Slowing down the BT motor. On purpose.

[Tom Slick]

That is a valid point. Perhaps the reason nobody has reported a problem is that it takes prolonged usage to damage the bearings, or maybe it's because it is too embarrassing to admit that you kayoed your table saw trying to sand with it.

For what a cheap disc sander costs, why would you wish to try anything else??

IMHO if the arbor uses ball bearings the they are designed for axial or radial thrust, it doesn't matter which way you load them. the same argument is made for using a sanding drum in a drill press.

The other point brought up was the hassle of having to change over to the sanding disc vs. the ease of a dedicated sander.

I have the beveled disc and it works very well for taking the blade marks off and any waviness out. it will burn easily if you don't use the right technique and you can only remove 1/32 with each pass.

[leehljp]

For what a cheap disc sander costs, why would you wish to try anything else??

I found an old/very early model BT3000 sitting out in the weather without the SMT or fence at a shop here about 5 years ago and inquired about it. The owner said it didn't work well with parts gone and gave it to me. When I retire, I will have 2 BT 3000s and a 3100. I plan on making a Frankensaw to have one dedicated to dado. The third and old one will be ideal for setting up a precision sander if I add a miter slot to it.

The one thing I dislike about most affordable disc sanders (cheaper ones) is the inability to set the tables and miter gauges precisely without lots of fiddling. I personally do not view a disc sander as a "general" round over or edge sanding device. I view disc sanders as a piece of equipment that should enable precision finished edges - at least as fine as the sanding grit can allow.

I can't count the number of times I have wanted to remove 1/2 a degree off of an angle (on a board) quickly without running it through a saw. To get this degree of accuracy on disc sander without fiddling, one has to spend at least $125.00 (Grizzly 12") to get a disc sander with a halfway "decent" table.

Combo belt/disc sanders are great for general purposes but they do not give me the one tool that I really need to compliment the others that I have - a precision disc sander. The BT with a sanding disc will be ideal.

[Uncle Cracker]

But not everybody has three of them lying around, Hank... If you only had the one, or even a second set up as a dado machine, changing out to a sander all the time would be a PITA. And a dedicated sander takes up so much less space than a BT. I use my Hitachi with an Incra V27, and have not exceeded it's capabilities to date, and have the bonus of a 4" belt sander that a BT setup could not give me. I guess, like everything else, it's a matter of personal preference...

[gsmittle]

I wonder what other great things the BT can do, rocket ship, make tea - BEER?

It can't make beer, but it tenderizes steak really well...

g.

[leehljp]

But not everybody has three of them lying around, Hank... If you only had the one, or even a second set up as a dado machine, changing out to a sander all the time would be a PITA. And a dedicated sander takes up so much less space than a BT. I use my Hitachi with an Incra V27, and have not exceeded it's capabilities to date, and have the bonus of a 4" belt sander that a BT setup could not give me. I guess, like everything else, it's a matter of personal preference...

I agree with you on your points and I think there can be some fine setups. The BT is kind of large, but I do have an extra one. If I didn't, I would be looking at some other way including the Grizzly Disc or a good horizontal sander. A "good" horizontal belt sander would be best IMO, but the cost is still more than I would like to put out. I still might go that route when I retire and I think it could offer more versatility for sure. However for what I would like to achieve, it will take up the same floor space as the BT frame and short rails.

My one gripe with belt sanders is the belt "seam". If the seam is raised or not flat to the tune of 1/100 inch, it defeats its purpose for getting that 1/2 degree sanding potential perfect. Cheesy miter gauges, small tables and cast slots in cheap tables also make for blemishes and none precise angles and sizing.

[eccentrictinkerer]

FWIW, the electronic router speed controls have a distinct advantage over the variable transformer.

The router speed control senses the load on the motor and will supply more voltage in response to an increased load. This helps maintain a more constant motor speed.

One major disadvantage of a variable transformer is that at low voltages it cannot supply anywhere near the current that it can supply at full voltage. It's a volt-amp thing.

Fer'instance, at 120 volts, a 2000 VA (volt-amps) variac will supply 16.66 amps. However, at 30 volts the variac will supply a maximum of 120 VA or 4 amps. Trying to pull more current can overheat the brush assembly of the variac.

[sparkeyjames]

It had never even occurred to me to use the BT as a sander, where do you get the disks, do they come with abrasive already on or use stick on?

I wonder what other great things the BT can do, rocket ship, make tea - BEER?

