Today in the shop (poof) and other adventures

JPG · Post by **JPG** » Mon Sep 30, 2013 4:30 pm

Ed in Tampa wrote:Do we get a 5% discount?

No but you get a warranty and a Helluvalot of good Customer Support!;)

dusty · Post by **dusty** » Mon Sep 30, 2013 6:18 pm

HEY!

The set screws in the hubs come loose from time to time and not just if you have the Power Pro.

If the set screw comes loose on my 510/520 it doesn't bang but it is loose. Why does it not bang? Because the direction and rate of rotation is constant at any given setting.

I don't know exactly how the Power Pro works but I know that the rate of rotation is not constant. It changes as a function of the Power Pro and when it changes, it appears that the results can be heard as well as seen.

I don't think this is necessarily a "Power Pro" problem but rather a symptom of something that is recognized only when using the Power Pro.

Does Shopsmith have work to do? Yeah, I think so but I don't believe that degrades the tangible results of the Power Pro.

What I do believe, however, is that Shopsmith should be more forthright about the existence of this phenomena. If I owned one, especially one that chattered like this, believe me there would be a lot more chatter here on the forum and elsewhere about that chatter and what is or is not being done to eliminate it.

reible · Post by **reible** » Mon Sep 30, 2013 7:35 pm

Hi,

In this case I don't think it is powerpro related. I could be wrong. I think it is quite likely I simply never got the setscrew as tight as it need to be. I have also had setscrews come loose before way before I got a powerpro. Again I think those were related to me.

My bandsaw runs fine on the powerpro, I've posted it running over on youtube and no matter how hard you listen there is no banging, just the same running or while cutting.

I don't hear it hunt while using the bandsaw, I can hear it when using the sanding disk. In fact that is the only operation when I can notice it.

I have done a fair amount of cutting since this happened and so far all is well.

I know some people have had issues, I don't believe I am one of them. Just like my bandsaw run normal with out any squeal, my powerpro doesn't bang....

For those wanting a discount, good luck with that.

Ed

BuckeyeDennis · Post by **BuckeyeDennis** » Tue Oct 01, 2013 12:01 am

charlese wrote:I'm pretty sure the Hub loosenes is just a symptom of the PowerPro issue. You can tighten and re-tighten and etc. The banging will return.

The banging is a non-issue with a speed reducer.

I have a lot of experience with similar issues on industrial CNC lathes. High-performance motors simply put more stress on shaft couplings. Rare-earth permanent magnet brushless servomotors, for example, can and will chew up and spit out shaft keys within a matter of weeks, ruining the motor shaft in the process. A bullet-proof solution is to attach the driven load to the motor shaft with a zero-backlash friction-clamp coupling.

For those of you with seriously enquiring minds (or that otherwise suspect I'm full of baloney) here's a link to a brochure for friction couplings that we have used with great success at work: http://www.fennerdrives.com/FetchFile.a ... 122779674c. The brochure describes the key-failure phenomenon quite elegantly and accurately.

Fortunately, it sounds like SS and Technatool have already done a good job of minimizing the shaft-coupling stresses from the PP. But I think it most unlikely that it will ever run as smoothly as a good ole' induction motor. If a dollop of Loctite on the set screw solves the problem, that is a tiny price to pay!

BTW, you are dead-on regarding the speed reducer eliminating the coupling problems. The "reflected inertia" of the load, as seen by the motor, is inversely proportional to the square of the speed reducer ratio. Switching back to plain English, the speed reducer ratio is 7:1. So the inertia seen by the motor is reduced by a factor of 49. Unless you mount 50 or more sanding disks on the output of the speed reducer, you should be good to go!

skou · Post by **skou** » Tue Oct 01, 2013 5:36 am

OK, Dennis, my antique ER runs a "Skip built" dc motor conversion. I've NEVER had these issues, except sometimes the motor will slightly lag, at a high power cut. Certainly not loosening set screws.

Guys, don't get me wrong, this antique ER has a MkV headrest, and supports the MkV bandsaw. (At least, until that schumbuchet {mis-spelled on purpose) STOLE it.) While I had it, the bandsaw ran flawlessly. (Search for "rusober", and you'll see what I'm referring to. Since the mouth-breather posted his phone number, call him up at 3:00 am, please.)

steve

BuckeyeDennis · Post by **BuckeyeDennis** » Tue Oct 01, 2013 6:37 am

skou wrote:OK, Dennis, my antique ER runs a "Skip built" dc motor conversion. I've NEVER had these issues, except sometimes the motor will slightly lag, at a high power cut. Certainly not loosening set screws.

steve

Ah, I see that I left out something important when re-typing, after my iPad ate my original response. The coupling problem isn't caused by high torque per se -- it's caused by high torque ripple and/or rapid torque reversals. Anything that "works" the coupling back and forth rapidly. This tends to loosen set screws and wallow out keyways.

The PP DVR motor inherently has a lot of torque ripple, which the controller does its best to reduce. Closed-loop velocity control will also tend to cause rapid torque changes - the tighter you tune the feedback loop, the more rapidly the motor accelerates in response to velocity errors.

For the price that Skip charges for the DC motors, I assume that they are brush-type motors, probably running open-loop. A fine solution, BTW, except that the brushes will have to be replaced eventually.

JPG · Post by **JPG** » Tue Oct 01, 2013 11:05 am

BuckeyeDennis wrote:Ah, I see that I left out something important when re-typing, after my iPad ate my original response. The coupling problem isn't caused by high torque per se -- it's caused by high torque ripple and/or rapid torque reversals. Anything that "works" the coupling back and forth rapidly. This tends to loosen set screws and wallow out keyways.

The PP DVR motor inherently has a lot of torque ripple, which the controller does its best to reduce. Closed-loop velocity control will also tend to cause rapid torque changes - the tighter you tune the feedback loop, the more rapidly the motor accelerates in response to velocity errors.

For the price that Skip charges for the DC motors, I assume that they are brush-type motors, probably running open-loop. A fine solution, BTW, except that the brushes will have to be replaced eventually.

So IMHO tis the nature of the beast, not a downer! When ya 'gain' advantages, there are usually 'tradeoffs'. Rapid 'correction' has high acceleration(both ways) attached.

Smooth usually accompanies slow response.

And yes the SS DVR motor brakes as well as runs constantly to maintain reasonably constant rpm(it will vary a few hundred as I observed during a shaping demo).

nuhobby · Post by **nuhobby** » Tue Oct 01, 2013 12:04 pm

I have speculated to myself that a DVR motor & control-loop dedicated only to the Bandsaw could be made 100% bang-free. What I'm guessing is the rub is that the headstock has to support many roles / many speeds, without a foolproof way of knowing exactly what's hooked to it. 900rpm could be the bandsaw, or it could be a drill-bit. Those are vastly different loads in terms of rotational inertia.

JPG · Post by **JPG** » Tue Oct 01, 2013 2:59 pm

nuhobby wrote:I have speculated to myself that a DVR motor & control-loop dedicated only to the Bandsaw could be made 100% bang-free. What I'm guessing is the rub is that the headstock has to support many roles / many speeds, without a foolproof way of knowing exactly what's hooked to it. 900rpm could be the bandsaw, or it could be a drill-bit. Those are vastly different loads in terms of rotational inertia.

Which is why I continue to be 'amazed' at how well it works on this multi-function machine.

If you are using the built in speed setting 'guide', you are 'informing' the controller what operation you are doing. I assume that is not being ignored by the controller.

If not, it should be 'paying attention' IMHO.

If so, a case can be made to not manually set speed.