Initial Layer Temperature Setting with Raft

[LouisvV 0]

Hello,

 

I'm having trouble with rafts gluing to my print.

The best solution I have found so far is lowering the print temperature to 180 degrees and the raft peels away. I do not want the whole print to be at this lower temperature though as it causes a few other small issues. From playing around it seems that the "Printing Temperature Initial Layer" changes the temperature of the first layer of the print but when a raft is used this change in temperature still only applies to the layer being printed onto the build plate.

Is there a way of lowering the temperature of only the first layer of the print above the raft?

[johnse 31]

You could use the technique often used for temperature towers. Select the menu Extensions->Post Processing->Modify G-Code.

Press the "Add a script" button and select ChangeAtZ. In there you can select a height (either mm or layer number) and select something to modify.

 

You can add the script multiple times.

[gr5 2,094]

johnse has great advice.

 

But you shouldn't need a raft.  Raft is an old technology and there are several newer generations of materials and printers since then.  What kind of printer do you have?  What material are you printing?  You don't need raft with PLA.  Ever.  If you are printing ABS (don't print ABS) and you have a reprap style printer - like the prusa i3, then raft might be a good option.  But if you have a printer with a heated bed you don't need raft.  I talk about raft and the newer technologies - why they are needed - the purposes - and solutions - here:

 

 

 

[LouisvV 0]

Johnse

I like the theory but it took a while to make it work.

When using the layer number Cura seems to start its numbering from the first layer of the print piece and doesn't take into account the raft. Then, when the height is set to layer 1 or 0 the extruder temperature changes on the 2nd layer both times instead of the first.

Using the mm height was better but I still couldn't seem to completely understand what the printer is doing. The print is small, approx. 20mmx20mm, so when setting the temperature change for one layer the extruder doesn't have time to cool down before it starts to heat back up again. When changing the 'behavior' to 'keep value' and setting the layer number to 2 so that the extruder cools down for the last raft layer and the first print layer the temperature only drops to 195 instead of the set 180. I'm don't think I understand what the layer number set at 2 actually represents nor what the text that is displayed on the LCD screen when the set layer height is reached, "printing... ch@ 0.7"?

Ultimately, I have a good print that separates well from the raft by setting the printing temperature to 180 then using the ChangeAtZ (Height - 0.9mm, Behavior - Keep Value and No. Layers -  1) to make the rest of the print 210.

 

 

Gr5

I'm using an Ultimaker 3 with PLA and had some trouble with a print a week ago. At the time I managed to fix my issue of the print not sticking using what you called "squish" (I moved the bed closer and it stuck). I had previously tried the raft but it glued to the piece. Now I am simply experimenting trying to get the raft to work so if there is ever a time in future where I need one then I know what to do. Hopefully, I can just use all your suggestions from above instead because this is proving challenging.

 

 

Thank you to both of you for the help 🙂

[gr5 2,094]

Well I'm not sure the Cura version of raft is worth it - I'm not sure the people who wrote Cura (mostly Daid) understood the purpose fully - it's from the days when people only printed ABS and before heated beds and I suspect Daid wrote this *after* that and didn't have a lot of raft experience.  I say this because I don't think the raft is designed correctly in Cura.  It needs to be very flexible - the raft needs to contact the bed say in horizontal lines - then connect to a new section of raft in vertical lines such that there are only tiny points of connection.  Then connect to the part. 

 

I've never had to use raft.  PLA never needs a raft and if you do the 4 things in my video you can print much more difficult materials like ABS, Nylon without a raft also.

 

[LouisvV 0]

Ah well,

I still learnt some things! I was previously unaware of the ability to modify the g-code in any way and now I have a few more options if I stumble across the need for them.