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Thanks to all who replied. I had 17 replies which basically said they
all learned to hold the bread to be cut, straight and to use a sharp and
thin knife preferable an electric one. 2 were using a knife with a
guide. 1 built a cutting device out of wood with the thickness that he
wanted.

The solution ......
Learn to hold the bread straight and use a sharp knife...... and
practice
Harold Wolofsky