How to dimension a center of a slot?

sergey_gromov

Hello everyone,

I have a project, an additional collet for a small lathe. The collet has 3 slots 120° apart. I want to dimension this spacing on the right view in my drawing. But I'm unable to use the angular dimension tool because there are no lines on the drawing which would pass through the center of the slots. I'm also unable to use the 3-point angular dimension because there are no points that I could snap to in the middle of the slots.

Right now I'm dimensioning the angle between some lines on the right side of two slots. This gives the correct dimension but is kind of ugly. Is there another way?

In F360 you can draw a center line as a median between any two other lines on your sketch. I would draw a center line for each of the slots using slot sides as a reference, then dimension the angle between two center lines. However in Onshape 1) a center line can be only point to point, which I don't have, and 2) you can't seem to dimension off a center line.

shanshan

sergey_gromov ，you can try to draw some center lines for every slot, I do not know what shape the slots are, could you share your document as public ?

sergey_gromov

shanshan, thanks for your answer.

My document is public and I provided a link in my OP. Unfortunately the text style in this forum makes the link so subtle that it is easy to miss. Here it is again, now on its own:

https://cad.onshape.com/documents/17d8106cc94c4d55a09269f2/w/c3da60a563d340f4bf65b6c6

_Ðave_

It looks as though you have done as well as possible until onshape can fix this issue.

P.S.It doesn't look too ugly.

sergey_gromov

DaVicki said:

P.S.It doesn't look too ugly.

I agree it isn't too bad, but it doesn't communicate my intention either. I want to specify spacing of the slots as whole features, not some particular walls in them. Of course it's not really important in this particular drawing, especially when I make the part myself. But I anticipate it can become critical in certain circumstances.

andrew_troup

sergey_gromov 
The trick here is to switch linetypes once you've applied the dimensions.
You can draw solid lines and dimension them as you wish. You can actually leave them solid, but if you want the sketch to be more human-friendly :

you can then select them and click the construction line icon to make them into centrelines.
You do not even have to do this before using them in a symmetric constraint (unlike, say Solidworks) to position your slot lines equidistant from the line.

In most cases (possibly all?), Onshape does not care if a centreline is solid.
On the other hand, a construction line cannot be used to define a profile for a feature such as extrude, loft etc.

sergey_gromov

andrew_troup, you sound like you're talking about sketches, not drawings. There is no such thing as a construction line in a drawing.

andrew_troup

sergey_gromov
Sorry about that - I should have read more carefully !

viru

@sergey_gromov , Currently user cannot give dimension from center-line in Onshape drawing. You can raise ticket for this. You can refer below (video) workaround for center-line creation and dimensioning. In future we hope that Onshape will provide this facility and user will able to give dimension from center-line.

shanshan

@ sergey_gromov,I can draw a center line for each slot, please refer to the  attached video,now we can not give any dimensions between any center lines. kindly remind that sometimes we can not select some circle point easily , we can move the mouse near the circle to activate it , then we can choose the circle point.

sergey_gromov

Thanks viru, shanshan -- nice trick to use an opposite arc's midpoint to position the center line precisely. Too bad it only works for regularly spaced odd number of slots. So I should probably file two enhancement requests. One is to be able to position a center line based on two existing lines, and another to be able to add dimensions to center lines.

andrew_troup

I would like to recommend a more general set of requests, which would solve a much broader range of problems, and bring the "Drawings" interface more in line with the "Part Studio" one:

1) Enable all Onshape constraints (except "Pierce") between user-added lines (both solid and broken), and with entities created by the Drawing module. 
2) Implement the same tools currently available in the modelling modules for auditing and deleting constraints (updated as those tools are enhanced)
3) Enable switching linestyles for all added lines, without losing constraints and dimensions. 
4) Line styles to include solid, dashed (various dash lengths), dotted, chain, chain with pairs of dashes. Also permit variation of thickness.

david_stafford

Andrew's list is most excellent. I'm having the same trouble getting my drawing marked up correctly. I'm fortunately submitting my drawing as a PDF so I use a PDF editor to add in the few missing marks. I deal with piping/ducting/chutes as well as pressure containing equipment (vessels). So I need to be able to dimensionalize the main body of a vessel as well as all the nozzles. Attached is a simple piece that I used OnShape to model.  I can't show that the nozzle coming out the side is at a 3° slope toward the center. I also can't show that the center line of that nozzle is 6.25" down from the top nozzle's center line. Nor that the projected length of the nozzle (distance from main body center line to face of nozzle flange) is 11.5". This is a VERY COMMON measurement for me, as well as from nozzle flange face to surface of nozzle attachment. Suggestions 1 and 2 from Andrew cover my needs, 3 and 4 make my want list, but those are big wants.