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This is a linear actuator based on the Openbuilds C-Beam design, which uses V-wheels and a leadscrew. I designed this version so that it can be lasercut out of sheet material, because the Openbuilds plates can be expensive since they have to be CNC machined. The design could also be cut out of plywood on a CNC router, or hand cut out of various sheet materials. I've attached SketchUp files and PDFs of the 2D designs; the SketchUp files can be used to generate cut paths for CNC / lasercutting the parts, and the PDF files can be printed at 1:1 scale and glued to sheet material, so you can cut the parts out by hand. In the PDF files, the parts are labelled, and the centres of the holes are marked, to make it easier to drill them out by hand.

A linear actuator combined with a stepper motor is a basic building block of CNC routers and milling machines, time lapse photography setups, or rigs to film tracking shots in videos.

This Instructable incorporates 2 videos. The second video shows a better motor mount than the first, so I will describe how to build the motor mount based on the second video. Please excuse the differences between the video and my instructions - I've found better ways of doing things since I made the video, and I want to share those with you!

You will need:

  • 3mm and 5mm thick sheet material: acrylic, plywood, MDF, delrin, etc.
  • Glue compatible with the sheet material: for acrylic, use solvent cement, for wood, use wood glue, etc.
  • C-Beam V-slot - at least 15cm in length, so the carriage has room to slide along it. I used a 50cm length.
  • NEMA 23 stepper motor with 8mm shaft - other shaft diameters will work, you'd need to use a different sjaft coupler though.
  • 2 x RepRap - style endstops (optional)
  • 4 x mini V-wheels
  • 8 x 105ZZ bearings to fit the mini V-wheels
  • 8 x precision shims: 8mm OD x 5.1mm ID x 1mm thick
  • 2 x standard V-wheel spacers: 10mm OD x 51.mm ID x 6mm high
  • 2 x eccentric V-wheel spacers: 8mm OD x 5.1mm ID, 6mm high, for a 7.12mm hole
  • 4 x M5 x 25mm low profile hex bolts
  • 4 x M5 locknuts
  • Shaft coupler: 18mm OD x 8mm ID, 25mm long
  • 2 x 8mm ID collars with grubscrews
  • 2 x 'thin' washers: 12mm OD x 8mm ID
  • 2 x 688ZZ bearings
  • M8 threaded rod: the length of the C-Beam, plus 25mm - so mine was 525mm long
  • 2 x M8 nuts
  • Compression spring: 9.5mm ID x 15mm long
  • 7 x M5 x 16mm low profile hex bolts
  • 2 x M5 x 16mm countersunk bolts
  • 2 x M3 x 25mm bolts
  • 5 x M3 x 10mm bolts
  • 9 x M4 x 16mm bolts
  • 4 x M5 nuts
  • 9 x M4 nuts
  • Assorted M5 nuts and bolts, to hold parts together while the glue dries
  • Aluminium foil
  • Superglue
  • Solvent cement + a small, old paintbrush
  • Handheld drill
  • Pillar drill + angle grinder, a lathe, or a hand drill + file
  • Socket set
  • Hex keys / Alan keys to fit the hex bolts
  • Pliers / spanner for M5 nuts
  • M3 drill tap - this might not be necessary if you make plywood parts
  • 10mm drill bit
  • (if you will make the parts by hand) - 2.5, 3, 5, 6, 7, 12 and 16mm drill bits
  • File
  • Screwdriver

Method

First, cut out the parts, either using the SketchUp files for CNC / laser processes, or print out the PDF files if you want to make the parts by hand. The top layer of the carriage is in a separate file and should be cut out of 3mm sheet. The rest of the parts should be cut out of 5mm sheet.

First Video

0:00 Parts list: this is slightly different to the parts list for this Instructable, because the Instructable shows how to build a better motor mount than the one in the first video.

