From 6e95e8baf786bce78b497157310fdc49794570b7 Mon Sep 17 00:00:00 2001 From: Mohammed Omer <momer93@hotmail.com> Date: Mon, 22 Feb 2021 20:12:11 +0100 Subject: [PATCH] writing --- docs/machines/Desktop3DPrinter.md | 1 - docs/mechanics/3D Printer Mechanics.md | 30 ++++++++++++++++++-- docs/mechanics/Ball Screws.md | 39 ++++++++++++++++++++++++++ docs/mechanics/Belts and Pulleys.md | 17 +++++------ docs/mechanics/Linear Motion.md | 1 + 5 files changed, 76 insertions(+), 12 deletions(-) create mode 100644 docs/mechanics/Ball Screws.md create mode 100644 docs/mechanics/Linear Motion.md diff --git a/docs/machines/Desktop3DPrinter.md b/docs/machines/Desktop3DPrinter.md index bff073b..5f13b67 100644 --- a/docs/machines/Desktop3DPrinter.md +++ b/docs/machines/Desktop3DPrinter.md @@ -71,7 +71,6 @@ Various repositories such as Youtube, Github, Instructables, GrabCad, Thingivers 2. Creality Ender 3 - --- ## Choosing a 3D Printer for the OLSK The Open lab 3D Printer must be a reliable machine with quality components that can be built from scratch with having to source as few components as possible. The printer can be built locally without having to purchase an expensive Kit or fully assembled 3D Printer. The printer should make it possible for users to choose their own components for key elements depending on local availability of components and budget. diff --git a/docs/mechanics/3D Printer Mechanics.md b/docs/mechanics/3D Printer Mechanics.md index 9ea679a..cab86f8 100644 --- a/docs/mechanics/3D Printer Mechanics.md +++ b/docs/mechanics/3D Printer Mechanics.md @@ -22,9 +22,10 @@ - Kinematics are difficult for firmware to calculate - Inefficiency of height since extra height for machine required to accommodate the arms and print head. - Circular build plate can be a disadvantage for some + - 3. **Core XY:** Mix between cartesian and delta in characteristics. Single stepper motor to control the Z-axis moving bed up or down. 2 Stepper motors work to create the X and Y motion. Calculations are tricky and benefit from 32bit mainboard. Also optimal when printhead and extruder have minimal mass  -- Pros: +- **Pros:** - Boxed Frame design commonly found in Core XY is more rigid compared to Prusa i3 style open frame - More efficient in Y space usage > High space utilization - Lighter moving weight on extruder and so head can change direction easily and quickly @@ -32,8 +33,31 @@ - Printhead does not need to carry mass of X-stepper motor. This reduces burden of the shaft, compared to designs where motor moves with axis - Future compatibility with tool changing systems - Printers can be easily enclosed -- Cons: +- **Cons:** - Complicated assembly and belt system design - Long belts required and so difficult to tension belts - X and Y cannot be driven by lead screw, only with belt -4. **Hbot** printers are similar to Core XY with a slightly different belt setup \ No newline at end of file + - The frame design in CoreXY is also a source of inaccuracies. While the frame is relatively stable compared to other 3D printers, it can be inaccurate if the frame is not assembled perfectly square. However, this problem can be resolved with a fixed square. Corner brackets can also help keep the CoreXY printer permanently square. + +**Some notes on CoreXY Mechanics:** +CoreXY has long belts. The belts can contribute to ringing in the prints because long belts will tend to stretch more under acceleration than shorter belts, but the ringing problem isn't nearly as bad as the ringing you get when you try to move the massive bed at print speed. Using wider belts can help keep ringing to a minimum in a CoreXY mechanism (or any other printer type). + +Of course, you can always build it poorly create problems. One of the common errors I've seen in a lot of CoreXY builds is not keeping the belts parallel to the guide rails. That causes the belt tension to vary depending on the extruder carriage coordinates and results in distorted prints, and if it's bad enough, causes belts to slip on drive pulleys. + +The other thing to be aware of is that when printing lines at 45 or 135 degrees, such as solid infill, only one motor is moving the entire mass of the X and Y axes. You have to choose your motors accordingly and set speed, acceleration, and junction deviation (or jerk) to values that will work with your printer. When you see people complaining of layer shifting problems in a CoreXY machine, it almost always occurs when it is printing 45 or 135 degree infill. Don't skimp on motor torque. + +In a machine with the bed moving in the Y axis, the typical end-supported guide rails will flex and the bed will move in an arc instead of a straight line. In a coreXY mechanism if you use end-supported guide rails you can have the same problem, usually to a lesser extent because of the lower moving mass in the CoreXY. It's pretty easy to build a CoreXY mechanism using fully supported linear guides in the Y axis and even in X and have very few problems with rails sagging. + +In the CoreXY design, the tension of the belts plays a major role. For example, if the belts are selected from inferior material, they can stretch more quickly and therefore wear out more quickly. This often causes the 3D printer to lose accuracy after a short time. + +4. **H-bot** printers are similar to Core XY with the biggest difference being that CoreXY systems have two timing belts and H-Bot systems have only one. This means that CoreXY systems have less vibration and can print