Advice: Avoid this brass for your hobbed drive wheel

This is my experience with brass as a drive wheel.

I hobbed this naval grade 485 brass from Mcmaster Carr.

The teeth are too soft and collapse, and break off, thus jamming the nozzle.

I did have a bit come through the .4mm diameter nozzle, and end up in the print. ( flake image)

You can see the wheel has folded over teeth, and the flake of one ready to come loose.
I put a circle so you can see the dent made by the PLA into the teeth.
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This wheel was only 4 hours old.

Just an FYI. I'm moving to stainless steel and using a #0 center drill, pecked 18 times into the diameter.

Hi,

I have some brass hobbed gears that I purchased recently. The teeth are nowhere near as sharp as what you show. Maybe you should try rounding them off a bit so that they aren't so flimsy at the tips. Your drawings show the edges coming to a knife point.

it's funny. I have made several of these, using a scrap piece of brass I had laying around.
Those had sharp teeth and have no issues. Might be a better grade or alloy of brass/bronze.

The hobbing could be done less deep, and should create less sharps.

I'm also thinking of using an endmill to cross cut a wheel. Not extremely sharp if I keep the number of teeth low.


Credit due: that peck drilling with a center drill comes from the Stratasys Uprint head.

Imagine creating a hollow hobbed bolt, where the filament that gets chewed-up gets put through to the center of the bolt where it can be cleared out with a small toothpick

The center-driller hole way of making a hobbed bolt also looks very promising, I have ordere a bunch of bolts to experiment with, since my current hyena-clone bolt is starting to fall apart around the M8 threads.

I think the chewed up bits are something to be avoided.

I don't know if you ever saw one of those Bits for Bytes heads working. They had a bolt spinning and pressed the filament into bolts thread, nearly running parallel to each other.

The one I saw looked liked it was heavily dusted with a fine powder, since the bolt thread was basically grinding into the filament to feed it.
I bet the oil soaked rag idea, to lubricate the incoming filament, helped those heads a ton.

Must be why that method fell out of favor with folks.
There is a lot of mechanical advantage with it.

Alloys are like a cookie, that is to say there are many recipes and some brass is softer some harder so yes, the type of brass it is would make a difference.

I think the center drilled idea is fantastic for a drive wheel design wish I thought of it. The only drawback I can see is less points to grip the filament if at first it doesn't give you good results I would try going with a larger diameter which in turn were one tooth bites in the center there is teeth above and below engaged in the filament also. But because of that a larger diameter might not work with direct drive.

Edited 2 time(s). Last edit at 01/08/2014 04:29AM by cnc dick.

Quote
davew_tx

Just an FYI. I'm moving to stainless steel and using a #0 center drill, pecked 18 times into the diameter.

FYI - That's how stratasys makes them.

18 stroke/peck drill cycle per hole is a bit excesive, two or three pecks using lube, proper feed and speed should do it.

my poor choice of words. I was meaning that I'll have 18 holes around the circumference.

I would expect a single plunge or as you mention, 2 or 3.