This carriage was inspired by Trick Laser's Trick Truck and a desire to have an easy, reliable and repeatable method of adjusting belt tension. While it is far from trick, the Belt Tension Adjust Truck is tight (much tighter than the molded carriages), fairly light at about 90g including the back shell, utilizes twin eccentric bushings (printable) to precisely set carriage clamping force and incorporates an easy to use belt tension mechanism.

Note that this truck requires OpenBuilds style Mini V Wheels (with extra Precision Shims) and is for use with 1" x 1" slotted extrusion.

Also note that as well as eating up some of your time, these trucks will eat about 25mm or so of Z height.

If you go to the trouble of making these trucks, the aluminum Machined Ball Joint "Barbells" from SeeMeCNC are strongly recommend as flex in the plastic ones appears to be the next largest source of motion in the system after slop in the spring loaded molded carriages. In addition, the aluminum barbells are quite true whereas this is not necessarily the case for the plastic ones which can create lack of parallelism and effector tilt problems as well as wide variation in end stop offsets if you use multiple hot ends.

Carbon Arms from Trick Laser are highly recommended.

Parts to Purchase (Note: if you are bereft of bolts see also tool section before ordering)

Running Gear

• Mini (15.23mm/0.600" OD) V Wheels Qty 9
  Available from MakerParts, OpenBuilds and of course a variety of suppliers on AliExpress including Fussnor
• Precision Shims (5mm ID x 8mm OD x 1mm Height) - TOTAL required QTY 27
  Each Wheel Requires 3!! Carefully check how many shims are included with the wheels from your supplier to determine how many additional shims are required.
  i.e. Fussnor, MakerParts, OpenBuilds
• 5mm x 40mm Socket Head Cap Screw Qty 9
  Note: Recommend cutting a 50mm bolt down to 40mm in order to get a longer unthreaded shank for a more plastic friendly bearing surface..
• 5mm Lock Nut Qty 9

Ball Joint Attachment

• 3mm x 18 or 20mm Button or Socket Head Cap Screw Qty 6
  (for aluminum barbell)
  or
  3mm x 16 or 18mm Button or Socket Head Cap Screw Qty 6
  (for plastic barbell).
• 3mm Lock Nut Qty 6
• 3mm Washer Qty 6

End Stop Adjustment

• 3mm x 16 to 20mm Flat Head Screw Qty 3
  (hex drive recommended)
• 3mm x 2.5mm Thick Plain Nut Qty 6

Belt Clamps

• 2.5mm x 10mm Nylon Pan Head Screw Qty 12
• 2.5mm x 8mm Nylon Pan Head Screw Qty 12
• 2.5mm Nylon Plain Nuts Qty 24
  (metal screws +/- lock nuts may be substituted but the screws need to be trimmed by ~ 1mm).

Tension Adjuster

• 2.5mm x 16mm Socket Head Cap Screw Qty 3
• 2.5mm Lock Nut Qty 3
• 2.5mm "DIN125" (5mm OD) Nylon Washer/Spacer Qty 3

Optional End Stop Switch Mounting Hardware Upgrade for Max V2

• M2.5 x 18 or 20mm Socket Head Caps Screw Qty 6
• M2.5 Lock Nut Qty 6
• M2.5 Washer Qty12

Printed Parts Note that dimensional accuracy is important. See instructions for specifics

• Body - Qty 3
  Recommend material with a higher flexural modulus such as PLA (i.e.PETG not recommended). Support required. Brim recommended as the wheel bosses are the only bed contact points. Strong cooling recommended to avoid curling as the wheel boss features gradually taper into the body. If possible, (i.e. Slic3r) slow speed considerably for the final layers associated with the barbell mount boss layers to minimize ovality. Overall it is probably better to print at a lower speed. Extrusion Width 0.3 to 0.4mm recommended. Shell Thickness should be about 0.9 to 1mm. Infill 15% Honeycomb. Layer Height 0.2mm or less.
  

