DIY Linear Translation Stages

In 2017, I presented a [»] motorized linear translation stage based on cheap components and SLS printing. Here, I revisit the concept to produce a complete family of the most commonly required translation stages in an optical lab and add a few newer concepts as well. All the translations stages were printed on my Bambulab X1C printer using matte PLA and uses readily available components from [∞] Thorlabs and [∞] Misumi.

The various translation stages proposed in this post are shown in Figure 1 and can be downloaded [∞] here under an open-source CERN OHL V2 license for reproduction. The proposed family comprises X, XY, Z, XYZ and cage mountable translation stages. Holes in the carrier plates are designed to accept short M4 threaded inserts from [∞] CNC KITCHEN.

The overall working and assembly concepts are the same for all stages and is summarized in Figure 2 with the X-only axis. A carrier plate moves relative to a base plate using a fine-pitch lead-screw from Thorlabs (250 µm per revolution). The carrier plate is guided by two brass bushings and 6 mm rods. Here, I opted for brass bushings instead of the linear ball bearings used in the [»] previous post. The bushings have E7 tolerance which gives, with h7 axis, a minimum clearance of 20 µm and a maximum clearance of 44 µm. The wobble is therefore expected to be contained to a maximum of 15 arcmin (44 µm on 10 mm). Slightly better tolerances could theoretically be achieved with m6 shafts. Here, I chose to rely on Thorlabs ER rods instead of toleranced shafts. Although they do not give any tolerance for their rods, I found that the match with the E7 bushings was pretty good and gave satisfactory results at lower prices. ER rods also have the advantage of enabling newer application types such as connecting the stage directly to a cage-mounted system as shown in Figure 1 (“cage compatible” configuration).

The assembly is broken down into multiple steps:

Step 1: add the threaded inserts. Technically you can do it later but if you screw up your work it’s easier to fix it from the beginning.

Step 2: add the bushing and leadscrew inserts. I systematically rework the holes with drill bits before inserting the parts.

Step 3: glue the bushing and leadscrew inserts. I recommend a thick epoxy glue like Scotchweld DP190 for this job. It is also important to have decreased all surfaces in contact using acetone first except on PLA where it’s preferable to use isopropanol.

Step 4: insert the rods and leadscrew as you place the carrier plate. I recommend assembling the screw button to the leadscrew first using some gentle torque to avoid it getting loose later.

Step 5: apply glue to the ball bearing and rods fixture groove. Again, I recommend a thick epoxy glue and to degrease all contacting surfaces first. Pay attention that you don’t pour acetone into the ball bearing itself!

Step 6: retract the leadscrew by about 3 mm and apply some thin glue, like Loctite 638. You will have to thoroughly decrease the leadscrew in the contacting area for the glue to adhere properly.

A relatively central aspect of all stages is the mounting mechanism used for both ER rods, bushings and threaded lead-screw inserts. Because of the relatively low precision of 3d printers (compared to professional CNC milling machines), it is difficult to design holes to capture the mechanical elements: the holes are either too tight or too loose. A convenient property of plastic printed parts however is that they deform moderately very easily. All holes are therefore designed as a compliant snap-in mechanism, as shown in Figure 3. The holes are designed slightly too tight at first but have some deformation capabilities such that you can press-fit by hand the various mechanical elements into place. Once in place, some epoxy glue can be poured into the groove to fix them once and for all.

All translation stages also feature ball bearings to hold the lead-screws. To keep the stages as compact as possible, I used miniaturized ball bearings with a 6 mm shaft hole and a 10 mm outer diameter. Because of the miniaturized aspects, it is very difficult to use a nut locking mechanism and I relied instead on glueing the leadscrew to the ball bearings. This was however not without consequences because the glue will not adhere to the leadscrew if it’s not properly degreased. On the other hand, you do not want to degrease the complete screw because the grease prevents backlash in the system and keep the screw running smooth. This was not necessarily easy because I had on one occasion glue leaking into the ball bearing itself. I also don’t know how the system will respond to excessive torque. Later, I implemented a nut-locking system which worked fine but required a slightly larger bearing (see below).

Finally, an attentive observer will notice that the system depicted in Figure 2 is over-constrained and should, in theory, not be working. In practice, I found that my Bambulab X1C was accurate enough to have all stages operate properly. Printing orientation of parts should however be taken into consideration for smooth runs, and I noticed that the XY brackets tended to be firmer to operate on one axis and do not run as smoothly as the other axis. Nothing too serious to prevent practical uses, however.

Still, I will never stress enough that plastic parts should never be used for precise alignments that are to be maintained over time. Plastic will slightly deform over time and have bad temperature response, leading to loss of alignments. On the other hand, they are perfectly fine for all operations that require on-the-go alignment such as positioning a sample in the field of view of a microscope or alignment tooling in more sturdy metal-based setups.

Last but not least, the stages shown in Figure 1 are by no means the only systems that can be built and should only be seen as examples of a more general concept. To illustrate this, I also designed the cage-system alignment tool of Figure 4. Its purpose is to be snapped on a cage system to be aligned and have a fine-pitch screw drive the adjustment of cage plates elements. Typical usages are, for instance, to set in focus a camera, pinhole etc. where fine motion is required. I haven’t seen such tool before at any of the common optical suppliers and can therefore be considered as an original concept. It can be downloaded as a prototype version [∞] here under an open-source CERN OHL V2 license as well for reproduction. Note the usage of the larger bearing this time with a nut-locking system, avoiding the issue of having to glue the leadscrew.

If you wish to have one of the translation stages shown here but don’t have a 3d printer, [∞] get in touch with me as I’ll be happy to ship you one at a fair price.

I hope this post has been useful for you :) don’t hesitate to share your comments on the [∞] community board to let me know!

I would also like to give a big thanks to Young, Sebastian, Alex, Stephen, Lilith, James, Jesse, Jon, Cory, Sivaraman, Samy, David, Themulticaster, Tayyab, Michael, Shaun, Kirk, Marcel, Dennis, Onur, Max and Natan who have supported this post through [∞] Patreon. I also take the occasion to invite you to donate through Patreon, even as little as $1. I cannot stress it more, you can really help me to post more content and make more experiments!