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Handle pulsation when quill is extended at low speeds

Matanuska

The quill extension handle on my 520 pulses at low speeds (900 rpm) as the quill is extended in drill press mode. It's more of a slight vibration at sawing speeds. Interestingly, the pulsing only happens while the quill is being extended. Stopping the quill extension stops the pulsation. Watching the quill extend with the cover off it seems the drive & idler shafts are rotating smoothly and the belt tension is balanced. My initial hunch was that the metal spline shaft that slides into the nylon spline sleeve is slightly bent but that doesn't explain why the pulsing occurs only while the quill is being extended. Removing the quill and rotating the spline shaft I don't see any obvious lop-sided rotation. The quill bearings rotate freely and without any noticeable slop. It's not an issue on the other end of the quill (no excessive runout on the sawblade). Now I'm thinking there may be some slop in the way the pinion gear mates with the quill but the teeth on both look fine. With that in mind I tried adjusting the set screw that holds the quill in place but that doesn't help. Any ideas or suggestions?

edma194

What were you drilling with what kind of bit? I got a lot of pulsation using a 2-3/4" Forstner bit with a PowerPro at very low speeds (250-450RPM). I've been wondering if it's the pulsing of the motor needed to turn it at those low speeds. OTOH I have to check that the quill barrel is securely held in the old Type A headstock, might just be that.

Matanuska

This was with the machine running unloaded and nothing mounted on the shaft. Pulsation occurs while quill is being extended or retracted, and stops when quill extension or retraction stops.

DLB

IMO some amount of pulsation is normal. In my shop, sample of one of each, the pulsation is more noticeable on my conventional headstock than on a PowerPro. But both exhibited it. I'm sure there is also something called excessive pulsation, but I'm not sure how we would measure or define it.

Getting back to your original thought regarding quill spindle runout at the spline end... My PowerPro kit came with a Drive Sleeve Assembly with excessive runout. This is the same problem but with the opposite cause. I didn't notice it for quite a while, but the runout (wobble) is extremely noticeable if you mount a sanding disc on the upper auxiliary spindle and run at low speeds. This was documented here:(https://forum.shopsmith.com/viewtopic.php?p=302299#p302299)

- David

Matanuska

I'm glad to hear it's not just my machine. I had wondered if the pulsation might have something to do with a misaligned drive sleeve assembly so I tried mounting the sanding disc on that end as you suggested but didn't notice any visible runout. That leaves the engineer in me wondering how drive shaft rotation along the spindle axis is transformed 90 degrees into handle pulsation (rotation) since it is only noticeable when the quill is being extended or retracted. Handle pulsation must mean the pinion shaft gear teeth are rocking slightly back and forth against the quill teeth as the quill is extended or retracted while the spindle is rotating, but why? I did notice that after I lubricated the spline with some dry lubricant the pulsation lessened but didn't go away. Hmm . . .

Matanuska

Matanuska wrote The quill extension handle on my 520 pulses at low speeds (900 rpm) as the quill is extended in drill press mode.

Today I tracked down the source of the handle pulsation I was experiencing when extending the quill in drill press mode. Previously I had adjusted the quill shaft retaining setscrew so that the quill retracted easily when pressure was released on the drill press handle. On a whim I tightened the setscrew even further and the pulsation went completely away. Unfortunately that meant the quill no longer retracted on its own when handle pressure was released. I removed the quill and set screw and examined both. I found that the quill slot that the flat headed setscrew rides in had several nicks along both edges and the bottom of the slot also had some rough spots. I think the nicks and rough spots were caused by previous less than careful setscrew adjustments that had damaged the edges and bottom of the slot. I carefully filed the inner edges of the slot to remove the burrs and used a thin whetstone to smooth the bottom of the slot. I also carefully filed the end of the setscrew to smooth its flat profile. I cleaned and re-waxed the quill paying special attention to the slot and the end of the setscrew, then re-assembled the quill. I was then able to tighten the setscrew enough to get rid of the pulsation while also allowing the quill to retract on its own when handle pressure was released. The setscrew sweet spot with no pulsation and good quill retraction was quite small. I also found that the setscrew was not tight in its threads which might cause it to back out with use so I added couple of small drops of blue thread lock on the outer end of the setscrew making sure to keep it away from the slot. So far so good!

Matanuska

DLB

I don't understand the connection between the quill limit setscrew and the pulsing. But I looked in the manual and it says to tighten it until it bottoms out in the groove, then back it out 1/16 turn. (It actually says 1/16" turn, so I checked another manual.) I normally back mine out about 1/4 turn, so I'm definitely loose according to the manual. But that's because I never thought it mattered. 1/16 turn suggests minimal clearance between the tip of the "dog" portion of the setscrew and the bottom of the groove: a touch over three thousandths if my math is right. And your results suggest that is critical. But why?

- David

Matanuska

I think the pulsation in the handle might be caused by gyroscopic precession forces creating torque at right angles to the spindle's axis of rotation. These are the same sideways forces that make the point of a spinning top move in circles rather than staying in one spot. Fixing the axis of rotation like the spindle would create the torque and then moving the quill in and out might cause the torque vector to rotate around the spindle axis. When the torque vector lines up with the axis of the handle rotation it might cause a force pulse in the handle that goes away until it lines up again. Tightening the set screw might damp the pulsations. Just a thought - its been a long time since I took my engineering dynamics course.

edma194

Matanuska wrote Tightening the set screw might damp the pulsations.

Often you need to minimize the ability of something to vibrate and keep out of the range of some kind of harmonic frequency that creates a self sustaining major vibration. Can't say about this case but when I can get my shop warm again I need to check this out on my drill press.

DLB

FWIW, I find the pulsation during extension / retraction is much more pronounced if I put a steel sanding disc on the spindle.

- David

Matanuska

I've been thinking some more about this and now I'm leaning toward Ed's resonant frequency vibration explanation. Doing a bit more reading it appears gyroscopic precession forces are a response to a torque applied at right angles to the axis of rotation. Gravity might do this as the quill is moved in or out in the horizontal boring position but it wouldn't explain pulsation in the vertical drill press mode. Whatever the explanation, deburring and waxing the quill and tightening the setscrew have fixed the problem for me.