3D Printing for Manufacturing Jigs

When talking about 3D printers in industry, most think about their use during prototyping and initial design studies. This is changing as the technology is improving, increase in material availability, better design methods, and widespread acceptance of 3D printing as an alternative to conventional methods. Even so, use is mostly limited to high-end components that cannot be constructed in other ways, or where conventional methods are just as time consuming. The best example is aerospace parts where the complex geometries possible with 3D printers provide design flexibility, and normal machining is labor intensive and require many hours on expensive machines.

As exciting as that world is, it’s rarified air and not readily accessible to most designers. Instead, I’m going to talk about a completely different way that 3D printers can improve manufacturing processes. An  approach that doesn’t use exotic materials, expensive machines, or the resources of an aerospace company. That leaves us with a lot of limitations, but there is one area where limited numbers of custom plastic components have a place in manufacturing – making jigs.

Why Jigs

I learned a lot time ago that the extra effort of creating good jigs will pay long term dividends in repeatability and efficiency when creating copies of the same item. There is a trade-off between the amount of time spent making these jigs and the number of copies to be made. This used to be a complex decision process because making a jig was not an insignificant effort. The accuracy of the final part can only be as good as the accuracy of the jig, and often worse, so jig accuracy is critical.

That’s all turned on its head with 3D printers. Achieving high levels of accuracy is simple and does not require diligent attention or skill by the jig creator. This lowers the cost of jig production and enables use of a jig methodology in production for even small part runs.

Types of Jigs

There are essentially three types of jigs – templates, guides, and machines. Templates provide a sense of the final part and provide for a reference frame when manufacturing the final part. Guides assist the manufacturing process by controlling or limiting the process to conform with the requirements of the final part. A machine automates some aspect of manufacturing to maximize control over the final part’s characteristics.

Templates

Templates are certainly the easiest type of jig to create and use. They also provide the least control over manufacturing. In their simplest guise, these can be full scale drawings of the final part that can be laid on top to transfer cut lines, compare shape, or provide other information on how the final part should look. In all cases, guides are full scale so they can be directly compared to the workpiece. Templates are very useful when performing simple operations that require low amounts of control. They are also the simplest to create as they can usually be directly derived from the part to be produced with little effort and don’t have to account for interaction with the tooling to be used.

Guides

Guides are where most 3D printed jigs reside. Similar to templates, they represent the final product in some form and are generally derived from the part design itself. The major difference is that guides interact with the tooling and are specific to the manufacturing process to be used. An example I’ve been using frequently is a guide that rides on the collar of a router to shape a part. It precisely controls the limits of where the router can go over the part, but I’m still required to operate the router. This type of jig also only works with the intended tooling.

Machines

Machines are the most complicated of jigs and completely control some part of the manufacturing process. In the most generic sense, a basic milling machine is a jig designed to make rectilinear parts. More often machines that would be considered jigs are more specific to a feature, such as a key cutter for a shaft or custom tooling in a lathe to make a specific profile. The major differentiator between a guide and a machine is that the jig and tooling are integrated as a unit in a machine.

What Type of Jig to Use?

The decision space has shifted on the use of jigs with 3D printing from “should I put the effort into creating a jig” to “what type of jig should I be using”. This is because the labor required to create a jig shifts from jig creation to jig design. To help make that decision, the following questions should be asked at a minimum.

·        How important is the accuracy of the final part? – This factor really determines whether a template is sufficient. In cases where final accuracy is not very important, a template should be used as it requires almost no extra design effort. It may not even require use of a 3D printer.

·        What type of tooling will be used to make the part? – The compatibility of tooling with jigs will be a large determiner on the amount of effort required to make a jig. If integration with a guide is difficult to achieve, dependent on the required accuracy, a template may be deemed sufficient with extra diligence required during manufacturing, or development of a machine may be necessary.

·        How many copies will be manufactured? – The number of copies will determine how much effort should be put into the front end of jig design to minimize work once in the manufacturing stage.

Weighing these questions will help make a decision on the amount of design effort to expend on jig design, therefore answering the ultimate question of what type of jig to make. Even within the three categories of jigs, various levels of fidelity and control of process must be considered to optimize the time spent on design and production.

An Example

I’m going to use a current example of jig use to illustrate the points discussed above. I have been manufacturing drum practice pads for KLS Percussion that consist of a wooden base, gum rubber playing surface, and hollowed out section to receive a snare assembly.

Template Use

The practice pad is in the shape of an octagon. I do not have any readily available machine for cutting the gum rubber, so I’m having to cut the appropriate shape out manually. Since the gum rubber sits on top of the wood and therefore does not mechanically interact with any other feature, this is a prime opportunity for use of a template. I printed (in paper) a full-sized version of the octagon which I can lay on top of the rubber and trace out. This ensures that all of my pads are the same shape and size (within my control to cut along a line) with almost no design overhead. It also significantly reduces my manufacturing time as I don’t have to measure each octagon and I can lay out multiples on a sheet of rubber before cutting, improving my efficiency.

Guide Use

The bottom of the practice pad has a recess machined out to receive a custom snare unit. The snare unit is produced on my 3D printer, so its dimensions are fixed. To ensure a proper fit, and that the final assembly looks decent, the recess must be pretty accurate. In this case, the tooling to be used is a router, and it would be difficult for me to control manually. So tracing the required shape with a template does not provide the necessary amount of accuracy. Therefore, I developed a guide for the collar of the router which prescribes the bounds of where the router can go. The design effort put into the guide was minimal as I already had a solid model of the practice pad. I only had to consider the collar size and tooling to be used, and I could easily create a new part that would guide the router. In this case the use of a guide allowed for me to make an accurate feature repeatedly. Arguably, I could have done the work more quickly with an oversized template, but it would have been a mess and looked terrible. The extra work in design, and the marginal extra work installing the guide to each part is well worth the effort.

Machine Use

I did not develop any machines for this process, but rather used the ones already at my disposal. Specifically, I use a radial arm saw to cut 45 degree angles in the wooden base, a drill press with depth stop to remove excess material for the recess prior to routing, and a router with depth control.

Summary

In a world where 3D printers are readily accessible, we need to consider how they improve our ability to make better products and not just be a novelty that sits on a table. One of the best ways to leverage the accuracy and flexibility is to use these machines to make jigs. Often jigs are much larger than standard prints on a 3D printer, resulting in long print times, but this is unsupervised time which is essentially “free” to the designer. So rather than shy away from jig making because the prints are so long, we should instead think about all of the time saved, and the fact that it’s not our time being taken to make the jigs.

Your Dose of Aphorisms

In many ways, making jigs is like many other things in life – you get out of it what you put in. The more you put into their conception, the better the end result (generally). Of course there’s the concept of limiting returns, but we’ve covered that before. The aphorism today is about that topic, but it’s not unique to jigs. Expecting more than would be more than what is warrented by your effort is an exercise in wishful thinking. In some industries that may have its place, but in engineering that kind of approach will lead to failure.

You get what you plan, not what you plan on getting.