Making Timing Belts & Robot Tank Treads Using Scarf Joints: Splicing Openbuilds GT2 & GT3 Belts Using a Scarf-joint or Lap-joint
Introduction: Making Timing Belts & Robot Tank Treads Using Scarf Joints: Splicing Openbuilds GT2 & GT3 Belts Using a Scarf-joint or Lap-joint
I want to build some toothed tank-treads for a robot, and I also want to make timing belts. I have some Openbuilds GT2-3M timing belt material, which is a toothed belt 5mm wide with teeth spaced at a 3mm pitch. This tutorial shows how to make a continuous loop of belt from Openbuilds GT2-3M belt (https://openbuildspartstore.com/3gt-gt2-3m-timing-belt-by-the-foot/ ).
Toothed belts are often used in making 3D printers and driving linear actuators, and we use lots of Openbuilds components (www.openbuilds.com) for student projects at the University where I work. I evaluated several processes for splicing these toothed belts together, including testing multiple different adhesives, and surface treatments to evaluate how to make strong loops of belt from toothed belting material.
The GT2-3M belts are neoprene belts with built in lubricant, and a fiber reinforcement layer in the middle. The top layer has rubber teeth, the middle layer is a fiber layer, and the bottom layer is a smooth layer. To make the belt loops, I used a scarf-joint / lap-joint. I used a blade to trim away approximately 6-9mm of material from the top side (2-3 teeth from end #1) down to the fiber layer. For end #2 I trimmed the same length of material (2-3 teeth from end #2) from the smooth bottom layer, down to the fiber layer. These are the scarf joints on the ends of the belt. 807
I prefer using 3 teeth length for a scarf joint. --EDIT: I have also been told that this is also called a lap joint. ---
Now I used IPA (Isopropyl alcohol 100% concentration) to wash out the lubricants that had been baked into the neoprene rubber. Let the exposed scarf-joint ends soak in the IPA for roughly 20 minutes. Now pull the scarf joints from the IPA, and let the alcohol dry away. Now apply Neoprene contact cement onto the exposed & alcohol cleaned ends of the scarf joint, and push the overlapping ends together (use a toothed spacer (either an oiled piece of GT2-3M belt, or use the 3D printed jig included in this tutorial, lightly covered in oil) to maintain the 3mm pitch spacing between teeth.
After the contact cement dries over 24 hours, you will have a loop of belt that is strong and nicely flexible. You can then reinforce the belt using contact cement to glue a strip of fiber reinforced neoprene sheet (ideally 1/16" thick ex: https://www.mscdirect.com/product/details/31937212) onto the back of the belt after it had been cleaned using alcohol.
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I ran tests using over ten (10) different types of adhesive and selected the best adhesive for use. Please note that the adhesives used were not necessarily used for their intended purposes, and this in no-way reflects the quality of the brand when used for their intended purposes.
References:
a) Alcohol treatment of belt material and use of Neoprene adhesive were taken based on advice from the reprap forum, shown here https://reprap.org/forum/read.php?1,670647,888356
b) Making a scarf joint was taken from this youtube tutorial, by <PERSON> https://youtu.be/1zdl_kSc0Ik
---EDIT: I got the name scarf-joint from <PERSON>'s tutorial, but people have informed me that this type of join is actually called a lap-joint. Please watch <PERSON>'s tutorial, it is very good.
Supplies
The basic supplies include
a) Openbuilds GT3 (Openbuilds SKU 626). This is a GT2-3M belt, single sided, 5mm wide, and with a tooth pitch of 3mm (https://openbuildspartstore.com/3gt-gt2-3m-timing-belt-by-the-foot/)
b) exacto-blade or box cutter (ex: https://www.rona. 981