• Back_Shell - Qty 3
  As above, except Infill 10%
• Adjuster_Clamp - Qty 3
  Recommend PETG for layer adhesion and toughness. Support Required. Extrusion Width 0.3 to 0.4mm recommended. Shell Thickness should be about 0.9 to 1mm. Infill 20% Honeycomb. Layer Height 0.1mm or less.
• Fixed_Clamp - Qty 3
  As above, except support not required.
• Eccentric - Qty 6
  Recommend ABS for natural lubricity and ease of "machining" to size. Extrusion Width 0.3 to 0.4mm recommended. Shell Thickness should be about 0.9 to 1mm. Infill 50% Honeycomb. Layer Height 0.2mm.
  TEST PRINTING TO MATCH SIZE TO YOUR 5/16 OR 8MM "BORING TOOL" IS STRONGLY RECOMMENDED. See Prepare Eccentric section of Instructions.
• Wrench - Qty 1.
  Any rigid material. Extrusion Width 0.3 to 0.4mm recommended. Shell Thickness should be about 0.9 to 1mm. Infill 20% Honeycomb. Layer Height 0.2mm.

Recommended Tools
Drill Bits

• 2.5mm
• 3mm
• 1/4" or 6.5mm

Reamers (Note: could substitute end mills, drill bits, bits of emery tape wrapped around a shaft etc.)

• 5mm
• 5/16" or 8mm

Optional tools for optimizing aluminum barbell sockets

• 1/4" 4 Flute End Mill
• Counter Sink suitable for 1/4" hole.

Ablating Devices

• Riffler or similar small file set
• 1" bastard, aluminum or similar coarse flat file
• Emery Tape 200 - 300 grit

Knifes

• Reasonably stout and sharp hobby knife or similar

Hex Drivers

• 2mm
• 4mm

Sockets and Wrenches

• 5mm Wrench or Socket (if upgrading end stop switch hardware)
• 5.5mm Open Ended Wrench
• 8mm Nut Driver or Thin Walled Socket

Screw Drivers

• Small Phillips (cross head)
• Small (3 to 4mm width) Flat

Pliers

• Medium Slip Joint
• Small Needle Nose

Measuring Instruments

• Caliper
• A method of measuring belt deflection force to 1 - 2 kgf
  i.e. Hanging,Fish,Luggage Scale

Power Tools

• Variable Speed Drill

Fixtures and other Handy Items

• 2.5mm x 20mm or so fully threaded Socket Head Cap Screw
• 3mm x 25mm or so fully threaded Socket Head Cap Screw
• 5mm x 20mm or so fully threaded Socket Head Cap Screw
• 5mm Lock Nut to be sacrificed as a poor persons lathe fixture
• 4 or 5mm width x 200mm or so length plastic cable tie
• 1-2" 6mm GT2 Belt Scrap

Firmware (SeeMeCNC Repetier)
The inner face (mounting surface for the Ball Joint barbell) distance from the Delta Radius (i.e. 200mm for a MaxV2) matches that of the molded carriage. Consequently, the Horizontal Carriage Offset distance does not need to be changed if you already have molded carriages (i.e. 26.5mm for a MaxV2). However the aluminum Machined Ball Joint Carriages have 1mm more of horizontal offset than the plastic barbells so if you are upgrading to the aluminum ones you need to add this distance (i.e. 27.5mm Horizontal Carriage Offset for a MaxV2).

Instructions

• Dimension Check
  See below for major dimensions, the width (37.5mm) across the two parallel sides at the level of the barbell mount posts is critical for proper functioning of the eccentric wheel adjustment. Best to be within +/- 0.2mm. If the mount posts print a little oval, the major axis should ideally be at least 6.35mm.
  

• Prepare Barbells
  Placing a chamfer on the sockets (A) will provide a little relief for the mounting posts where they rise from the body. Size sockets to 1/4" (C) to facilitate fitment.
  

• Clear the Extrusion Tracks on Body and Back Shell
  Remove support, then clean up any debris with a course file. Start with the bodies. Remove enough material to achieve a thickness of 10.5mm at the top of the body and 9.5mm at the bottom. Use your eyeball calipers to achieve a similar level of finish on the Back Shells.
  

• Size Barbell Mounting Posts
  Probably a good idea to get the posts covered up before they suffer any insults. Measure the posts carefully, the model is sized slightly large to ensure enough material for a good fit. Use a folded over strip of emery tape to work diameter down towards 6.35mm. Work both posts evenly to maintain centre distance and horizontal alignment. This is important to achieve a light press fit and avoid dread effector tilt. Be sure to keep an even dimension along the length of the post and remove (just) any protrusions from the surface were the barbell will seat against the body. As you approach dimension, check the fit regularly as described below in order to avoid the lament "i sanded it twice and it is still loose..."
  

