# Just a quick one, how can I draw and arc to a specified length using a radius?

Just a quick one, how can I draw and arc to a specified length using a radius?

In Rhino for Windows the Arc command has a Length option.

Start the Arc command
Select the center point.
Select the start point which will be constrained to the specified radius.
Select the length option.
Change the direction if the opposite direction is needed,
Type the desired length and the arc will complete.

I cannot seem to make it work. I did using my calculator, with the circumference divided by 360 deg
then I divided 50, my needed length by the 1deg and found the total degrees needed and just trimmed the circle…very tiresome. When I try your method I use the default arc mode, specify the centre then specify the Radius then length but its way too big…not sure what Im doing wrong or am I using the wrong arc mode?

Did you use Length command to check the length of the arc made with your method?

Is the circle too big or the length too long?

If the circle is too big then have you confused radius and diameter?

If the arc is too long did you start the Length option in the Arc command after picking the second point?

Hi Stu,

Can you post a 3dm file with an arc made using David’s steps above that ended up too big? Also indicate the radius and length you’re aiming for. This is working here in Rhino for Mac 5.1

my length is over 300mm. I want a 50mm arc length with a radius of 408mm

I’m just using the Arc command. Here are the exact steps I’m using to make your 50mm arc.

• Using a MM template
• Run the “Arc” command
• Type “0” and enter to specify the center point
• Type “408,0,0” and enter to specify the radius
• Click the word “Length” in the command dialog or type “L” and press Enter
• Type 50 and Enter

You can use the Length command to check the length of the arc created. The result is written to the lower left corner of the interface.

Any luck?

Perfect!
Thank you guys. I was using the tool bar options rather than line command
Works perfectly. Cheers and thanks again…