Observations on First Layer Speed setting...

[dkightley]

I've spotted something that at first glance looked very odd....but after looking more carefully is something worth documenting.

The First Layer Speed setting adjusts the speed at which the first layer is deposited on the printer build plate. But its not quite as simple as that...

When printing with no raft or skirt/brim, then the setting simply adjusts the speed of the first layer. If you have a skirt or brim, the setting has the same effect...and the skirt/brim will print at the set percentage of normal print speed.

If you print with a raft and disable the raft base layers, then the first layer is also adjusted to a percentage of the normal print speed. However, if you include the raft base layers, then the first layer of the raft prints at a percentage of the raft print speed...which I believe is already 20% of the normal print speed.

This could account for the comments about raft printing speed being painfully slow. If you have a first layer speed set to 50% then the first layer of the raft actually prints at 10% !!

[Konky]

BUMP!
This bug is causing me huge problems !
My first layer on the raft takes like 20 minutes....

I've made 4 prints with S3D and the first 3 prints where normal, raft was printed at expectable speed.
The last print was a larger one in size and there the raft was printed at 50-60 mm/MINUTE with no setting anywhere that would explain that.
I was even scared about damaging the printer at that low speed, the noises were not pleasant.

What to do?!

[CompoundCarl]

Increase the first layer speed if you want it to go faster. The raft is printed slower by default, so if you have a really low first layer speed AND you enable a raft, it's going to be pretty slow.

Personally, I would always rather use a brim instead of a raft. It's a lot quicker, gives better adhesion, and saves a lot of plastic.

[jimc]

i agree there. i realize this isnt a debate over rafts but in over 3 years and 1000's of hours of printing i have never once used a raft. there is just no reason for it. if you need a little extra holding power then just a small brim is fine.

[Konky]

slow Raft speed is multiplied by first layer speed, that's a bug in S3D actually.
The raft has an absolute speed setting (I don't know if that can be changed) so the first layer speed needs to be ignored.
Or better, let people choose the speed by USING the first layer speed but making it an absolute value (viewtopic.php?f=23&t=4620)

@jimc
I use rafts frequently, I think you are not completely right (you do have a lot more experience so I am a bit careful
I have observed these positive effects of rafts:
1) Very good bed adhesion (better than anything else as it is model independend)
2) Temperature barrier!
I noticed inaccuracies in my first layers, I was printing mechanical ABS parts on a 110deg heated bed.
The lower part is a bit smaller, maybe just by 50um but enough to cause issues in my setting.
When using a Raft the ambient temperature and cooling temperature is stable.
3) Damage free removal of the object, with a brim I have to cut away the plastic damaging my object!


Positive effects of a brim:
1) faster
2) the bottom side of the object becomes very flat from being pressed on the glass/kapton/tape
3) in S3D the generation algorithm somestimes does not work properly with brims (only partial support that can cause a mess on your print)


So I might be wrong but rafts are easier to use, cause more exact object dimensions (ABS) and allow separation without damaging an object.
I do not like rafts but I do not have an alternative, a 3mm high brim would not be removeable at all.

[jimc]

well generally you wouldnt make a brim 3mm high. it only needs to be 1-3 layers depending on your layer height. the brim usually breaks right off at the edge of the model with your fingers. no real need to cut anything most of the time. to each his own though. i know everyone has their way. i have seen the effect your talking about with the bottom of a model come out smaller. that happens when you use the extremely high bed temp. abs doesnt really need 110deg. 90 deg is about all you need. i have actually seen warping get worse at those high temps.

[Konky]

I'm still experimenting.
I've used 2 layer brims, maybe it's better at 1 layer brims.
But the deformation is really an issue.

The standard raft from S3D is quite tall. It has 2 or 3 thick layers and on top another 2 or 3 dense layers.
I think it's around 2mm, but enough to keep the heat away from the object.

Maybe you are right with the bed, I'll give some more tests with 90 degree (however I had warping from time to time at 90 with my blue tape).
I also use the bed as heating element for my chamber, so higher bed temp results in higher environment temp which again helps for precision and probably also on layer bonding.

I'm not happy with rift nor with brims, I guess 3d printing needs a while to get better;)

[jimc]

actually what you need to do is ditch abs all together lol. i know it prints nice and from time to time i still use it for certain things but overall i switched over to petg a long time ago and never looked back. all i ever printed was abs too. there are some new filaments coming out also that are low or no warp. esun has abs+ now which is only a couple bucks more than their regular abs and its supposed to warp waaaay less. i havent tried it yet. esun also has a carbon fiber filled nylon being released soon as well. i have beta tested that and its really amazing. absolutely zero warp and ungodly strong. imagine a zero warp nylon that sticks down to a hairspray or glue treated print bed with no issues at all. pretty amazing stuff.

[Konky]

From what I have seen PetG is mostly transparent and does not produce the same fine details.
Can it be vapor enhanced using acetone ?

ABS so far got me the best results in terms of quality and strength