DiY MK-7 Gear Hobbed gear experiments. Part II

[Edit] I think that I might be barking up the wrong tree that my gear is slipping on the  filament …  I believe that it is more the case that my extruder is skipping.  The motor hasn’t been calibrated yet.  I reached this conclusion by holding the extruder wheel  with my thumb and tugging on the filament.  No slip… Sooooo. It leads me to believe that I was barking up the wrong tree on this on…. Regardless, I to think a V-notch shape would grip better.  Think V-belts…  But perhaps why I haven’t seen this is that the other solution works good enough??

This a continuation of experiments tried here:

So I was tried making my own hobbed gear using my mill and an spin indexer and I was really rather pleased with the machining outcome… Unfortunately it didn’t work in my qb-db extruder.   I think I used a 10-32 tap and the radius was too big for the filament to grip properly..  I don’t have small metric traps in my in home shop tool inventory, but I to have some small english style ones and plenty of steel to experiment on.   One a side note.   In my first experiments, I machined a radius, to hob into, but I found that I could just plunge it in and it works.  (I wonder if I might be getting some rounded edges because of this, but that might be something I look at in future experiments.

Eyeballing the Qu-db extruder gear and my taps it seems it might be fun to try hobbing the following sizes:2-56, 3-48,4-40

Oth…maybe I should try to be a bit more scientific about this.  I just measured some sample PLA that I got from and it mic’s up around  .068″ (1.73 mm) I’m thinking I need the minor diameter of the tap to be some where around there, so I have nice full contact around the filament.   So as that guy David Brancaccio say on marketplace…. Time to run the numbers.

I’m using Machinist handbook 23’rd addition page 1303 as reference.

So.. I need to figure to figure out a shim for my stop in my mill.
I measured the Qu-bd gear OD ~.457″
The slot diameter ~.416
.457-.416/2 = .205
Offset = .205+ thread depth.

Major Diameter Min Diameter Thread Depth Offset
2-56 0.086 0.0804 0.0056 0.205 0.2106
3-48 0.099 0.0928 0.0062 0.205 0.2112
4-40 0.112 0.1052 0.0068 0.205 0.2118

Hmmm.. I didn’t realize that my smallest tap still had a min dia larger than the filament .080 vs .068.   It’s better then what I had before but not really  it the best.
I wonder if I could machine a small V-notch and get it there with a knurl or better yet coat it with some type of abrasive. I was looking at some stuff here.  It doesn’t appear that anyone has tried this… Interesting…’
I was going to make my blanks and use a boring bar to single point the 5mm bore… I think I’m going to invest in a chucking reamer… Something  tells me I’m going to be making more than a couple of  blanks, and it gets a little tedious to  single point these little bores….
Oh well.. The day is gone.. No chips cut, but did have a good day with the family..

I think I’ll fire up the extruder and see if anything has magically changed before bed..[Edit]  Ahhh geezz… I should have just went to bed and left things alone.   It seems that my extruder x-axis is loosing steps all over the place… I did some quick googling and I found an interesting discussion here.!topic/deltabot/zUq0C2i18FY

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