I got the 10" metal disc at the local Woodcraft store and I bought standard 10" sanding discs at McMaster-Carr and cut the hole in the center myself (2 1/4 inch will do but not smaller). $4.99 per sanding disc at Woodcraft vs $3 and change per disc at McMaster-Carr (pack of 5 for about $16 or so included shipping). Basicly Woodcraft charges $2 to put a 3" whole in the center of a 10" sanding disc.


Edit: those are peel and stick discs.


Looked sorry no beer tap.

[sparkeyjames]

I read discussion about these discs loading the arbor bearings in a way they aren't designed to handle but I haven't read anyone who actually noticed wear from their use.

The amount of pressure you have to apply is not that great. Since I have yet to reduce the RPM factor I can tell you that with minimal pressure against the blade it could sand down a 2.25 inch X 1.25 inch thick piece of wood to a nub in nothing flat. Great care is recommended hence the need to slow the thing down.

[LCHIEN]

FWIW, the electronic router speed controls have a distinct advantage over the variable transformer.

The router speed control senses the load on the motor and will supply more voltage in response to an increased load. This helps maintain a more constant motor speed.

One major disadvantage of a variable transformer is that at low voltages it cannot supply anywhere near the current that it can supply at full voltage. It's a volt-amp thing.

Fer'instance, at 120 volts, a 2000 VA (volt-amps) variac will supply 16.66 amps. However, at 30 volts the variac will supply a maximum of 120 VA or 4 amps. Trying to pull more current can overheat the brush assembly of the variac.

There are multiple incorrect statements here (pulling out my Electrical Engineering hat).
1. External Router speed controllers are phase-angle conduction devices. None I know of can compensate voltage for load... they are not constant speed controllers. However universal motors usually hold a realtively contant speed to voltage relationship, both these controllers (phase-angle controller or variac) hold the voltage close to the settings, independent of load.

2. Variacs/variable transformers/autotransformers by their basic design should be able carry full rated current on the output as the brush contact goes from zero to full voltage. The current density does not change so the brush will not burn out. If you maintain the current draw on the output (secondary), the current (and hence power) in the primary (input) will fall as the output voltage is reduced. This is perfectly fine; the variac is quite efficient.

For both the phase control and the variac, when running at half voltage, the ultimate motor power will be significantly reduced.
Other than the cost, size and weight I mentioned earlier, there's still no real theoretical advantage of one over the other at mid to high speeds. If anything, the variac has better current output at the low voltage because at low voltages the conduction angle for the phase-angle controller becomes very small and the current is on for a short time and has to be quite high during this time to get any appreciable average current out. The Variac then probably would have better low speed torque, by my hypothesis.

[eccentrictinkerer]

There are multiple incorrect statements here (pulling out my Electrical Engineering hat).
1. External Router speed controllers are phase-angle conduction devices. None I know of can compensate voltage for load... they are not constant speed controllers. However universal motors usually hold a realtively contant speed to voltage relationship, both these controllers (phase-angle controller or variac) hold the voltage close to the settings, independent of load.

2. Variacs/variable transformers/autotransformers by their basic design should be able carry full rated current on the output as the brush contact goes from zero to full voltage. The current density does not change so the brush will not burn out. If you maintain the current draw on the output (secondary), the current (and hence power) in the primary (input) will fall as the output voltage is reduced. This is perfectly fine; the variac is quite efficient.

For both the phase control and the variac, when running at half voltage, the ultimate motor power will be significantly reduced.
Other than the cost, size and weight I mentioned earlier, there's still no real theoretical advantage of one over the other at mid to high speeds. If anything, the variac has better current output at the low voltage because at low voltages the conduction angle for the phase-angle controller becomes very small and the current is on for a short time and has to be quite high during this time to get any appreciable average current out. The Variac then probably would have better low speed torque, by my hypothesis.

1. Most electronic router speed controls use back-EMF to adjust phase-angle which gives a moderate amount of speed (actually torque) regulation. This is the same technique as used in the internal-type speed control. You're right, light dimmer-type controls don't have any ability to sense load. Mine works great. LINK to speed control

2. I mis-spoke re the current limitations for variacs. My last dealing with a variac was when a friend wanted to use my 15 amp Variac to run a hot-wire cutter for cutting foam. The resistance of the wire was extremely low and would have burned the Variac out in a New York minute.

I had a 120/12 volt-20 amp transformer that stepped the voltage down very well. So well that I had a tough time getting the rig back!

After thinking about a bit, I'd be inclined to go the Variac for sanding. Unless you're hogging off lots of wood in one pass the Variac would give more precise speed control.