Drawing accuracy

[dcurtis]

I’ve just started using SketchUp for woodworking projects. Something I find irritation, and cannot seem to get around is the drawing accuracy. Initially, all edges of the objects I’ve drawn align perfectly but when I go back I’ll see a 1/64th inch difference in one axis or another. All the objects are really simple planes following one of the axis. I’ve checked under Model info and accuracy and snap is set to 1/64". When I discover two shapes not lining up I’ll pull out copies and measure them. Measure shows they are the exact same length but clearly they’re edges do not align. I can modify either of the objects by 1/64" to align and it continues to show the same matching dimension as if I didn’t just change it.

Is there some other accuracy setting I’m not setting properly? Perhaps Move/Copy/Pull is contributing?

Thanks in advance.

[slbaumgartner]

It sounds like you need to do two things: 1) learn to enter exact dimensions into the measurements box (aka VCB) so that you get the precise size you wanted rather than eyeballing it, and 2) learn to use the inference engine snaps to cause new items to match and align with existing ones. Watch the online tutorials to learn best practices.

[whiterabbitdesigncompany]

1/64th seems like a high setting for woodwork?
I’m not sure you need the snapping? the inferencing should help you.
just be sure you see the green dot when drawing a new item to be sure the new line has joined a connecting line or zoom in more to see it. Sometimes the use of the “crosshairs cursor” can help better if the inference isn’t working for you?

[SketchUp_Moderator]

To expand on that which @slbaumgartner and @whiterabbitdesigncompany have already discussed, here is a link to several videos describing the inferencing engine and how it works in SketchUp.

Video Links related to SketchUp Inferencing

There are very many vids in this sampling so scan through and select those you deem most applicable to your needs. The order does not necessarily signify appropriate value however.

[Geo]

@dcurtis

Is there some other accuracy setting I’m not setting properly?

• Tun Length Snapping off.
It is not an internal grid system extending from the Origin.

• Embrace decimal units.
Entering fractional inch units is cumbersome, inaccurate and slow.

Learn to employ SU’s guidance system of dynamic guides and snaps, Inferencing.
SketchUp’s Inference Engine uses the Arrow Keys to lock direction.

Inference Locking — SketchUp Help
https://help.sketchup.com/en/sketchup/introducing-drawing-basics-and-concepts#find-lock 1

→ locks to the X axis … red

← locks to the Y axis … green

↑ locks to the Z axis … blue

↓ locks to a plane and also locks parallel or, on 2nd click, perpendicular, to an edge … magenta

Shift locks to the current inference direction or plane … black or magenta

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Accuracy — Aidan Chopra

SketchUp: Injecting accuracy into your model

[Box]

@dcurtis

When I discover two shapes not lining up I’ll pull out copies and measure them. Measure shows they are the exact same length but clearly they’re edges do not align. I can modify either of the objects by 1/64" to align and it continues to show the same matching dimension as if I didn’t just change it.

Could you attach an example model of this phenomenon.

[g.h.hubers]

@dcurtis

I can modify either of the objects by 1/64" to align and it continues to show the same matching dimension as if I didn’t just change it.

Not sure if you changed dimensions as in changing the value shown. That doesn’t work. The geometry drives the dimensions. The dimensions can only show exact values of measures.

[whiterabbitdesigncompany]

If you lower the “precision” factor you will then get the two dimensions to “read” the same,
as it will round up/down to that precision factor. In the fractional world you are at the limit of this which is why you see no change. As mentioned previously, for a woodworking project 1/64th seems like an extremely high tolerance?

[slbaumgartner]

I generally leave 1/64 not because I size parts to that precision but because it flags when I goof (yes it happens to all of us sometimes)

[dcurtis]

Hello All,

Apologies for the late reply, I’ve been away. I sincerely appreciate all the responses. Being a new SU user you’ve given me new insight which is very helpful indeed! Given the replies, I’m very impressed with our shared appreciation for this application. Thanks for your support!

Since my request for info on my problem I’ve audited my model and corrected “my” mistakes. Based on what I found, objects were actually 1/128" off, not 1/64". Not sure how I could have miss typed a 1/128" into the VCB… Smallest dimension I typed was 1/8". That said,

I’ll try to answer all of your questions, but if I miss something please let me know.

I don’t do measurements by eyeball. Everything is input exactly through the VCB and on axis, And the smallest increment is 1/8". That is, I already know what I want with regards to dimensions. My reference to eyeball in this discussion refers to when objects which should line up (via eyeball) don’t.

Yes, I agree, 1/64" seems to be a high setting for woodworking. Not really necessary for my work. I believe this is the default for the woodworking template? Don’t recall venturing off the change this value… In any case, it should be supported. Don’t understand how fractions are less accurate then decimals. Aside from woodworking, I come from a background of sub-nanometer semiconductor design. 1/64" = 0.015625" right? I have to believe internally SU doesn’t really care how you input values.
Not that I profess to accomplish this accuracy in practice but many hardwood veneers are 23/32" in thickness. Centerline of that? 1/64" granularity. What’s the downfall if I enter a value of 1/64" when the precision is set to 1/4"? Don’t know. Have to believe many users need smaller dimensions than this.

