Planetary and Multi-Disc Sanders 101: A Technical Primer

At the end of last year, I made a few training trips, and while doing that training, I found out a lot of folks didn’t know there were different types of multi-discs and planetary sanders or understand what the differences were between them. I also found out a lot of folks hadn’t actually used or experienced these machines before, so I figured it would be good to put a quick primer together on the different types of machines on the market.

At their most basic function, multi-disc and planetary sanders are a great example of a force amplifier: These units decrease the physical contact area between the abrasive and floor while they increase the abrasive surface pressure by moving the focus point of sanding pressure to a small pad around the perimeter of the machine’s sanding disc. These units also create higher disc speeds on the accessory pads by imparting rotation on the pads via different means. All of them can be a great tool to add to your arsenal, but there are important differences between their operations and functions.

Multi-discs/passive planetary accessories

Examples:

Ceno Satellite, American Sanders HydraSand, Bona MultiDisc, Lägler 5 Star

The American Sanders HydraSand on a Ceno two-speed buffer. (Photo courtesy of Will Lacina)
 

How they work:

Multi-disc, or passive planetary sanders, lack a true gear drive. These units use free-spinning discs driven in the opposite direction of the main disc by the friction of the abrasive being drawn across the floor. The maximum reverse rotation of the pad can never exceed the maximum forward rotation of the main disc, and these units all operate on a counter-rotation principle, meaning as the buffer disc rotates counterclockwise, the sanding pad rotates clockwise, counter to the rotation of the main disc (see the arrows on the photo at right). This makes these units very well-balanced for the tasks that we typically would have used a hardplate or screen for. In good operating condition and in the hands of a skilled operator, all of these units can put out an excellent scratch pattern and can take up the function of mid, fine and final sanding.

Because the pad rotation is directly opposed to the rotation of the main disc, these units can be paired with multi-speed, high-speed or variable-speed buffing units to increase their effectiveness or aggression, or improve dust ejection to allow the abrasive to contact the floor. However, because of the pad direction and lack of a “braking” effect, these units often can’t force themselves through most finishes. Within the scope of multi-disc sanders, there are also two different types of multi-disc: straight shaft and pitched shaft.

A multi-disc operating on the straight shaft principle (Bona MultiDisc, Ceno Satellite) has a sort of “loping” effect about its pad rotation. Because the entire pad is in constant contact with the floor, the pad is often accelerating or decelerating (sometimes different pads at the same time) during sanding. This can put down an excellent scratch pattern, or it can work against the operator without adequate experience.

A multi-disc operating on a pitched shaft (American Sanders Hydrasand) uses a slight pitch to the shaft to push the contact area to the outside of the sanding disc to force more consistent rotation. These units can also be used as a finish sander, and a good amount of folks say they flatten faster or feel more aggressive. With all multi-disc sanders, a decrease in the pad size or a decrease in the number of sanding heads increases the abrasive surface pressure per square inch, often increasing aggression or flattening faster.

All multi-disc sanders are a combination of weight and surface pressure. These tools are the easiest for most contractors to understand because they largely clock and operate like a traditional floor buffer with some minor changes to the thought processes necessary.

Pros:

• Fit the buffer you already have.

• Great mid/fine sanding characteristics.

• Easy to adapt to because they operate similarly to a buffer. Can be fast flatteners.

Cons:

• Typically not suitable for heavy finish removal or aggressive leveling.

• Often can’t get its own scratch out under 60-grit.

Types of Planetary machines

There are actually only two categories of planetary sanders, but for the purpose of this article we need to break it down into three categories to avoid a confusing amount of information being in one category.

1) “First generation” counter-rotating machines (belt-drive)

Examples:

Lägler Trio, Clarke 3DS

The Lägler Trio. (Photo courtesy of Matt Lindenmuth)
 

How they work:

These machines use three large pads on a large plate driven by a belt. They put a lot of weight on a large, diffuse area to create an exceptional scratch pattern and can keep a floor very flat. These machines operate on the principle of counter-rotation but do so with a disc that rotates clockwise and a sanding pad that rotates counterclockwise (see the arrows on the photo below) because they have no reverser in their gearboxes. So the sanding pad is driven in the opposite direction of the main disc, feeding the outside edge of the abrasive away from the primary direction of rotation.

These machines operate at relatively high RPM on the sanding pad and a relatively high RPM on the main disc. This makes them exceptional finish sanders, second to probably only an orbital buffer or oscillating sander, but it also means they aren’t exactly getting finish off or the floor flat in a hurry.

The Trio now has an increasing range of accessories available for it that allow it to tackle more tasks than it could even a decade ago, increasing its utility. The 3DS has been discontinued. These machines are easy to operate: They run “wheels down” on the floor and are largely pushed around like a shopping cart (that’s what we called them). Contrary to popular belief, they do have a clock point located just to the right of the right wheel, between about 4 and 5 o’clock. This leads me to believe personally that they should be pushed, then pulled, and run left to right all the time to feather away from that point. Jorge Perez used to do a lot of good videos where he would clock the Trio to the perimeter of the room and lift up on the handle to “grind” with the right side.

Pros:

• Exceptional scratch pattern.

• Easy to run—little knowledge required to operate.

• Can keep a floor very flat.

Cons:

• Heavy.

• Slower working rate.

• Can glaze certain species easily.

