Inconsistant Extrusion Rate With PLA

Hello Everyone,

I'm having difficulties caliberating a Wade style extruder with a J-Head. If I remove the hot end, I can set things in the firmware(Marlin) so that 5 mm of extrusion gives 5 mm of 3 mm PLA filament moving into the extruder. So far so good. When I add the J-Head to the mix, I get anything from exactly 5 mm to 3 mm or so of extrusion. The J-Head has a 0.35 mm orfice, so it is not the easiest to push PLA through. I've got lots of clamping force on the hobbed bolt, so that doesn't seem to be the issue.

My impression so far is that the brass hobbed bolt(cut with a M4 tap) is just not right for the PLA. They work fine for ABS which is tougher, but things seem to slip with PLA. Am I on the right track here?

If so, what type of hobbed bolt would work best? Maybe trying another one cut with an M5 tap?

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Yvan

Singularity Machine

Just and update... I've checked to see if the stepper driver was set too low, and it seems fine.

I also gripped the filament as it is being pulled in, and there is no sign of slipping or missed steps. It pulls very strongly and evenly.

So maybe my assumption that the hobbed bolt is not quite agressive enough to push PLA is wrong, I'm not seeing any clear signs of stripping and slipping.

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Yvan

Singularity Machine

Either the filament is slipping or the motor is not turning. Put a mark on the big gear and time it's revolutions with no filament. Put in filament and try to run it through the J-Head. If the revolutions per minute (or seconds per 5 revs) are the same, it's not the motor or the gears.

If the motor is running, make sure the gear is not slipping, make sure the pressure is tight enough.

Okay, I will try the suggestions tomorrow. It seems just from fiddle with the stepper trim pot, cleaning out the hobbed bolt and putting it back together(probably tigher now) it is not as bad. A test piece just finished and it looks cleaner, not for entirely know reasons!

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Yvan

Singularity Machine

Cleaning the trash out of the extruder every so often is indeed a good idea. The extruder is under more force than ABS really likes, so tightening / checking all the bolts is a good idea as well.

This extruder is new, so everything looks tight. It is printing much better than the other day, and it is feeding about 4.85 mm when I ask it to feed 5. At least now it is very consistant!

I marked the gear and when I tell it to feed 16 mm it makes one tooth short of a full rotation on the big Wade style herringbone gear. Also consistant.

Not entirely sure where the discrepency is from when I set it spot on the other day with the E steps at 1027(in Marlin without the hot end). I think at this point I can bump up the E steps again to get 5 mm of feed when I ask for 5 mm of feed.

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Yvan

Singularity Machine

It's worth the time getting the steps per mm to the point that you feed within 1% of your target. It is also worth trying to get your filament diameter in to the same sort of accuracy. You filament may or may not be made to that accuracy level. Last would be making sure that the Z steps / mm are good to 1%. More or less that is printing a 105 mm tall object and a 5 mm tall one. The difference in height between them should be 100 mm +/- 1 mm. On something that tall normal layer heights should not mess up up much. If you want to eliminate them as an issue, make both heights an integer multiple of your layer height.

I think I've got the Z dead on, over 24 cm or so of lift and it doesn't drift off the mark. I would need to get a more accurate ruler if I want it to be even more accurate.

At the moment I have only one spool of PLA(from Revolution Printers) and it is not the most consistant.

The feed rate is the only fudge factor left, but it is getting closer. I think I was loosing steps feeding and retracting, much better now.

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Yvan

Singularity Machine

Once you have all the calibration numbers set properly, you still have the flow rate setting in Slic3r to play with. It's your true "fudge factor" on all of this.

Investing in a reasonable set of calipers is a real good idea. There's a lot of measurement involved in setting up these printers.

Okay I got the machine all sorted out just in time, a friend came by and picked it up yesterday. I made a few PLA extruder gears with it(some say they are more durable than ABS) and I gave him my only spool of PLA to boot!

So now I will buy some more. I bought some cheap digital calipers and I'm hoping the next spool is more consistant than the first one. Although the test parts did come out nicely...

I also recently purchased a very inexpensive set of machinists squares which are perfect in size, cost and accuracy for setting up these machines. Now on to the next one...

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Yvan

Singularity Machine