I’ve been making my own 3d printer and I’ve finally at the the point where I can make use the kickstarter. QU-BD extruder.
The machining on these parts was superb but there where some deficiencies in the design, which are discussed here: http://www.fabric8r.com/forums/showthread.php?793-My-very-own-QU-BD-woes
So it sounds like the path I’m going to follow was cut by Mr. Bart Dring (http://www.buildlog.net/wiki/doku.php?id=ord_bot:qu-bd_extruder_improvements) with my little twist being that I’d make my own extruder wheel,
I found some interesting information here on making your own wheel:
On cutting a worm wheel I found some stuff here: http://www.practicalmachinist.com/vb/general/hobbing-gear-tap-how-160177/ I’ve seen some discussion that the blank needs to be gashed first in an indexer. (I wanted to see if I can avoid that.)
I have a very nice spin fixture/indexer with a 5c collet. Initially, my thought was to place the blank in the indexer on the mathematically correct center distance in my mill to the I’m wonder what would happen if I feed the tap axial instead of radial into the piece. I’m thinking the worst that can happen is that I snap the tap. I don’t have a large assortment of metric taps but it seem I’m good on inch, so if I’m going to break one or two or ???, I want it to be an inch tap. My hope that since I’m the correct center distance the timing thing should just work itself out. I wound up doing is just feeding in radially and it seemed to work just find. This approached saved me the hassle of figuring out/setting center distance. I not sure it would have worked anyway.
I wound up finding some pretty cool gear links, that might come in handy when I want to actually make a worm gear. I don’t need them for this project but they where interesting links non-the-less.
Ok.. So I found thread pds here: http://www.osgtool.com/_branding/osgtool.com/files/catalogpages/USCTS08%20314.pdf
Also I found some info on worm gears formulas here… http://www.roymech.co.uk/Useful_Tables/Drive/Worm_Gears.html
Ahh… Detailed formulas here for Metric (http://www.sdp-si.com/D805/D805_PDFS/Technical/8050T072.pdf)
Originally I was just going to use a 6-32 tap as a hob. Unfortunately, I don’t own a R-8 collet and I was in no mood to make an adapter sleeve or get a R-8 collet just for this.
I wound up increasing the tap size till I was able to get it to fit in my R-8 collet. So I wound up using a 10-32? tap.
The Geared wheel on the the QU-DB extruder is a brass spur gear with a circular slot cut into it. I figure I maintained the OD of the Gear and the Min Diameter of the groove, I should be ok.. (If not.. I let the moths out of the wallet and get a MK-7 tooth gear.
Basically I have a huge supply of 3/4 steel that seems to machine wheel so I thought I’d try that. I turned the OD down and cut a groove to the same diameter as the QU-DB gear. I didn’t bother drilling it and I just wanted to see what would happen. I was actually sort of pleased with the result although improvement is needed. The thing that I need to do is to set a stop to keep from hobbing too deep. A couple of tricks, I help the rotary rotate when the tap first started biting, that seemed to help. I suspect giving it a good bite (not enough to snap the bit probably helps too.
Experiment number two.
Ok.. I’m feeling lucky.. So I’m going to tap using a 10-32 Thread. I went wrong on my first attempt in that I didn’t add a stop to control my depth… So basically I need the whole depth of a 10-32 thread. Machinist handbook give me a internal thread depth of .019
I measured the Qu-bd gear OD ~.457″
The slot diameter ~.416
So if I touch the tap to the OD of the part. I need a block to set my offset of
.((457-.416)/2)+.019=0.0395 So If I set with a .010″ Feeler gauge I can use a .050 gauge block to set the stop…
It seems that it worked ok.. If someone wants to see pictures… Let me know an I can add some…. But now I’m to other things..