You actually get a bonus when you use this method; one gear requires about 3.75 ingots instead of 4. In long production chains they're quite good.As a note, sand requires a higher temperature (and thus more power) than glass will. Further, the Fabricator will continue to use power to keep itself hot, so you should work quickly.
More amusingly, the Fabricator can also melt metals - you can use this with wax molds to make things, although I'm not sure why you would.