• Place Barbells
  Test fit the posts one at a time, the goal is a light press fit. The barbell should slide down to within 2 or 3mm of the body with minimal effort. DO NOT FORCE (A). The reward for a partially jammed on barbell will likely be broken posts and a 4 hour reprint penalty (one might be able to drill and tap a 3mm thread and then place a bolt from the the backside through the length of the post to save the day). Once both posts are sized, apply a little lubricant (B) and test fit (C). There should be just a little resistance with 2 - 3mm to go (D), if this is the case, press the barbell with conviction to seat it fully and test for firmness (E).
  

• Size Post Holes and Prepare Nut Sockets
  Start with the 2mm drill and work up to 3mm (A). Be sure you are drilling true and are centred on the backside (B). Chamfer (C) and remove any support debris from the socket (D).
  

• Place Barbell Nuts and Bolts
  Prepare a longer M3 bolt, washer and M3 Lock Nut as shown (B), a little lubricant may be useful. Pull the nut into the socket taking care to achieve good alignment. Press the nut well into the socket (C). Install an 18mm (aluminum barbell) and seat nut firmly (D). Ensure bolt does not protrude about surface of extrusion track.
  

• Install End Stop Adjusting Screw
  While the 3mm drill bit is still in the drill motor, size the end stop screw hole (~20mm deep) to 3mm (A). Clean any debris from the captive nut slot (5.5mm x 2.5mm) (B). Position a 3mm plain nut (C) and carefully seat with pliers. Take care to avoid rotation of the nut. Otherwise you will be doing surgery on the fixed belt clamp. Run a plain nut up close to the head of the flat head 3mm screw and install.
  

• Install Fixed (Top) Belt Clamp
  Mount up the 2.5mm drill bit. Size all 8 belt clamp holes to 2.5mm(A), as well as the holes in the fixed belt clamp (B). Remove any debris from the fixed belt clamp receptacle (C). Jump down to next step and then return. Once nuts are placed (see below) place a belt scrap in the belt groove (D), install clamp with 2.5mm x 10mm plastic screws and check for protrusion (E), trim if necessary (F).
  

• Install Belt Clamp Nuts
  Place a M2.5mm plastic nut on a longer M2.5mm bolt such that the bolt protrudes ~2mm beyond the nut (A) and gently seat into socket maintaining alignment (B). Place a M3 socket head cap screw over the protruding bolt (B) and then PRESS the nut into the socket (C) to achieve a good seat (D).
  

• Prepare Adjusting Clamp
  Remove support debris from Adjusting Belt Clamp (A). Check fit and smooth motion of a M2.5mm plastic screw in groove (B). Clean slot sufficiently so that with a little applied seating force, the screw travels smoothly along the full distance of the slot and the head does not protrude (C). Remove any debris and surface protrusions from the adjusting clamp receptacle (D) so that the clamp slides smoothly along its travel whilst applying a firm finger squeeze.
  

• Install Adjusting Clamp
  Size hole in end of adjusting clamp with 2.5mm drill bit. Remove debris from slot (5mm x 4.5mm) for captive nut (B). Position M2.5 Lock Nut in slot with lock ring facing belt teeth and seat full (C). Place a M2.5 washer (max OD 5mm) on the M2.5 x 16mm socket head cap screw and install adjusting clamp (D).
  

• Prepare Eccentric Boss Faces
  Identify the junction of the built in support for the eccentric boss faces of both the Body and Back Shell (A). Remove squarely with a sharp and stiff blade (B). Taking great care to maintain a perpendicular face, remove the small joining castellations (C). It should only take a light stroke or two (i filed it twice and...") to reach the required dimensions of 14mm for the body (D) and 8.5mm for the back shell (E).
  

• Prepare Wheel Bolt Holes and Eccentric Bore
  Using (ideally) a 5mm reamer and a little lubricant, size the two fixed wheel boss holes in both the body and back shell to 5mm (A). Remove any swarf (B). Size the inner bore of the eccentric to 5mm (C). You may want to hold the eccentric with something safer than the printed wrench if you are boring with something less friendly than a straight reamer but take care not to crush the eccentric. Size the bolt hole in the eccentric boss to a minimum of 6mm and no more than 1/4" (D).
  

