Granite Sanding Slab

[Colin Brown]

I'm trying to find an alternative to using a thickness sander for nuts and saddles and have heard talk of granite sanding slabs? I did some searches on the internet and they seem to be super expensive.
Does anyone have any idea of where I might want to search for something like this...Im open to ideas.

Also what do you think of using a firm set piece of glass as a flat sanding surface?

[Ned Knepp]

Hi Colin,
I use an 10"x 12"x 3/8" pane of plate glass as a surface for sanding things like this and for sharpening tools. Those precision granite slabs are nice but not too portable even if you can find one reasonable priced. I don't know if any of us are working to the sort of tolerances that would demand one of those.

I have a friend that uses the cast iron surface on his table saw for sharpening his chisels. It works find too.

Ned

[Bob Webster]

I went to a local stone and tile merchant and got them to cut me a 24"X24"X3/4" chunk of gloss faced granite for around $35. I use it for a backer for planing and graduating tops, etc. Frankly, I've also had just as good success using one-off marble tiles from Home Depot.

For what you want to do, you don't need an engineered ultra-flat surface which is what those expensive slabs are. In fact, they're normally used in engineering environments that require ultra flat repeatable setups of optical components, for example. Someone is just trying to expand the market for them and they're overkill, in my exalted opinion. Go to Home Depot.

Cheers,
Bob

[Russell Vance]

Yep, Bobs on the money - I use plate glass for flattening things (wish I could get my gut on it) and also you can wet it and surface tension a piece of emery paper on it to sharpen your chisels or plane blades when you don't have stones available (my cabinet-maker friends refer to my planes as 'cheese graters' but they are just rude boys!)

Adhesive backed abrasive such as Stikit is also a handy companion to this for flattening. And, bone machines a treat with a laminate trimmer/small router chucked with a follower bit and a straight edge or template for cutting precision flat and square nut bottom edges and top profiles.

[Bob Webster]

The wetting routine is a nice trick. Might even work on marble tile. Instead of spray adhesives or Stikit abrasives, I'd gone to backing the sandpaper with the wide double sided tape from Stew-Mac. It's not cheap but there's no need for cleanup after peeling it off the flat surface. You also can then use finer grits than are available in Stickit. But, the wetting method solves all that very neatly.

As for the router method, I assume you're using something like an all-carbide laminate trimmer bit, ja? Would you recommend it over something like the Robosander? By the way, do you know what a Luthiers' Friend is? In this economy, it's someone who pays you for the pizza.

Regarding your gut, I can only commiserate. Back in the mid-'70s, I made a 4 week business trip around Australia. After 4 weeks of multiple beers every night and lamb's fry at the breakfast buffet, I came back packing an extra 2 stones weight. Damned near didn't have anything I could wear on the return flight. And I'd do it again in a heartbeat.

Cheers,
Bob

[Russell Vance]

Bob, yep - carbide tipped 3/8 bits keep the tip speed down and manoeuvre well - for some reason they are expensive through the Luthier's supply shops but brands like Vermont and stuff from Grizzly (which I saw last trip) are relatively cheap and do the job just fine. I just clamp the bone under a straight edge or curved template for the tops and use the follower bit.

The finish is dead flat and square and the time saved vs remove stock (bust the blank in half!) file/sand flat, check, check again, repeat etc is definitely contributing to my accuracy, quality and profit margin - it is also the bomb for accurately machining the bottom of saddles to allow for undersaddle transducers.

If you have ever had to install an undersaddle transducer in a vintage Martin bridge (the one with the bone saddle extending into the bridge wings) you will appreciate the abilty to machine a dead flat rebate into the bottom of the saddle blank (around 35 thou deep to allow a Fishman 3/32 transducer to have sufficient pressure) leaving the bottom ends of the saddle intact and then have it pop straight back into the extended slot looking like new.

Getting these saddles out is a chore - they are glued in and you need to 'worry' them out (I use my big end nippers and a couple of guitar picks to apply gentle leverage at either end of the bridge in equal amounts (the Swedish way) and haven't lost one yet - but it is only a matter of time.

Bob, why is it that clean living, fit and intelligent blokes can't go to another country without having to pack a Spandex suit and 200 headache pills - must be the water , eh.
Gis a call next time you travel - the beer is still mighty fine.

Rusty.

[Bob Webster]

Thanks for the tip on the bits. Grizzly is just up the road a ways and I can get struff from them in a day. Pretty handy. As for the transducer saddle install, I had someone call me with just such a request last week and now I know how to handle it. I'll have to cobble together some sort of clamping fixture with a straight edge but that should be quite easy enough.

If I think I can survive another visit to Australia and book the trip, I'd love to swing by and see you, thanks. Do you ever make it out this way to go to the Guild of American Luthiers convention? If so, please consider my place your base camp.

Cheers,
Bob

[FRANK]

I use a Glass block 1/4 inch thick 3 inch wide and 11 inches long should be able to get 3 pieces on that no problem with 3m supper 77 spray adhesive

[Colin Brown]

Thanks for all the ideas fellas

[Bob Gaddis]

I used to be in the monument business so I have some old tombstones lying around that I use. Go to your local monument dealer and see if he has any messed-up stones(wrong names, misspelling, broken corners, etc) he'll sell cheap. You can order a 1' x 2' flat marker that's about3" thick that will do nicely and won't cost that much.

[Michael Breid]

I went to my local Bed, Bath, and Beyond and found a marble cheese cutting board about 8" X 8" X 3/4" thick. It was dead level flat. There's a slot in it for a cheese knife which I filled with a strip of hardwood using epoxy. I glued(epoxy) four small makeshift legs(1/2" dowel) to each bottom corner. When I have to size up small stuff like nuts ,saddles, inlays, etc. I tape a piece of sandpaper to the surface of the marble and work the piece of bone, pearl, ebony, rosewood, etc. to shape. If I recall the marble cheese cutting board wasn't that expensive(made in India probably) and the size is perfect for doing small things on the bench. I have also glued glass pane on different blocks of hardwood and made nice shapers from that. The glass idea is a good one, but you only drop it....once.

[Frank Ford]

Here's a way to go -

ENCO has a great deal on granite surface plates. (www.use-enco.com) They have the 12 x 18 (stock number 640-0120) for 24.95 as a Web special, and if you add some other stuff to your order, you can can get free shipping:

"Free UPS Shipping on all orders over $25.00 Use promo code PRSMAR offer expires 4/30/09"

Totally nuts, if you ask me - the UPS fee would be a killer!

[Colin Brown]

Good call Frank, That is exactly what I had in mind when I posted this question!