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kc-li

Sharp/fineness of UM2

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Hello everyone,

Firstly, thank you in advance for your contributions.

I"ve been doing a lot of research on the potential to buy an ultimaker 2 to print some dental crowns for my research project. So far what I know is the layer resolution is 0.02 mm (20 microns) but what I would like to know is how well does this translate onto an edge.

Basically what I want to print is something like this (cross sectional view)

img_cemented.jpg

Think of the whole cast metal coping and porcelain as one structure for now. As you can see, as we get closer to the margin of the tooth, the edge finishes off quite sharply. The edge has to be quite sharp and accurate since marginal accuracy for dental restorations are quite important to reducing the likelihood for future caries to develop. The typical marginal accuracy requirement is about somewhere under <100 microns (0.1 mm). Do you think it's possible? If not, what is the typical knife edge dimensions one would expect from the ultimaker printer. (if I'm not explaining myself well enough, just try to imagine you're printing a plastic knife, how sharp would you expect that knife to be?

Thanks!

 

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.02mm is the resolution in Z but the nozzle has a hole in it on the UM Original and UM2 that is .4mm in diameter. Or .2mm in radius. That means in XY you can't print anything smaller than about .4mm. Also it means you can't have sharp corners any sharper than a radius of .2mm in XY plane. However you *can* print objects "sideways" so that you get the best resolution in a particular dimension.

If I print a knife flat on the glass bed I can make it amazingly sharp - sharp enough to cut my finger. But if I print it vertical it will be quite dull (.2mm radius).

I recommend you look into the b9creator (google it). This can print equal resolution in X, Y, and Z. Not just Z. Or look at the more expensive form1. I believe you can use the prints from these printers as investment casts.

 

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To get the type of resolutions you will need for a dental crown you will need a Stereolithograpy 3d printer. They basically use light to cure resin. The B2 uses a projector, the Form 1, a laser. I ran across a new printer from dwslab.com. You might want to check that out too. I have also seen specific resins that will burn out cleanly. A lot of jewelers are designing jewelry in a CAD program like Rhino, then printing out a pattern and investing it just like the traditional lost wax process. That being said, I am not sure if any of those printers have the resolution you will require to have an accurately fitting crown.

 

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I have another question. Say I do go ahead and print a PLA crown design. How would the machine cope with the xy dimensions which is thinner than it can print. Does it try to do as good a job as possible or does it compensate by making the wall thickness comply with the inner or outer wall? (which one, this is quite important). For the latter, I wouldn't mind if it had to print a slightly thicker wall on the outside since it would be simple to manually adjust. (so in this situation we would have the crown fit well on a tooth preparation but there will be an overhang). The other situation would be it compensates inwards and the crown now doesn't fit on the tooth prep since the inner dimensions are now too small.

I guess the short question is: does the machine take priority on getting the inner or outer dimensions correct if it's trying to print something thinner than it would allow.

 

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Thanks for you input :), I too agree that the B9 or the Form1 are much more ideal options. Especailly the B9 since it has good resolution in all xyz dimensions. The one thing I have to also consider is cost however. I know the light cure resin comes a bit more expensive per kg compared to PLA. I'm also not sure if the resin is used 100 % without waste (or a certain amount has to be wasted per print. I'll do a bit more digging on that.

 

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How would the machine cope with the xy dimensions which is thinner than it can print.

 

You can download cura (the program that prepares the files for printing) and try it out yourself.

Here's a quick example. The ring at the bottom is 0.5mm thick, then 0.4 and finally 0.3. As you can see the result is less than desirable on the thinner areas as cura will discard the geometries it feels the nozzle can't fit into.

tooThinToSlice

 

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The radius of the nozzle is .2mm (diameter=.4mm) so Cura moves the tool path towards the inside of the object (not inside of the curve) by .2mm. So when doing the outer wall of a hollow cylinder the path is .2mm inward and when printing the inner wall it moves .2mm outward.

You can buy smaller nozzles (e.g. .25mm) for the UM Original but for the UM2 you would need a good mechanic to do it as soldering (filling existing hole) and precision delicate drilling is involved.

 

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Hmm, I've been doing a little more reading. Out of interest about the potential to use a smaller nozzle (browsing the forum a nozzle diameter of 0.2 mm appears to be possible although questionable, perhaps 1.75 mm filament would work better with a 0.2 mm diameter nozzle)

Putting aside it's practicality I don't understand the bit gr5 referred to about requiring soldering and drilling to change the nozzle. I thought the nozzle bit was a simple screw design and nozzle replacement can be easily done by loosening the screws and unscrewing the nozzle ad popping in a new one with a different nozzle diameter? (there appears to be quite a few third party providers of such nozzle)

At least this was what I made out of after looking at this small tutorial

http://www.fablab-regensburg.de/wp-content/uploads/2014/04/Ultimaker-2-Nozzle.pdf

Am I mistaken somewhere?

 

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I do not think any of the 3th party nozzles currently fit on the UM2. You want an UM-Origonal for that.

Still, for things "tooth" sized, I wouldn't try FDM. The Form1 or B9 would much better suit your goal. We have a B9 at the office, but we're currently not that impressed by it. But we haven't played with it a lot. However, for tiny prints, it does a lot better then an Ultimaker.

(I've done lots of tiny prints on my personal Ultimaker. I kinda know what it can do and do not in that area)

 

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Thanks for the response :) Guess I'll have to consider the other two options.

I'm just trying to figure out how they manage to 3d print wax dental crowns commercially because the equipment exist (http://www.3ders.org/articles/20140514-stratasys-launches-two-highest-precision-wax-3d-printers-for-dental-industry.html) but as with many things in dentistry, the price is obscene (upwards $25k and you can only imagine the upkeep of the wax cost). The claimed resolution on theirs is 50 microns xyz. I guess they must have some secret to it.

Thanks a lot again for all the responses!

 

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The nozzle and heater block is a single piece on the UM2. I think what you've found is replacement nozzles for the original UM which does indeed use a separate nozzle that can be unscrewed easily and changed. Since the nozzle+heater block that Ultimaker uses for the UM2 only comes in one size, 0.4mm, you have to fill in the original hole and then re-drill it to a smaller size.

The wax printer you found uses a completely different printing technology:

http://www.stratasys.com/3d-printers/technologies/wdm-technology

 

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You should be able to get 50 micron XYZ no problem with resin technology (form1, b9creator, titan). But not with FDM (heated plastic). Plus my understanding is you can use these resins for lost casting technology which is what you want. You really really should look into form1 or b9creator. These are amazing machines although the resin expensive.

http://b9creator.com/

I just looked at the above page and there are several sliding "pictures" at the top and one of them talks about investment casting and even mentions metal casting and jewelry.

 

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