help with sprocket please...

i am trying to draw a sprocket to be sent to the waterjet. i have the information i believe i need. when i searched the forum i found this link- http://www.gizmology.net/sprockets.htm

that was reccommended. i have tried over and over but i keep getting the wrong size tooth.

i understand the polar array and the cad stuff, just not sure what it is i keep inputting wrong that gets me the wrong tooth.

here is the info i have: sprocket od =29.091,pitch diameter=28.652, number of teeth=120, 3/4 inch pitch no. 60 chain, 15/32 inch diameter roller.

if you follow the gizmology procedure here are the inputs i use with the number used in their instructions-

1.3 lines 1'2.5455" long spaced 3 degrees apart(like shown on their example)

2. i offset lines .75 inch(pitch of chain)

3. circles are .46875 diameter

4,5,6 followed their instructions.

i will attach what i come up with. hopefully someone on the forum knows what it is i am doing wrong.

tooth.dwg

i am trying to draw a sprocket to be sent to the waterjet. i have the information i believe i need. when i searched the forum i found this link- http://www.gizmology.net/sprockets.htm

that was reccommended. i have tried over and over but i keep getting the wrong size tooth.

Change your units to decimal with the max amount of precision.

Change Decimal degrees to the max precision also and try the drawing again.

tds73, please keep in mind, not all are usin' '07 or newer AutoCAD.

I do have '07 on my desktops however, I working from my Thinkpad™ with AutoCAD 2005. Couldn't view your *.dwg file.

Why not save to an earlier version before posting? I always save to AutoCAD 2000 for clients and, if needed, for posting.

sorry, i was so frustrated i forgot all about saving to an older version. here it is again.

tooth[2].dwg

Change your units to decimal with the max amount of precision.

Change Decimal degrees to the max precision also and try the drawing again

i tried again like you stated, same result. here is the profile i keep getting. something is just not right. not sure what it is , or maybe there is another step i need to take afterwards?

tooth[2].dwg

Contruction on left, solid on right. (You might want to dimension my construction sketch on left.) (my construction taken from Machinery's Handbook, not that website)

Polar array solid 120 copies and union.

No 60 120T.zip

JD Mather,

looks good. I noticed when checking your const. sketch, that it is 2 degrees, not 3 . is there a way i can see the formula/process you used to arrive at this? or is having the book in hand the only way?

Bump up your precision - I didn't use anything at 2° that I recall. Bisect angle is 1.5° or 3°/2. The formulas are in the Machinery's Handbook. I set these up in a spread sheet for easy calculation with a look-up table to the chain sizes. I added a just a bit of clearance for the roller radius.

Hold the horses - I just realized that the roller radius is not part of my look-up table - I made a mistake and will post the corrected geometry in a few minutes.

Check this one instead - I thought the last one looked a little fishy, but I had never done a sprocket with that many teeth and was in a bit of a hurry.

No 60 120T.zip

sorry if i am a pain in the butt. i only have 2007 and cannot open your file.

on a side note, you said you added a little for roller clearance,how do you know how much is a little? past experience or is there some sort of guideline?

Try this 2007 dwg file.

No 60 120Tv2007.zip