The tangential oscillating cutting knifes (TOCK) are used for cutting cardboard, rubber, plastic films, etc. They use a sharp edge knife which is moving (oscillating) in vertical direction and in the same time can be rotated to follow the tangent of the curve.
The oscillation of the knife up/down is done through a DC motor from some old ink jet printer, the rotation of the knife is done through stepper motor.
Normally the price of the TOCK is exceeding 1200 EUR and here you can make fully functional TOCK for less than 80 EUR on your 3D printer.
You'll need a CNC machine or router to connect the TOCK head, also one additional axis to control the rotation.
Here you can find a complete documentation how to build such TOCK by using 3D printer.
Video in YouTune showing how TOCK works on cardboard for making boxes (notice the smooth cutting of rounded shapes)
Attached is also the program which takes PLT and converts it into GCode with the following features:
- if the angle of the segment is bigger than some threshold - lifts the head. rotates it to the new angle and bring it back. This improves significantly the cutting quality of sharp edges
- the program optimizes the order of cutting segments to minimize the head lift
- the program makes possible to do the creasing without changing the tool (the knife was moved down partially and rotated by 45 deg to make semi cut). Lines in PLT file with red color are treated as creasing lines.
- The program can also take GCode and add tangential commands
- The generated GCode can be executed on Mach3
Oil less bushes are from RS components:
The shaft is calibrated 5mm steel, if using hardened steel shaft it will be more difficult to drill the holes (you'll need carbide drills).
The stepper motor is standard Nema17 42x42x38 or 42x42x48 with 200 steps per turn. technically you can use motor with more or less steps - it's possible to adjust this in Mach3
I'll add in the next few days more info about some details (like stepper motor, shafts, oil less bushes, etc.), images of the working head and links to video on YouTube - stay tuned!
Adde IGES model of the design in case you can't open the SolidWorks files.
04/10/2016 - Increased limits of feed rate in Software
Adding the oil less bushes
The bushes are from RS Components (part number 521-7758)
Another bushes could also be used but the oil less bushes offer long life, can withstand large forces and have low friction so they are ideal for this application.
The holes created during the 3D printing are not very precise - diameter and colinearity are far from ideal. Adding the oil less bushes should be done in the following steps to allow smooth movement of the shaft:
before you start the procedure ensure the bushes move freely on the shaft
Insert the bushes into the holes, use rubber hammer to push them to the bottom of the holes.
Insert the shaft 5mm. It's not necessarily to drill the holes in the shaft on this stage, actually drilled holes will make things more difficult.
Notice that the shaft goes with effort through both holes
Use hot air gun (300 degrees Celsius, strong blow) for ~20s to 1 min to heat one end of the shaft. Ensure the hot air is not heating the plastic.
Once the shaft is hot enough (it should be between 100-140 degC) push the hot end down to go inside one of the bushes. In 10-20s you'll see that the shaft moves freely inside the hole
Warning - when you heat the bushes from the shaft some oil is coming out of them. Don't move and push the shaft and bushes at this moment until they completely cool down otherwise it's possible to increase the hole diameter of the main body and get gap between bushes and body.
- Do the same operation as (5) for the other bush.
Once you completed steps 1..6 your shaft will move freely up and down. If the shaft can fall out by its own weight from the holes - the friction is OK. If you still have friction - repeat step 5 & 6.
Shaping the blade
Knife holder assembly
The knife holder was 3D printed, two main parts were tighten with 3mm screws to hold the blade. A metal insert was used to redirect the forces from the blade to the base material - it's a thin strip of steel sheet metal - see images below.
Rotating shaft unit
The shaft rotation is done with stepper motor. The simultaneous rotation of the shaft and the movement up and down is done through the shaft lever and stepper motor lever coupled by two balls 6mm diameter (from ball bearing). The balls touch into two sheet metal bars (so contact is metal - metal), lubricate this area with grease. A 2.5mm screw was used to support the balls and to keep them in the center position. The hole diameter for the balls is increasing inside the body so when you push the balls they will snap and stay in place.
See image below for detailed view of this area.
There are several holes in the TOCK body used in assembly process for supporting parts or accessing screws - see images below.
Supporting the pulley with steel rod when inserting the 2.5mm spring pin
Supporting lever when inserting the 2.5mm spring pin
Screwing the stepper motor through these holes
Screwing the DC motor through these holes
Final assembly sequence
The TOCK assembly process is following:
Insert the bushes and ensure the shaft is moving up/down free (see description above). On this stage remove the shaft
Insert the push-pull pulley and then insert the shaft through the bottom bush and pulley. Use supporting rod and hammer the 2.5mm spring pin into the pulley. Now the pulley is fixed to the shaft. The push-pull pulley is the most critical part of the assembly, if 3D printed it should be used 100% fill and draft quality (to get maximum strength) or it should be be made on lathe from aluminium or brass.