• Still largely needs a “big machine” as a leadoff hitter.

2) Counter-rotating planetary (gear-drive)

Examples:

Bona Power Drive, Klindex K Sander 430, Hypergrinder I4-Wood, Roll RO800-SA

The Bona Power Drive. (Photo courtesy of Devan Hale)
 

How they work:

These machines use a moon and pinion setup, i.e., the ring gear for these machines is on the outside of the pinions. These machines also operate on the principle of counter-rotation, though the rotation is a counter-clockwise disc and a clockwise pad.

The abrasive is always retreating from the primary direction of the main disc on the outside edge of the sanding disc. Because the pads spin opposite of the main disc’s rotation, this causes the machine to want to “stand up” or “float” across the floor. This is a complication of the double-reversing of the motor’s output. This allows the machines to be run fairly easily with the handle in the upright position or in any number of other configurations but causes the machine to “clock” heavily toward the wheels (again, contrary to popular belief, these machines do have clock points and sanding directions). Because of this, these machines are often fitted with nose weights and folding handles, and for best finishing results the machines should actually be run with the handle mostly upright in order to keep the center of the pad from trying to climb into the soft grain on most species and also to prevent aggressive scratches subsequent grits can’t remove.

These machines can be very good finish sanders in the hands of a skilled contractor, but many contractors still prefer to pull the planetary for the final pass and switch to a multi-disc, orbital, oscillator or round buffer. They utilize high speed more than they do motor torque to achieve a result and are suitable for all levels of sanding from coarse to fine, and can drive all manner of accessories including diamonds and poly crystalline diamonds and do high-speed polishing (although many contractors still prefer to lead with a belt sander). These machines should still be clocked more like a traditional buffer, and for best results, work toward yourself.

Pros:

• Good scratch pattern.

• Easy to run.

• Can sand from coarse to fine.

• Can produce a flat, fine floor.

Cons:

• Slower working rate.

• Intermediate knowledge level required to produce a finely sanded floor.

• Most contractors still prefer to lead with a belt machine.

3) Co-rotating, or contra-rotating planetary (gear-drive or chain-drive)

Examples:

FG Floortec Discus, Wolff/Pallmann Spider, Woodcrete/MSF 2500hd

The FG Floortec Discus. (Photo courtesy of Josue Vargas)
 

The Pallmann Spider. (Photo courtesy of Derek Swegle)

How they work:

These machines use a sun and pinion gear setup, i.e., the ring gear is inside of the pinions (or chain drive for the Spider). These machines operate on the principle of co-rotation, or contra-rotation, wherein the rotation is a counter-clockwise disc and a clockwise pad. The abrasive is always advancing from the primary direction of the main disc on the outside edge of the sanding disc. Because the pad spins the same direction as the sanding disc, this causes these machines to want to “dig in” or “eat.”

Like a typical buffer, these machines only have a single reversing of the motor’s direction to the pad, and thus tend to want to run exactly like a buffer with a single disc would—while being more aggressive and achieving higher finish and stock removal rates. These machines clock approximately like a typical buffer but tend to want to lean more toward the 3 or 4 o’clock position on the sanding disc as their most aggressive points. For best results, they should truly be clocked like a single-disc buffer with the “hard edge” advancing across the floor. These machines are often fitted with heavy counterweights or weight kits that are actually recommended to be run through the entire sanding procedure, as they balance the scratch better across the disc plane.

These machines have the highest stock and finish removal rates among planetary sanders and often take the place of the big machines for their users and can be run through to final sanding, though many contractors still prefer to pull the planetary plates and finish with a multi-disc, orbital machine or single disc. Because these machines are feeding the abrasive forward into the floor, they need only half the pad rotation speed compared to a counter-rotating machine to achieve the same abrasive feed per minute. These machines can still be “heeled” like a normal buffer to put more pressure on the room edges or to work out scratches or sanding marks.

These machines operate on a high-torque and high-speed principle and are well-suited for driving all manner of accessories including poly crystalline diamonds, diamonds and scraper heads. Many contractors are having great success using these units for concrete prep segments and subfloor prep.

These machines can leave heavy scratch patterns and serious dishout when not properly handled and can require more advanced knowledge to operate successfully. If you’re bad with a buffer, you’re not suddenly going to be good at operating this category of machine. These machines must be clocked and operated with care and knowledge for best results.

Most contractors rely on these machines day-to-day instead of a belt machine.

Pros:

• Heavy stock/finish removal.

• Higher working speed.

• Often replaces the big machine.

Cons:

• Heavier scratch pattern.

• Steeper learning curve.

Mike Somodean

They can all make a fine wood floor

As a parting note, let me be clear that all of these machines in the hands of a skilled operator can produce a fine finished floor (I’ve done it, with many witnesses). Many things should be taken into consideration for operation, because no two machines in the same class operate exactly the same (due to changes to gear ratios, power, weight and fitment). Every operator should take time to consider which machine is right for them, their needs and their methods. Do you plan to use the machine to rough off floors and grind substrates? Do you plan to use it to replace your big machine? Complement your big machine? Are you trying to use it as a finish sander? Would you have been better off sticking to a screen and pads? I’m only presenting the information I’ve accumulated through use. The rest is for you to decide, but maybe I’ll do some pushing along the way and in Part II of this article (stay tuned).