Are Two Motors Better than One on a Two-Head Sander?

      Some two-head sanders drive both heads with a single motor. What difference does it make? February 6, 2007

Question
I've seen a couple of SCMI/Sandya machines come on the market after just a couple of years in operation. They have a single motor driving both sanding heads. Some of the newer Far East machines have this same configuration. I'm going to be in the market for a 2-head machine next year. My existing electric service in my leased space is just 200 A, so a machine like this is tempting. But will the single motor limit performance?

Right now I don't hog off much on the sander, just use it to take off .01" to .02" per pass. We sand planed door panels and finished doors/drawer faces only - we use a planer with shelix head for thicknessing. So are these low hour machines a good option, considering the workload, or will it be a limit later on?

Forum Responses
(Cabinetmaking Forum)
From contributor M:
My 2 head sander has a single motor, just as you described, driving both heads and it has never been a problem. For the right price, I'd say go for it.



From contributor D:
If incoming power is limited, be sure to check the amp requirement for the machine. It takes a certain amount of energy to do a particular job. If one motor is doing two jobs, it will have to be a larger motor, thus consuming more current.


From contributor P:
Really the only thing you save with (1) motor is during the initial purchase, and it should be less expensive. A (2) motor machine gives you the option of using only (1) sanding head when only (1) is needed. Less wear on bearings and belts over the years. Less wear and tear on the machine will equal a longer life and less repair cost. The other factor to consider is what if (1) motor/head unit is down. With (2) motors you can still function. Contributor D hit on a point. (1) 30 Hp motor at 230 volts can draw up to 97.30 amps at full load. (2) 15 Hp motors at 230 volts will draw approximately the same. The fact is if you are running only (1) 15 Hp at a time, you will find your kilowatt usage to be less per hour. What will it cost to replace the (1) motor?


From contributor J:
It all depends on how the machine is configured. The first head is typically used for calibrating lumber (whether doors, boards, etc). Calibrating is bringing the part to a uniform thickness. Calibrating requires the most horsepower in a wide belt sander.

Typically, for your application (doors and door components), you will be calibrating with 80 or 100 grit paper on a 90 shore (hardness) rubber coated drum. Steel drums (not recommended for your application) should only be used with paper below 80 grit, and they are notorious for leaving chatter marks.

You typically need 15 to 25 Hp for the first head, depending on the head type, head width and grit.

The second (and third) head(s) are mainly used to remove the scratches from the calibrating head. These heads should have drums with progressively larger diameters and softer rubber coatings, in order for the finer grits to work effectively. (Think of how you hand sand - a hard block with coarse grits and a cork covered block with finer grits). These heads use considerably less power than the first head.

For a two head 43" wide sander, you probably want a 30 Hp motor or a 20Hp + 15Hp (if a two motor machine). You can get a one pass sander (for doors) with a machine that has 3 heads and two motors (25Hp + 20Hp). This will typically payoff much faster than a two head machine when you look at the amount of time spent making two passes and changing belts on the two head sander.



From the original questioner:
Right now, I'm using a 36" 7 1/2 HP double drum sander with 120/180 grit wraps. I leave it set up this way for everything, and it only bogs down on hardwood panels wider than 20". The finish surface is almost where it needs to be. Dust collection could be better. The wraps usually load up at about the same time, and I spend an average of $360/year on abrasive.

More questions: What grit do you typically platen sand to for door finishing?
Aside from premature wear of belts, which is a cost issue, is there a quality downside to running a 2 head sander with finer grits to get a single pass finish?
How long do abrasive belts last on your grit sequence? Cost per year?



From contributor M:
I'll try to answer as many of your questions as I can. I run an 80-120 grit sequence on mine and it comes out pretty good. If I only have a few doors that have been run through, I don't even bother to go any finer than that. I move to a random orbital sander to take the cross grain scratches out. I still have to do it when I go to 180 grit. When running flat stock, I'm done in one pass. As far as power goes, I have a single 25 hp motor running both heads and have never been close to bogging the motor down. I too have a Shelix head in my planer and only have to take .010" -.015" per side to get thinks to clean up, less if I'm running just single boards. As for abrasives costs, I'm getting at least 20 hours out of a set of belts, maybe more, but I'm sure not less (this is just a guess - I don't track actual times, I am very happy with belt life). I watch my rate of removal and don't try to take too much off, and that greatly extends the life of the belts, plus I buy good ones rather than some of the bargain basement brands that wear out very fast. I use Klingspore cloth backed belts.

SCMI and SAC are both good Italian sanders, and I would buy one of those before an Asian import. Setup is crucial on a multi-head sander. All you want that second head doing is taking out the scratch marks from the first belt and not any more, otherwise you're wearing it out prematurely and driving up your abrasives costs.

A good source of reading material on the subject can be found in the archives of Modern Woodworking and the Sanding Sense articles written by Howard Grivna. He also has a book for sale that covers all that. If you do decide to go the widebelt route, by all means study it, as he covers rates of removal and setup as well as many other topics you'll need to be versed in to run a widebelt effectively.



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