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israelcw

Expected Tolerance

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I'm looking at purchasing a 3D printer for work (we design and manufacture small orthopedic devices). The Ultimaker seems to have the most accuracy of printers that don't cost a fortune, but I can't really get an idea of how close the tolerances will atually be. I have two questions:

1. What are the expected tolerances of a part that is about .75" long and .25" in diameter?

2. Could someone print a part for me from my CAD file? Obviously I can compensate you.

An answer to either will suffice.

Thanks,

Whitt

 

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When one firsts prints something simple like a cube, cylinder or cube with a round hole, the tolerance is annoyingly off. Converting to mm, a 20mm by 5mm part will probably print out to about 19.5mm by 4.6mm. However this is easily fixed by increasing the part dimensions by .5 and .4mm respectively. After doing that you can easily get tolerances (repeatable tolerances) to about .1mm error.

The z distances are usually spot on because the lower portion of the part is cool while it is printing the last few layers.

Inner holes in the part (like a shaft or a cylindrical hole) are much worse. For many reasons they come out quite a bit smaller than expected and a 3mm hole will come out probably 2.4mm.

If you change filament, change printing speed, tighten your belts, change printing temperature then you might have to readjust your settings by another .1mm if you need that kind of accuracy.

If you will be printing lots of small parts (under an inch long) and you don't need to print quickly you can switch your nozzle to a .35 or .25mm nozzle and get finer detail. Your corners of your cubes will have tighter radius. You can't switch nozzles on the UM2. But on the UM1 you can get lots of other nozzle sizes for well under $5 per nozzle including shipping.

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By the way these "outer dimension" errors are caused 90% due to how much PLA shrinks as it cools. Very little of the error comes from errors in the printer. Different PLA shrinks different amounts. PLA45 (from germany) shrinks much less and is much easier to print because of this and your cad model needs less adjusting. But it costs much more and only comes in one or two colors (black and white I think).

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Hi Whitt

Do you have a cad file you would like to see printed. this sounds like a small print I, or some one else, could give it a go (I print up a lot of little cubes to test different pla, so I figure I can just print something of use to some one else instead of a cube)

I am currently using an original ultimaker, I have it running fairly smoothly, but I have never tried to print tight tolerances. I guess if I can do it within your desired tolerances I would safely say that any run of the mill ultimaker could.

 

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Wow...great information and thanks a ton. Iron Gland, that would be very helpful if you don't mind. How can I get the file to you (I have .STP btw if you need that)? Also, how much would you charge for something like this? FYI, it's basically a small screw.

Thank you both. I wish I had posted here before I spent hours scouring the internet!

Whitt

 

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I wouldn't ask for money in this case since the material cost is going to be about 10 cents... and Ill just post some pictures and dimensions my caliper measured. As far as getting me the model, I think an stp file should work, but you can also export it as a .stl or .obj with your cad program, and then I know it will work.

As far as getting me the model, I would bet there is a nifty way to send these types of files on this forum, but I haven't figured that part out.

Just send it to thestooges4000 at gmail.com

it's my spam email so it's not a good contact method, but it'll work for this.

 

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You say it's a screw - that suggests that it will probably have a complex profile that changes layer by layer and involves overhanging parts. Depending on your needs, you might do better to look at alternative technologies. For shapes that have a complex profile with numerous small cross-sectional areas on a layer, something like the FormOne might be a better fit (http://www.formlabs.com). Those are a bit pricier, but much better suited to printing arbitrary fine details.

Extrusion-based printers are good when there is a perimeter of at least a few mm that they can trace out - but every time you have to start and stop the extrusion to print a new 'island' in the cross sectional layer it's going to introduce a little bit of error due having to start and stop the flow of plastic, which inevitably causes a tiny blob. Unsupported overhangs within 10 or 20 degrees of horizontal can also be a challenge.

 

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I was thinking the same thing too illuminarti, and if this is for the workplace whitt can probably scrounge up the money for a resin based printer and it's supplies. One issue I have heard with the resin printers is their parts are not as mechanically strong as our FDM type printers; depending on the type of prototype needed this might not be a problem.

Whitt, a good way to see if your part is 3d printable would be to actually download Cura, and have it slice up the model. Then switch it over to layer view so you can see the path the printer will print in. if those lines don't have anything supporting or if there is too much overhang there is a good chance that it would be a very difficult print.

Also look at the overhang view option if you need help identifying overhang.

 

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I'm no expert, but looking at the MSDS paperwork on their site (http://formlabs.com/products/material) it doesn't look especially hazardous in general use to me. The chemicals and plastics that we work with routinely in the Ultimaker world - PLA, ABS, Nylon, alcohol, acetone, etc - have pretty intimidating MSDS specs too... but so long as you don't inhale concentrated vapors or eat them, they are pretty safe for practical purposes. I think it's the same for the formlabs stuff too - they don't call for any highly specialized handling or disposal requirements. Probably not biocompatible, I'm sure, but for high tolerance prototyping of very small, complex parts it might be a better route.

