I saw the Kingroon KP3S selling for the price of about four spools of filament and figured I would buy one.  After I set it up and used it for a while, I was very impressed with this little printer.  Direct drive, linear rails on X and Y, and a perfect compact size.

But like many inexpensive Chinese 3D printers, it has some odd design choices.  It almost felt to me that they forgot a spool holder and a power supply when designing this, and both were an after thought.  I'm sure this is not the case, but that's the best way I can describe it.

Both issues needed to be fixed to make this printer close to perfect, all for a printer that is very affordable.  Other issues are less important.  I replaced the stock print surface with a textured spring steel sheet, and the bed springs will be replaced.  The hot end seems fine, but that will be replaced so I can go above 240C.

The first issue I decided to address was the filament spool holder.  I first used my triangle spool holder that I have published here on Printables, and it was fine.  Except I did not like the path the filament took to get into the extruder.  When the Z hight was high, the filament would go into the extruder at a sharp angle.  This was easily fixed by using an 8 inch (about 200mm) piece of PTFT tube I had laying around.  This reverse Bowden worked great, and I was happy that the tube fit securely in the extruder as if it was design for one.  But this made it a little inconvenient to change the filament.  And this little printer was still taking up more bench space than it needed to with the filament on the side.

I looked at some other spool holders that mount on top of the aluminum extrusion, which is a logical place to put it.  But all required bolts and threading the aluminum extrusion to make sure that it stayed in place.  I prefer to design things that are easy to use, and do not require any permanent changes (like tapping threads.)  So I designed this one.

This simply slips securely over the aluminum extrusion.  It not only fits around it, but designed to follow the aluminum extrusion to also fit in and around it.

I also like to design everything to print in place and not require supports.  The first design met these goals, but was difficult to print because there was a long narrow part that would not stick to the bed properly.  So I resigned this to be printed in two parts, and screw together.

However, and this is important, it screws together with left hand threads!  Please pay attention to this or you will not get the two parts to screw together!  The reason for this was simple.  As the printer is printing, the spool will rotate (obviously.) But the way it rotates may unscrew, or loosen the spool post from the base.  Probably not, but it was something that I felt needed to be considered.  So this uses left hand threads so as the spool rotates, it will not loosen the post from the base.  Again, when you screw the post to the base, screw it in backwards!  Lefty-tighty!  NOT righty-righty!!  I will mention this again below.

The first two images are renders done in Cinema 4D with the Arnold render.  The next two pictures are of an actual print.

Printing

This was designed to be printed on the Kingroon KP3S, and is a very easy print.  This print will use 178mm of the 180mm Z height of the Kingroon KP3S.  It will take some time to print.  Both parts are properly positioned for printing.  Do not change or rotate anything.  I even have the part with the female threads facing the front so the air duct on the KP3S is blowing on the treads to help with the overhang.  If you print this on a printer that has the part cooling coming from the side, then go ahead and rotate it 90 degrees if you want.  No supports are needed.  I used the default settings, but you can always increase the parameters to make it stronger.  I would recommend at least three parameters, and at least 20% infill.  PLA works best, but of course PETG can be used for this (as long as your PETG is DRY.)

I have three files uploaded here.  The first file is the STL that contains both parts for you to print.  The next two files are the STEP file for each of the two parts.  I included the STEP files for you so you can make any changes.

Assembly

LEFT HAND TREADS!!  (I told you I would mention this again.)  Screw the post into the base.  Remember, I used left hand threads so screw it in backwards!!!!

Then simply place the assembled spool holder on to the aluminum extrusion.  Remember to remove the plastic cap covering the top of the extrusion first, and then push your new spool holder all the way down.  That's it, you are done!  This will fit tight, but not too tight.

Conclusion 

Like I said before, I am very impressed with this printer.  Outside of a few odd design choices to save money, it is a great value for a 3D printer.  I designed this spool holder for myself, but while designing it I knew that others will find value in this.  That is why I changed it a little bit to make it easy to print.  

I have used this spool holder for a while now and have gone through many spools of filament with this spool holder.  And I printed this using PLA.  I even hung a 20lbs (9Kg) weight on the end of it for a day without any issue at all.  So it is more than strong enough for a 1Kg spool.  

This took some time to get just right.  I think I printed almost a dozen of these, in different brands, and in PLA, PETG, and ABS.  (ABS was printed on an enclosed printer, not the KP3S.)  I finally decided on this version with looser threads to make it easier to screw in.  So it will seem a little loose, but once tightened in will stay in place.  Just keep in mind that you made this out of plastic, so don't over tighten or you will be printing this again.

If you were wondering about some of the design choices, I'll explain.  The hole down the middle of the post is there to give the post more strength.  It may seem counterintuitive that a hole makes it stronger, but it does.  Additionally, the spool will hang on the back of your printer, and not over the print bed.  My first version had the spool over the print bed which made for a nice direct path into the extruder.  But the old design limited the hight you can print, so this is why the spool is on the back.  So to be clear, this design allows you to continue to use the full 180mm Z height as the printer was designed to use.  Finally the print orientation.  Yes, it would be stronger if you printed this horizontally to take advantage of the layer direction.  But then supports would be needed, and would be nearly imposable to remove from inside the base.  And as I said, this is more than strong enough for 1Kg spools.  I already mentioned why I used left hand threads.  This was all designed in Fusion 360.

Please let me know if there is anything that I can do to improve this design.  And of course, good luck with your 3D printing, and your Kingroon KP3S!