• Prepare Eccentric
  First bore the eccentric boss receptacle in the body and back shell to 5/16" or 8mm with (ideally) a reamer (B). Test fit the eccentric (A), if loose reprint - a snug fit is important. A little too tight is perfect as now there is an excuse to turn the eccentric boss down to size with a Poor Person's Lathe (C) using fixturing along the lines shown (D). Any day involving a lathe operation is a good day indeed. The goal is to have the eccentric require a moderate amount of finger force in order to rotate the eccentric when fully seated (F). Once fairly satisfied with the rotational fit, check the depth fit of the eccentric (E) and deepen the receptacle (B) if required until the eccentric just seats (F).
  

• Install Nuts for Fixed Wheel Bolts in Back Shells
  Start (A), press (B), seat (C).
  

• Eccentric Orientation
  The dot on the eccentric face denotes the face furthest from the eccentric bore. A little ink on the dot may be useful. Not the outward orientation of the dot when the eccentric in the tightest position. When the dot is positioned towards the centre of the extrusion track the eccentric is in the loosest position which is where it should be for installation.
  

• Mini V Wheel Assembly
  Note that there must be a shim between the two bearings. Some suppliers ship the wheels with bearings already installed but without a shim. Inspect carefully. The wheel bolts need to be drawn up tightly. Consequently, the shim between the bearings is essential in order to avoid excessive axial bearing load. Remove a bearing from preassembled wheels and install the shim if necessary.

• Truck Installation
  Prepare a truck by using a M5 x 40mm socket head cap screw and M5 lock nut to mount the eccentric wheel. Note that there must be a shim on EACH side of the wheel (A). Be sure that the dot on both eccentrics is facing inwards (A). Gently snug the nut, splay the truck and position the truck on the extrusion so that the end stop adjusting screw winds up facing upwards (B)! Rotate truck halves into position (C). Install the fixed wheels with a shim on each side of the wheel and tighten firmly (D).
  

• Set Eccentric Wheel
  After the fixed wheel bolts are tight, set the tightness of the eccentric wheel bolt so that eccentric can be turned with the wrench but not freely (A). Minimize displacement of the eccentrics by holding the hex driver fixed and rotating the nut Place the wrench with the handle facing upwards (B) and rotate down (whilst pushing to engage the wrench firmly onto both eccentrics) (C) to obtain the truck tightness that your heart desires. Ensure both eccentrics turn together (D). Tighten eccentric wheel bolt and recheck truck motion. A couple of iterations may be required.
  

• Install Lower Belt - Step 1
  Loosen adjusting clamp screws until just engaged by a couple of threads (A). Loosen adjusting screw until the clamp is just able to reach the top of its travel (B). Place a little curl in the belt and feed it through the central hole in the body. On a good day the belt end can be caught with a screw driver (C). With the clamp in the lower position, feed the belt underneath (D). A little lever action should handily feed the belt under the clamp (E & F).
  

• Install Lower Belt - Step 2
  Ensure belt is fully seated in clamp (A). Turn screws in evenly to just take up the slack (B). Pull down on belt to position clamp at top of travel (C). Tighten screws just a little to give the clamp a bit more bite (D).
  

• Install Upper Belt
  Loosen fixed clamp screws until just engaged and fully unseat clamp (A). Place a curve in a mid size cable tie and use it to fish the upper belt through the centre hole in the body (B). Use a screw driver to feed the belt under the clamp (C) until the belt comes out the top and can be nabbed (D). Use needle nose pliers in conjunction with the end stop adjusting screw (carefully) as a fulcrum to take all the slack and then some out of the belt and GENTLY snug the screws - the teeth will hold belt as long as the clamp is in the general vicinity (E). Verify the bite is good (F).
  

• Position End Stop Switches
  Position end stop switches as shown. If replacing original mounting bolts with M2.5, the mounting and switch holes may need sizing with a 2.5mm drill bit.
  
  .
• Tension Belts
  Position truck at top, check tension at middle against fixed distance reference. Tension at will!! GENTLY snug screws when finished.