 

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It seems to me that there is probably some sort of formula/rule of thumb that could be derived that describes how well a shape will print on an Ultimaker or other extrusion printer - something to do with the ratios of cross sectional area to perimeter; minimal perimeter and area required; and the amount of overhang and layer-to-layer variation in shape.

Hmm; something to think about.... might be an interesting thesis in there somewhere.

 

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It sounds like the Formlabs printer is going to be my best bet, but I'd still like to see the example if it's not too much trouble. I'll send you the gmail and if you can, I'd love to see what the Ultimaker can do!

 

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Haha, that's why we're here: to drive away customers!! :-)

Honestly, there's a lot that the Ultimaker and UM2 are great at. But i think it's also important to recognize the limitations of the technology. Sometimes other systems are simply a better fit for the application. Without seeing specifics of your needs, it's hard to know for sure... but it does sound like the sort of case that can be better served elsewhere.

 

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Resin printers like Formlabs only print ONE material. I know little about that material. I don't know if it can handle temperatures found in a hot car on a sunny day. ABS can. Normal PLA can't. I don't know if you can change the color. I don't know if you can get multilple colors. But the UM can print dozens of material types and lots of colors. The UM can print nylon, PLA and ABS all easily. And there are many varieties of PLA including PLA45, PLA90, PLA with wood or stone powder mixed in, PLA with carbon fibers mixed in. But right now the B9Creator only prints in red or another shade of red. Those are the only 2 colors and they are both red.

That is typically the biggest reason for not getting a resin printer - the material you get out of it.

On the plus side they are AMAZINGLY precise and small and accurate.

On the negative side they have all the same issues as a FDM printer regarding support, overhangs. e.g. you can't print someone's face easily on either printer because the chin and nose hang over "thin air". There are tricks! But it's a challenge.

 

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Illuminarti was correct. The piece was too small and I had difficulty obtaining adiquit cooling. The piece looks like a very small spiraled hose barb with two groves running down the center. The side not facing the fan had significant blobing issues. I tried two other versions and this was the best result.

Small screw print

It's not that the ultimaker can't handle the detail, it's that the cross section is too small. The overhangs didn't bother the printer too much since the tapers of the barbs were going upwards. It seemed to be mostly cooling and oozing issues.

I feel it would be possible to print this on a modified ultimaker, but a lot of love, care, and experience would be required to print it.

Either way it was a fun challenge.

I would recommend looking at some printing services that have some very large and expensive printers (sls and all that stuff). Because the part is so small it wouldn't be that expensive to get made. I could have it made by shapeco for about 8 dollars in aluminide or a resin. At that price it might be wort it to try ordering a couple.

as is you could by 350 of them made out of aluminide from a service before it would cost that of an ultimaker. Food for thought.

If you scale this model up by 50% I think it would be printable.

Oh by the way Whitt, that big flat thing on the right side of the screw like print is known as a brim, it's to help hold the part to the platform, it shaves off with a knife or your finger nail fairly easily.

 

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I think it is still printable. Print 3 at once and set "gantry height" in the machine settings to 0 so it prints them at the same time. It will alternate between the 3 prints and the other two will have time to cool. It's the trick I used to print these little people:

HO Scale people and cars

 

Also set temp to 190C and print at 20mm/sec and I hope your retraction is dialed in nicely or you might get lots of stringing among the 3 parts.

 

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I agree with everything you said gr5, I'm positive we can print these parts, but it will take a little experience to print. Ill try again tomorrow.

I also must admit that I have not dialed down my retraction and need to put some time into figureing that out.

One thing I am a little afraid of is their stability when the print head comes back and "brushes" the part. these parts have a rounded tip, the only way I am keeping them standing is with a rather large brim.

Also that looks like a great grumpy pumpkin print in the background!

 

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Also, printing 3 rather than two at once may give better results not only because it takes longer, but because Cura reverses the object order on each layer - so if there are two objects, A and B, it will print the first layer of A, then the first layer of B, then immediately the second layer of B, then the second layer of A, then the third layer of A and so on...

So every other layer gets laid down very fast, without regard to cooling time.

If you print three things at once, then the order becomes A-1, B-1, C-1,C-2, B-2, A-2, A-3, B-3 etc - so the middle one should always have a reasonable amount of cooling time between layers.

 

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Hey guys

Another day another try.

So here is what I came up with by printing three at once. Thanks for this tip guys.

IMG 20131114 140549

 

It's definitely better. Next I wonder if my layer heights are too small, this is the same profile I use to print DnD minis, so I thought it would work. What do you guys think?

 

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