The economical manufacture of your concept is critical and depends on many factors that should be taken into account from inception. As in part one, your mechanical device is machined steel. You need to design it for manufacturability.
Recognize that while designing the mechanism you are also forming the process to build it. Start by imagining what a machine shop considers when quoting your job, everything that effects the production of machined steel parts and the resulting assembly. Refine your device with these aspects in mind.
During product development I use a simple three step formula. I start with a prototype or proof-of-concept model. After testing I improve, establish final dimensions and then build a pre-production prototype which is a tooling, fixture design and measurement reference sample. I then construct a production ready example produced from the newly built fixtures and check against the reference sample.
Simple is always better. You started with a napkin drawing, revise it. Analyze component geometry and purpose. Eliminate parts where you can. I got my apparatus down to five parts held together with one bolt. Draw and re-draw, isometric drawings if possible. Understand proportion for the task then dimension. Get nice prints and make a device out of wood if you can.
Materials dictate much in production — O1, stainless steel, 1018 cold rolled, etc. Each has its own properties and machining qualities. This governs factors like speeds and feeds, the use of carbide or high-speed steel tooling and tooling wear.
Research machine tools, they are the means to your end, understand the methods. Envision what kind of equipment is needed to make your mechanism and how each part has to be held in a machine. This is known as the set up. Count how many set ups are in the process.
Machining is subtractive, you are starting with simple geometric shapes like plate, rounds or squares making little ones out of big ones and routing the portions through a series of steps to completion. Plan the order. Envision machining paths, tooling changes and think about batches, bottlenecks and flow. The goal is to keep the machines running. To do that you need to get as much as you can out of each set up.
I like using ground flat stock. It costs more but because of its accuracy I save in material preparation, set up time and finishing operations. Using wire EDM, I can stack material and get multiple parts or blanks in one set up after which I send them to other machines for additional operations.
An example of the aforementioned set up progression would be first, clamp one side of the material against the rail. One, maybe two dial indicator passes across the top of the plate along the X and Y axis to adjust for level. Then a couple additional passes against the edge opposite the rail to adjust for squareness and then a level recheck.
The human interface is often the most costly part of any process. The speed of a set up depends on the skill of the operator. This inconsistency dramatically effects throughput and cost per minute. Clamping, indicator sweeps, programming, it can take longer to set up a part than it does to cut it. Eliminating a step eliminates a set up. Don’t waste time setting up to mill a round piece square, buy the proper stock in appropriate dimension, length and finish.
There are specialized work holding and clamping devices that save time. Custom fixtures may be needed to hold the part in proper orientation to the cutting implement or allow multiple parts to be machined in accurate, rapid succession; my particular area of expertise.
Surface finish, clearances and tolerances can make a big difference in cost. Less than .001 inches gets pricey. +/- .002 inches is easy for a good shop but wider is better. +/- .010 inches is like a football field. Beware the stacking tolerance phenomenon. Will your device operate with wide tolerance swings? Do the pieces fit?
Consider finishing operations like hardening, which can cause distortion, special coatings, de-burring and polishing. Eliminate all hand fitting possible, file work is expensive.
Assuming your device is bolted together, limit fasteners to standard dimensions — something you can buy off the shelf. Tapped holes are another set up and broken taps are a real pain. Then there is final assembly which can be labor intensive, and don’t forget packaging, shipping, product liability, etc.
So you have absorbed all this and reduced the device and process to the bare minimum. You have outgrown the incubator discussed in part one and hope to need to make thousands. You have decided to set up the manufacturing base yourself and are looking for a machine shop for order fulfillment or maybe even a partner. Hopefully your marketing activities have yielded interest because volume often dictates cost and service.
Regardless, an initial batch of twenty is a good number to continue process refinement. This also gives a portion for further R&D, some samples for marketing purposes and some for you. Always have one at home and one in the trunk of your car.
Most mom and pop shops are a mix of old and new equipment. Regionally, good to great machine shops charge $75 to 125 or more an hour. That could mean over two dollars a minute. Research their reputation. Walk the shop, review their quality control and safety policy and meet some employees. Form a relationship. Also consider your commute to the shop and how much time you will spend there.
Plan to make fixtures and special tooling a separate deal. Pay for their construction up front and if the relationship goes bad get them back. You may also be able to amortize their cost over the run and add that to your price per unit. Discuss lead times, get a firm quote and negotiate terms.
Don’t lose heart. Unique situations require novel solutions. You are alive with creativity and drive. Enjoy it. Tweak your product and process for optimum efficiency.
Next we will discuss the marketing and funding of your creation.