Slowing a Feed Motor with Variable Frequency Drive

      Motor speeds can be adjusted with electronic add-ons, but there are complications. October 4, 2007

Question
I have a Crescent P24 planer with a 3 phase 1 hp feed motor driving a variable speed feed mechanism. The variable feed runs from 25 to 50 feet per minute. The motor runs at 1750 RPM. I would like to slow the feed rate down to achieve a finer finish. Has anyone out there used a variable frequency drive to slow the feed motor down, thereby running speeds of around 5-15 fpm? I have found variable frequency drives for about $200 (Hitachi L200 series) and thought this would be much cheaper than the spiral head option.

Forum Responses
(Solid Wood Machining Forum)
From contributor L:
It will work. I'm assuming the main drive is three phase, so you will need to power the main motor separately from the feed motor with separate VFD for each motor.



From contributor C:
As contributor R said, it will work. One thing to keep in mind is motor cooling. If you slow the motor down too far, you will lose efficiency of the motor fan for cooling. In some cases an aux fan may be required. I put VFD on a line borer to slow it down from 2800 RPM to 900. It gets a bit warm, but the one installed on the moulder hasn't effected the motor at all.

One other side effect to note may be noise in computers/networking and radio station signal. The moulder destroys AM, the line borer is fine, but the VFD for the CNC spindle takes out DSL (been told there is a filter for this, but no one will tell me what or where I can get it).



From contributor T:
As others have mentioned, it will work. However, many people don't realize that frequency drives are meant to be used with motors specifically designed for this purpose. Off the shelf stock motors are designed to operate at a certain voltage and frequency to achieve the rated HP and RPM. All you are doing with the VFD is changing the frequency to change the RPM. Running the motor at a low frequency will greatly reduce the motor's torque. It will also heat the motor up and in time deteriorate the wire insulation. As I remember, your machine has a separate motor with an expandable pulley sheave. The belt powers up to the feed works that are gear driven. If you plan on running the VFD down to a slow speed, you might have problems with the torque needed to power the feed works. I don't understand what you are hoping to gain from the planer. Slowing down the feed will give you more knife marks per inch, but it will also increase the friction on the blades. The blades will dull a lot faster and you will be changing or sharpening the blades a lot more often. What are you trying to achieve? If you are looking for a finished surface, then you really need to be sanding the surface. That is why drum sanders, then later, widebelt sanders were invented.


From contributor B:
Perhaps more expensive, but certainly problem free, would be to replace the motor with a low RPM motor.


From the original questioner:
As to what I am trying to achieve, I use the planer after flattening stock on the jointer. I am trying to reduce tearout in cherry and maple specifically, even though the next step is to the AEM 75-25 sander. Sometimes if I plane to 13/16 fat and then go to the widebelt, there are still one or two nicks that aren't sanded out at 3/4. I have the bed rollers set at 5 thousandths and the pressure bar, chip breaker at 1/32, infeed at 1/16 and I think the same for the outfeed, but I'd have to check. I use a micrometer to set the knives, which were new at the last change.

The planer is new to me, so I'm not adverse to looking at different solutions. I thought that the 25 feet per minute was a bit high for achieving a finish that I could start sanding at 150 on an orbital (assuming a run too short to fire up the widebelt).

One note as an aside is that an employee just brought in his Dewalt planer that has two speeds, and although the finish is great on the slow speed, it does dull the knives quickly at that rate.



From contributor B:
Are you checking the grain direction before inserting a board into the planer? I know cherry can be chippy (have not had that problem with maple, although I have with birch), but you should be able to get a clean cut.

You're right that 25 fpm is very fast for a finish planing surface. I think 10 to 15 fpm is adequate, though, with anything below 10 likely to dull knives.

I modified my Powermatic 100 planer so I can slow it down to about 5 fpm (while maintaining cutterhead speed) on woods like curly maple, etc. It does do the trick, but I wouldn't use that speed on anything I didn't have to.



From contributor T:
Are the problems with tear out on figured material? It doesn't have to be curly maple to be a problem. A simple change in grain direction and most straight knife planers will get some tear out. Maintaining sharp blades will help considerably. If you are not getting end snipe or a wavy surface planing, your machine is set up properly in regard to the bed rollers, chip breaker, and pressure bar. Slowing the feed speed will give you more cuts per inch and should help some. Spiral heads work a lot different than straight knives. More of a shearing action, and that is why they don't have as many problems with figured woods. You can try the VFD route and see how it works for you. In the long run you are much better off changing the head or the machine.

I have had multiple planers over the years, including one of the P24s. What I would consider my finishing planer is a Delta/Invicta 24" planer with a Newman helical carbide head. It has two speeds, 25 and 46 FPM. I generally run it on high, and have no problems with any tear out. I do send everything that is going to be finished through the widebelt after the planer. So I can't speak for trying to go directly to hand sanding with an orbital.



From contributor K:
Grind a 15 degree face bevel just long enough to register, about an eighth of an inch or so. Be sure it does not reach to the gibs. This will reduce the effective cutting angle to around 15 or 20 degrees. It will increase noise and power consumption, but it should do the trick. Worked for me.


From contributor K:
The edge, being blunter, is more durable.

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