What Fillament, wall thickness and Fill Percentage for Patterns

[GreenTwin]

I would like to thank Jason B for opening this thread and to all members that have contributed thus far. I have been involved with model engineering for over 40 years but a complete novice, nay beginner in this field of engineering.
I have made hundreds of patterns over the years, I would now say, the hard way! Father Christmas arrived early on Christmas Eve with a Bambu Labs P1S which has seen a crash course in virtually every aspect of things unknown to me personally. We have already gone through a whole reel of filament with a couple of patterns breaking at the foundry. They mainly use Air set which does have a tendency to grab the pattern and I think we were trying to skimp a little with the pattern making material.
Having followed the advice from several members here the engine bed pattern, shown below has all the latest information built into it. We’re currently using the 0.2 mm nozzle, which has been mentioned as problematic, but we have had no issues with. However perhaps someone could explain what happened to the initial layer where a slump has occurred. It’s no problem as the Cope is moulded on a flat surface.

Cheers Grum.

3D printed patterns must have a smooth surface and be waxed before each mold is made, else they will stick in bound sand.

3D prints with sharp corners make the sand sticking problem worse, and tend to cause corner breakage.
Sharp corners also add stress points in the casting; which may not be a big deal on a small engine casting.
It is best to fillet all corners/plane intersections.

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[Grumage]

Problem

If you click on the thumbnail twice it zoomes in and looks as though there is a small bead intended to run around the inside approx 5 layers high. Crisp at the end and only a bit of a blob on the longer internal edge so may be something other than nozzle height. Again if it here Nozzel height related I would have thought it would also show on the outer edgeGraham or Alan can you post a screen shot of the part in Alibre?

Problem solved. It seems that the door to the enclosure was opened during the initial phases and the room the printer is installed in was very cold. Below zero C outside.

 

[mrehmus]

It is fortunate that the Bambu Labs slicer automatically compensates for Elephant Foot unless you disable it. I have had my X1C for a little over a month and have never seen the phenomenon. My Qidi X-one (December 20216) does create an Elephant Foot using their slicer. You can manually compensate for that in the slicer though.

 

[Grumage]

Ok, this time we cannot atribute to operator error. Photo taken using the onboard camera. The print is lifted away from the heated bed plate.

 

[GreenTwin]

Luckily (knock on wood) the Prusa XL has not been prone to bed lifting across the 14" bed, which is impressive to me.

The XL does have a sophisticated bed heating system, and the bed heat is controlled by section.

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[mrehmus]

Ok, this time we cannot atribute to operator error. Photo taken using the onboard camera. The print is lifted away from the heated bed plate.

How did you treat the bed before printing?

 

[Grumage]

It’s just one very great learning curve. Because we increased the initial layer thickness the bed temperature wasn’t high enough to keep the print from curling up. Problem solved.

 

[vk7krj]

ennech (post 17), you can get brass "heatset inserts" designed especially for this sort of job. For example-

https://hackaday.com/2019/02/28/threading-3d-printed-parts-how-to-use-heat-set-inserts/

 

[GreenTwin]

I have done a similar thing to what vk7krj shows, but with wood dowel rods epoxied in place.

The holes in strategic places for the inserts seems to be what would make it work.
Screwing into a normal surface of the pattern generally does not hold because the screw goes into a cavity beteen the infill material.

Perhaps a threaded hole would also work, with a coarse thread.

Or a keyslot, where you could instert a small round shaft with a "T" on the end.
Turn 90 degrees to lock it in.
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[Jasonb]

The patterns I have done the CAD work for if they are split or single sided generally have holes modelled in. Both larger ones for alignment pins and also smaller ones that can have say a screw driven into them to give something to get hold of to pull the pattern out of the sand. CNC cut metal patterns I have drilled and tapped for extraction screws

Pat why do you say 3D printed patterns should be waxed, what is wrong with the usual limestone based "talc" or graphite powder?

 

[GreenTwin]

why do you say 3D printed patterns should be waxed, what is wrong with the usual limestone based "talc" or graphite powder?

The art-iron folks wax their patterns, they don't use graphite powder, and that is where I learned it.

I do have graphite powder, but I never use it, because it is very messy to work with, and basically turns everything you touch black.

The wax is clean to use.

It is paste wax, any brand will work, that you would wax the floor with.

