Two suggestions (from a graphic designer / typography nerd turned woodworker). These are a little hard to explain so I just whipped up a little photoshop demonstration.
- Quick fix - notch out a little big of the top crosspart of the 7.
- Slightly more in-depth fix - notch out a full-height area on both the left and the right.
Both of these accomplish the same kind of thing. The main reason it's hard to read as a 7 is that you're using the left side of your bounding area (cutout) and making the viewer imply the edge of the top of the 7. By defining that left side, it's much faster and easier to read as a 7. This actually is true of all reading in general. The top half of letterforms are much more recognizable and unique than the bottom half, and when you read quickly, you unconsciously flow over the top half of words without necessarily "mentally consuming" the entire letter form. To prove it, just take any sentence here, hold a piece of white paper over the bottom half of the words - you should still be able to read it quite easily. Do the same thing and hold the paper over the top half of the letters and it's way harder.
As for the two different options above - The first one is easy and would be relatively small work, however it makes the 7 look a little bit off-balance to my eye, like it's going to fall over to the right with it's stubby crossbar at the top. By just opening up a bit more of the left of the entire 7, you get the full crossbar and the benefit of the more defined number, however it would be unbalanced as a whole, so opening up an equal amount on the right side of the 1 would balance it a bit more.
Edit: that said, I initially didn't even notice the 711, and thought it was a cool modern looking cutout for pure aesthetic purposes, which I liked. It then becomes a "bonus" to realize that it's the numbers. So maybe don't change anything if that's more what you're going for. The above rec's are mainly just to increase readability of the numbers, not necessarily "better".