Inference is one of the coolest, and intuitive features of SU, hands down. All the tools depend on it and so do I.

Tried “True Length Snapping” but didn’t see any difference. Not sure what “internal grid system” means/works. Need to investigate further.

And yes, locking to an axis is great. Although I don’t use the keys so much as the visual feedback that you are on the axis.

I always employ copies to see what’s up when I suspect issues. I don’t use dimensioning until all done. Just a publishing tool for cut sheets, etc. I rely on measurement “T” when designing.

Lowering the precision factor is an interesting idea, and I believe this may be the origin of the problem. That is, under what precision is an object created, then manipulated, then measured, etc.

So my conclusion is, on my next model I’m upping the precision factor granularity and double checking everything to make sure my pushes, pulls and aligns really do match up with references objects.

Thank you all for your help. I, as others count on your support!!!

[DaveR]

@dcurtis

I agree, 1/64" seems to be a high setting for woodworking. Not really necessary for my work. I believe this is the default for the woodworking template?

The majority of my work in SketchUp is woodworking related and I usually work in Fractional inches. I very rarely ever model anything with dimensions intentionally to 64ths of an inch. The reason I have precision set to 1/64", though, is to help identify potential issues and deal with them before they are a problem. I’ll sometimes run the CutList extension on a model so I can quickly check dimensions. 64ths raise flags.

@dcurtis

My reference to eyeball in this discussion refers to when objects which should line up (via eyeball) don’t.

Why don’t they line up? It’s totally possible to make them line up even in the most complex models. If they aren’t doing so for you, the reason should be identified and fixed.

[Geo]

@dcurtis

… 1/64" seems to be a high setting for woodworking.

Not really necessary for my work

The functional accuracy necessary within SU’s internal 3-axis Cartesian coordinate system has nothing to do with the dimensional tolerances a user deems acceptable in the workshop.

SU does tolerate a certain miniscule amount of nonplanarity and still supports an unbroken single face.
But an error of 1/64" is far beyond SU’s internal tolerance.

SU’s Length Units and Precision settings pertain to the user’s preferred system of measurement and the level of precision those units are displayed onscreen. Changing Length Units and Precision settings does not alter SU’s minute internal tolerance of errors.

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@dcurtis

Don’t understand how fractions are less accurate then decimals.

Coarse Unit/Precision settings result in equally coarse unit precision displayed onscreen.
When SU is set to display fractions at 1/64” precision, there are situations when it cannot display errors much smaller than 1/64” to the user.

• Errors propagate by inferring to errant geometry when creating new geometry.
• Extruding errant geometry increases the magnitude of error.

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@slbaumgartner

… I goof (yes it happens to all of us sometimes)

True @slbaumgartner, we humans goof.

For an experienced modeler to whom proper technique is routine, entering fractional inch units is no less accurate than entering any other length unit.

Nonetheless, typing within the numeric keypad adjacent to the mouse involves less travel time and fewer keystrokes likely to induce error than traversing the keyboard to enter feet, inches and fractions.

Horses for courses, of course.
Unit/Precision settings, experience, technique and muscle memory; all can have an impact upon accuracy.

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Example:
Leader Text attached to an endpoint automatically displays its coordinates in the current Unit setting.
Here, two sets of Leader Text have been placed at the four corners of a slightly non planar face.
Also, one Edge of the ‘square’ Face is slightly shorter than the rest.

One set of Text was placed with fractional unit settings, the other with decimal unit settings.
Styles > Edges > Color > By axis indicates the Edges are coplanar.

Notice the decimal unit settings reveal two tiny errors, while fractional unit settings do not.
In the attached model, extruding the Face into a larger cube magnifies the errors.

Accuracy.skp (20.9 KB)

[Geo]

@dcurtis

Tried “True Length Snapping” but didn’t see any difference. Not sure what “internal grid system” means/works. Need to investigate further.

2D CAD programs typically feature a user defined fixed snap grid. Like so…

Occasionally we hear from experienced 2D CAD users puzzled by the absence of a snap grid in SU.
And so some new SU users misinterpret Length Snapping is a fixed snap grid akin to 2D CAD.
It’s not.

In SU, the start point of the ‘length’ in an operation subject to Length Snapping is anywhere in 3D space the user makes the first click. If the first click happens to infer to an errant piece of geometry, it propagates the error. If the ‘length’ falls short or runs past the intended destination, it may create an error.

Length Snapping set at 1/64” is barely perceptible, except to experienced users accustomed to the silky, fluid behavior of the tools when LS is off. Larger LS settings make its characteristic tool stutter more pronounced.

[Geo]

A bit OT, yet relevant to the topic of accuracy in woodworking.

The Architectural Woodwork Institute publishes standards for the millwork industry.
They inspect, test and certify millwork companies capable of meeting AWI Quality Standards.

Quality oriented millwork companies typically hold AWI certification(s), under which they produce millwork meeting one of three AWI standards; Premium, Custom, Economy.

Fractional dimensions do appear in the text of AWI Standards.
But the actual tolerances of AWI Quality Standards are stated decimal inches and mm.

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