Try using a bow style bread knife.
It works well because it allows you to put pressure on the opposite side of the loaf.
Also, the bow helps you visually line up the slice.
cooking.stackexchange.com/users/1148/Chris Cudmore
Try an electric knife if you have one hanging around for carving meat.
The small stroke of the two blades causes far less squashing/skewing of the loaf than the conventional serrated bread knife and leaves only one dimension to focus on, down.
When I really need accuracy, I'll cut the loaf in half lengthwise and with the cut
faces placed against the countertop, cut slices horizontally off from the bottom of each.
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A serrated blade, sharpened bevel on one side only.
Use the flat non-beveled edge against the loaf, the beveled side on the slice being cut.
Use a bread board.
Keep the knife for bread only, so that it stays sharp, hand wash & dry.
Take your time starting through the crust, so you don't crush the loaf.
If you start near the loaf center, the two halfs can be slid back together for freshness.
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A variety of bread slicers are available - it's just a box that you put the bread in, where the sides have pre-cut slots that guide your knife
so you get the uniformity you desire.
I don't use one of these for two main reasons: You can't adjust the thickness of the slice
- whatever the manufacturer decides is what you are stuck with.
Some breads just don't fit in them.
Most of the bread slicers I've seen are designed for a sandwich-loaf-shaped bread: very rectangular.
If I make a loaf of no-knead bread in my cast iron dutch oven, it ends up as a round loaf with too big a diameter to fit in any bread slicer I've seen.
But if you're making a rectangular sandwich loaf, getting a bread slicer is probably the way to go.
However, I've found that I can get straighter slices by experimenting with the angle at which I am holding and cutting the bread.
It will vary by the size and shape of your loaf, but with the big round loaves I was talking about earlier (which usually are not very tall), I find that I can cut straighter if I turn the loaf on its side so that I have a much narrower piece of bread to deal with.
That reduces the likeliness of my knife getting stuck.
cooking.stackexchange.com/users/6808/Laura
I often encounter this problem when using a serrated one-sided blade.
Having the bevel on one side of the knife seems to make the knife angle toward the opposite edge.
I haven't successfully been able to compensate for this while cutting, so I threw away that (cheap) knife.
Maybe this is part of your problem?
To be honest, I've had no problem whatsoever when using a blade with both sides sharpened (unless cutting a very wide or otherwise difficult loaf).
cooking.stackexchange.com/users/3747/Max
We make bread for sandwiches a few times a week, but slicing them is always a pain.  The pieces just don't come out uniform. I end up with angled pieces as the knife doesn't end up going  straight  down.  Is there a trick to getting uniform pieces from a loaf?
How to get uniform slices from bread?
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Try a bow-style bread knife, an electric knife or a serrated blade, and use a bread board or bread slicer with pre-cut slots that guide your knife. You can try an electric knife or a bow style knife. You can also buy a bread slicer to help you slice.
Try using a bow style bread knife or an electric knife. Make sure you have a bread board. You can buy bread slicers that hold the bread in place and guide your knife.