Problem printing loco - help?

[rholgateau]

I am trying to draw up and print the body for a Johnson 0-4-4T loco in N, to fit on the Dapol M7 chassis as is.  (Having to make a few dimensional compromises to enable it to fit on the M7, so purists should look no further.)

 

CAD model is pretty well complete, for 58084 and 58042:

The printing is looking pretty good as well, except for one major problem – the model is “creased” on one side – and I cannot work out how to resolve this.

 

Printer is an Anycubic M3 Plus. 

Resin is Monocure Rapid.

Supported and sliced in Chitubox.  Model currently tilted at X+20, Y-40, Z+40 degrees.  Supports are auto-supported at Density=65%, with finer supports manually tweaked on fine details.  Plus extra Heavy supports on the skirts all around the model.

 

Settings are:

with the printer UV power set to 60%.  Layer height is 0.050mm, but would like to reduce that when the models are looking good enough.

 

General supports look like

with the problem area also supported:

 

Results are promising – the pipe-thingy in front of the side tanks is drawn at 0.15mm, yet prints well. 

The problem is the horizontal creasing on the LHS of the model (well, horizontal when being printed, diagonal on the resulting model).  This is on the “downhill” side of the model; the other side is almost perfect.  I’ve run numerous tests and cannot get rid of this.

 

Does anyone know what the issue might be (and how it might be addressed)?  I’ve been thinking of:

·         Insufficient supports in that area (I’m trying hard not to have any supports on the outside flat areas of the model)

·         Wrong exposure settings (but have rerun calibration models)

·         Wrong/dud resin (and it’s over 12 months old – but Monocure says that it should be fine)

·         Overly optimistically fine model (the cab sides are approx. 1 mm thick – and other parts of the model are thinner)

·         Wrong tilt angle (and I’ve tried a lot of different variations)

·         Or something else

 

I've been printing quite a few other models, but mainly old buildings or tree skeletons, where exact precision is not critical.  This is my first item of rolling stock, and my skills are clearly lacking!

 

Thanks

 

Rob

[billbedford]

You don't have enough support on the read buffer beam, here:-

[rholgateau]

Bill

 

Thanks for replying so quickly.

 

I had seen the misaligned corner, but am surprised that it might impact up the whole footplate?  But, hey, that's why I'm asking for help...

 

I do have a fair bit of support in that bottom corner, but it's on the underside of the skirts that surround the loco.  Maybe these skirts are detaching from the loco - or being stretched a bit?

 

I've just put 5 heavy supports right on the loco body around that corner, and I'll run the print again overnight.  If that sorts out the creasing, then the cause is confirmed, and I'll have to work out how to provide such additional support on a more cosmetic manner.

 

Back in 24 hours...

 

Rob

 

[The Fatadder]

I think I’ve read previously that this sort of error is down to pressure build up inside the print.  Are there any holes in the top that resin can escape from?  

 

the other reason I’ve seen before is a lack of lunrication on the screw mechanism the build plate raises and lowers on.  I need to try this on mine  as a cure for a similar issue

 

I think in both cases the extra pressure results in a jerk in the movement causing the lines 

[JimFin]

Two thoughts - light off delay is at the lower end of the range in my experience, possibly try 1sec. Other thought is are the slide bearings and z axis well lubed? May be some jerky movement. There are grease nipples on the underside of the slide blocks but it's easier to take out the screw centre top and pump them full of lithium grease.

[rholgateau]

Some good suggestions here, guys - thanks!

 

I've tried Bill's "additional supports", as shown above.  Unfortunately, that didn't seem to help...

... just off the printer, with the outer supports removed.  You can see the substantial supports bottom left, yet the creasing still occurs.  I'll try it again with extra support at the bottom of the cab side but in front of the opening...?

 

Resin holes: yes, I had thought of that.  The bottom of the coal bunker is open, and I have a couple of holes between the cab and the coal bunker

 

Z lube: I haven't done this recently, so will add some grease and see if that impacts this.  I haven't (ever) lubricated the sliders - they have always appeared quite dry and I had assumed that no lube was required?

 

Light off delay: I understand that a "delay after light off to enable the resin to cool/set before lifting" is a good idea, but Anycubic doesn't support this (at least via Chitubox).  The Light Off Delay setting merely specifies a minimum time for the light to be off before turning on again - Anycubic says that it's to allow resin with poor fluidity to reflow"?  I confirmed this just now by setting this param to 10s and running a "dry print".  It was clear that an extra delay was inserted after the raise/lower of the platform, before the light came on. So, as my raise/lower time is perhaps 5s, this param won't have any effect unless it is more than this.  But it is pretty cold here in my shed in Sydney, so I should crank up my resin heater to be sure.

 

Further question: I am using the side "skirts" to support the model: I have seen this recommended under rolling stock to obtain a smooth contact along the edge of a straight-sided item such as this.  I have reduced my contact thickness as much as possible, to make the removal easier - it is currently around 0.13mm - is this too small to provide a firm support?

 

So, I will now (a) try even more supports, (b) grease the z-axis, (c) heat the resin, (d) set a cautious Light Off Delay, and try again

 

Fingers crossed!

[billbedford]

6 hours ago, rholgateau said:

 

I've tried Bill's "additional supports", as shown above.  Unfortunately, that didn't seem to help...

 

... just off the printer, with the outer supports removed.  You can see the substantial supports bottom left, yet the creasing still occurs.  I'll try it again with extra support at the bottom of the cab side but in front of the opening...

 

That photo is not clear enough to show what is happening at the end of the buffer beam. 

 

This video might help you understand what is going on, especially the part where he talks about curved edges:

 

 

[JimFin]

8 hours ago, rholgateau said:

I haven't (ever) lubricated the sliders - they have always appeared quite dry and I had assumed that no lube was required?

That is a regular service job for me, makes quite a difference. Important to get it into the block, not applied to the rails. Pump it in and then run the carriage up and down a few times to ensure all the bearings are coated.

 

Did not know that was how Chitubox handled light off so thanks, don't use it myself but useful to know.

 

Keeping temperature around 25c is always helpful, try and make sure the build plate is warm as well otherwise you are dipping a cold heat sink into the resin.

[The Fatadder]

10 minutes ago, JimFin said:

That is a regular service job for me, makes quite a difference. Important to get it into the block, not applied to the rails. Pump it in and then run the carriage up and down a few times to ensure all the bearings are coated.

What lubricant do you use?  I have never done this in the year and a half ive owned the printer and it feels like something I need to get done ASAP.

[JimFin]

I use a multi purpose Lithium grease. comes in a toothpaste size tube with a screw on dispenser -  like this  https://toolshouse.co.uk/products/neilsen-grease-gun-ct4136

[Trainshed]

Also check that the Z-axis motor turns freely. My prints kept failing and it turned out that some resin had found it's way into the top bearing and it was struggling to turn. I replaced the bearings in the motor and the prints stopped failing.

To prevent this happening again, I printed a small collar from Thingiverse that blocks most of the Z-axis hole.

My printer is an Elegoo, but shouldn't be to hard to design one for the Anycubic.