We have a machine shop in our portfolio right now. Interesting business but tough to grow. Requires the right part mix to maximize capacity but winning new business is tough. Also extremely capital intensive as you've said. We've been lucky to not have to sink too much capital in but are on the cusp of several prospective projects that would require another $1-2mm capex, but they're huge so ROI would be pretty significant.
Looking at some smaller machine shops as add on acquisitions ($1-2mm EBITDA range) and would be fun to buy but that's a lot of equity.