Double Bass Glass as a scraper

[Matthew Tucker]

Could someone describe to me the use of glass as a scraper in instrument building? I've read quite a few luthiers talking about using it as a scraper (as well as steel burr scrapers of course)

Is it using broken glass? specially cut? Any special applications or tricks?

 

[M_A_T_T]

Never tried it. I personally would see it hard to shape the glass to a specific shape, like I do with my steel scrapers. Glass probably stays sharper longer, though.

 

[arnoldschnitzer]

The thin plate glass is purposefully broken into pieces of a roughly triangular shape. Generally, one of the surfaces will be slightly convex and therefore good for scraping small areas. They are very sharp but don't retain the sharpness for long. Many luthiers love glass scrapers; I have a few but prefer thin steel.

 

[M_A_T_T]

Can you resharpen glass scrapers?

 

[Martin Sheridan]

I don't think glass scrapers are all that hot of an idea. Perhaps you can resharpen by re-breaking? I used to use a glass cutter, but I still cut myself to the bone once, and as AS says they don't stay sharp very long.

Use steel. Grind the part you want to use to 30 degrees.
Take a very flat piece of steel like the back of a chisel, place the scraper burr side up on a good flat work surface, rub it flat, then place the edge over the side of the work bench, and take the flat side of your chisel and draw it across the edge just once at a 90 degree angle. It will be very sharp and every time you do it, it will become sharper. I only use two scrapers of different shapes, but I know others who have more.
Although thin steel is normally used, Sacconi said that Stradivari used broken sword blades!

 

[Damon Rondeau]

Anything with an edge will scrape -- the question is how well it will scrape. Glass seems like a good idea until slash yourself with it, and that bloody outcome is only a matter of time.

Steel!! It's the latest, greatest thing.

 

[Martin Sheridan]

Anything with an edge will scrape -- the question is how well it will scrape. Glass seems like a good idea until slash yourself with it, and that bloody outcome is only a matter of time.

Steel!! It's the latest, greatest thing.

That's exactly why I stopped using glass. I cut myself often enough, but glass does a really terrific job on you, and like Arnold and I said, it doesn't stay sharp very long anyway.
But it is sharp when you break it and it doesn't break where you think it will, but right under and through your thumb!
Thumbs are useful to keep around.

 

[M_A_T_T]

I would've though gless would stay sharp for a long time because it's hard. Oh well, I wasn't going to try it anyways, I like my specifically shaped steel scrapers.

 

[Jeff Bollbach]

Some of the advantages of glass scrapers are that no sharpening is needed and you can recycle plenty of glass that would normally just be trash. Once you become adept at the cutting it can be economical in both time and money spent. That being said, while I know many violin makers who swear by glass, i never use it myself. I love the versatility of steel, you cantake a straight edge scraper and bend it creating infinite curves. You can also make very specific shapes that you never could with glass. I have a set of scrapers made from heavy feeler gauges just for getting into scroll volutes.

 

[Matthew Tucker]

Thank you for those views. I guess I'll try it out when I get a chance, and try not to cut myself. I used to make stained glass windows, so I am familiar with how glass breaks.

 

[Eric Jackson]

Tried glass, didn't particularly like it. Tape the edges you're going to handle with a layer or two of duct tape or masking tape to prevent gashes.

I've found grinding and stoning a 90 degree edge on a piece of .030" spring steel then turning the burr makes a good scraper. I use a hard 1/4" steel dowell in an old screwdriver handle for turning the burr.

 

[Jeff Bollbach]

Eric, I used to use the prescribed 90 degrees until Michael Krahmer showed me the way he did it at around 65 degrees. you lose having 2 sharp sides but it can be way sharper-for those really fine finish scrapings. Also very easy to grind and hone.

 

[Silversorcerer]

To date I have used mostly steel or other metal scrapers but I resort to glass for some special shapes that I might only use once or twice.

Contrary to popular beleif, glass is easy to cut to shape if you know how to use a cutting wheel. A stained-glass person knows all this but I encourage others who might need the odd scraper to pick up a glass cutter at the hardware store and try it out. Actually the wheel just puts a score line on the glass and you can then easily tap the glass to complete the break along the score. It works best with light pressure and continuous motion. A spotty score line will usually not break clean. With a few practice tries flat glass can be cut to almost any shape quite predictably, the best for this to me is double strength B glass which is the same as window glass. Window glass is much less expensive than blank metal so if you get an unlucky break at first it's no great loss in material expense.

I don't see why it would be any more or less likely to wound than other scrapers if you tape or dull the other edges. I experienced many minor and a few not so minor glass cuts in the picture framing business and even a deep cut will usually be clean and heal very quickly compared to a metal or particularly a paper cut.

