Official Luthiers Forum!

If you are in the Chicago area and are looking for free granite cutoffs;
http://chicago.craigslist.org/wcl/zip/4140827259.html

I have no connection with these folks so can't comment on the quality.

Kent

i got a chinese marble or granite surfacing stone awhile back and i love it. i think i got it at rockler or woodcraft; they don't seem to carry them anymore. milled to 0.001" tolerance i think, which is plenty good enough for me to get crisp bevels on my chisels, etc
also: kfish, thanks for the craigslist tip, i am definitely going to check that out !

edit: or maybe it is 0.0001" tolerance, i can't recall

Wow, that's huge!! Must weigh a ton. Sure those dimensions are correct?

I bought a 24"x18"x3" thick granite surface plate new for $75 that is accurate to .0005" across the entire surfact (not that that much accuracy is really needed. I use it a lot. Very handy to have a reference that I know is flat for checking things (straight edges, etc.) ,sanding and clamping. I also use it as the base for my go-bar deck with 1.5" thick MDF radius dishes on top of it.

I built a frame to hold it out of 2x4's at seating height with 4 legs with locking swivel casters on them. I can easily move it around. Only supported on the outsides edges by the frame. VERY heavy but does not sag It is a rolling work table, reference plate, sanding surface, clamping table, and go-bar deck base. Well worth my money.

delete double post

i think i'd be more comfortable with at least one center support member, especially if using it to clamp...rock doesn't like to flex, and i'd think gravity alone will someday break it. that someday may be 147,000 years, but still...

Yes, these dimensions are absolutely correct.

The plate weighs something like 700 -800 kilograms (can't remember exactly) but that is the ballpark.

I had to fabricate a welded steel box section frame with castors, for the plate to sit on . It required an engine hoist to lift it off the delivery pallet and relocate it on its new stand.

Prior to my acquiring it the plate had served its time in the laboratory of British Aerospace. Now it serves to make aluminum sanding beams, precision straight edges, and occasionally to flatten plane soles.

A few years back, I went to a local glass company and asked what they had that was 'dead flat'. They had an off-cut from a commercial job that was 3/4"x 14"x18" that they were happy to get rid of for
$10.00. Best $10.00 I ever spent. Large enough for most things and light enough to easily handle.

Brent

I've got a 400 x 635 x 100mm granite surface plate, 80Kg, flatness is 0.002mm (better than 1/10th of a thou). Xmas present to myself last year.
Just been flattening/tuning my planes/blades so far.
To be honest, it's a PITA just sitting in a corner/end of a bench of my workshop. Been trying to think of a way to incorporate it into a workbench, but haven't managed to come up with something sensible, for my workshop set-up, - yet.
Also got a float glass plate 24" x 10" x 3/8".

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The name catgut is confusing. There are two explanations for the mix up.

Catgut is an abbreviation of the word cattle gut. Gut strings are made from sheep or goat intestines, in the past even from horse, mule or donkey intestines.

Otherwise it could be from the word kitgut or kitstring. Kit meant fiddle, not kitten.

...i was wondering about "float glass" earlier today, and wondering how flat a one meter panel of the earth's surface would be(as in, perfectly still liquid), compared to say a 0.001" tolerance on a square meter surfacing stone. not being a mathematician, i couldn't guess.

I have also wondered about that in the past ... my guess is that it would be flatter than a metre square surface plate with a tolerance of only .001" , but most surface plates, even workshop grades are manufactured to at least an accuracy of .0001". An AA plate will have an accuracy exceeding .00001".

So ... the question is ...will a one metre long arc described by a radius of 3959 miles have a sagitta greater or lesser than .00001" ? .... I have no idea, but somebody will no doubt work it out ...

btw I know the Earth isn't a true sphere, but taking 3959 miles as the mean radius is pretty much in the ballpark.

Remember we are talking about wood here.

A piece of MDF or MDO, a piece of plate glass with rounded edges, a piece of cherry out of the surface planer, or if you want to go crazy:

http://www.albertidesign.com/sander

Note that this is flat enough for violin makers, although $650 for a hand operated disc sander is a bit out of my league

Ed Minch

Convex, 'bout the same radius of the earth I would think.
6,371 km and http://liutaiomottola.com/formulae/sag.htm

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The name catgut is confusing. There are two explanations for the mix up.

