Is it or center mark or not? Pics included. Please help.

[Depsas98]

I'm trying to get to whats pictured with the red outline. The best I can figure out after messing with settings for 2 hours is the second pic. How in the world am I supposed to draw this? Thanks.

[rkent]

You draw a center line from the center of the main object through the hole, then a bolt hole centerline circle. In hand drafting you can get it drawn the way you show but with cad you just have to live with what you get. You could start breaking the circle and so on but I wouldn't recommend that.

Edited October 5, 2010 by rkent

[Grant]

Try doing an ARC in your center layer

Type arc - End Point - Center Point - End Point

 

In the end you will have an arc to the circle (bolt hole) another arc through to the other side of the small circle (bolt hole) and another arc after that.

[fuccaro]

An "Arched center mark" could be an interesting subject for a dynamic block. Unfortunately I don't have AutoCAD right now to create one

[Cat]

Looks like they just offset a circle and put it on a layer using centerline as the linetype, but then again, you wouldn't necessarily get the perfect crosshair in the center of the circle. You might be able to fudge it by making your center marks smaller.

[Tiger]

I would guess that they have used Break on the circle running through the hole and changed the linetype of the piece of line inside the hole.

 

If I had done it, I think I would have made the entire circle running through the hole as center-line (i.e dash-dot)

[ReMark]

The original image looks like it was drawn on a drafting board. To get the end result pictured would have been extremely easy to do. Now you're attempting to reproduce that same affect using CAD. The system is a little more rigid.

[JBullseye74]

Looks like they just offset a circle and put it on a layer using centerline as the linetype, but then again, you wouldn't necessarily get the perfect crosshair in the center of the circle. You might be able to fudge it by making your center marks smaller.

 

did i hear someone say 'Fudge it'..... lol

[Cat]

Fudge....it's not just a dessert.:wink:

[ChrisGrady]

I had to draw something similar on my training course which was a mechanism drive - could you not draw one section of the mechanism and use the array command to complete the circle then you should have a centre line to add a circle on to? maybe like this? then use mirror command and the array command then perhaps you wil be able to draw your circles on the centre line

 

maybe thats not what your after but thats my understanding of it

[ReMark]

Chris:

 

Nice sequence. However, the point of the conversation is really about getting the radiused center mark as depicted in the very first image posted by the OP.

[ChrisGrady]

My apologies ReMark - I misunderstood the point!!

[ReMark]

That's OK Chris. Been there...misunderstood that...several times myself. Today in fact! LOL

[ChrisGrady]

I suppose we are all fallible at times!!! even the great ones!! lol

[nukecad]

I do this sort of thing all the time for pipe flanges, etc.

 

Yes that first image has been drawn by hand but you can obtain the same effect on CAD.

 

First using a centreline draw a circle at your PCD and where it crosses an axis draw your hole.

Now trim the PCD to the hole and EXTEND the ends by the same amount each end.

Doing this ensures that you get an arced centreline equal about the axis at the hole centre as in your first image.

You can now use the ARRAY command to get the number of holes that you need.

 

Not quite the same as your image as there is a centreline arc at each hole, but that is the standard way of doing hole centres anyway.

Edited October 5, 2010 by nukecad

[JD Mather]

Would you be interested in hearing how trivially easy this is in a modern CAD program like Autodesk Inventor?

 

Students can download Inventor for free from http://www.autodesk.com/edcommunity

 

in AutoCAD I would create a block for this situation. You can make it dynamic, or if your company tends to use a small set of standard sizes you can make one for each size.

Edited October 5, 2010 by JD Mather

[digger]

CMK.LSP by Tony Hotchkiss might help some.

I couldn't locate the routine at Cadalyst, but I found this:

http://www.oocities.com/wpsmoke/acadalisptrng/aastart/evaug.html

[ReMark]

The above is just JDM's way of bragging. For those of us still chiseling in stone the technique is a little more involved. LOL

[rkent]

Would you be interested in hearing how trivially easy this is in a modern CAD program like Autodesk Inventor?

 

.

 

JD,

Can you use this on the iso view?, I have tried and can't get it to work.

[Cat]

The above is just JDM's way of bragging. For those of us still chiseling in stone the technique is a little more involved. LOL

 

Remark, I still ride my brontosaurus to work every morning too. :wink: