# SLS Hole & Shaft Gauge



## CliffyJ (Apr 29, 2009)

To get a better feel for shrinkage or growth of a 3D printed part, I made this "hole gauge."









There is a hole and a shaft at the middle that have the nominal 1/8" size in the model. To the left, the model was incremented at each hole by .0025". To the right, decremented. I had this printed in "White, Strong and Flexible Plastic" (SLS or Selective Laser Sintered nylon) at Shapeways, and took some measurements. Here are the results.









So, the holes are trending very close to Shapeways' stated tolerance. And, the shafts are even tighter. From this, for holes near this size, one might wish to make them about .006 larger to come out closer to the nominal. However, depending on the situation, one might want to leave them be, if the holes are going to be drilled out anyway (for a cleaner / more exact diameter). 

Hard to turn down a 3D printed shaft though, so perhaps this information will be useful to someone on that account. For myself, I wanted to determine how to make a free running fit, vs. a slight interference fit, between an unmodified hole and shaft part. True, there's no guarantee of these deviations being perfectly constant from part to part, but the trend seems fairly clear with at least the features here. 

I've got a similar part in the works for 3/16" and 1/4", and will at some point add that data here.

===>Cliffy


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## bnsfconductor (Jan 3, 2008)

No pic Cliff!


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## CliffyJ (Apr 29, 2009)

Ugh, I'm really struggling with pics tonight. I see them, but no one else does.... Craig, do you see them now?


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## grsman (Apr 24, 2012)

*Pics*

CliffyJ
I see the pics just fine!
Tom


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## CliffyJ (Apr 29, 2009)

Thanks Tom!!


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## SD90WLMT (Feb 16, 2010)

I see them when logged in "only"...

I like your approach to modeling Cliffy!! 
Great idea...
Great work up....
!!!!

;-)

D


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## CliffyJ (Apr 29, 2009)

Thanks Dirk, I appreciate that.


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## bnsfconductor (Jan 3, 2008)

Worked for me now!  The real test would be to have this printed again without changing anything to see if the tolerances are the same...


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## SD90WLMT (Feb 16, 2010)

Ah...repeat-ability.....
Repeatability...

Hear an echo....

;-)


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## CliffyJ (Apr 29, 2009)

bnsfconductor said:


> Worked for me now!  The real test would be to have this printed again without changing anything to see if the tolerances are the same...


True Craig. However, with the 2 more (3/16 & 1/4), it should become apparent whether the trends continue or don't. But you're right. Maybe have 4 or 5 done at different times even. It's $10 per gauge though, so we'll see.


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## bnsfconductor (Jan 3, 2008)

Burl was mentioning that some of his designs came out well, and then later prints would be ruined. I wondered if this had anything to do with where Shapeways laid the order of the parts on the printer. I wonder if some areas of the printer have tighter tolerances than other areas. But based on your numbers I'm not 0.006" would make that much of a difference...


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## SD90WLMT (Feb 16, 2010)

If .006" is a normal limit or range..it is far better than most of the molded cars we get now...

I usually see them running .010" & lots more from car to car...granted in our scale that is small change...
I have been trying to maintain better than .005" tolerance when I hand cut parts for locos...but I use a tolerance like this for better building to eliminate parts stack up errors:

+ .0000"
- .005" or better for best fit...

rather than a plus & minus figure...which would cause greater fit up problems...if all parts tended towards a plus tolerance..things will start getting tight to fit together....

D


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## CliffyJ (Apr 29, 2009)

bnsfconductor said:


> Burl was mentioning that some of his designs came out well, and then later prints would be ruined. I wondered if this had anything to do with where Shapeways laid the order of the parts on the printer. I wonder if some areas of the printer have tighter tolerances than other areas. But based on your numbers I'm not 0.006" would make that much of a difference...


Huh; maybe they've gotten better on their QA? Because 2 out of my last three orders got held up because they said the parts needed to be re-run. So that means they at least caught the problem, and fixed without asking. I'm pretty sure they'd re-run a failed part that shipped, but maybe they'd want a photo.


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## CliffyJ (Apr 29, 2009)

SD90WLMT said:


> If .006" is a normal limit or range..it is far better than most of the molded cars we get now...


I agree Dirk. I'll be getting the next 2 hole gauges in on Friday or Saturday, so I'm looking forward to seeing what those numbers are, and getting them posted over the weekend.

[edit: well, I just bit the bullet and made / ordered gauges for 5/16" and 3/8".]


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## CliffyJ (Apr 29, 2009)

Here are the results of two more gauges.

















So, the seeming trends in the first gauge didn't continue. As a matter of fact, the holes can be sometimes a tad elliptical, I'm seeing now. 

I think that all one can really take away from this is that the Shapeways stated tolerance of .5mm (~.006) (either way) is reasonably confirmed. Within one batch or part, things can be quite accurate; but the next time, maybe not as much -- as Craig was pointing out.


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## SD90WLMT (Feb 16, 2010)

So your symbolism means + or - for tolerances...

a combined possible total of .012" variance advertised......

D


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## SD90WLMT (Feb 16, 2010)

I did the math.....

for .5 mm, this comes to 0.01968".....

nearly 20 thou. Quite a bit of range for those "fancy machines" .

;-)


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## Burl (Jan 2, 2008)

It may depend on the orientation of your part in the printer. I think some have a different resolution in the z-axis, as compared to x/y. And Shapeways is going to want to stuff as many parts as possible in a print job.


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## CliffyJ (Apr 29, 2009)

I apologize Dirk, I typed in .5mm and I should have typed .15mm. .5 is the minimum gap between separable parts, .15mm is the tolerance (+/-) for this material.

Burl, to your point, SW states "± 0.15 mm, then ± 0.15 % of longest axis." So if you have a 10" long part, maybe the little nuts and bolts will be relatively in tolerance at wither end, but the length might grow or shrink by .15". And if it's not too tall, your Z axis, that dimension would be tighter. Ditto for a narrow width dimension. Is that how you guys interpret that?


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## SD90WLMT (Feb 16, 2010)

I interpret your wording as simply meaning the longest length is subject to increased error..regardless of the axis that length is built on ....x ..y..or z
May explain your recent test pins and the relative out of roundness....

Dirk


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## SD90WLMT (Feb 16, 2010)

Seems "Our" math is correct in both cases Cliffy...
Appolgy noted...;-)

D


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## CliffyJ (Apr 29, 2009)

Here's a final update on this. I received gauges for 5/16 and 3/8, and here are the results.

















Here are the average and min/max deviations for all sizes (1/8, 3/16, 1/4, 5/16 and 3/8 gauges):









BTW, here's what they all look like together:









If someone wants to purchase some gauges (at cost), let me know and I'll make them available through Shapeways. 

===>Cliffy


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