Comments within this thread advising you to encourage this guy's behavior are insane, to put it kindly. Its a rare bird who can get anything done with any sort of efficiency by spending 70-80 hrs/week on the job, yet there's a common tendency to blindly classify such people as hard working heroes without whom the business would fall on its face. I think you're well aware that's not the case at all, and that such people can become more of a headache than an asset over time.
This man has a primary job of pushing work thru the shop as efficiently as possible. Obviously, he's not doing that. But, by giving him the ability to also take in work, the company has given him an excuse to not focus on the primary responsibility. Customers are taking advantage of his desire to please everyone, and the company is partly at fault for this too, in that you're allowing too much public access to people whose sole job should be to get the work out the door.
This isn't a machine shop issue. Its a basic business issue, and things that work in a 1 or 2 man business simply don't work in a business with what sounds like 50 or more employees. With 10 sales people out beating the weeds for work, there's no reason whatsoever to have your foremen selling work too. There's one simple goal that should always remain at the top of the list of priorities, and that's getting the work out the door as efficiently as possible. That's the only thing that generates money, and in a business that's all that really counts.
I'd add an inside sales person who'd be there all the time to take care of call ins and walk ins, and I'd stop all foremen from functioning as salesmen. This gets rid of the conflict of interest arising from a foreman taking in a job, promising delivery, and then possibly pushing other work back to make good on his own promise. It also relieves the foreman from spending what sounds like a lot of his time interacting with customers, and neglecting his primary duty in the process.
I'd also add a work planner whose job is to schedule based on an overall view of work on hand, and who would also be the sales force's contact for promised deliveries. This relieves the foremen from having to juggle schedules and talk with salesmen about how hot one job or another happens to be. Once again, it allows the foreman to concentrate on one thing, which is getting the work out the door. The work should go from the planner to the foreman as a job package with any necessary drawings and/or instructions, and with notes indicating whether material is in stock, or on order with an expected delivery date. Juggling jobs based on material deliveries becomes the duty of the planner, so this is one more distraction removed from the job of the foremen.
If this foreman is bringing in more work than any of the current outside salesmen, there should be no problem in justifying an inside salesman. In shops of significant size, a planner/scheduler with an overall view of all work logged or in progress is just a necessity that can't be avoided. Having half a dozen different people setting work priorities is a sure recipe for having the shop operating like a Chinese fire drill. When a shop is doing repairs, modifications, and one-off parts, a foreman will have a full time job in keeping 10 men headed in the right direction even without the distractions of playing salesman, planner, drawing chaser, stock chaser, or any other jobs they may be doing now.
This should leave each foreman with plenty of time to review each day's work, have the saw man cut any necessary stock in advance, and keep the machinists moving smoothly from one job to the next with minimal delay. The foremen would also have time to provide job time feedback to the planner. Personally, I'd avoid the normal tendency to place an experienced machinist in a planning position that's essentially a clerical type job. The planner needs job time input, and the ability to produce work schedules. In my own experience, women are better at this type job than men are. If you end up getting 20 additional minutes per day of productive time from each of 30 machinists, the cost of your planner is covered and anything more is gravy.
Unfortunately, I'd lay odds your problem foreman likes the way things are now and likes the degree of control he's able to exert over multiple facets of the shop. In working with and managing people and jobs for 40 yrs, I've found its pretty simple to assess a person's technical ability, but it takes a lot more effort to figure out how their heads work. I've encountered a few over the years who have an overwhelming desire to put their hands in multiple aspects of the business at the expense of doing their best at what they were hired to do. I'd guess you can expect quite a bit of resistance when you begin to clip his wings and focus him on his primary responsibilities.