How can small manufacturers improve cash flow forecasts amid late payments?

[Brandon75]

As the owner of a small manufacturing business, I've realized our quarterly cash flow forecasts are consistently off, usually because we underestimate the lag time on client payments and overestimate how quickly we can move raw materials. This makes it difficult to plan for equipment upgrades or hire new staff with confidence. For other small business owners, what tools or methods have you found most effective for creating more accurate cash flow forecasts, and how do you build in realistic buffers for variables like late payments or sudden supply chain cost increases without being overly pessimistic?