Catgut is an abbreviation of the word cattle gut. Gut strings are made from sheep or goat intestines, in the past even from horse, mule or donkey intestines.

Otherwise it could be from the word kitgut or kitstring. Kit meant fiddle, not kitten.

That is real close to my work, thanks kfish

Enco currently has 12x18 granite surface plates on sale for $46 (Model #640-0120), and they often have promo codes for discounts - right now it's NOVPRM for 15% off a $150 order. A 12x18 holds two sheets nicely, side by side.

Some time ago I bought a couple of them for the shop, and inlaid some magnets so I can hold regular sandpaper down easily. It's no trick to drill the granite with a regular masonry bit, and with a few rare earthies epoxied in place, simple steel strips hold any old paper down nice and flat, so there's no bother or expense with sticky back stuff.

A couple of weeks ago Tom Erlewine (Dan's bro) was in the shop for a visit and he shot a sequence that I think will be sent around as one of their "Trade Secret" videos, in which the surface plates have a small cameo.

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Cheers,

Frank Ford

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yes i was just wondering how a pane of floated glass that followed the earth's radius compares in flatness to an engineered piece of granite.....i'll still probably be able to sleep tonight if i don't find out.

Hi Frank. that Stewmac Video is up and running now, and very informative it is too...excellent stuff.

Not that I would even dream of trying to teach my grandmother how to suck eggs, but by far the most efficient way to batch thickness nuts and saddles is to do it on the table saw (you do kinda have to have an Incra saw fence to do this ...) anyways , you just stick the blank nut or saddle (one side already flattened on the surface plate) with double sided tape into a rebated hardwood block, and just feed it through the saw. Obviously you would use a blade with at least 80 teeth ( on a 10" blade) to mimimize subsequent sanding.

We can easily batch things through the bigger sander on a pocketed sled, without needing to double-stick anything, but in reality, everything in the repair shop is in batches of one.

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Cheers,

Frank Ford

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Indeed, Frank, indeed.

My point about the Incra fence is that you hit the ground running, first time, every time ... no trial and error, which is endemic in any sanding system ...but hey, I do accept that a few minutes here and there doesn't matter all that much in the greater scheme of things ...

If I understand correctly, you put on a special blade, set the fence, double-stick blanks to the jig, and run them through your table saw. That seems to me to require quite a bit of setup, which, I suppose, is amortized over the number of units you might make. But it seems to me that just the act of sticking the blanks down and releasing them would be more time and effort than my entire process.

My adjustable table is always set up under the little belt sander, so I simply over to it, set the table screw to approximate depth, slide the blank through, measure and reset the table, slide through again, and repeat as necessary to achieve tolerance close to .001".

TOTAL elapsed time is predictably under a minute. No resetting would be required for multiples, of course, so they'd be super fast to make, but that's not my goal - I only use saddles one at a time, usually of unpredictable dimension.

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Cheers,

Frank Ford

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.....i dropped by this place the other day and yes, they do indeed have lots of marble/granite scrap. ongoing situation i guess. there were a couple of pallets of it behind the business, and a big dumpster about half full of small stuff(gonna be one insane heavy dumpster!)......

I have been thinking about getting a piece of granite for this type of stuff. Currently I use the jointer table for this type of stuff. I know other who use their cast iron table saw for this type of stuff.

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Another day, another dollar.

We no longer have a table saw or jointer in the shop, but I still use the band saw table for small flattening jobs when it's more handy - especially for quick small tool sharpening with silicon carbide paper.

In fact, I don't see the need for any serious precision, but those 12x18 plates were pretty cheap, and they're so thick and heavy, they don't get moved or put away, so they're always right at hand. Float glass, countertop granite or marble, old headstone granite, machine tables, even flattened MDF - they're all great for the use.

If you like the sticky back sandpaper, that's fine too. Me, I'm too cheap to spend the money on it, so I've found ways around using it at all in the shop. And I have trouble deciding on grits, too.

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Cheers,

Frank Ford

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