suction when printing a wagon

[Fen End Pit]

I'm going to try and print an open wagon on my Anycubic photon. I've orientated it at the 10 degrees in X and Y to give the best chance of printing. One question I have though is whether I should model a small hole in the base of the wagon, not to allow resin to escape but to prevent the wagon from acting like a suction cup as it prints.

 

Is this necessary or am I being over cautious?

 

David

[5D_Stoke]

If you are printing on an angle then a hole in the floor of the wagon isn't going to make a lot of difference to the suction forces, you'll already have dealt with those through the angle you choose. In your slicer program browse through the layers and see whether there are any points at which there are large areas that need to pull off the plate, if so it may be worth angling a little more or less, or printing in a different orientation. I use a Photon S and have had trouble with suction and "elephants foot" when printing flat on the plate but since angling prints using the optimum angles for different layer heights (as far as I can given the size of the model on the plate) I have had no suction problems. Other problems yes of course, we all do, but not suction...

[regme]

By the sounds of it you have the supports within the wagon, I have been printed open wagons so that the supports are on the under side that way you don't have to worry too much about pitting  since it's underneath.  I have also found that if I print at 30deg all the supports are on the underside and nothing on the sides or ends that way they are all clean.

 

Post a pic of the supported wagon will make it easy to provide a comment.

[billbedford]

12 hours ago, Fen End Pit said:

I'm going to try and print an open wagon on my Anycubic photon. I've orientated it at the 10 degrees in X and Y to give the best chance of printing. One question I have though is whether I should model a small hole in the base of the wagon, not to allow resin to escape but to prevent the wagon from acting like a suction cup as it prints.

 

It would depend on the resin and the size of the wagon. I found that the deeper the wagon the more I'd get distortions and blowouts, to the extent that I now print wagons with separate floors. Resins that are relatively stiff while printing were not too bad, but when I changed to a softer, tougher resin I found more there was more warping. Some times to this extent:

[njee20]

I incline only in the Z axis. there’s an optimum angle depending on your printer and layer height, more like 30-45 degrees. I try and avoid any supports on visible faces, that also mitigates the need for drain holes on open wagons. 

[Fen End Pit]

 

Thanks for the responses.

 

I'd planned on adding a couple of supports to keep the sides apart while curing, all the generated support is on the bottom of the wagon. The trouble is that there is a point in the print where all four sides are being printed at once (or 3 sides and a bit of the floor). This I think might result in the inside of the wagon forming a 'suction cup' against the FEP. I wondered if adding a small hole (currently drawn in the top right corner) might mitigate this.

 

David

[billbedford]

That's not going to work. Remember that the print is made from the bottom upwards, so the sides are going to be finished before the crossbars are started. 

[5D_Stoke]

The image from Chitubox is very useful. What is your layer height? following guidance on a much-circulated graph (though I've only tried limited validation of it myself)  I print at 32.14 degrees for 0.030mm layer height and 40.25 degrees for 0.04mm layer height. If you use the  slider on the right to browse through the sliced layers you will get a good idea of how much suction there might be from large areas having to print at once. at only 10 degrees inclination in one axis there is going to be quite a lot of the floor printing at once, so you might have suction issues at that point.
I agree with Bill, the supports for the sides might help keep things square while curing but are in the wrong place to avoid distortion while printing, what you may need is a few horizontal sprues drawn in CAD inside the wagon between the side knees  and/or one or two isolated Chitubox supports on the outside of the wagon to keep the sides vertical as it prints. I also find extra support is worth adding in Chitubox to the ends of the headstocks as these extremities tend to be a vulnerable area for slight distortion, especially when printing wagons larger than 4mm scale. Also when printing at any angle it is worth checking and repositioning supports so they touch the lowermost edges of the headstocks otherwise you can end up with a rounded or uneven corner rather than the crisp 90degrees the printer is capable of, due to unsupported areas.
A nicely drawn 4 plank dropside wagon, by the way, what's the prototype?

Edited December 28, 2020 by 5D_Stoke
spelling!

[Fen End Pit]

Thanks for the advice. I think I will go back into CAD and add some supports at that stage rather than just in Chitubox. Chitubox is a heck of a lot better than the default Anycubic slicer for support but still does things like try to support every bolt on the outside of the wagon as soon as the angle gets too step.

 

Prototype - Something obscure and Irish - Cavan and Leitrim 3' narrow gauge open wagon with a pair of doors in each side.

 

David

[regme]

One thing I do not seem to get is, we are told to put the model on an angle to reduce the surface area being printed to avoid suction issues, yet the model sits on one big flat raft with a bigger area than that of the model.

 

How much of an issue is it really?

[Fen End Pit]

1 hour ago, regme said:

One thing I do not seem to get is, we are told to put the model on an angle to reduce the surface area being printed to avoid suction issues, yet the model sits on one big flat raft with a bigger area than that of the model.

 

How much of an issue is it really?

But most of that raft if printed with a layer exposure considerably larger than the actual print.

David

[Fen End Pit]

I printed a pair of wagons last night, at 90 degrees to each other on the build plate. Both came out pretty well.  I altered the internal bracing based on Bill's comments and the sides came out nice and square with no visible warping. The bracing cut away without too much issue. I printed at a 20 degree angle in one direction only. This seemed to work fine and only required a few supports on the downhill side.

 

I didn't make a hole in the bottom of the floor but actually looking at the very slight diagonal line on the I wonder if I should. That line would have been where the suction off the bed would have been at its maximum. As it is it will disappear with the slightest sand and paint.

 

I'll stick some more pictures on my blog.

 

For the record the wagon is ~60mm x 30mm and the print time for the pair was 3hr 45mins.

David

 

 

[5D_Stoke]

You've got a very nice result there David.

 

[Fen End Pit]

I made a couple of changes to the wagon. I decreased the length of the bolts a touch (.6mm down to .45mm) and increased the size of the gap between the planks (.2mm to .25mm). I also added a 1mm hole into the floor and to my eye this has reduced the severity of the diagonal striping on the ends.

 

I've just removed the support and haven't sanded the base at all.

David