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[GreenTwin]

Some of the inserts are on the pricey side.
I think the zinc inserts for soft wood would work well, and they are inexpensive.

I would use the screw-in wood inserts, so that I did not have to use a soldering iron.
I am not aware of any reason why the inserts must be heat-set.

For a limited use pattern, some screw holes like Jason uses will work fine.

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[Jasonb]

The threaded (external) inserts for wool have quite an aggressive thread and you would really want to print a mating female thread in the plastic. having used a lot of them in wood I suspect trying to screw them into a plain printed hole will see the layers coming apart and a big bulge around the insert. Having broken or stripped the drive slot/hex out of zinc alloy inserts I would think twice about using them, Solid are worth the extra.

The heat set ones are heated to save using adhesive suitable for each type of plastic/ metal combination and again less likely to damage a print that driving into a plain hole and hoping the barbs will retain it.

Still can't see why wax is needed on 3D prints, even more so if the print has been sprayed with say a high build primer to smooth it. It is then the primer to sand contact which will be just the same whatever the pattern is made from. What are the Arty types wanting and getting from it that is not normally needed on engineering castings?

 

[Grumage]

In the good old days when most founders were using the ‘ Green sand ‘ technology. ie moulding sand, Bentonite and fine Coal dust tempered with water, then a wax coated pattern would definitely help with the ‘ draw ‘ Most founders are now using chemically bonded sand and for Iron, missing the all important Coal dust. Plumbago powder mixed with Isopropyl alcohol can be sprayed into the cavity and ignited just before the mould is closed and poured. This helps reduce friction during the pour and may well help offset the Carbon migration as the metal cools, reducing the engineers nightmare, chilling.

Back on topic, our flywheel half print is nearly done. I shall post the results shortly.

Cheers Grum.

 

[GreenTwin]

The threaded (external) inserts for wool have quite an aggressive thread and you would really want to print a mating female thread in the plastic. having used a lot of them in wood I suspect trying to screw them into a plain printed hole will see the layers coming apart and a big bulge around the insert. Having broken or stripped the drive slot/hex out of zinc alloy inserts I would think twice about using them, Solid are worth the extra.

The heat set ones are heated to save using adhesive suitable for each type of plastic/ metal combination and again less likely to damage a print that driving into a plain hole and hoping the barbs will retain it.

Still can't see why wax is needed on 3D prints, even more so if the print has been sprayed with say a high build primer to smooth it. It is then the primer to sand contact which will be just the same whatever the pattern is made from. What are the Arty types wanting and getting from it that is not normally needed on engineering castings?

I use the same resin-binder that they do, and without a waxed pattern, there will be too much sand sticking to the pattern.
The "stickyness" of sand binder varies. You really need the wax with the binder I use.
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[GreenTwin]

The heat set ones are heated to save using adhesive suitable for each type of plastic/ metal combination and again less likely to damage a print that driving into a plain hole and hoping the barbs will retain it.

The inserts seem to be kind of a moot point, since if you add screw holes like Jason has, those would work well to pull the pattern from the sand for a limited number of pours.
If you use a plastic pattern repeatedly, generally I have seen the PLA crack over time, with or without inserts.

Perhaps if the pattern were printed in some tougher material, the inserts would make more sense.

For a pattern that will be used multiple times, I think creating a permanent pattern in 356 aluminum would be a more cost effective method.

Some of it depends on how light you 3D print your pattern.
A light 3D pattern will not last as long as one that has more density/fill.

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[Jasonb]

So are you saying they would use wax on all types of patterns as the problem seems to be the resin sticking rather than using wax because it is a 3D print.

 

[GreenTwin]

So are you saying they would use wax on all types of patterns as the problem seems to be the resin sticking rather than using wax because it is a 3D print.

Yes, that is correct.
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[Grumage]

So are you saying they would use wax on all types of patterns as the problem seems to be the resin sticking rather than using wax because it is a 3D print.

In all my 40+ years of foundry experience never seen the use of Wax polished pattens ever. A good quality paint finish with parting powder or, better still…. Brightly polished Aluminium can’t be beaten. Mould and core in place, all Airset sand.

 

[Grumage]

Ok, the results could have been better but a little bit of ‘ Knifing putty ‘ will fix it. Just starting off another flywheel pattern with the platform temperature set 20 degrees higher.