Potentiometer shafts too fat for old knobs. How to thin them down?

[Uncle Thor's Hamer]

As the factory was shutting down I bought a new improved 2 knob stereo FET preamp and piezo saddle for a 1983 Ovation 1537 acoustic guitar. This is a bit of a holy grail guitar in the Ovation world. The old preamp still works but the new one is supposed to have better fidelity. Plus this model preamp will be extremely difficult to find in the future now that the factory is gone. Having a spare preamp on hand seemed like a smart idea.

Apparently the new pots have a metric dimension. They measure out at .27x", whereas the old pot shafts are .250". The original knobs are walnut with a brass insert. There's no way I'll consider drilling those old knobs!

Other than spending a couple hours manually filing down the new shafts, are there any better/smarter ways to knock them down to .250" while keeping them fairly round and concentric?

[Punkavenger]

I'd start with filing and then go to emery cloth/wet or dry sandpaper. Shouldn't take that long. 1/2 hr or so.

[cynic]

It may be easier to get identical (or similar enough) knobs in the metric dimensions. There's seemingly no end to the assortment of knobs available on eBay.

Worst case, perhaps just the knurled insert can be removed and replaced with a metricified version?

[Uncle Thor's Hamer]

It may be easier to get identical (or similar enough) knobs in the metric dimensions. There's seemingly no end to the assortment of knobs available on eBay.

Worst case, perhaps just the knurled insert can be removed and replaced with a metricified version?

Not likely at an affordable price, unfortunately. Currently $199.99 on the evilbay. http://www.ebay.com/itm/OVATION-ADAMAS-WALNUT-VOLUME-TONE-KNOBS-NOS-NEW-OLD-STOCK-ACOUSTIC-ELECTRIC-/161342649835?pt=Guitar_Accessories&hash=item2590c575eb

[Uncle Thor's Hamer]

I'd start with filing and then go to emery cloth/wet or dry sandpaper. Shouldn't take that long. 1/2 hr or so.

I was hoping somebody knew of a pencil sharpener type of gizmo. Half an hour with a file seems a lot quicker than I am likely to be, but I can be a bit perfectionist sometimes.

[Thundernotes]

.020"?

back out the set screw and get a drill bit

But that's just me….. if you don't want to drill them, pinch the shaft of the pot between two flat files and turn slowly. It shouldn't take long to grind off that little bit of metal

[Studio Custom]

What if you use a Dremel with sandpaper? Tape up the crest to keep dust out.

[cmatthes]

They are still keeping the Ovation repair shop going though, aren't they?

[Uncle Thor's Hamer]

Nyet. The repair shop is closed. One or more former employees are opening their own business(es) to service Ovation and Adamas guitars. Availability of parts and materials may be an issue with some of the unique items such as carbon fiber "fibronic" tops to the Adamas guitars, and Ovation branded hardware.

This preamp seems to have several metric dimension parts. The nuts on the pots and the output jacks are not the standard 1/2" wrench, they are slightly smaller. My guess is parts were changed to accommodate Asian production. FMIC appeared to be planning to move all production offshore on the entire line, while blurring the distinction between USA premium product and the lower design/price point Asian built products. Fitting new metric replacement parts onto USA built non-metric guitars was apparently not a concern.