UPDATE 2024/29/05: Added holder for stone 51,2x19,6 mm. Name is KSJ-06-06.
UPDATE 2024/31/03: Added revolving grinding stone holders. KSJ-06-04 is for attaching three stones at once and KSJ-06-05 is for attaching four stones. That means that you do not have to change the stone each time but after you are done grinding with one grid simply rotate the rod and you are good to go. Also added simple tube KSJ-01-02 which goes above the adjustment screw. If you screw the adj screw all the way down and insert the tube the grinding stones are parallel to the base so you do not have to find the ideal angle to sharpen your blades. Because the KNIFE_HOLDER is already under 17°.
GENERAL
- Several design versions and printings scrapped and finally I have this knife/scissors sharpening jig. I wanted to design it to be as strong and precise as possible. So 3D printed threads and knobs were not an option. Therefore to adjust anything you need a 3 mm Allen key which is conveniently located on the jig itself. In the models and pdf the 3D printed parts are umber and bought parts are grey.
- It consists of two bases connected by two 8 mm rods. This allows the bases to change distance and the jig to sharpen smaller curves. To keep it from sliding there are holes on the bottom for rubber feet of diameter 10 mm or use those antislide rubber pads for phones cut in the shape.
https://www.aliexpress.com/item/1005005710035199.html?
- In the STAND_1 is inserted another 8 mm rod which supports the rotational assemblies. These enable the sharpening stone to rotate freely in two axes and slide in another two. Besides these assemblies there is a stopper which restrains the rotational assemblies from sliding upwards (sometimes happened when too much force was applied) and an adjustment screw for precise adjusting of an angle, use some lube in the threads. It also has one free nut in case i would like to add some accesories.
- The KNIFE_HOLDER base is angled under 17° which is the most common grind for kitchen knives. So you just need to level the stone to grind it properly. To grind under different angles just move the grinding stone holder up or down. The series of holes is for inserting short 6mm pins which serve as stoppers for the knife blades. The two sets of two nuts are used to move the clamp backwards or forwards according to the width of the blade. You just need to find the right combination of pin holes and clamp holes to suit your knife. Moreover the base has two attachment points for another angled piece which is used for sharpening scissors. It is detachable in order to quickly print and change angle in case this angle is not suitable. Firstly I had fixed angle as for the knife angle but the scissors grinds are all over the place and I did not want to reprint the whole KNIFE_HOLDER base every time. The clamps tend to bend under higher loads but you can use a little bit of heat from lighter to bend them back.
ASSEMBLY
- In the folder there is a pdf attached which shows a bill of all the material to print/buy on the first page and then individual assemblies with instructions how to assemble everything.
- The assembly technique I used the most is slotting a hex nut into the hex hole. I used two types of M5 nuts but you can easily use just one. I used the ones with polymer inserts just because I had access to them. They are used in places which are not going to be disassembled frequently.
- I will probably design a model for heat set inserts because it will be easier to print. I just did not have any on hand and no soldering iron so I used nuts.
- To retain bearings I used 3D printed safety rings and so far they are working surprisingly well.
- The adjustment screw has three tolerances because it needs to be tight on the rods in order not to spin while sharpening but not too tight so you still can adjust it with your fingers
- The spring which is in the BOM is not strictly required but helps to retain the clamping force needed to hold the sharpening stone. You just need to follow the instruction in the PDF for the spring to work.
- Watch out while assembling ROT_ASSY_1 because you firstly need to insert hex nut into its slot and after that insert the linear bearing LM8UU
PRINTING
- Each STL file is oriented the right way for printing
- Everything is printed from Prusament PETG except those two clamps KSJ-08-02 and KSJ-08-4 . These I printed from Prusament PLA because of higher stiffness - you can tighten it more without warping. These are printed with 100% infill as well. If it bends permanently you can use a lighter and bend it back. Or reprint.
- The rest of the prints I printed with higher perimeters - around 6, adaptive cubic infill of 30% and for the two stands I used adaptive layer height.
- The printing is easy I did not have any troubles printing it but you will need supports in some parts. Some parts have harder to reach areas. So it is good to have your supports dialed in.
- Assemblies KSJ-04-00, 05-00, 06-00 can be printed without supports
- KSJ-07-02 use supports only in the slot used for clamping
- KSJ-08-01 use supports only in holes for nuts and to support the top wide part
- KSJ-01-01 use supports only in holes for nuts
PS
The last picture shows my skillfull girlfriend that the knives sharpened on this jig are indeed sharp.
Bobino
