dmoore99 wrote:
Menzerna polishing compound - I've been using this product for a few years with generally good results. However, recently I seem to be building up light layers of compound on the guitar finish as I buff. I'm using a buffer that turns at 1725 RPMs but I try to hold the work to the wheel lightly to minimize the heat. What is your wheel size? You mention that you've been getting good results in the past. Were the "satisfactory" results obtained with this same buffer and same wheel size? If you have changed any component that affects SFPM from your original (satisfactory) setup, i.e., shaft speed or wheel size, that is the first thing I would check.
The buildup is very difficult to remove and I have resorted to sanding the surface to remove the buildup and start over. Naptha does not dissolve the built up compound. I'm using the paste compound in bar form. The compound and the buffing wheels are each 5 years old. The buffing wheels have been raked clean and do not appear to be loaded with excess compound. Even though the wheel appears to be raked clean, a well-used wheel can still hold more than what might be apparent. Anytime I have a wheel that's giving me fits, I rake it, then run it dry against some scrap, then repeat a couple more times before recharging the wheel. Doesn't always work, but more often than not it saves replacing the wheel.
Has anyone else encountered this problem or does anyone have a suggestion about how to prevent or remove the compound buidup? Thanks, Dean
Anytime you feel you have to use "light" pressure to make things work correctly, then that is a good indicator that something in the combination is not correct.
The "light touch" trick sometimes works, but more often doesn't. The problem is that if you go
too light on the pressure, you may not be letting the compound cut as designed, yet it's still moving across the workpiece. So you're getting friction with less than-optimal-cutting. This will definitely cause you problems. Plus, the "light touch" is more difficult to control in a consistent manner.
It's much easier to ensure you have the correct surface speed and proper amount of compound with the proper pressure.
If you were getting satisfactory results in the past, you need to determine what has changed in your combination that now causes problems.
1. Is shaft speed and wheel diameter the same as when you were getting good results, or have you changed one of the two (or both)?
These two factors determine your
surface speed (SFPM). With the 1725 RPM you stated, the largest wheel with which I would feel safe for buffing finishes is only 6". Actually, I would like it slower yet, but that's already a relatively small wheel for this type of application. Better to slow the shaft speed and allow a larger-diameter wheel.
Whatever your combination, best results for finishes call for surface speeds well below 3500 SFPM, and personally I like it considerably lower than that (1100-2500 SFPM has always worked best for me). Your "safe window" for surface speeds is pretty wide, but the most common error is to go too fast. Sure, your goal is to speed up the process; otherwise you'd be polishing by hand. But keep in mind that you're not polishing metal.
But that's me; everyone has different results based upon their overall combination and application.
2. If nothing has changed with your surface speed (shaft RPM and wheel diameter are the same), and you were getting good results with that same speed in the past, then consider the condition of the wheel itself. Often we get a "cruddy" wheel, then think all we have to do is rake it and everything is fine. Quite often, that's the case, but not always.
Here's food for thought- if you think the buildup is difficult to remove on the workpiece (guitar in this case), how difficult is it to remove from the wheel itself?
The ideal scenario is to not overcharge the wheel and ensure proper speed and pressure for the application at hand. If, while charging the wheel, you're leaving the compound on the wheel for more than a second, then you're probably overcharging the wheel.
Once the wheel is overcharged (or improper speeds/pressures have otherwise rendered it problematic), the best process to get things right again (short of replacing the wheel) is to rake, run dry, rake, run dry. I like to do that a couple of times on a somewhat rougher piece of scrap before recharging the wheel with compound again. When I say "rougher", I don't mean run it against sandpaper or anything else that may introduce contamination to the wheel. A freshly-planed (not sanded) scrap of maple works great for me. A
clean piece of aluminum tread plate has also served me very well for this purpose.
In my experience, this does a much better job of restoring a really messed-up wheel than simply raking it.
And then you always have the option of getting a new wheel, but it's usually best to first determine the source of your problem.
3. And finally, check to see if your technique has changed from when you were getting good results. Too much pressure is bad, but so is too little. We're all human, so application pressure will never be the same, but the need for the "light touch" has me wondering.
Don't know if any of this helps, but it's where I would start.
Rob
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