PLA not sticking

First off, Thank You to Everyone here on the Forum for helping me get my printer working.

And to the issues, when I try to print the 20mm solid cube test object the print does fine until about the 8th layer. At this point the print detaches from the bed and is moved by the printer head. So I guess my questin is what is the best way to get PLA to adhere to a heated bed? Also when the Z axis is homing should the nozzle touch the glass or be a paper width above?

Thank You, Garrett

Printing at 190c for extruder 50c for bed

Raise the temperature to 70 on the first few layers and then lowered, but PLA is better printed with a bed at 70 degrees. When your Z switch is triggered the nozzle needs to be 0.1 mm away from the built plate when both bed and nozzle are at printing temperatures, get a feeler gauge and use that instead of the paper. Clean your glass and apply a couple of coats of purple glue stick from Elmers. Lower the printing speed of the first layer to half of regular printing speed.

Thank You for your response. Ill try your suggestions and see how it goes.

At Z=0 the tip of the nozzle should be on the verge of contacting the bed. If you have the nozzle 0.1mm above the bed at Z=0, this is too high and will result in poor adhesion. Most people find that lowering the head until it grips a piece of standard 80gsm paper is accurate enough, because there is enough give in the printer mechanism that this doesn't actually leave the nozzle a paper width above the bed when the paper isn't there.

Heat the nozzle and bed to operating temperature before you set the Z=0 height.

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Large delta printer [miscsolutions.wordpress.com], E3D tool changer, Robotdigg SCARA printer, Crane Quad and Ormerod

Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].

I respect dc42 comments, but for the last two years I have printed using this method and as you can see on the attached pictures, don't have any "poor" adhesion issues nor I have lost one print to it. This is a 26 hours print running now, (I will post the picture when done) and the least I want to is loosing it due to adhesion.

But I assume everyone have it's own method and opinion, and I respect them all.

Edited 1 time(s). Last edit at 05/17/2015 02:18PM by ggherbaz.

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ggherbaz
I respect dc42 comments, but for the last two years I have printed using this method and as you can see on the attached pictures, don't have any "poor" adhesion issues nor I have lost one print to it. This is a 26 hours print running now, (I will post the picture when done) and the least I want to is loosing it due to adhesion..

I guess you may get away with that if your first layer height is small enough compared to the nozzle width. But you won't get a glassy finish on the bottom of the print, I expect you to have gaps between the strands.

To clarify: the gcode generated by the slicing program places the nozzle at a height equal to the configured first layer height before it starts printing. So if you have the first layer height configured as 0.2mm and you set Z=0 to place the nozzle 0.1mm above the bed, then you will start printing with the nozzle at a height of 0.3mm, which is 0.1mm higher than the slicing program intended. If your nozzle width is 0.4mm then it will probably touch the bed, and with luck will adhere. But there will not be enough filament extruded to completely fill the space.

I use the paper method, but I have not checked to see what height this actually gives me. It is entirely possible that I am starting my prints with the nozzle 0.05mm too high, or perhaps even 0.05mm too low.

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Large delta printer [miscsolutions.wordpress.com], E3D tool changer, Robotdigg SCARA printer, Crane Quad and Ormerod

Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].

dc42,

One of the things I do all the time is to check my layers height with dry runs (before every single print I do for my customers), I set my printer to 0.1, 0.2 and 0.3 depending on request and start the print, once the print start the first layer I stop it and measure the distance with a feller gauge to verify that I am at the correct distance. I do this for business and I have very demanding customers, most of the time I print at 0.1 layer height (reason for long printing times). A difference higher than 0.05 might cost me the print been rejected by the customer.

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But you won't get a glassy finish on the bottom of the print, I expect you to have gaps between the strands

Parts are shinny and no gaps, I always check the first layers for any issues and if I see them I will stop the print, correct any issue and start again (can't afford bad reviews) I rather loose material than a customer. Regarding the nozzle, I don't know what to tell you, I use all of them from 0.2 to 0.5 (wish I could use bigger ones)

It might be the slicer used? I use Simplify3d, I don't know but I don't suffer any of the issues you mentioned.

Regards.

Are you printing directly onto glass ?

I dab a bit of water mixed with PVA glue (50/50) on my heatbed- once its reached temperature it looks frosty and PLA adhesion is very good.

Also is your bed temperature maintained throughout the print ? It's possible to lower the bed temperature after a certain time, but this has always caused the issue you described when I've used it.

Usually we stick masking tape to the glass, then set hot bed 50-70 degree.