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# How to develop a octagon in sketcher

#### vijayprasanna

##### New member
Hi all..
I am vijay ,i am very new to this form and catia.
i have a doubt that how to create a octagon in catia.there is no constrain equal (like in proe).
i have developed it by giving tangency constrains.is there any other way to develop it?

regards
vijay

give a dimensional constrain to one line
edit with desired value
copy dimensional constrain
select each line and paste on it

or u can use relations
give all dimensions
edit one and give it the value
at the other db click on and right click on the value box
from contextual menu select edit formula
and then click on the dimensional constrain wiith the real value
OK
....

Hi givi,
Thanks for ur reply... i didn't understand the first one.
i am trying to make the Knuckle joint.in that there is a octagonal cut.i know only the length and width (25x25mm),now how to produce it?.in proe- i used to draw a construction circle and i will draw 8 lines and constrain it with EQUAL.how to make it in catia?

pls explain me.

hello vijay

step 1 use the profile icon to create a eighted sided octagon

step2 now give two angular consrains at the botton line for 45 degrees like this

step 3 now dimension all the lines the image will look like

Step 4 now make all the dimensions same value

this you can manully give or if u are familier with formulas you can equate all the dimensions to one dimensions using the F(x) formula function

your octagon is ready

here also you can draw a circle as a construction element

and now you can build ur octagon on it