Editing circles into gear shapes

Hello,

I am currently in an intro course for AutoCAD for engineers. I have spent quite some time on what I believe should be a simple problem. I am unable to create the attached drawings, which are very similar. I learned about arrays and how to make circular arrays but can't seem to understand how to create the images below. Any help would be greatly appreciated, thanks in advanced for any feedback!

The first image is created using one gear tooth and a circular array with the center of the gear as the point of rotation. Just enter the number of Items you want the final array to consist of.

As for the second image there are a couple of ways it could be done. One way would be to array the circles every 30 degrees and erase the ones that aren't needed. The second way would be to use a combination of the array and mirror commands. Create one side then mirror to the other. Pick the one that works best for you.

#1, '20°' (apart from using to construt 1 x tooth) indicates you will need 360/20=18 items when you array.

approximately:

draw a circle, diameter 6

another circle, same centrepoint, diameter 5

another circle, same centrepoint, diameter 1.5

a horizontal construction line - startpoint as per circles above

another horiz construction line, then rotate it -20deg

draw tooth segment

polar array it, centrepoint as per the circles, angle 360°, number of items = 18

do the keyway

edit your construction lines & circles

dimension it

some other niceities that won't be apparent on paper

You will need three layers for each of these drawings, besides layer 0. Don't draw on layer 0. Assign a different color to each layer, assign the continuous line type to two of the layers, and the center line type to the other one. Put all your dimensions on one of the cont. line layers. Put all of your object lines on the other cont. line layer. Put all of your center lines on the center line layer. Name your layers what they are for.

Remark's and Mikes ways works very well, But i'd let AutoCad find the start and end points of my teeth for me.

I'd start the first drawing by drawing the three circles, (make the object line layer current first) then draw one horizontal line from either the right or left quadrant snap marker of the outer large circle until it hits perp on the large inner circle at its quadrant snap marker. The resulting line will be 1 unit long. It is the "straight" side of one tooth. Then polar array that line @ 20 deg between, to fill an angle of 360 degrees. +360 will array counter-clockwise, -360 arrays clockwise. In possibly less than a minute you now have the start and end points of the angled sides of the teeth. Draw one angled side, and polar array the rest using exactly the same parameters as the straight sides. Now trim away the parts of the two outer circles you don't need. So far no math needed.

The reason I started at the left or right quadrant marker for the teeth, is that the "straight" side of two opposing teeth are exactly horizontal at both the 0 degree point (right) and the 180 degree point (left), and are very easy to draw in there, then array the rest, as mentioned.

The hardest part of that whole top drawing is getting the rectangular key slot on top of the center hole, and even that is a can 'o corn as they say in flyover country.

I think one should keep trimming to a minimum. Create a single tooth and array it. Period.

Problem #1

Well, ok then. Humph. You are probably right, especially since I saw nestly's method. It's much more efficient than mine. Trimming the circles is moot anyway, they get erased, not trimmed. My wife was calling me to dinner and I got rushed. Didn't think of all the other possibilities. I thought we were having something involving red meat and beer. Boy was I disappointed. Cold turkey wraps, Hummas, pita chips and iced green tea. What the "H" "E" double hockey sticks?

Start the array with ARRAYPOLAR, and the objects pre-selected.

I gotta learn me that animation stuff.

Hey guys, thank you for everyones input! It's very helpful to see multiple ways of approaching certain designs. The only thing I still don't understand is how to add that line to the inner circle for #1. I try calculating where the line should be and creating the lines that way, but I must be off because it isn't working out. Any advice? Thanks again for everyones input! Everyone's been very helpful

Hey guys, thank you for everyones input! It's very helpful to see multiple ways of approaching certain designs. The only thing I still don't understand is how to add that line to the inner circle for #1. I try calculating where the line should be and creating the lines that way, but I must be off because it isn't working out. Any advice? Thanks again for everyones input! Everyone's been very helpful

that line to the inner circle for #1.

By the way, #1 is not a gear, it is either a ratchet or escapement wheel, or the worlds most coarse saw blade.

I'm not sure why I am typing this, because nestly will have it animated and posted before I am finished.

Never try to calculate when you can construct.

Do you have your center snap turned on? If not, turn it on.

Do you have Otho mode on? If not, turn it on too. Ortho will hold the lines to 180 and 90 so you don't have to squint and pucker to get them perfectly horizontal and vertical. If you are drawing anything at an angle other than perfectly horizontal or vertical, turn Ortho OFF, turn Polar Tracking on.

Now, there are at least two ways to draw the notch without calculating anything. You could draw a rectangle (REC) using the "dimensions" option (enter D, or down arrow after clicking the first point) starting at the circle center for a length of 0.25, and a width of 0.875, right click to get the rectangle to appear, and do that while holding the cursor in the general area where you want the rectangle to appear. You will see as you swing it around that it will let you put it in any of four positions relative to the beginning point you clicked. Now move the rectangle by its bottom midpoint, so it's bottom line is centered on the circle center, in both directions, and then trim off the parts of the notch lines and the circle you don't need.

OR you could do the following to simply draw some lines in the right place.

Start a Line on the center of the circle snap, move the cursor to the right and enter 0.125 (half the notch width).

Then without stopping the Line command, move the cursor up, and enter 0.875,

Then move the cursor to the left and enter 0.25, Ortho will hold the lines to 180 and 90 so you don't have to squint and pucker to get them perfectly horizontal and vertical.

Then move the cursor down until it is well inside the small circle, and click the end of the line in place.

That end doesn't have to contact anything, simply has to have crossed inside the circle.

Now hit escape to end the Line command.

Select the small circle, and the lines that make up the notch. Execute the Trim command, and click on the parts of the circle and lines that need to go away. They will be trimmed away. Hit escape to end the Trim command

You will have to erase the first 0.125 line segment that started at the circle center. It can't be trimmed because it didn't cross anything else.

I beat nestly? Wow.

Good, it'll give him and Remark a chance to pick my stuff apart looking for amateurish approaches (that I sometimes do come up with:facepalm:). But that's good, it helps me get better. I don't hold it against them. It's quite helpful to me.

I figured out how to create both images, thank you to everyone who submitted feedback. You have all been very helpful

I figured out how to create both images, thank you to everyone who submitted feedback. You have all been very helpful