What Scheduling Software Really Does
Since our lead time is generally two-three weeks we maintain a four week schedule, which is nothing more than what looks like a monthly calendar with jobs (or parts thereof) on each day. Every week we copy and paste the whole thing up a week, gaining a fresh week at the bottom. We use Google Docs, because it's easily shared with various employees, and any changes immediately are updated even if the doc is open on their local machine. In our case only the master scheduler has permission to modify it, but with Google docs you have the ability to give individuals editing permissions as well.
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From contributor L:
We bought software but gave up on it as it was taking too much time. We now use a spread sheet in a much simpler form.
From contributor N:
We've also struggled with this and have not found a perfect solution. The more sophisticated solutions I have looked into would seem to take too much time to maintain accurately. Our quoting software produces a total number of hours for each job. We split this up into machining, construction, spraying and assembly using fixed percentages based on experience, then use these blocks of work in an MS Project plan to produce the schedule. Of course it is out of date as soon as it's produced, but at least we can be confident where we are once a week. It takes our administrator about a day a week to keep all of it up to date.
More recently we've been tracking the actual hours spent on each project in each category to see where we're getting it wrong (or right). We just use a spreadsheet to track the hours - it's too complex in MS Project. Have a look at Smartsheet. We already use it for project management (ticklists really) but I think we might move from MS Project to it as is much simpler. Some people swear by Basecamp, but I found it too restricting.
From contributor L:
A Gantt chart is the basis of the critical path method. CPM is the standard system for scheduling in construction and works for manufacturing too. The thing about all the methods is that you need to know process times, sequences, overlaps, etc. If you batch process in any way that has to become part of the equation as well. Once the chart is setup for your product(s) and the job starts you need to enter the data showing the level of completion of each operation, daily!
Not so bad for one product or batch moving through. Now you have to make multiple products show in the chart, not so hard if each product has the same sequence or nearly so. When the first product completes the first operation the second product can start in that operation and so on. The chart gets looking pretty long if you've got many products or projects scheduled. That's OK, computers can scroll! Be sure to have all the products for one job linked so they all will update when it becomes necessary to move start or completion dates. One of the most useful things about scheduling software is to be able to backward schedule - to find out when the project has to start knowing the ship date. Forward scheduling will tell you when you can have it done given a start date. Small shops with experienced management can probably use the seat of the pants method to come close without spending nearly as much time as a reasonably good software takes. The more projects you can have running at once the more valuable the software solution becomes and the more time has to be dedicated to it.
If there is one thing that can screw-up scheduling/ delivery in a job shop itís trying to expedite a job around already running jobs. It's bad practice and if you are setup correctly it isn't necessary. Control your batch sizes! If a batch has been released to the shop floor it should be through step one before the rush job can be left the office. The original batch keeps moving one step ahead of the rush.
An illustration if needed - simple box cabinets. The router can process 40 sheets/ shift. The bander can process those parts in 1/2 shift but shares an operator with the CNC bore and insert machine. So banding and inserting is completed on job #1 before that station needs to work on #2. If your shop is balanced the same thing goes on through to shipping. If it is out of balance you will quickly see where the work is on the conveyors. Is it backed up at some station? Add bodies there or cut batch sizes. You can also resort to using an older less efficient machine to help the bottle necked station get it moving. That is less expensive than not fixing the bottle neck. Work not at a station yet? Move the operator to where the work is and here's where cross training pays off. At the end of the day you can see progress by looking at the conveyors or pile of completed work. Go in and adjust the scheduling software to represent where you really are. You can then plan on what to do to correct the situation.
From contributor V:
I agree with your practical insights into scheduling. But I want to make a technical clarification about Gantt chart Vs. Critical Path Method (CPM). Gantt chart is not the basis of this method. Morgan Walker of DuPont and James Kelley (a mathematician) of Remington Rand developed CPM in 1957/58 for project scheduling using Operations Research methodology. The project schedule generated by this method can however be presented in a graphical form using Gantt chart which was developed by Gantt for scheduling in manufacturing environment more than a century ago.
It is true that CPM became the standard method for project scheduling in construction. While scheduling operations, CPM implicitly assumes that resources are unlimited. Such assumption does not hold in production systems and therefore, CPM is inefficient for scheduling in manufacturing environment. CPM users tweak a critical path schedule by delaying some tasks for removing resource contentions which arise in the critical path schedule. This corrective process is often laborious and time consuming. Project scheduling software like MS Project which basically adopts CPM offer an unreliable option for automatic resource leveling for overcoming this problem. CPM-based approach is not efficient for scheduling production which requires several resources of limited capacity. If a specific job needs to be expedited for some reason, then good scheduling tools will show the adverse impact on the flow of other jobs. Those tools facilitate powerful what-if analysis and capacity planning.
From contributor L:
The Gantt chart is basically a visual aid and that CPM has to include limits which can become part of it. Construction uses CPM and does not have unlimited resources. Time/rate can be applied to CPM. At any rate to be useful any scheduling system has to have a constant update system. In manufacturing of flow/assembly lines those updates can be automated. Few wood job shops run on assembly lines or have the ability to automate the required inputs to make scheduling software anywhere near real time. When a shop reaches the size that they can afford both the software and the input costs it seems like a fine idea. What size shop is that for the product you are selling?
From contributor V:
As you implied any good scheduling system frequently revises the schedule using project (job) status update because the actual workflow gradually deviates from the calculated schedule due to natural variation and uncertainty in the production system. The schedule is like a weather forecast and it needs to be frequently updated for its dependability.
One of my initial questions to any prospect is about the issue of project status update. I usually advise schedulers to reschedule production at the beginning of the day after updating project status information. Small shops may have on the average about 40 operations actually in progress at the time of scheduling, that is, we have to estimate the remaining hours for each of those 40 operations. With right user interface of the software and prompt help from shop floor, scheduler can easily revise 40 operation durations within 30 minutes.
Later, the software takes only a fraction of a second to generate and display a meaningful schedule from the input data and save the schedule output. The gain from an allocation of half man-hour per day to the task of scheduling can be substantial for a job shop with meager resources and tough scheduling problem. A good scheduling tool with what-if analysis and capacity planning functionality not only generates daily dispatch lists for resources and displays them graphically but also serves as a powerful, intelligent decision support system for the control and management of custom production.
I think one of our job shop clients (a machine shop in South El Monte, CA) has less than ten workers who have different skill sets. The shop has been regularly using our scheduling software since mid-2007. The same software is used by some custom manufacturers to schedule thousands of operations on a large number of resources but the job status is automatically updated by a shop floor data collection system.
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