Raft issues... Again.

Slic3r is my slicer of choice, but I cant, for the life of me, change the distance from the raft to the part. 3 layers is far too high to print correctly, the first layer of the actual part is just a poo-nado. I just came up with that term.

Anyway, I need the raft because my prints are in ABS, and I am printing on a COLD printbed. I know I need a HPB. HOWEVER, the prints stick to my printbed SO WELL, that the first layer seperates from the object and stays on the printbed.

I was wondering if I could just use this quirk to my advantage, and print a 1 layer think raft with a distance of 0 layers between the print and the raft, and so I tried, but this is always my result, no matter what version of slic3r I use, and what setting I apply:



Anyone got any ideas? Software is Repetier Host, Printer is a Makerbot clone.

Edited 1 time(s). Last edit at 01/14/2015 10:46PM by iamdarkyoshi.

I print in ABS also. For parts with small perimeters and for tall thin parts I will add my own raft of a solid rectangle 1 layer thick and suitably larger than the base of the part. It is easy to remove from the finished print by filing it off with a needle file. Either modify the part to add the raft, or make an STL of a suitable thin cube with whatever 3D software you use (e.g. OpenScad) and drop it onto plater, then drop your part onto plater also and manually position your part on top of the raft (I've not tried the latter method but it should work).

If your first layer stays on the bed and separates from the other layers I suspect your layer adhesion (at least for the first few layers) is very poor and your parts will consequently be weak. This is probably because you are not heating the bed and so the first few layers get cooled rapidly by heat conducting to the cold bed - later layers are insulated by the thickness of the layers below so will be less affected. Either use bed heating (I use 110 degrees), or increase your hotend temperature for the first layer(s) Rubbing down the part after printing with a paper towel generously soaked in acetone will result in the acetone soaking partially between layers and chemically bonding them, which I find improves the strength and so I do it routinely for all my prints (it also improves the finish).

Dave

The issue is that my bed does not have a heater. It is a pice of acrylic plastic clipped to the existing bed. Is there a way to make the first layer adhere LESS to the bed? The rafts are easy to remove because they can be bent and peeled off, but a solid part cannot be peeled.

If you make the raft oversize you can peel the edges of that raft and hopefully the part will come off with it. Otherwise I sometimes use a sharp knife blade flat on the bed and carefully push it under the part (I have used a sharp vegetable knife and also a scalpel-like craft knife). I suspect that the ABS is heat-bonding to the acrylic in the same way the layers bond. You could try a coat of hairspray on the acrylic (in this case hoping to weaken the bond rather than increase it), or cool the acrylic in the freezer before printing, or use a lower 1st layer hotend temperature.

Dave

Well, with a raft, the part comes off the raft easy, and the raft comes off the bed easy, and I do not care about scratching it, so I just go ham on it with a paint scraper. I just grabbed a bed sized piece from my school's scrap bin and clipped it to the bed. But with a solid part and no raft, I cannot remove the part without damaging it. I could not get slic3r to change my raft seperation height, so I moved to Cura. Cura wont print a skirt though so i have to click extrude 10mm twice and then hit print.

Edited 1 time(s). Last edit at 01/17/2015 01:09AM by iamdarkyoshi.

Quote
iamdarkyoshi
Well, with a raft, the part comes off the raft easy, and the raft comes off the bed easy, and I do not care about scratching it, so I just go ham on it with a paint scraper. I just grabbed a bed sized piece from my school's scrap bin and clipped it to the bed. But with a solid part and no raft, I cannot remove the part without damaging it. I could not get slic3r to change my raft seperation height, so I moved to Cura. Cura wont print a skirt though so i have to click extrude 10mm twice and then hit print.

Cura can print a skirt - I have used it often. Have a browse through the settings.

Dave

I cant seem to get it to cooperate. is it not working because it is used in repetier host? It just makes a raft with no skirt.

Quote
iamdarkyoshi
Well, with a raft, the part comes off the raft easy, and the raft comes off the bed easy, and I do not care about scratching it, so I just go ham on it with a paint scraper. I just grabbed a bed sized piece from my school's scrap bin and clipped it to the bed. But with a solid part and no raft, I cannot remove the part without damaging it. I could not get slic3r to change my raft seperation height, so I moved to Cura. Cura wont print a skirt though so i have to click extrude 10mm twice and then hit print.

Just confirmed that Cura version whatever-comes-with-repeteir-host will only print a skirt if the raft is disabled.

If the raft is larger than the print, surely the raft serves the same purpose as the skirt and will be enough to get the plastic flowing?

Dave

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dmould
If the raft is larger than the print, surely the raft serves the same purpose as the skirt and will be enough to get the plastic flowing?

Dave

sometimes. but it results in a raft with a missing middle section. I print without a raft now, I made a heated printbed completely out of items I found in the dumpster. I can print large ABS things without warping. gluesticks are awesome.

I am new at this game but I print on cold glass by cleaning the glass well and spraying it with a very light coating of 3m contact adheasive. (very light)
Once the glass is dusted with the adheasive it becomes almost difficult to remove the parts but they have never broken free or peeled up like the blue tape trick.

