Grizzly - T27417 Oscillating Belt/Spindle Sander (Rating: 4)
Since the two are so similar, it is inevitable that there will be comparisons between the Ridgid EB4424 and the Grizzly T27417. But the two products are quite different.
Some of the most obvious differences were covered in the first part of this review. The table on the Grizzly unit is smaller and the whole package has a much smaller footprint (16 1/2" X 18 1/2" as opposed to the Ridgid's 19 1/4" X 23 1/2"). Because of this, I think the Ridgid on-board storage is better organized - there is simply more room across the front of the unit to organize most of the on-board accessory storage up-front where it is more convenient while the Grizzly unit scatters some of the accessories around the sides where they are less convenient. Drive rotation is opposite - the Grizzly drive shaft spins counter-clockwise while the Ridgid spins clockwise. Thus the belts and drums turn in opposite directions on the two units. A consequence of this is that the Ridgid unit requires a left-hand thread on the knob that tightens down the sanding drums and the Grizzly unit uses a normal right-hand thread to keep things from working loose during sanding.
These are just the obvious physical differences readily apparent from the outside. Inside both units things are really different!
As with most toys, errr, tools that I buy, I couldn't resist tearing the Grizzly unit apart after I made sure that it was working. To my surprise, I found that the Grizzly unit is powered with a permanent magnet DC motor. The AC power is rectified with a full-wave bridge rectifier and fed to a brushed DC permanent magnet motor. A little Googling convinced me that the Ridgid unit has a more traditional AC induction motor. I don't believe it has brushes.
![Image]()
The DC motor in the Grizzly unit suggests an interesting possibility. A simple DC PWM controller would convert this sander to variable speed quite easily. I haven't used the tool enough to judge whether variable speed control is advantageous in a belt or spindle sander but I read about owners of large 3-phase spindle sanders outfitting them with VFD's and praising the ability to vary speed. The downside, of course, is that the DC motor has brushes and brushes wear out! As a matter of fact, the user manual for the Grizzly unit has detailed instructions on how to change the brushes.
There is another advantage to a permanent magnet DC motor - it uses electricity much more efficiently. An equivalent DC motor is usually smaller than its AC cousin. If you look at the specs for the two units you will find: Ridgid - current draw = 4.6A, motor = 3/8 HP; Grizzly - current draw = 3.5A, motor = 1/2 HP. AC induction motors run with a power factor approaching 0.5. This isn't surprising, they are basically huge inductors (coils) connected to an AC power source.. If we calculate backwards from the current draw and remember that 1HP ~ 750W, you get (120V X 4.6 A X 0.5PF) / 750W/HP = .368HP - very close to the 3/8 HP spec. DC motors do not suffer from PF (DC = 0Hz, after all) but have larger I2R losses in the winding resistance. Again,calculating backwards from the current requirements, we get (120V X 3.5A) / 750W/HP = 0.56 HP. After accounting for winding losses, the real number is probably about 0.5HP. The Grizzly motor is 33% stronger but draws less current and is smaller than the Ridgid motor!
The size difference between motors is not just due to AC vs DC, however. It is also due to differences in mechanical design. The oscillating mechanism that drives the spindle up and down is built into the motor housing in the Ridgid. On the Grizzly unit, the oscillating mechanism is separate from the motor. In fact, this picture of the plastic mounting plate seems to show mounting holes for a larger motor.
![Image]()
That suggests the possibility of swapping in a larger motor in the future. Of course, there are issues with mating the shaft to Grizzly internals, whether or not the mechanism can actually withstand more power, etc, etc. I don't know whether that's feasible. And, without more time on the sander, I don't even know whether it is necessary. But it is obvious that, with the Ridgid design, incorporating the oscillating mechanism into the motor housing leaves you with no possibility of upgrade at all.
Oscillating mechanisms for these two sanders are completely different. All of the small oscillating spindle sanders on the market today seem to be based on one of two different patents from the mid-90's. If you are interested , you can look up the details of operation in these two patents:
Emerson patent - US patent #5549507, issued in 1996 - used in the Ridgid sander, this design uses a hypercycloidal planetary gear with a pin follower that rides on a pattern formed in the motor housing to generate the up-and-down motion.
Ryobi patent - US patent #5558566, issued in 1996 -used in the Grizzly sander, this design uses two belts, spinning at slightly different speeds with two molded plastic forms that generate the up-and-down motion.
On the web, you can find these two links that provide more information about these designs:
Here is a link to a teardown by an owner of the Ridgid sander with pictures of the disassemebled mechanics. This also provides some insight into the problems suffered by some Ridgid owners. (Note: this seems to be the older Rigid design - EB44240. The latest is the EB44241 and I couldn't find any teardowns of this design.)
Here is a Youtube video that shows the operation of the same mechanism used in the Grizzly sander.
What I find fascinating is the two completely different design approaches to achieve the same basic functionality. Which is better?
From a design standpoint, I honestly don't know. Maintenance issues on the Grizzly design in terms of brush and belt replacement may be an issue. The Ridgid design may lead to lower maintenance costs but higher replacement costs when things do break.
From a tinkerer's standpoint, I like the Grizzly design. That may not apply to everyone, though. I simply can't resist the urge to modify and tinker with things but many just want a tool that works.
From a manufacturing standpoint, I think that the increasing number of complaints about the Ridgid unit have already made it clear that they went too far in cost-reducing what was basically a good tool to start with. Sadly, with the current business climate, the Grizzly tool may suffer the same fate as time goes by.
