White Strong & Flexible plastic Push Fit Tolerances ?

Hi all,

With White Strong & Flexible plastic prints what are the tolerances for achieving a good push fit with other items like ball bearings and carbon shafts etc. that will be attached to the 3D print once I have received it. For instance if I have a carbon rod 2mm in diameter that I what to insert into the 3D printed model how big should I design the hole to make sure I get a nice snug push fit ?

My initial guess is a hole of a diameter of 1.9mm, perhaps 1.8mm, that way the White Strong & Flexible can stretch a little to make sure the components I will be adding to the print will be snug and not loose and fall out of the model. Or do I need to make the hole slighter larger to guarantee it will fit into the hole ?

This is a crucial point for me in designing models that will "snap" together like Lego or at least as best as can be expected and managing my expectations of what this creation process can achieve.

Many thanks in advance for anyone who knows the answer to this question ,

Cheers.

there must be some designers here who might have a suggestion on this
Please

fits and tolerances are a tricky game for machined parts. Moreso for 3D printed parts. The printing tolerances are usually larger than the accuracy required for making consistent fits, so keep that in mind...

In my (limited) experience, the model will print slightly larger than the data set of the model, though not as a function of scaling but rather as additional material on each surface. This is likely due to latent heat of the fused plastic partially melting adjacent powder. The bond to this additional material is weaker than the properly fused material, but it will interfere with the fit up of parts. The difference can be accounted for in shaping the model but results will vary for different model thicknesses, as thicker parts are trying to release more latent heat. I have found different print runs to be reasonably consistent in dimension but I wouldn't rely on it for something as finicky as a snap fit. (The studs on Lego blocks are molded to tolerances on the order of 0.0001" or so.)

In WSF, for wall thickness of approximately 1/8", I have found the surface to retain approximately 0.005" of additional material. This amount seems to vary significantly with both geometry (wall vs. hole vs. pin) and thickness. Repeated mating of parts results in some of this material bedding into the model surface as well as some burnishing of the surface, both loosening and smoothing the fit. I recommend printing some small test parts featuring near-identical geometry and size to confirm behaviour and performance.

Thank you FreeRangeBrain,
that is extremely informative, such stuff needs to be on Shapeways web site as part of their information and guides to modelling and design.

I had a feeling that there might be a requirement for some post processing, I think my inclination will be to make the relevant holes to small and drill out as required using successive drill bits to get the required, then with ensuing prints adjust accordingly until I get the required fit, or at least ones that require minimal post processing.

I have seen a demo of the Ultimaker filament extruder print Lego blocks that worked, and it can print down to a resolution of 0.05mm (0.002") although I have heard they are getting them down to 0.02mm resolutions now !!!
But there are issues with overhangs and the like and making something that works in one print is very tricky etc. though there are some modification for dual head extruders and dissolveable support material etc.

WSF using SLS seems the way forward for me and the models I want to make given the intricate frame works required.

Good to find out about prints acquiring an additional thickness to the surface of the models.

Anyhow, your input is hugely appreciated, thank you very much

Going the opposite way, I've found you need to allow about 0.2 mm clearance between two parts in WSF if you want them to fit together easily, but this could just be manufacturing tolerances in the material (± 0.15 mm, then ± 0.15 % of longest axis)

Tom

Cheers Tom, your input is hugely appreciated

In FFF/FDM printing where accuracy is lower, it depends a lot on the geometry and print orientation but I usually go with 0.15mm clearance on all sides. So I would estimate 0.05-0.10 mm will be the right range for SLS 3D printing.
Does anyone else have any experience with creating snug push fits?

I generally go for exact fit between wsf parts, so if I have two parts fitting together, one with a peg and one with a hole for that peg, they'll be exactly the same in width/diameter/etc. Although I have found sometimes that you wont get the really tight friction fit you might want that way so shrinking the opening on the receiving end .1-.2mm will usually ensure that there is a bit extra material where the parts meet each other.

The way I look at it, you can always wear away some material but if the fit is too loose, there isn't much you can do to tighten it up. I've actually applied a single layer of masking tape to the inside part before to get a tighter fit on a prop that had a removable base for inserting other parts within. It's not ideal but it got the job done. Another thing you could do in such cases is brush on a layer or two of something like varnish or lacquer where the part fits into the 3d printed model, covering as much of that inside surface area as logistics allows. That'll add a bit of thickness and create more friction between the parts.

It sounds like for your situation, implementing foreign parts into a 3d printed model, you'll want to make the 'holes' smaller than the parts that fit into them by about .2mm overall (ie for a cylindrical rod of 2mm diameter, create a hole of 1.8mm diameter) and use sanding or other techniques to adjust the fit to your preference. Every time I get a new set of parts that are designed to fit together, I tend to have to work them in and out of their proper placements to get them to fit right. Especially with smaller parts.