The primary advantage is that one can quickly and cheaply produce a scraper with a specific shape. You can make another one from glass faster than you can resharpen a metal scraper, too. The downside is that you really can't easily resharpen the glass at all. You have to score and break off about .25'' or more to get a consistent edge. My rule: metal for the ones I need all the time, glass for the single use scaper. Be careful with either one.

 

[Nick Lloyd]

I love glass scrapers. They aren't a substitute for flexible steel scrapers, but another fast and sharp way to scrape/prepare the top before varnishing. No, you can't re-sharpen them. Just throw them away and make another.

The method taught to me is: take two backwards swipes on the edge of a pane of glass with a square-edged bastard file. Now place the file under the pane, just to the right of the 'nick'. Give a quick flip with the wrist and shazaam! you have a very sharp glass scraper. You can control how long/short the length and radius is of the scraper by how you flip the file. It's something that is much easier taugh visually than on an internet forum...

 

[Eric Jackson]

Nnick, I'm tryna unnerstand this but I'm stumblin'...
Do you start with a strip of glass 4" wide or so, and break 2" pieces off? Do you break triangles as Arnold says? I understand the idea of scoring the edge of the glass to give the crack a place to start, but I can't see how you get a curved crack by how you flick the file. Does the angle of the file to the edge of the glass do that?

Edit: What thickness glass do you use? I tried garden variety hardware store single diamond window glass, cut instead of just broken from an edge. Maybe breaking to a scored line doesn't give as sharp an edge.

I'm assuming when Jeff says 65 degrees and Martin says 30 degrees they're talking about roughly the same angle. I'm gonna hafta try that, not that I do anywhere near as much scraping as you guys do.

 

[Matthew Tucker]

Old glass never cuts or breaks well, its a liquid and the "grain" is much stronger in old glass that has settled with time.

there are two ways I know to break glass safely ... both involve scoring the glass first with hard steel or a diamond tip, right up to an edge. Just a score is sufficient, but the more even, the better. New glass is easier.

1. place the glass on a clean flat surface with a matchstick under the score at the edge close to you, then push down on the shorter piece of glass next to the matchstick, it should snap off neatly, even if the piece of glass is quite large.

2. hold the glass each side of the score with the thumbs on top facing away from you, fingers underneath. then twist your hands *apart* as if you are breaking a biscuit. the glass should "snic" and break leaving you with a neat break. I prefer this second method but its not as safe as the first. You can cut very long thin curvy slices this way.

If your score is only a "start" from the edge, the break will tear away from the score as the glass breaks, often a curve.

Or you can score the entire curve first. Even with a scored line, the bottom part of the break is very sharp.

cutting glass is quite fun if the glass isn't too old. (If it is, it must be a bit like bending the ribs on the Pappas bass ...)

 

[Nick Lloyd]

Nnick, I'm tryna unnerstand this but I'm stumblin'...
Do you start with a strip of glass 4" wide or so, and break 2" pieces off? Do you break triangles as Arnold says? I understand the idea of scoring the edge of the glass to give the crack a place to start, but I can't see how you get a curved crack by how you flick the file. Does the angle of the file to the edge of the glass do that?

Edit: What thickness glass do you use? I tried garden variety hardware store single diamond window glass, cut instead of just broken from an edge. Maybe breaking to a scored line doesn't give as sharp an edge.

I use whatever glass panes I can get for free from the hardware store down the street. It's a standard window-pane thickness. You could start with a strip 4" wide, then "flick" off smaller or larger pieces as you need them. The file is positioned under the pane, at a slight 1 or 2 o'clock position. The break usually has some kind of curve to it. If you position the file with more angle, you will end up with a smaller scraper. The size of the scraper also depends on how far in you make the 'nick' from the right edge. If you are right-handed, you would be breaking off scrapers from right to left.

I'm using glass scrapers as a file prep-scraping before varnishing. There are other metal scrapers for doing various jobs, as well.

The score does not need to be that deep. Cutting off scrapers wouldn't produce that razor edge that you want. You want to break them off in a relatively controlled way.

 

[pkr2]

First off, let me make it clear that I dont claim to be a luthier.

I do however consider myself a very good furniture builder.

I have used glass as a scraper for more years than I want to admit to.

The way I have always gotten the glass is to simply put a piece of window pane glass under a piece of cloth and whack it in the center hard enough to break the glass.

Some of the pieces are usable,some are not. I throw away that which is not and use that which is.

I have used steel scrapers and there are jobs where only they will work. Glass works just fine for most jobs, though.

A steel scraper with a properly turned edge is a pleasure to use. A piece of broken glass is also a pleaure to use and there is no maintenance when it gets dull.

If you need to smooth a piece of wood, try it. If it doesn't work to suit you, throw it away and use a steel scraper. It costs nothing to try.