Blade anatomies
One of the most used tools in model railroading is the hobby knife. Probably the most popular is the Exacto knife. While it may be the most popular, it may not be the best blade to use for your application. It all depends on WHAT you are cutting, and the TYPE of cuts you are making. Curved cuts of any kind, as well as cutting in tight places, are done well with the pointed end of an Exacto. An Exacto also has unlimited other uses.

If you are making repetitive straight cuts in wood or styrene up to 1/8" thick, then a SERB (Single Edge Razor Blade) is best. The reason for this is the "included blade angle". Careful measurements and some basic trigonometry produced the data for the following sketches, which show the angles for 4 popular blades.

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Clearly the SERB is thinner, and has a much more acute blade angle than the others.

If you cut (or score and then snap) styrene or similar materials with an exacto blade, box cutter, or utility knife, you may wind up with a ridge on the cut edge. Using a single edge razor blade eliminates this ridge, due to the thinner blade, and a more acute angle to the cutting surface. AN ADDED BONUS IS THAT IT WILL HOLD ITS EDGE LONGER THAN AN EXACTO BLADE. Also, no ridge means that sanding can be almost eliminated.
Blades are cheaper too (100 for about $6.00).

This thread is NOT to convince anyone to use a different blade. Look at the sketches and then decide for yourself. More importantly, use what you are comfortable with.

I made a cheap SERB holder and I have sketches and pics so you can make your own.
Charter member of CAMRRA.
I've never used a hobby knife because I so can not make a good vertical cut.
My favored cutters are some medical scalpels which have a very fine cutting edge, around 2 dregrees, I think. The problem is to get these old scalpels today because such with changing blades now also are used in medicine.

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From time to time I find such old scalpels at flea markets, but they are in many cases not worth the money. The steel is too soft and I can not use to cut wood. Really, a difficult problem for my modeling jobs in future.
A good and usable solution could be these razor blade holders.
Cheers, Bernd

Please visit also my website
You can read some more about my model projects and interests in my chronicle of facebook.
Sorry, big mistake!
I have my scalpels blades measured and calculated their angle with trigonometric functions - and I have calculated a value of 12 degrees. I'm very surprised about this great value!
Again sorry for this false value that I had only estimated. I was sure that scalpels have many times smaller values.
Cheers, Bernd

Please visit also my website
You can read some more about my model projects and interests in my chronicle of facebook.

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