2x72 sander

[George]

So, to get the discussion going, here is what I am starting with. ....the pulley (more like a flywheel) on the motor is about 5 3/4" in diameter and about 1" wide. The grooves you see are for a micro v belt. So, to me, the wheel is too narrow to be a direct drive pulley, and I would like a larger diameter to increase surface feet per minute. Most knife makers ( correlating to efficency) seems to be about 5000 sfpm. I would like to keep the RPM in a reasonable range, although not sure what that is yet for these motors. Having said that, I have not tested the motor to see what it actually like to run at. But I had a 7 inch diameter in mind ..about 2700 RPM. I would start with anything from the existing diameter to a custom made 7 incher (when stock avails itself to me. )
The thread holding the flywheel on is a 1/2" left hand so easy enough to make a whole new drive pulley. Casting one? Making one out of pipe and plate? Modifying the flywheel? I have seen plans for shop built stuff before using MDF as the pulley. On a machinist's forum, this would be frowned upon but practically speaking, to bond a piece or two of MDF to the existing fly wheel to have a 2" wide drive pulley,with the cast iron flywheel as the base ...... might actually work....

Mounting the motor...I don't like the existing mounting brackey but would reuse the holes in the motor chassis.

I would put a tach on it but one that displays SFPM instead of RPM. Couple ways to do this, Microcontroller (Arduino) to do the math and display it or a pulley sized so that the RPM reflects the SFPM ie if the circumference of the sensing pulley is ten inches, then SFPM is 10 times the tach display or add magnets as multipliers.

I have 4 scrapped treadmills and 3 complete controllers/motors. One motor where the controller was pooched. So saying, if you want to do this and have not looked into Treadmills as resources, it might interest you.

Cheers,
Shawn

A good thing about stripping treadmills is the rollers are seamless you get 4 decent bearings and excellent tubes for casting aluminum inside, once the aluminum is cooled it just slides out, i also have 3 treadmill motors for planned projects. Always on the lookout for treadmills FREE ones are always being advertised on a local buy and sell site, also get some nice smaller gauge steel round square and oblong, and if the driver board is fried, just buy a PWM off AliExpress, cheap as chips.

 

[Chris Cramer]

I tested what I have built so far, and it doesn't really look like it does any more than my craftex belt sander. The craftex has a 1/2 hp motor that reaches 3500 rpm, but the marathon 2hp motor only reaches 3450 rpm. Does the rpm make more difference then the torque?

 

[Dabbler]

A 3450 rpm motor never reaches a full 3450 rpm except under non-loaded ideal conditions the speed of the ebelt depends on the size of pulley. The HP rating of the motor will tell you how much force it can overcome when sanding. For instance:

I run a 1HP on a 6X48 sander on an 8" drum at 1725 RPM that works out to about 3500 spfm with enough torque for everything I do. My other 6X48 uses a 3/4 HP 1725 on a 4" drum or about half the sfpm at about the same (or a touch more) torque. the both cut about the same (for the work I do) I run 2" 4o grit belts on the 3/4 Hp sander and 6" 80 grit belts on the 1HP model.

I like working slow and careful, so these sanders suit me.

Your concern should be that you have enough torque to not stall the motor (or heat it up too much) The speed is just how fast you can remove the metal under non-stall conditions.

I've been toying with building a 2X72, but I'd probably go for a 1HP 1725 motor, with about a 10" driving wheel. that gives 4500 sfpm, which is a little fast, but will make for nice finish with fine belts.

 

[Chris Cramer]

Right, a 2 hp motor is probably recommended so it can drive a 72" long belt and withstand the force of both the tensioner and the user. It may be that the force of the tensioner is too high. I used a 100N gas spring for the tensioner, what would be recommended?

 

[Dabbler]

Lots of guys overpower 2X72 sanders. They want enough torque to *almost* break the belt, in order to increase metal removal. I want less removal, as I don't like burning the metal. Fireball tool build a sander with (i think) a 5HP motor.

 

[Chris Cramer]

Yeah, I read online that the recommended speed of the delt depends on numerous variables, like the grit and type of abrasive, and the intended purpose of the tool. I'm using zirconia belts, the grit is 85, and my main purpose for this grinder is stock removal. Ceramic belts require high speed to work well, and fine belts would heat up too much over higher speeds - but that is not my intended use. If the motor does reach 3450 rpm with a 50N(11lb) gas spring, then the belt would run at 3643 SFPM with a 4" drive wheel.

 

[Chris Cramer]

I made an upgrade on my 2 x 72 belt grinder. I decided to add a 6" contact wheel to the system to use for grinding a blade bevel more accurately. Many commercial grinders have a set up that allows you to change the contact point between the use of a contact wheel and a metal plate. I also purchased a single phase VFD from ATO that I can use to add variable speed to the 2hp single phase ac motor as well as the direction that it spins.

