[Page start date : Aug. 20, 2020]
There are many valuable uses for 3D printing in the shop, as well as many uses which at first seem like a good idea but just don't work out for one reason or another. This page is an attempt to discuss some of the considerations for using 3D printing in the shop, including considerations for more successful prints. There are many different types of 3D printing:
At this time, my entire 3D printing experience is with FDM (in other words, extruded plastic filament), so this discussion will be pretty much limited to what I have learned in that regard. FDM and SLA are the 3D printing methods likely to be found in the home shop, and some of this discussion is also likely applicable to SLA but I have no hands on experience with that technology (yet!).
The broad areas for which 3D printing may be used in the home shop include:
Here are some of the factors which must be considered :
Many hobbyists enjoy restoring, re-building, or repairing old machines, tools, etc. and when they do they often like to have the restored item look as much as possible like the original (this is what I mean by "authenticity"). For example, a missing/broken competent made of brass is re-made in brass, a steel item in steel, etc. In such cases, even though 3D printing can produce a serviceable replacement part it may be be desirable to replace a brass part with a plastic one. On the other hand, some parts may be so complex in shape that 3D printing is a viable option even though the material is not the same. Further, there are many types of filaments available now with a "metal look" so that (to repeat my example) a brass part can be replaced with a "brass looking" part. When replacing a missing/broken plastic part, this becomes less of an issue, but even then getting the part to "look right"may still be a concern.
In other cases, where the primary goal is just to replace a broken part as quickly, easily, and cheaply as possible this may not even be an issue. Ultimately this issue is a personal choice.
When making or replacing metal parts with 3D printed plastic ones, the strength of the replacement part becomes a concern. In many cases the strength of metal is required and 3D printing is not an option. However, 3D printing should not be automatically ruled out - there are many high strength filaments available today, and parts printed with these materials can be surprisingly strong. In addition, the low cost and easy replace-ability of 3D printed parts creates the option of "disposable parts" (for example lathe change gears) which can simply be "used up" and replaced as necessary. Further, even though plastic parts may not be as durable as metal ones, the less intensive use usually found in the home shop can result in a long useful part life. Other options for addressing this concern are addressed under Durability and Design Considerations.
Durability in terms of wear resistance becomes an issue when a part is used in a sliding or rotating mode. For example, if a part has a hole in it fitted with an axle, then the rotating axle may quickly wear out the part. This may be address by choice of materials (for example, using a filament type with high strength and low friction such as nylon), or by building the part with a metal insert (such as a bearing hub in this example). In fact it is not unusual to see factory parts designed in this way, and bronze bearing sleeves and metal inserts for screws are readily available.
PLA is commonly used for 3D printing, but can deform or melt when exposed to such temperatures as a car parked on a sunny day. This is easily remedied by using filaments such as PETG or ABS (and many others) which can withstand higher temperatures. Of course none of the plastics used for 3D printing can hold up to heat like metals can, so this limitation must be kept in mind.
This issue is similar to the heat resistance concern. Many 3D printing filaments will dissolve in common solvents used in the shop. Again, choosing the right filament for the job should be a concern.
This might more properly be called "liquid proofing" - it has to do with the potential problem that 3D prints which appear to be solid may in fact be micro-porous and thus prone to leak when used to contain liquids. This is due to the nature of 3D printing (at least FDM) which can leave tiny voids between the deposited filament strands. This issue is typically addressed by post-processing, such as painting or spraying with polyurethane (for example).
If you are making replacement parts for a machine, you may find yourself "copying" parts that were original made of metal (stamped, cast, etc.) or plastic (usually injection molded). Keep in mind that the original design of these parts was influenced by the process used to produce them. For example, parts that were made by casting or molding will have "draft" (slightly angled sides) to enable removal of the part or mold pattern from the mold. You can either choose to include these features (to get an authentic look) or eliminate them for simplicity. Further, parts will generally be made to keep material costs to a minimum, by "hollowing" the part (which may then include internal ribs for improved strength).
Keep in mind that plastic is typically not as strong as metal, so you may need to add additional reinforcement. If you are not concerned about making a close replica of the original part you may want to redesign it completely to take advantage of the capabilities of 3D printing. This may even be advisable in the case of an original part that failed, as the failure may be due to a poor design of the original.
Frequently it is necessary make parts which include threaded holes. In these cases plastic holes can be easily tapped with a conventional tap. For parts in which the threaded holes do no undergo much stress, this can work very well. However, for parts where the thread will take some stress (or there is frequent removal of the threaded part), stronger threads can be provided using threaded inserts(which are typically melted into a provided hole).
Similarly, plastic parts with holes that take a rotating shaft can be reinforced with metal bearing or bushings in much the same way as is often done with metal parts.
No doubt there are many other ways that 3D printed parts with metal attachments can be constructed, so it is worthwhile to bear this option in mind.
3D printed (FDM) parts typically show layers where the filament has been deposited, and although this can be minimized with the use of thin layers (at the cost of longer print times) they cannot be entirely eliminated. In my experience this is a purely cosmetic issue and does not effect the function of the parts. Of course post-processing is also an option in the form of sanding, filling with primer, painting, etc. but of course this considerably increases the time and effort required to finish the part.
In general, the size of the parts you can make will be limited by the print envelope of your printer. The exception to this is those cases where a large part can be broken up into smaller pieces which are then fit together after printing. Of course this introduces additional complexity in designing the parts, as well as additional time and effort to fit the pieces together after printing. Options for joining pieces into a larger part include snap fits, nuts and bolts, screws, and gluing. Another possible option is to design threaded shafts and threaded holes into the pieces which an then be joined by screwing them together.
Just because you don't have a 3D printer doesn't mean that you don't have access to 3D printed parts. Many hobbyists with 3D printers are more than willing to print parts for you at minimal cost (often just for the cost of materials). In addition, there are commercial printing operations which will print your part for you in plastic, metal, ceramic, or other materials. In all cases you must be able to provide a CAD or STL file for printing.
It is possible to make quite accurate parts on a 3D printer, but don't necessarily expect this "out of the box." If you want dimensionally accurate parts it is worthwhile to print some calibration prints and adjust your printer's settings accordingly.
Also, in making parts to fit existing machines, I have found it is often difficult to get exact measurements for making the needed part, either because the original part is missing or damaged, or access to the machine area where the part is needed is restricted. A good way to address this issue is to make the best measurements that you can (or even just make estimates), and then print a "skeleton" using these measurements to make a test fit. A skeleton, in this case is basically a framework which include the "footprint" of the part along with essential features such as mounting holes. The printed skeleton is fitted to the machine so that any required adjustments can be noted. The skeleton model is then modified, another test fit is made, and so on until a good fit is obtained. printing a skeleton is much faster than printing an entire test part, and also saves on filament costs.