i noted that there are few router whom offer variable speed and others are just 1 kind of speed. as newbie, i wonder:
1. what is the different with speed control and non?
2. what are the advantages and disadvantages? (for a normal user)
3. under what situation or project that u need to have speed control router?
have a nice day.
This goes in a whole bunch of directions, all at the same time.
The dominant criteria is the bit. David nailed it. The tip of the outside of the cutting edge is where everything is happening. Too fast and the bit spins and doesn't get moved fast enough so it sits and burns. Remember, that at 25,000 rpm that's 50,000 "cuts" per minute. Can you move your router fast enough to get a clean cut each time without overloading the motor?
The speed control (either internal or external) is the method used to control the speed of a router motor and subsequently the bit. The larger the bit, the more horsepower it takes to push that bit through the workpiece but the bit must work at a slower speed. Here's where I have a problem. Is a large bit balanced the same way a small one is? What happens when a large bit is overspun? Does a high-quality large bit spin faster than a cheaply made one? I have several large bits, some good quality and one really cheap one. The biggest expensive one whines. The biggest cheap one grumbles.
The speed control actually takes on two aspects. You have your starting speed. This is the maximum speed that your bit is intended to run at. Then you've got your operating speed. This is controlled by your feed rate. Too fast and you bog down the motor, too slow and the bit doesn't get enough of a bite and it sits there and burns the cut.
Listen to your router. It will tell you when it's working proficiently. Push it too hard and the tone will lower. Maybe as much as an octave. Let it sit and it will not change at all but will burn the cut. (it must be said that dirty bits also cause burning as do dull ones.)
Most production level routers (> 3HP/2100W) have built-in variable speed controls. Porter-Cable is the one exception. They have some fixed speed models and some single speed models on their 3 1/4 HP lines. This is a pretty good explanation why Porter-Cable proponents thrust PC's low power models as a direct competitor to the Production Routers of other manufacturers.
Makita is renowned for having produced 4-pole motors for hand power tools but I can't find information on which models have that motor. This makes a very powerful motor and a more compact package. Variable speed on 4-pole routers is more complicated but the result can be excellent == more power at lower speeds.
Consider that variable speed gives you access to a broader selection of router bits and a larger number of methods of using a router. Roughly half of the router methods use variable speed.
This isn't going to help a bit but maybe it can be a basis for expanding this discussion and developing some real answers.