You would think that making straight lines with a striping machines would be automatic. Try this. Close your eyes while you are mowing your lawn and walk about 40 feet. When you open your eyes you will still be going the same direction but your line will most likely not be perfectly straight. The same applies to a parking lot striping machine. It is made to go straight but must be guided by the operator in order to create a perfect line. To create a perfect line with a striping machine you have to follow a benchmark like the old stripe, a chalk line, painted dots or a cord pulled tight. Again, when you are mowing grass, you always follow the edge of the last row. If you pull away you will miss areas and have to go back. If you overlap too much you will create more work for yourself. So a good lawn mower keeps their eye focused on the last row and follows that exactly. The same thing applies for striping.
For re-stripes the old line is normally clearly visible and is easy to follow. If it is a little crooked you can do some correction with no additional benchmark. However, if it is too far out you really should either pop a chalk line and follow that or pull a cord tight and use that as your benchmark.
I have personally found that using a chalkline is too time consuming and normally requires two people to do. My favorite way to mark straight lines is to take a roll of cord and pull it tight from one end of the line to the other.
I use an extension cord reel that you can get at Lowes or Home Depot and I roll a hundred or so feet of rope onto it. If I have someone with me I weight my end down and have them hold the other tight. If I am by myself I weight both ends down. After I stripe the line I just move both ends over and pull tight.
For curved lines I use dots sprayed on the ground with a spray wand. I double check the marks then start at one end and connect the dots to the other.
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