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hobbed bolt maintenance?

Posted by TheCase 
hobbed bolt maintenance?
September 16, 2011 05:58PM
Just when I thought I could start a non-stop printing process, I've noticed that I need to go into the extruder (Wade's accessable, thankfully) after every couple hours of printing and use a dental pick to get bits of PLA out of the teeth of my hobbed bolt. Otherwise the extrusions are less than ideal.

Is this a common issue? I doubt it, but I'm stumped as to how I might prevent it...
Re: hobbed bolt maintenance?
September 16, 2011 06:42PM
If you're generating that much plastic dust, perhaps the idler is not pushing strongly enough against the filament? If it isn't tight enough, it'll slip, and grind through the plastic. I use a cobbled together extruder unlike yours, but tightening the idler helped it for me.
Re: hobbed bolt maintenance?
September 16, 2011 06:46PM
Yeah, ok, I probably need a stronger spring.

Here's what I was thinking could be the causes (why do I always think after posting?)

1) temperature too low: extra work for extruder to push filament.
2) spooled filament is dragging/catching and/or tough to pull
3) idler is too tight
4) idler is too loose

I was going on the assumption (based on Greg's pictures of his) that one bolt was good enough on the accessible extruder. I'll go with two bolts and heavier springs to see if that improves.

Thanks for the reply!
Re: hobbed bolt maintenance?
September 17, 2011 05:50PM
I have been using 2 bolts for a while and using the silicone pads in place of springs seems to work well.
Re: hobbed bolt maintenance?
September 17, 2011 05:51PM
I've had much better results with both bolts now.

I've gotta learn to stop trying to cut corners, at least with the reprap stuff smiling smiley
Re: hobbed bolt maintenance?
September 17, 2011 05:56PM
This issue combined with your "Skeinforge thread" about to much material on the first layers makes me think that your extruder is not calibrated correctly and its trying to push to much material through the hotend.

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Re: hobbed bolt maintenance?
September 17, 2011 06:06PM
It is calibrated accurately. I bumped up the Filament Diameter a bit and it is extruding less material. I was also able to raise the Z home a bit as well - between those two issues, I'm now able to lay an initial layer that doesn't bulge up and get in the way of the second.

Now I'm just trying to get the W/T ratios dialed in... it really is down to the fact I have to use a microscope to tell the difference. I'm so close I can smell it!

I have a feeling I'll be in for a shock once I run out of this black PLA and have to move to another color. At least I know what I had to do to get this close...
Re: hobbed bolt maintenance?
September 18, 2011 11:51AM
You shouldn't change the filament diameter to adjust your W/T ratio. You should use the measurement using a caliper to set it. You also don't want to use the first layer to adjust the W/T ratio since the first layer depends heavily on your z zero position. Calibrate you extruder by measuring the actual feed pulled in by telling the Mendel to extrude a set amount. I usually use 50 mm but others here like 100mm. My prefered choice is to measure the hobbed bolt diameter at the narrowest section and enter the calculated value based on that in the firmware. Then measure the actual feed length and enter the ratio of actual divided by the entered length in the SF parameter Filament Packing Density ratio.

Then you can tweak the actual z zero position by raising or lowering the z end stop and measuring the layer thickness on a filament extruded on the first layer. I like to use the skirt to do this.
Re: hobbed bolt maintenance?
September 19, 2011 03:07AM
Well I have an original mendel and have worn a groove in my hobbed insert because it is brass

Experimenting in 3D in New Zealand
Re: hobbed bolt maintenance?
September 19, 2011 03:16AM
Everything is sorted out. Now printing my first child in ABS. Everything is nice and smooth now that I re-homed my Z.
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