Mk8 extruder adjustment on I3 Aluminum printer

[dhardyuk]

Hi there,

I bought this printer on eBay https://www.ebay.co.uk/itm/232228378933

I've received the 3d printer and assembled it.

Unfortunately the test prints I have made show that the filament isn't extruding smoothly and there is no tension adjustment on the extruder.

The extruder that was supplied is plastic, not the same as the aluminium one in the pictures on the auction listing.

How can I adjust the filament tension on this extruder?

Thanks

David

[bang]

Hi,David
Could you extrude the filament smoothly with your hand(when the temp reaches)?
If you couldn't in this situation,then your extruder may have a clogging.
If you could while it is not consistent when printing,then your feeder on extruder may have a problem.

[dhardyuk]

Hi Bang

When the extruder is at 180 degrees I can push the filament fairly easily. When printing I can improve the flow by pushing the filament.

I have adjusted the steps per mm and increased the current to the stepper without any improvement. The extruder just doesn't push the filament through as it it's not gripping it. When I manually assist it the flow is much better.

I have calibrated the stepper with and without the hotend, nothing is making an improvement. The drive wheel is securely fastened to the stepper shaft.

Can someone tell me or point me towards what the vref should be for the A4893 driver?
I have a couple of drv8825 drivers that I can try as well if I can find the vref settings for them.

Also what the is the max current for the stepper on the extruder? I can't read the markings on mine so I can't find a data sheet on it.

Thanks

David

[bang]

Hi,David
Did you fix the problem?
I guess the max current for that motor is 1.2A or 1.5A.
And i'm not sure if your extruder has the issue as the following post shows:
viewtopic.php?f=19&t=18507

[dhardyuk]

Hi Bang,

I changed the original filament drive gear to one with fewer, more defined, teeth. That improved things a little but the tension spring was still not strong enough to pull filament smoothly off the spool and push it through the hot end.

In the end I changed the whole filament feeder for an aluminium one with a screw adjustment on the tension spring.

I also bought some PEI heat film for the glass sheet and supported the bed from underneath with some 18mm mdf to try and even out a dip in the middle which has worked wonders for getting prints started. So far I've successfully printed calibration pieces, a cover and brackets for the PSU. I'm currently printing a pair of anti z wobble brackets to see how they improve the layer lines on printed objects.

So, along the way I've cooked a USB port on my laptop and the FTDI chip on the Sanguinololu when the PSU spiked (when I dropped an allen key which rattled into it); changed the filament feeder completely; rigged up a Pi3 with camera running Octopi. I've bought a temporary Sanguinololu to get things running again and ordered a GT2560 controller and an autolevel sensor to make bed levelling quicker between prints. I've redrawn [ur=http://www.thingiverse.com/thing:2178701l]the touch sensor mounting[/url] in Sketchup with a rectangular base so it can be printed upright (rather than rotated 90 degrees as the curved one on Thingiverse is) so it has fewer z layer wobbles.

I've dismantled and reassembled the extruder/hot end so many times I've invested in a second complete hot end with stepper and everything so I can at least print whilst I'm fiddling with it. I've also managed to cook some of the A983 Pololu modules so I replaced the lot with DRV8825 boards and set the Y axis and Extruder drivers to a vref of 0.75 volts which gives them a max current of 1.5 amps.

Everywhere you look the advice with the Sanguinololu is to cut the 5volt line on the FTDI to USB port link which I think this is something that Geeetech should adapt with header pins and a jumper. I now only have the left side usb ports on my laptop and have ordered some of these USB to USB isolaters to prevent this kind of clumsy mishap destroying my computer in the future!

It's taken a little while to get there but I am having a lot of fun - my friend bought a genuine Prusa I3 MK2 with the MK42 heat bed and auto level/axis calibration which is undoubtedly 3 times better at 3 times the price, with the drivers pre-calibrated and every wire exactly the right length. I've learnt much more about the nuts and bolts of 3D printing with this, if I was to be buying now I'd definitely go for the external control box and screen to avoid the risk and potential problems of having exposed mains connections again.

Regards

David

[bang]

What an unforgettable experience