Variable speed belt sander?

[welldigger]

Has anyone ever used a variable speed router control on a belt sander? I need to sand a butcher block down and am wanting to slow the sander down a little for better control. Will it work or will it fry the sander?

 

[CoolHandLuke]

Im not 100 percent on this one... but I believe if you are using one of those little rheostat type controls on a larger capacitor motor you are going to do some damage. Now, this damage may not actually be "burn up your sander" type damage, but it will not be running in an ideal fashion. This is the reason that people in the knife making industry get variable frequency drives. One additional thing is that if you slow the motor by limiting current (I believe that is what happens with one of those controls) and it isn't a DC motor, you are losing significant torque as well. If I am technically wrong on this guys please forgive... I have seen many back and forth commentaries on this in the knifemaking world and I do know that they say it's a bad idea. The details I may not have completely though. Now if this is a handheld brush motor type belt sander it may work fine (those motors should be almost the same)

 

[NCTurner]

Is this a handheld belt sander or a stationary unit? AC/DC?

 

[Glennbear]

I recently tried this on my my Hitachi SB10Y combination belt/disc stationary sander:

1) Horrible racket from motor and sander would not run.

2) Sander appears to not have suffered permanent ill effects.

3) Back to the drawing board. :rotflm:
My portable belt sander is already variable speed so I did not try that. :wsmile:

 

[welldigger]

Handheld belt sander.115volt AC

 

[NCTurner]

Nope not unless you want to burn it up. Needs to be a universal motor.

 

[junquecol]

Nope not unless you want to burn it up. Needs to be a universal motor.

Bad answer, bad answer. Even though sander is rated for 115 volts AC, it most likely has a universal motor. Seldom do manufactures rate tools for DC operation. About the only source of 115 volt DC is some OLD engine driven welders, and I mean OLD. Most newer welders produce a combination of 115 / 230 AC, which allows them to be used as a generator. I have two PC 3 X 21 belt sanders, and one is variable speed. I usually grab which ever one is closest at hand. As long as sander doesn't have a "soft start" feature, you should be doing OK.

 

[NCTurner]

So Bruce let me get this straight, it does need to be a universal motor or it would burn up. If assuming the sander is a universal motor the rheostat can be used?

 

[Charles Lent]

To make it easier to verify, check the motor of the tool to see if it has brushes, most hand held tools do. If it has brushes, and it doesn't already have a variable speed control module in it, then you can use a router speed control with it. However, the early router speed controls controlled the unloaded speed and did not maintain the speed as the load was applied. The newer speed controls monitor the motor speed and add power to keep the motor running at the same speed, or nearly so, when a load is applied.
You should find one of these "newer" type speed controls and use it.

Charley

 

[ehpoole]

So Bruce let me get this straight, it does need to be a universal motor or it would burn up. If assuming the sander is a universal motor the rheostat can be used?

Just a point of clarificaiton. The router speed controllers are not rheostats. They are simple triac (thyristor) devices activated at the zero-crossover. The potentiometer simply controls how much of the 180-degree half-cycle the triac will be activated for (the pulse width). They also commonly include some crude feedback circuit activated by the back-emf generated by the motor to try and compensate for load variations with varying degrees of success.

By comparisoin, a rheostat (potentiometer) would simply increase the series resistance of the motor, limiting the current that can pass through the motor. A rheostat capable of handling a 6+amp router would be a rather impressive device and a not-terribly good speed regulator. Such rheostats do exist, but are not something you are ever likely to encounter.

The few aftermarket speed controllers I have tried never really gave useful results with my routers, so I broke down and purchased routers with built-in speed control (which often include tachometer feedback). Just beware that when you lower the speed of a universal motor you also reduce the cooling airflow through the motor, so you will want to be careful not to overload the motor and give it regular no-load cooling periods when it starts to get hot. On my old belt sander the difference between low speed and high speed covers a range of 70% to 100%, so don't slow your sander by more than 1/3rd normal.