The coating lasts a long time and many parts can be made before a recoat is needed.

Edited 1 time(s). Last edit at 02/03/2015 10:44PM by lumen.

Hey thanks for the suggestion! I have a whole roll of (useless) PET tape to use up, so I might as well use it and a gluestick, even though glass would work just as well.

If a heated bed can solve the warping and other issues, then I think I'm going to try to convert one of those $18.00 griddles from walmart to a heat bed.
The 10-1/2" X 20" is a bit small for my printer but it should work for a test.
Has anyone had any luck doing this?

Quote
lumen
If a heated bed can solve the warping and other issues, then I think I'm going to try to convert one of those $18.00 griddles from walmart to a heat bed.
The 10-1/2" X 20" is a bit small for my printer but it should work for a test.
Has anyone had any luck doing this?

I suspect you are the only person attempting such a thing, but it sounds like a reasonable idea. Most people will be using the standard PCB bed heaters (albeit costing close to $40 for 200mm X 200mm), or the older method of bolting a matrix of high power resistors to the bottom of a thick aluminium plate.

Safety is a concern as you are dealing with higher voltages than are present on most printers. How are you planning to control the temperature? An optically isolated triac would probably be best to switch the heater. You could use a relay instead of a triac, but I prefer solid state because relay contacts at those voltages & currents don't tend to last all that long if they are switching on & off frequently. A mechanical arrangement such as a bimetallic thermostat is unlikely to keep the temperature stable enough, and you need lower temperatures than most cooking appliances are designed to operate at.

You may find that the heater is too powerful for a simple "bang-bang" temperature controller to hold it stable enough, and so you might need variable power PID control, either implemented in the printer controller if it has spare capacity, or on separate CPU hardware such as a PIC processor board. A triac is well suited to PWM power control (with the shortest pulse lasting several mains cycles), but a relay would be useless for that task.

Dave

Quote
lumen
If a heated bed can solve the warping and other issues, then I think I'm going to try to convert one of those $18.00 griddles from walmart to a heat bed.
The 10-1/2" X 20" is a bit small for my printer but it should work for a test.
Has anyone had any luck doing this?

Seems like it woudnt be very acurate. My bed works very well, and it is just a sheet of document scanner glass with nichrome wire from a hairdryer zigzagging the bottom. It is held in place by a fiberglass cieling tile compressed between the glass sheet and the stock printbed. It heats up in a couple minutes. want a tutorial? This method costs almost nothing to make and works extremely good.

Well I already have an extra PID controller and a solid state relay @ 25 amps so I figured it would be easy to put together a heat bed from a griddle that should be reasonably accurate.

The idea of constructing a heat bed is a good idea since I also have three sheets of old scanner glass and a roll of nichrome wire that I use for cutting foam.

I have a large part that I need to print now and that's the main reason I thought of the griddle, since that is overly industrial and is already built. Just needs to be wired up!

Hmmmm

Thanks for the ideas.

Edited 1 time(s). Last edit at 02/05/2015 04:11PM by lumen.

I am trying to get my head around the purpose of skirt, brim and raft. Please correct me if I am wrong. The purpose of brim is basically the same as skirt to get the plastic flowing smoothly except the brim is attached to the part whereas the skirt is separate from the part. Does it make sense to use both skirt and brim? While raft is used for a part with a small footprint, correct? Does using both brim and raft have any advantage or is that overkill? I am using SolidWorks to design parts and am thinking about modeling parts with a small footprint with a base for better adhesion to the bed. Then cutting the base off after printing. So am I making any sense here?

Gil

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GKpro
I am trying to get my head around the purpose of skirt, brim and raft. Please correct me if I am wrong. The purpose of brim is basically the same as skirt to get the plastic flowing smoothly except the brim is attached to the part whereas the skirt is separate from the part. Does it make sense to use both skirt and brim? While raft is used for a part with a small footprint, correct? Does using both brim and raft have any advantage or is that overkill? I am using SolidWorks to design parts and am thinking about modeling parts with a small footprint with a base for better adhesion to the bed. Then cutting the base off after printing. So am I making any sense here?

Gil

The skirt is to prime the printhead so it has fresh plastic, and i also use this to calibrate height after the print has started.
The raft is to elevate the part so it is not being printed on an unlevel/irremovable surface, or to combat warp by adding a larger footprint.
The brim is to add a larger footprint to the part so it stays in place, kinda like a suction cup around the part.

The brim and raft serve the same purpose, but accomplish it in a different way.

If you are printing a tall thin item or an item with a very small footprint, you will need a brim or raft to prevent the part becoming detached from the bed or getting knocked over as Z gets higher. A brim is attached only to the outside of the part, so if the part has a separate small perimeter inside it (e.g. a column inside a tube or hollow box), a brim will not attach to the inside bits, and so you should use a raft instead which puts a platform under the whole thing, but is a bit more difficult to remove afterwards than a brim.

Dave

Anyone know how to check the version/upgrade curaengine in repetier host? I really need a smart controller so I dont have to use repeteir host for manual control. Then I can just use cura's software.