Draw your own conclusions.
Since the two are so similar, it is inevitable that there will be comparisons between the Ridgid EB4424 and the Grizzly T27417. But the two products are quite different.
Some of the most obvious differences were covered in the first part of this review. The table on the Grizzly unit is smaller and the whole package has a much smaller footprint (16 1/2" X 18 1/2" as opposed to the Ridgid's 19 1/4" X 23 1/2"). Because of this, I think the Ridgid on-board storage is better organized - there is simply more room across the front of the unit to organize most of the on-board accessory storage up-front where it is more convenient while the Grizzly unit scatters some of the accessories around the sides where they are less convenient. Drive rotation is opposite - the Grizzly drive shaft spins counter-clockwise while the Ridgid spins clockwise. Thus the belts and drums turn in opposite directions on the two units. A consequence of this is that the Ridgid unit requires a left-hand thread on the knob that tightens down the sanding drums and the Grizzly unit uses a normal right-hand thread to keep things from working loose during sanding.
These are just the obvious physical differences readily apparent from the outside. Inside both units things are really different!
As with most toys, errr, tools that I buy, I couldn't resist tearing the Grizzly unit apart after I made sure that it was working. To my surprise, I found that the Grizzly unit is powered with a permanent magnet DC motor. The AC power is rectified with a full-wave bridge rectifier and fed to a brushed DC permanent magnet motor. A little Googling convinced me that the Ridgid unit has a more traditional AC induction motor. I don't believe it has brushes.
The DC motor in the Grizzly unit suggests an interesting possibility. A simple DC PWM controller would convert this sander to variable speed quite easily. I haven't used the tool enough to judge whether variable speed control is advantageous in a belt or spindle sander but I read about owners of large 3-phase spindle sanders outfitting them with VFD's and praising the ability to vary speed. The downside, of course, is that the DC motor has brushes and brushes wear out! As a matter of fact, the user manual for the Grizzly unit has detailed instructions on how to change the brushes.
There is another advantage to a permanent magnet DC motor - it uses electricity much more efficiently. An equivalent DC motor is usually smaller than its AC cousin. If you look at the specs for the two units you will find: Ridgid - current draw = 4.6A, motor = 3/8 HP; Grizzly - current draw = 3.5A, motor = 1/2 HP. AC induction motors run with a power factor approaching 0.5. This isn't surprising, they are basically huge inductors (coils) connected to an AC power source.. If we calculate backwards from the current draw and remember that 1HP ~ 750W, you get (120V X 4.6 A X 0.5PF) / 750W/HP = .368HP - very close to the 3/8 HP spec. DC motors do not suffer from PF (DC = 0Hz, after all) but have larger I2R losses in the winding resistance. Again,calculating backwards from the current requirements, we get (120V X 3.5A) / 750W/HP = 0.56 HP. After accounting for winding losses, the real number is probably about 0.5HP. The Grizzly motor is 33% stronger but draws less current and is smaller than the Ridgid motor!
The size difference between motors is not just due to AC vs DC, however. It is also due to differences in mechanical design. The oscillating mechanism that drives the spindle up and down is built into the motor housing in the Ridgid. On the Grizzly unit, the oscillating mechanism is separate from the motor. In fact, this picture of the plastic mounting plate seems to show mounting holes for a larger motor.
That suggests the possibility of swapping in a larger motor in the future. Of course, there are issues with mating the shaft to Grizzly internals, whether or not the mechanism can actually withstand more power, etc, etc. I don't know whether that's feasible. And, without more time on the sander, I don't even know whether it is necessary. But it is obvious that, with the Ridgid design, incorporating the oscillating mechanism into the motor housing leaves you with no possibility of upgrade at all.
Oscillating mechanisms for these two sanders are completely different. All of the small oscillating spindle sanders on the market today seem to be based on one of two different patents from the mid-90's. If you are interested , you can look up the details of operation in these two patents:
Emerson patent - US patent #5549507, issued in 1996 - used in the Ridgid sander, this design uses a hypercycloidal planetary gear with a pin follower that rides on a pattern formed in the motor housing to generate the up-and-down motion.
Ryobi patent - US patent #5558566, issued in 1996 -used in the Grizzly sander, this design uses two belts, spinning at slightly different speeds with two molded plastic forms that generate the up-and-down motion.
On the web, you can find these two links that provide more information about these designs:
Here is a link to a teardown by an owner of the Ridgid sander with pictures of the disassemebled mechanics. This also provides some insight into the problems suffered by some Ridgid owners. (Note: this seems to be the older Rigid design - EB44240. The latest is the EB44241 and I couldn't find any teardowns of this design.)
Here is a Youtube video that shows the operation of the same mechanism used in the Grizzly sander.
What I find fascinating is the two completely different design approaches to achieve the same basic functionality. Which is better?
From a design standpoint, I honestly don't know. Maintenance issues on the Grizzly design in terms of brush and belt replacement may be an issue. The Ridgid design may lead to lower maintenance costs but higher replacement costs when things do break.
From a tinkerer's standpoint, I like the Grizzly design. That may not apply to everyone, though. I simply can't resist the urge to modify and tinker with things but many just want a tool that works.
From a manufacturing standpoint, I think that the increasing number of complaints about the Ridgid unit have already made it clear that they went too far in cost-reducing what was basically a good tool to start with. Sadly, with the current business climate, the Grizzly tool may suffer the same fate as time goes by.
Draw your own conclusions.
