Planer Woes... Cutter Head Bearings

[JPG]

The torque is applied evenly 'around' the periphery of the hub.

The torque is applied to one side of the pulley at a greater radius.

[dgreen810]

Sounds reasonable. However if that be the case wouldn't a 10" saw blade turning at about the same RPM tend to work it's self loose?? Or a sanding disc. I know the sanding disc is turning at a slower RPM (maybe for this reason), but still the pulley thing is somewhat a mystery. As I stated SS has gone to steel pulleys for some reason and not because they are "Cheaper". Cast aluminum is certainly less costly than cast iron or machined steel I would think.

James, I agree with your explanation except that in the case of a saw blade, the torque lever is also the distance between the wood being cut and the shaft it is mounted on or 5" so again why doesn't it work loose as well.

Don G

[crosscreekcraig]

The saw blade is being driven (versus providing the power) and again in line and concentric to the power source. Also, the headstock quill has a reverse Morse taper to it (notice the flat has a triangular shape), so that in the even the screw does back out, the taper will stop it.

[dgreen810]

Not trying to be argumentative

Not sure I understand that you say the saw blade is "Driven" and the pulley is providing the power.

At any given moment a tooth of the blade is engaging the wood and the torque required to keep the blade moving is provided by a lever that is approximately 5 5/16" long if its a 10" blade and the 1 1/8 HP motor is applying power to that leverage to keep it moving. I am aware that the spindle has a reverse taper to keep the accessory on the spindle in case it comes loose. My question remains, why does one application remain tight while the other tends to work itself loose???

Don G

[JPG]

I believe the need for the key is the belt.

Consider where keys are used in the headstock. Idler pulley and motor pulley.

Granted they both have movable sheaves.

An exception is the quill shaft, but the woodruff key is to prevent rotation of the sleeve, not torque transmission.

A belt presents a non constant torque, and introduces backlash forces that are best overcome with a keyed shaft.

[dgreen810]

James

You are probably right. I know Vee belt drives can create all sorts of harmonic vibrations which would tend to vibrate most anything loose. That is the reason I selected the Grizzley Twist belt to put on my Planer. It is supposed to eliminate a lot of the vibrations and according to the reviews it does just that. I know my planer now runs extremely smooth and much more quiet compared to the way it ran before.

Don G

[BuckeyeDennis]

I have a dumb question to ponder. I think it is correct that the input shaft is milled with both a flat and a keyway so the planer can be mounted as a stand alone or mounted so it can be driven directly by the SS power head, But , when using the planer why does the pulley come loose when it is tightened to the flat, but the drive hub doesn't. Or it doesn't seem to be an issue with the people that use the planer mounted on a Mark V using the drive hub.

The only thing I can see that might explain the problem would be the original pulley is cast aluminum and the drive hub is steel. and possibly the mating of the two may be less rigid in some way. SS has gone to steel pulleys. Thoughts?

Don G

Torque. The drive hub is little bigger than the shaft itself and driven in parallel to the power source. The pulley is 3" in diameter so the torque involved turning the shaft is greater and driven perpendicular to the source via the belt. Those forces are too great for the small surface area contact on a broader flat surface by the relatively smaller set screw.

I beg to differ, regarding the torque. The input shaft torque is determined by the cutting load. You could mount a pully that was three feet in diameter on that shaft, and the shaft would still see the same torque at the same cutting load. What would happen is a proportional decrease in drive-belt tension, and of course the belt speed would have to be proportionally higher to maintain the RPM.

So the answer has to lie somewhere else. Here are a couple of theories.

1) Loosening is related to wobble. The drive hub is a more precise fit to the shaft, and the coupling doesn't exert much in the way of "wobble" forces.

2) Strength of materials. The aluminum is less rigid, and so the hub and set screw hole will deflect more at a given loading. Enough deflection, and the screw could work loose.

The cutting action of the planer knives is discontinuous, so the drive torque has a large amount of "ripple" on it. Set screws aren't terribly reliable under that type of loading.

[dgreen810]

I like both theories since both applied to the problem I had with my machine when I purchased it. Especially since I mentioned that possibility previously, aluminum versus steel.

Don G