Grease should be placed to lubricate the contact with the bearing, between bearing and the pulley you need gap of 0.1 to 0.3mm in order to work correctly.
Put he screw on the shaft lever and then insert the balls (6mm diam). The balls should get support from the screw and stay tight in place. If the holes for the balls are too small the lever can break while inserting the balls.
Insert the lever onto to shaft, put the supporting rod and hammer the spring pin. Now the pulley and the lever are fixed to the shaft
Insert the stepper motor into the hole and also add the stepper motor lever. Screw the stepper motor through the mounting holes.
Screw the sheet metal plates to the stepper motor lever. Ensure they move free when inserted over the balls. If they stay tight - push apart the plates, if too much gap - push them inside. Insert some amount of grease between the sheet metal plates for lubrication the contact balls - plates.
Insert the bearing into the motor cap and then both parts into the push-pull pulley. From other side insert the DC motor for oscillation and screw it. Use metal O-ring to avoid bearing to come out from the cap, the gap between cap and bearing should be minimum and the bearing should stay tight on the cap.
Fix the DC motor to the box with 2 screws (by using the holes in the box you can insert the screwdriver).
Add some grease on the main shaft near the bushes. The bushes are oil less and they can work without lubrication but adding grease may prolong their life.
Screw the cover of the box. The cover could be 3D printed or made from 1mm sheet metal aluminium (in this case you get better appearance).
- The DC motor is normally powered from 24V but you can find the most suitable voltage for you depend on the motor type. It's a good idea to connect the motor to some relay on the CNC controller board and switch on the motor through GCode.
... to be continued...
Adjusting the zero level for cutting/creasing
The zero Z level is defined as the lowest cutting point, in zero Z level the knife should touch the bottom surface (some soft plastic or rubber base). The problem with cardboard is that you can't rely on the material thickness and use the top surface as zero reference, that's why I chose the bottom surface which is more reliable.
How to find the zero Z level point:
Lift the head over the cardboard surface and position it in some area where the base material (soft plastic or rubber) is visible.
Run the DC motor so the knife is oscillating.
Slowly move down the head until there is a small contact between the knife and the base. The knife in down position should penetrate a little in the base material (0.1..0.2 mm) otherwise the cut details will not come out easy.
- Set this level as zero level
Adjusting the creasing level
The TOCK can do also creasing by doing partial cut of the paper (cut half thickness) and also rotating the head on 45 deg relative to the movement vector to maximize the cut area. Such approach has some advantages - there is no need for second instrument for creasing (with separate Z control) but it's applicable mainly for cardboard.
The creasing level is set in the following order.
Find the zero cutting level - described in previous text
Run the motor and start moving the head up until it barely cuts the material. If you cut two layers cardboard ensure you cut the top layer but bottom layer stays intact. The Z level at this moment is the creasing level.
- Set also the lift head distance for creasing and cutting to be 3-4mm above the top surface level.
Setting of axis A (rotation) in Mach3
In order to make the generated from the program GCode working it's important to set the Mach3 correctly (if you go to SETTINGS tab in the "Tangential cutting" program there is a short instruction).
Required settings for Mach3 program:
In Mach3 Config /General do the following changes :
- Uncheck A axis is angular (Mach3 angular degrees do weird things so switch it off).
- Uncheck Rot 360 rollover (the program takes care for 360 rollover internally)
- Uncheck Ang short rot on G0
- Uncheck Rotational soft limits (soft limits on A axis doesn't make sense).
- Check "Constant Velocity" mode (makes the movent on curves smooth)
In Settings (Alt-6) - uncheck Tangential Control
Motor tuning for A axis - make settings in such way that 1mm movement on A axis yields 360 degrees rotation. The steps per mm settings in Motor Tuning for A axis is calculated by following formula:
steps_per_mm = motor_steps * microsteps
In case of Nema17 motor with 200 steps and if using stepper driver with 8 microsteps the result is:
steps_per_mm = 200 * 8 = 1600
Ensure you set properly the maximum velocity and the acceleration (the settings below are suitable for Nema17 with 8 microsteps).
Don't forget to press Save Axis settings button after changes were made (otherwise changes will be lost).
When using M07/M08/M09 for switching on the cutting motor ensure file M101.m1s contains (the macro can be generated from the program by pressing button in SETTINGS tab):
Call SetDRO (3,0)
Code "G4 P1"
If needed you have to invert the direction of A axis in Mach3 settings.
If you don't have homing for A axis you have to force the head to zero angle manually after main machine homing. In current design the stepper motor is directly rotating the head so it's possible to overcome the stepper motor holding force and bring the head into zero position manually. The other option is to use jogging for A axis in Mach3 and rotate the head to the desired position.
After the head was rotated in zero position don't forget to press "Set to Zero" A axis (set current A position as zero).