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RKStar

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Discussion starter · #1 ·
Hi all

I designed and built a circular knitting machine or CSM, mainly using 3d printed parts. There are many aspects in existing designs I did not like. Among these are bevel gear drive, sub-ideal bearing surfaces, difficult to implement moving parts etc.
This design uses a different approach to needle movement. There are basically 3 phases:
  • a needle moves up to place the previous stitch under the needle latch and accept the yarn in the hook to form the new stitch;
  • the needle is pulled down creating the new stitch;
  • the needle comes back up and does nothing.
In all machines I examined, during the third phase the needle moves halfway up, making the movement a-symmetrical. In order to make the machine bi-directional the internal configuration needs to be changed when rotating in reverse by using spring loaded "flippers" (The MrRoboto approach)
Another way I have seen is by implementing a second pull-down phase, making the movement symmetrical, but creating a lot of un-necessary drag. (JeepingJohnny)
My solution is to implement a second push-up phase after the new stitch is created. Now the needles are up during the third (do nothing) phase.
This would create problems when certain actions are required; for instance when a dropped stitch needs to be picked up. Therefore the needles can be pushed down during most of the third phase. These needles will be pushed up normally by the first push-up cam (but you need to make sure the latches are open!)
Instead of bevel gears I use a timing belt to drive the unit. This introduces a lot less friction. Also the machine rotates on 3d-printed ball bearings using cheap steel 4.5mm (.177 cal) BBs.
Finally to reduce friction I glued annealed steel wires into the push-up and pull-down cams. This eliminates the need for sanding these cams smooth, it creates a superior bearing surface for the needle movement and eliminates wear of the cams. It also reduces the need to lubricate. (the steel wire can be replaced)
I found that fluffy yarn tends to snag on 3D-printed parts, so I reduced yarn-on-plastic contact by using piano wire guides most of the time.
Image


I have been using this machine for a while now and it behaves very well. It does not like heavy yarns or very shallow stitches. It will require excessive force during these circumstances. I leave the timing belt relatively loose, so when it skips, you know not to continue.

I built the whole machine for less than 50 dollars, It needs about 45 hours to print, with one part 20 hours (the central cylinder). The assembly is straight forward with only the ball bearings needing some attention. Also sanding is kept to a minimum.

You can find the design on thingiverse (thing:6273014). It includes all the printable files and the OpenSCAD design. You can change it at will, or contact me to implement your wishes. ( I may help you out :p )
 
Discussion starter · #5 ·
Can you make a bigger one for hats? I want to find a machine equivalent to the 3/8” 80 peg from knitting board looms.
Short answer: Yes. There is a larger version already on thingiverse (thing:6325127). This one should fit in a 220x220 build plate with no brims or skirts. Also as part of the original version you will find an OpenSCAD file that can be modified to build any size machine (within reason).
I can generate .STL files for you if you are unfamiliar with OpenSCAD, I only need the required size of the central cylinder.
Please note that the size of your build plate is the limiting factor. I use a 300x300 build plate and the maximum size I could make is a cylinder of 240 mm (about 9.5 inch archaic) which is double the size of the original.
Also note that these large cylinders need a very long time to print (2-3 days).
Caveat: I do not intend to build a large version myself so I do not know if the design is adequate or strong enough, or that it will knit at all. You are on your own here.
I include my latest OpenSCAD file for your convenience (please remove the .txt from the filename)
 

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Short answer: Yes. There is a larger version already on thingiverse (thing:6325127). This one should fit in a 220x220 build plate with no brims or skirts. Also as part of the original version you will find an OpenSCAD file that can be modified to build any size machine (within reason). I can generate .STL files for you if you are unfamiliar with OpenSCAD, I only need the required size of the central cylinder. Please note that the size of your build plate is the limiting factor. I use a 300x300 build plate and the maximum size I could make is a cylinder of 240 mm (about 9.5 inch archaic) which is double the size of the original. Also note that these large cylinders need a very long time to print (2-3 days). Caveat: I do not intend to build a large version myself so I do not know if the design is adequate or strong enough, or that it will knit at all. You are on your own here. I include my latest OpenSCAD file for your convenience (please remove the .txt from the filename)
thanks. It might be a bit but I am going to try and figure this out.
 
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