at 20 amps without speed control.  The large raised panel bits are rated at 7000 rpm while the no load speed of the router is 26000 rpm.  I had a 15amp rated speed control that I tried with it but the router has very little power when slowed down.  Do you think the speed control could be the cause?

1. 
   Ray | Dec 12, 2006 02:20am | #9

   If you're using a variac, yes that's the problem.  That just lowers the voltage, causing the motor to overheat.  Routers have a "universal" motor (brushes), try a solid-state speed control - picture a really heavy-duty lamp dimmer.