0:45 Four of the M5 x 16mm bolts need to be modified. The diameter of the heads needs to be reduced to between 6 and 7mm. I fixed each bolt into the bit holder of a pillar drill and used an angle grinder to remove metal from the heads. The video shows 60mm long bolts, but because the motor mount is different, you should use 16mm long ones. It might be possible to buy specialist bolts with thin heads instead of doing this step.

1:13 The four M5 x 16mm bolts should now look like the one shown on the left at this point in the video.

Even if you CNC'd your parts, it's useful to refer to the PDF files because they contain labels that help identify each part.

1:42 Take 4 M5 bolts and 4 nuts. Remove protective film from the top of the part labelled 'Carriage layer 1 (5mm thick)' in the 5mm PDF file, and the similar 3mm thick part from the 3mm PDF file.

(if using wooden parts, apply glue to one face of each piece now)

1:58 Put the 2 layers together, lining up all the holes as precisely as you can.

2:07 Push the 4 M5 bolts through the holes near each corner, and tighten the nuts onto the bolts. Double check that all the holes are still lined up.

2:17 Repeat those steps, bolting 'C-Beam endplate 1, layer 1' to 'C-Beam endplate 1, layer 2' and 'C-Beam endplate 2, layer 1' to 'C-Beam endplate 2, layer 2'.

2:27 If you made the parts from acrylic, dip a small paintbrush in solvent cement and run it along each of the edges of the pieces you bolted together, letting the solvent be drawn into the gap. Use plenty of solvent.

Wait for the glue / solvent to bond the parts. If using wood glue, this could be 24 hours or more. Solvent cement usually bonds parts in less than an hour.

2:42 Unbolt all the pieces you glued together.

2:52 Using a 10mm drill bit, on both C-beam endplates, countersink the hole shown in the video.

3:00 The countersink should be deep enough that the M5 countersunk bolt held can fit flush with or below the edge of the hole.

3:04 Tap the 2 small holes next to the rectangular cutout with an M3 tap, in each of the endplates.

3:14 Ignore this - you don't need to tap anything with an M5 tap - that is for the weaker motor mount.

3:25 Remove any remaining protective film.

3:29 Fit a 688ZZ bearing into the 16mm hole on each endplate.

3:43 Cut 2 strips of aluminium foil to fit the little tabs sticking out from the carriage.

4:13 Glue the foil onto the little tabs.

4:27 Use gloves when you work with superglue. I'm bad at health and safety.

4:42 Gather the parts from the file with 'nut trap' in the title. One of the parts has a slightly smaller hexagonal hole than the rest, and 2.5 mm holes drilled at the sides.

4:54 Tap those 2.5mm holes with an M3 tap.

5:08 Press an M8 nut into the hexagonal hole on that part.

Remove all the protective film (if you made it from acrylic).

5:20 Stack the nut trap parts in the order shown in the video, and bolt them together with two M3 x 25mm bolts.

6:07 With three M5 x 16mm low profile hex bolts and one M5 x 16mm countersunk bolt, bolt 'endplate 1' (as labelled in the PDF) to the C-beam. My C-beam had all the holes tapped when I bought it. If yours aren't, tap them with an M5 tap now. The bolts I used in the video weren't low profile, but they should have been!

6:26 Assemble the mini V-wheels. For each V-wheel, you'll use two 105ZZ bearings and a precision shim.

6:46 Bolt the V-wheels to the 'gantry plate' (as I called it in the video), or 'carriage' (as I've called it here). For each V-wheel, you'll use one M5 x 25mm low profile hex bolt, an M5 locknut, a spacer, and another precision shim.

6:56 One pair of V-wheels bolt to the 7mm holes in the carriage. For these, use eccentric 6mm spacers.

7:38 Bolt the other pair of V-wheels to the 5mm holes opposite. Use the regular 6mm spacers for those.

8:03 Tighten the V-wheels with the regular spacers, using a hex key and spanner or pliers. Leave the ones with eccentric spacers finger-tight.

8:16 Fit the nut-trap into the rectangular hole in the carriage.