 

[Former Member]

I built mine a few years ago to solve a need using a single speed motor.

Personal observation is that it does a lot more than regular grinder with quick material removal.

Its is among the the top tools used in the shop.

 

[Doggggboy]

View attachment 28400

I made an upgrade on my 2 x 72 belt grinder. I decided to add a 6" contact wheel to the system to use for grinding a blade bevel more accurately. Many commercial grinders have a set up that allows you to change the contact point between the use of a contact wheel and a metal plate. I also purchased a single phase VFD from ATO that I can use to add variable speed to the 2hp single phase ac motor as well as the direction that it spins.

I never realized you could control a single phase AC motor with a VFD. I assume that is a better option then the old dimmer switch trick.

 

[Chris Cramer]

It isn't recommended to use a three phase vfd for a single phase motor. The single phase output VFD that you can get from ATO is available for different sized motors the 2hp VFD cost 218 USD but cheaper single phase to 3 phase VFDs should only be used with 3 phase motors.
Dimmer switches don't adjust the frequency, they only change the voltage which also changes the power of the motor. A VFD will change the speed with the frequency but the voltage will remain the same for power.

 

[Susquatch]

It isn't recommended to use a three phase vfd for a single phase motor.

I totally agree, but I'd use much stronger words than that! How bout - 3phase VFDs will not work with a single phase motor....... Heck, you can't even wire it up!

 

[Former Member]

It isn't recommended to use a three phase vfd for a single phase motor. The single phase output VFD that you can get from ATO is available for different sized motors the 2hp VFD cost 218 USD but cheaper single phase to 3 phase VFDs should only be used with 3 phase motors.
Dimmer switches don't adjust the frequency, they only change the voltage which also changes the power of the motor. A VFD will change the speed with the frequency but the voltage will remain the same for power.

The better VFD's change both frequency and voltage as it prevents over current, fail to do that and you greatly reduce motor life. i was involved in selling the first VFD elevator drives in Canada.

 

[Chris Cramer]

there is a way to wire it up, if you have it drawing power from all 3 phases, that is how the single phase VFD works, neutral is connected to one terminal, and the other 3 wires are all connected to the life terminal.

 

[Susquatch]

there is a way to wire it up, if you have it drawing power from all 3 phases, that is how the single phase VFD works, neutral is connected to one terminal, and the other 3 wires are all connected to the life terminal.

Really...... My brain just fried!

I would have thought that wiring all phases to one would create a massive short circuit and even if not they would all add to zero. But I confess I've never tried it. (And prolly never will.... ..... At least not from within the same room! LOL!)

But I'm always open to learning new things!

 

[phaxtris]

I can't imagine what @Chris Cramer is suggesting is ideal with a normal 3ph vfd, the phases being 120 apart and not 180 apart like in normal residential 240v power

I would also wonder if that third phase being returned to ground would cause some kind of load imbalance withen the circuitry of the vfd ?

Just some thoughts

 

[Dabbler]

I can see that the wave forms will not be ideal for a 1ph motor, but in a garage-tinkering-way it might work. -- Certainly not intended to be used that way. I'm prety sure a 1ph motor will also have problems with the balancing on the run capacitor winding because of the timing differences. It *should* cause extra heating in the primary winding, but most mills utilize only a fraction of the torque, so not so bad.

Hmmm might be worth a try one day...

 

[Chris Cramer]

Sorry, you don't use all three phases, you use only one phases. Commercial buildings that use 3 phase power still have single phase power outlets by dividing the 3 phases into different areas, and the lights only use single phase. They just need to balance it to make sure a cable does not make connection with the same phase.

 

[Susquatch]

I can't imagine what @Chris Cramer is suggesting is ideal with a normal 3ph vfd, the phases being 120 apart and not 180 apart like in normal residential 240v power

I would also wonder if that third phase being returned to ground would cause some kind of load imbalance withen the circuitry of the vfd ?

Just some thoughts

I wonder too. Here is a phase graph.


Note that every 60 degrees, two phases are opposite the other but half the voltage. A quick look says the voltage sum is always zero (what I guessed before). However, I think it results in some really nasty short circuits too. Again, kinda what I guessed before.

However, vfd control systems do read their own outputs and Lord knows how they might adjust their outputs with such a connection. I stopped being so sure of myself on such things 30 years ago.

 

[Susquatch]

Sorry, you don't use all three phases, you use only one phase. Commercial buildings that use 3 phase power still have single phase power outlets by dividing the 3 phases into different areas, and the lights only use single phase. They just need to balance it to make sure a cable does not make connection with the same phase.

Ah, I see. I thought you said all three wires were connected to one pole.

That makes more sense, but I can't imagine that the vfd would be very happy about it!

 

[Chris Cramer]

You can't do that with the input of the vfd. For single phase to 3 phase VFDs the output could be divided.