Tips & Tricks: Bonding Multiple Prints Together
Sometimes it is not feasible to 3D print an entire object at one time. Due to overhanging geometry, loading direction, or simply size, some parts must be split into multiple sections. Good bonding practices are critical to ensuring proper part fitment and bond strength.
At GZERO Additive we prefer to bond parts along flat planes if possible. We will use small dowel pins (typically 1/8” diameter) to align the parts relative to each other. FFF printing holes at nominal diameter typically leads to a slightly undersized hole, allowing them to be easily drilled to proper size. Take care to drill holes straight as this will aid in assembling the sections later.
Drill dowel pin holes straight to aid in part alignment.
Sanding the bonding faces will help address any burrs that may prevent complete alignment. This also helps with bond strength, especially on PETG and Recycled PETG parts. We typically sand bonding surfaces with 100 or 200 grit sand paper.
Use 100 or 200 grit sandpaper to flatten bonding surfaces. Be sure to remove any burrs.
Once the dowel pin holes are drilled to the proper size and the bonding surfaces are sanded it is time to install the dowel pins. A slight interference fit when installing the dowel pins is not a bad thing at all. A couple of light taps of a hammer will usually seat them properly.
Use light taps of a hammer to install the aligning dowel pins.
Using the proper adhesive for your material, environment, and loading conditions is critical to achieving a successful bond. When bond strength is important, we use 3M DP420. This two part epoxy adhesive works well with PETG, Recycled PETG, and Nylon Carbon Fiber. Use an applicator handle and mixing nozzles to aid in applying adhesive to the bonding surface. Mixing nozzles are consumable. Wax paper helps prevent parts from sticking to your work surface and makes cleanup easier.
DP420 with applicator handle and mixing nozzle. Putting down wax paper makes cleanup easier.
Use clamps to hold prints together while the adhesive is curing. It is important to have an adequate number of clamps for the bonding surface area. On this particular part, we did not have a good way to put more than one clamp across the joint so we 3D printed clamping blocks to match the part’s outer contours and provide flat surfaces for the clamps to press against. These clamping blocks are an excellent application for Recycled PETG with 5-7 outlines.
This assembled part does not have adequate space to place clamps .
3D printed Recycled PETG clamping blocks allow multiple clamps to be placed over a complex, curved surface.
Clamping can cause adhesive to press out of the joints, creating a budge or line on the exterior part surfaces. It is usually easier to wipe off this excess adhesive now rather than to wait until it hardens and sand it smooth.
Leave the parts clamped for as long as it takes your adhesive to set up. Note that cure times can vary greatly with temperature.
Once the adhesive has completely set up, clamps and fixturing can be removed. Some sanding, trimming, or crack filling may be required around the joint depending on the part’s function.
