Tangent Line

[#2#]

OK Guys,

I don't know how to do this. I've never done it before - hold the jokes please.

I've created a 10inch diameter circle and now I need to create a line which is tangent to it and runs through a measured point which is not located on the circle.

Any suggestions? I hope this is easy...

[cmmguy]

Assuming X/Y Plane

Set origin on 10" diameter Circle.
Align throught the point.
Offset rotate the point (See other thread))) until it is 5" plus in Y axis
Construct line at X/Y zero(center of circle) with 0,1,0 vector.
Intersect line and circle, choose Plus Y point.
Construct line through the original point and this new constructed point.

This line will be tangent to circle and go through your point

[#2#]

Assuming X/Y Plane

Set origin on 10" diameter Circle.
Align throught the point.
Offset rotate the point(there was a thread about this) until it is 5" plus in Y axis
Construct line at X/Y zero(center of circle) with 0,1,0 vector.
Intersect line and circle, choose Plus Y point.
Construct line through the original point and this new constructed point.

This line will be tangent to circle and go through your point

Doh! Thanks didn't think of that. Brain not work to good today.

[#2#]

Now I know why I didn't do that...

I don't know the angle. I also only know the length of one side of the triangle so I can't do trig.

Can you elaborate on step 3 or point me toward the thread?

[cmmguy]

the rotation angle = Inverse Sin of (opposite side divided by the hypotenuse)
or...
the rotation angle = InvSin (5/Distance between circle and point)

So...
In PCDMIS, I think the following is correct:
After you have aligned the Circle and Point
Using the Set an Alignment rotate the X/Y plane about Z

ROTATE_OFFSET,(RADtoDEG(ASIN(5/POINT.ACT.X))),ABOUT,ZPLUS

this should put the point at +Y of 5
If my syntax is not 100%, I am sure someone will be happy to correct me.

[#2#]

Well, I've run into this problem again. Maybe I'm going about this all wrong.

I've got a cart with no wheels. If the cart had wheels and was sitting on the surface plate, the plate is Datum A. I have a basic called out from datum A to the center of the axle. All of my dimensions are called out using datum A as the alignment.

Here is what I have thought in the past... I can measure the ends of the legs. I can measure the axle (center of the wheel). I need to be able to create a line from the end of the leg to a point tangent to a circle with the diameter of the wheel (2x the basic).

What has been posted above hasn't quite gotten me there in the past. Anyone have any ideas?

[#2#]

I'm about to say "screw it" on this part and refuse to measure it until the drawing is updated. There are two GD&T callouts (TP and //) using the same datum. Only one of them can be valid but neither of them are because the datum is not defined! That and the tol. block lists dimensions of l.xxxl as having a tol. of .030!?! I always thought l.xxxl was a basic dim. with no tolerance!

[cmmguy]

Why didnt the earlier post work?

[#2#]

the rotation angle = Inverse Sin of (opposite side divided by the hypotenuse)
or...
the rotation angle = InvSin (5/Distance between circle and point)

So...
In PCDMIS, I think the following is correct:
After you have aligned the Circle and Point
Using the Set an Alignment rotate the X/Y plane about Z

ROTATE_OFFSET,(RADtoDEG(ASIN(5/POINT.ACT.X))),ABOUT,ZPLUS

this should put the point at +Y of 5
If my syntax is not 100%, I am sure someone will be happy to correct me.

Why didnt the earlier post work?

Because I neglected some information. I order for the above to work I need to know the distance from the point to the center of the circle. The problem is that the point was a created point and not a measured point. The created point would be inaccurate because it is based on current alignment when created.

Basically, looking at it in two dimensions... I have a cylinder (cart leg) which intersects datum A at an unknown angle. I also have a circle (wheel axle) with a basic dimension of 5 inches from it to datum A. The axle is perpendicular to the leg. I am trying to create datum A.

I don't think it is possible to create the datum with the given information. What I ended up doing before was placing the cart on the plate and blocking up the axle until it was at the 5 inch basic dimension. This won't work this time as I can't get the basic close enough to work within my tolerance on other dimensions.

[cmmguy]

Is it the "Corner" of the cylinder diameter that makes up the point on Datum A or is it the centerline of the cylinder?

[#2#]

Is it the "Corner" of the cylinder diameter that makes up the point on Datum A or is it the centerline of the cylinder?

Corner.

[craiger_ny]

In order to help I need to know what kind of carts you guys make
http://www.designboom.com/history/cart/4.jpg
Your engineering drawing is a little shall we say "sketchy"? No pun intended.
http://www.designboom.com/history/cart/9.jpg

As long as I have you, are you working on the wobbly wheel problem right now? Is that what is confounding you?

[#2#]

These are two wheeled carts. A paint sprayer is attached to the cart.

The drawing is a sketch rather than an engineering drawing. Believe me though when I say the engineering drawing contains no more useful info.

[cmmguy]

Say it with me... "Fixture"

[#2#]

Yeah, that would be the easiest way to do it. Problem is that I have three of these carts to measure and then I'm done. They won't spend the time or $$ to make a fixture for this but they want accurate measurements.