Resin Printing Size Discrepancies?

[tehachapifan]

Purchased some 3D resin prints of some passenger cars online and, while they are of the same car, the size differences between the cars is quite noticeable. Maybe up to a scale foot difference between the longest and shortest car in the bunch (85' passenger car) and the rest fall somewhere in between. I can see some slight dimensional differences in height as well. Is this a common issue with 3D (resin?) printing?

[robert3985]

Purchased some 3D resin prints of some passenger cars online and, while they are of the same car, the size differences between the cars is quite noticeable. Maybe up to a scale foot difference between the longest and shortest car in the bunch (85' passenger car) and the rest fall somewhere in between. I can see some slight dimensional differences in height as well. Is this a common issue with 3D (resin?) printing?

It's a common issue with any scaling-down procedure.  As with nearly any production method (injection molding, spin casting, investment casting, 3D resin printing, resin casting, etc.) the medium used will shrink or expand a bit depending on what the medium is and what kind of process is being used.

With 3D printing, first the 3D model must be built/drawn...and if the creator does this using prototype plans, the 3D model will be properly proportioned (proper relationship between height/length/width), but, the creator has the option to make the 3D model in whatever scale he/she chooses, such as modeling it in actual 1:1 size, or scaled down to 1/160th scale...or whatever scale.

Then, for 3D resin printing, the 3D model must be sliced, and many slicers give an option as to what scale the print should be...and they interpret the scale differently sometimes.

When I print my first test print to see if I've got everything "right", I also take measurements of it to make sure that between my slicer and my printer that the finished product is actually being printed the correct size for the scale I want.  I do this by measuring the washed & cured item with my calipers, then, if it's not the correct dimensions, I'll correct that in my slicing app before printing again.  I'll do this until I've got its dimensions exactly where I want them.

I NEVER assume that my slicer is going to get it "right"...I always check to make sure my prints are correctly scaled.

But, some 3D resin print manufacturers evidently don't do this process, so their products are NOT correctly scaled...even if their 3D models are flawless...before slicing, printing, washing & curing.

I would contact the makers who sent you the most egregiously wrong-scaled items and let them know their product has a problem...because it's easily fixed if their 3D model is correctly done.  That's one of the big advantages of resin 3D printing, problems with the finished product are MUCH easier to fix than with processes that involve making molds out of tool steel, or RTV or whatever.

Cheerio!
Bob Gilmore

[tehachapifan]

Thanks for the info!

To expand on this a little more (pun intended), I'm either going completely nuts or this stuff does some expanding and/or contracting over time. I say this because the cars that were really different in length are much close to the same size now. They were all purchased a couple weeks apart, so I'm curious if some additional curing has had a bearing on this. The first car I purchased was probably around a scale 9" to a foot longer than the next two I purchased. Now it looks like maybe only a few scale inches longer. Now I purchased a 4th car and, when it arrived, it was significantly shorter than the other 3 but now, only a few days later, it's also approaching the same size. I see that shrinking is common, but does it typically expand?

[Peachymike]

It's a common issue with any scaling-down procedure.  As with nearly any production method (injection molding, spin casting, investment casting, 3D resin printing, resin casting, etc.) the medium used will shrink or expand a bit depending on what the medium is and what kind of process is being used.

With 3D printing, first the 3D model must be built/drawn...and if the creator does this using prototype plans, the 3D model will be properly proportioned (proper relationship between height/length/width), but, the creator has the option to make the 3D model in whatever scale he/she chooses, such as modeling it in actual 1:1 size, or scaled down to 1/160th scale...or whatever scale.

Then, for 3D resin printing, the 3D model must be sliced, and many slicers give an option as to what scale the print should be...and they interpret the scale differently sometimes.


When I print my first test print to see if I've got everything "right", I also take measurements of it to make sure that between my slicer and my printer that the finished product is actually being printed the correct size for the scale I want.  I do this by measuring the washed & cured item with my calipers, then, if it's not the correct dimensions, I'll correct that in my slicing app before printing again.  I'll do this until I've got its dimensions exactly where I want them.

I NEVER assume that my slicer is going to get it "right"...I always check to make sure my prints are correctly scaled.

But, some 3D resin print manufacturers evidently don't do this process, so their products are NOT correctly scaled...even if their 3D models are flawless...before slicing, printing, washing & curing.

I would contact the makers who sent you the most egregiously wrong-scaled items and let them know their product has a problem...because it's easily fixed if their 3D model is correctly done.  That's one of the big advantages of resin 3D printing, problems with the finished product are MUCH easier to fix than with processes that involve making molds out of tool steel, or RTV or whatever.

Cheerio!
Bob Gilmore

Have to agree with Bob, this shouldn’t be an issue. There are ways to deal shrinkage, etc, all it takes is some pre production testing to ensure they scale out properly. Once all the parameters are correct the finished product should be nearly identical each time. I check my stuff for consistency all the time, and adjust as necessary. I wouldn’t sell something that is substandard and I guarantee my kits so the builder is confident of a good build. If you break it or do find a part that’s not up to par, I replace for free.
One thing I have found is that I season my prints, first for a day after post print cleaning before I cure due to volatiles gassing of and then they sit for a week or two. At that point the seem to become very stable and I can confidently offer them. Maybe these prints were done to order and sent before the curing process was complete?
Mike

[tehachapifan]

I think these were printed and then shipped rather quickly, but I'm not positive.