8:27 You may need to file the top of the nut trap to make it fit. It's important to get a tight fit.

8:48 Adjust the eccentric spacers so that the carriage will run along the C-beam, but fits tightly and doesn't wobble. Tighten the bolts on the eccentric spacers.

9:05 (the video shows the nut trap taken out of the carriage again - there's no need to remove the nut trap from the carriage) Insert the spring, then another M8 nut, into the nut trap.

9:08 Holding the M8 nut into the end of the nut trap, screw the M8 threaded rod through both M8 nuts.

9:25 The threaded rod should be held tightly between the two M8 nuts.

9:33 Turn the threaded rod until the nut trap is roughly in the middle. You can use a drill to speed this up.

9:48 Slide the carriage onto the C-beam.

9:52 Push an 8mm ID collar, then a 12mm OD x 8mm ID washer, onto the end of the threaded rod which is next to the endplate you bolted to the C-beam.

9:57 Insert the end of the threaded rod into the bearing in the endplate. With the threaded rod inside the bearing, but not poking out of the other side of the endplate, tighten the grubscrew in the collar onto the threaded rod.

10:03 Push the other collar, and the other 12mm OD x 8mm ID washer, onto the other end of the threaded rod.

10:08 Stop watching the first video - it's time for the second video!

2:38 - 3:00 To make the motor mount, assemble the parts labelled with 'endplate 2', and 'motor mount box' - you should already have glued the two 'endplate 2' parts together.

3:35 Mark which surfaces of those parts were facing outwards, take the motor mount apart again, and countersink the 4mm holes on those outer faces with a 10mm drill bit.

3:56 Countersink the 4mm holes in the face of 'endplate 2' that will touch the C-beam.

4:30 Assemble and bolt together all the pieces labelled 'motor mount' but NOT 'endplate 2' with M4 x 16mm bolts and nuts, using the nut traps as shown at 4:00.

4:48-6:24 Ignore all of this

6:24 Insert three low profile M5 x 16mm bolts and one M5 x 16mm countersunk bolt into 'endplate 2'.

6:34 Push the 'motor mount' assembly into 'endplate 2' and bolt together with three M4 x 16mm countersunk bolts and nuts.

6:57 Double check that the heads of those countersunk bolts are flush with or below the surface of 'endplate 2', so they won't push against the C-beam.

7:14 Bolt the 'endplate 2' / 'motor mount' assembly to the C-beam, inserting the M8 threaded rod through the bearing.

(not shown in the video - sorry) Whilst pushing the carriage / threaded rod so that the collar on the other end pushes firmly against 'endplate 1', push the other collar against 'endplate 2' and tighten the grubscrew. The threaded rod should be held firmly between the endplates. It should not be able to move backwards or forwards, but it should be able to rotate.

8:01 Push the shaft coupler onto the threaded rod and tighten the grubscrews.

8:09 Push an endstop into the endplate and bolt with an M3 x 10mm bolt. (not shown in the video) - do this on the other endplate too.

8:19 Push the stepper motor shaft into the shaft coupler.

8:30 Push the M5 x 16mm bolts with the thin heads which you modified earlier, through the motor mounting holes. Semi-tighten M5 nuts onto the end of the bolts.

8:33 Rotate the threaded rod and feel how the motor moves. Try to find a position for the motor where it doesn't wobble as the rod turns. Tighten all the bolts.

8:49 Tighten the grubscrews on the coupler onto the motor shaft. If your motor shaft has a flat side, tighten one of the grubscrews from the coupler onto that.

9:01 Try turning the coupler and the threaded rod - the carriage should move and the motor shaft should turn without any wobbling. If something feels loose, double check and adjust it.

Well done. You have completed this epically long and unexpectedly complex Instructable. I hope the inconsistencies between the videos weren't too distracting.

I'm using four of these linear actuators in my CNC router to cut aluminium, which you can see on my YouTube channel. One day I will make an Instructable about that build!

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