much more accurately and quicker than H-Bot systems. + +Pros: +- Only one belt +- Purely theoretically a very high precision can be achieved + + More on the differences between CoreXY and Hbot [here](https://the3dprinterbee.com/corexy-vs-hbot/#:~:text=How%20do%20CoreXY%20and%20H,quicker%20than%20H%2DBot%20systems.) + +5. **D-bot** + +6. **Crossing gantry** or QuadRap mechanism like in the Ultimaker \ No newline at end of file diff --git a/docs/mechanics/Ball Screws.md b/docs/mechanics/Ball Screws.md new file mode 100644 index 0000000..c9bb2ad --- /dev/null +++ b/docs/mechanics/Ball Screws.md @@ -0,0 +1,39 @@ +# Home + +**Note on Ballscrews from user CMM on stackexchange:** + +- At the limits of the machine, precision is limited by the achievable positioning accuracy of the motors and the mechanical reflection of that precision into a linear position. + +- With a belt drive, the mechanical precision for a stepper-motor system is the circumference of the drive pulley divided by the number of distinct step positions. A 1.5 degree stepper with 10::1 microstepping (assuming everything works perfectly) with a 1 cm pulley gives a maximum precision of 0.013 mm. The same stepper motor with a 5 turns/in ball screw has a maximum precision of 0.0021 mm i.e. the precision is better. + +Other advantages may include: + +- A stiffer drive system with a higher resonant frequency + +- Ability to transmit more force to the mechanism + +- More precise slow-motion controls + +There are several disadvantages. + +- The rotating mass is increased. + +- Rotating ball screws have a maximum rotation rate depending on how the ends are supported. This limits the maximum movement speed. + +- The most economical ball screw size (at McMaster-Carr) is the 5/8"-5 ball screw with appropriate ball nuts. This is fairly high mass. It is also stiffer than thinner ball screws, and will have a higher maximum spin rate for a given support system. + +- For a particular linear speed, the motors must spin faster. Unless a more complicated, variable micro-stepping drive method is used, the I/O load on the drive firmware will be higher -- about 5 times higher in this example. + +- Other advantages of ball screws are less relevant in a 3D printer application. + +- Ball screws can generate and support higher forces + +- Ball screws are not subject to the belt stretching and skipping a tooth + +- Ball screws work well with human-controlled knobs and hand-wheels + +- If this is a larger bed size than a typical printer, you will probably be printing larger objects. To keep the printing time reasonable, you may want to print faster, which means higher acceleration and higher extrusion rates. + +For your particular application, you need to evaluate the tradeoffs. Either could be your answer. If the analysis is too complex, you could default to belt drive. You could put the money you would have spent on ball screws, ball nuts, and extra bearings into wider belts, higher torque motors with smaller step angles, and better (higher voltage, faster switching) motor drives. + +[Information](https://www.machinedesign.com/mechanical-motion-systems/linear-motion/article/21828146/the-importance-of-ballscrew-end-fixity) on fixing methods of ball screw ends and their importance \ No newline at end of file diff --git a/docs/mechanics/Belts and Pulleys.md b/docs/mechanics/Belts and Pulleys.md index 779b31a..6c60152 100644 --- a/docs/mechanics/Belts and Pulleys.md +++ b/docs/mechanics/Belts and Pulleys.md @@ -3,14 +3,15 @@ There are various mechanisms used for transmitting the motion on the X,Y and Z axes. Some of the most commonly used types are: 1) Rollers (Delrin wheels, metal rollers, bearings etc) rolling either on or within a straight or profiled extrusion (V-Rails) a. Delrin wheels rolling within the V-slot grooves of a Aluminium V-slot extrusion profile. These are most commonly used in budget DIY 3D printers, since they are ideally suited for low load applications. -i. Pros: -1. Ease of build and assembly -2. Robust and reliable -3. Com -ii. Cons: -1. Not as smooth as linear rails -2. The Delrin coating on wheel wears away with time -2) Linear rods with linear bearings or simply bronze bushings +- Pros: + - Ease of build and assembly + - Robust and reliable + - Com +- Cons: + - Not as smooth as linear rails + - The Delrin coating on wheel wears away with time + +2) Linear rods with linear bearings or simply bronze bushings 3) Timing Belts are toothed rubber belts reinforced with fibres within the matrix that provide the belts their strength and touchness. Timing belts require matching toothed and idler pulleys for motion. 4) A linear rail consists of a stiff, steel rail, along which a carriage slide. Most commonly, the carriage contains recirculating ball bearings that provide contact points between the carriage and the rail, as depicted above. This enables a smooth sliding motion as the balls roll between the surfaces. The shape of the shaft enables the carriage to stay locked on with tight tolerances, restricting the motion to strictly linear directions. https://i.all3dp.com/cdn-cgi/image/fit=cover,w=1000,gravity=0.5x0.5,format=auto/wp-content/uploads/2019/05/22192229/a-cut-away-depiction-of-a-linear-rail-and-its-rec-linear-motion-tips-190518_download.jpg diff --git a/docs/mechanics/Linear Motion.md b/docs/mechanics/Linear Motion.md new file mode 100644 index 0000000..291ca38 --- /dev/null +++ b/docs/mechanics/Linear Motion.md @@ -0,0 +1 @@ +# Home -- GitLab