[rustamd]

I'm need to model some gear rack for my router but do not know where to start. Here is the specs on it:

Preasure Ange:...............20°
Pitch:...........................16
Face Width:...................3/4"
Overall Thickness:...........3/4"
Pitchline to Back:........... .687

Can anyone help me model this please? or at least send me somewhere where i can find info on how to make this thing.

I need sections that are:

1000mm(39.37") long and 830mm(32.67") long(or something close to that in inches)


Thanks in advance...

[rustamd]

I did look at 3dcontentcentral.com but couldnt find anything that size...

[rustamd]

I think i just might have figured out on how to do it.

1. Create square stock(.750x.750")
2. Creat tooth profile
3. Linear pattern it.

The only thing is i dont know know how to properly calclate the tooth profile...

[CuttersCov]

Rust,

Open a sketch on the right plane and make a profile of one or two teeth. Extrude that to the width you need, create a line to follow for the length of the entire track, then do a linear pattern down the length of the line. Mess with the distances apart to get the patterns to align properly and merge all.

[rustamd]

the problem is that i dont know how to make correct tooth shape... Its not big deal its just that i wanted to learn how to do it. But linear pattern is the way to do it, either create one tooth and extrude or create profile than cut...

[JerryFlyGuy]

Rustamnd, don't worry about the proper tooth profile. Are you making the rack yourself? Otherwise [if not] just do a rough approx, tooth.. or better yet.. don't put any in.. it will eat up lots of RAM and rendering power to have those teeth in there.. and they have no use.. you already have the pitch line dimension.. all you need is the pitch dia of the pinion and you can calculate the engagement distance.. I've built my mill this way.. it's got 50ft of rack on it.. and it's not to perfect scale in the model..The only reason I put mine in was so that when I rendered pictures it looked like a rack.. afterwards I took them back out [suppressed them]..

This is something I had to learn the hard way.. all that detail.. for something your going to buy off the shelf.. it's a wast of time and computing power.. trust me..

[CuttersCov]

Ok, I'm assuming a tooth that looks like an inverted "V" is this not the same kinda tooth you're doing?

[Kiwi]

rustamd
Your rack tooth drawing should look like this (without details).
16 Pitch = 16 teeth on a gear with a diameter (DP) 1inch = circumference 3.14159 inches / 16 = .1963 inch per tooth.

(Correct me if I'm wrong.)

[rustamd]

thats exactly what i was looking for! Thank you

[kenbarra]

I have an engineering text here that describes the precise profile of a spur gear as involute curve.

You can also get this info from Machinery's Handbook.25ed p.1926 for racks and p1923 for gear. At least it approximates the rack profile with two tangential curves and gives relative center locations in ratios of diametral pitch and pressure angle. I wish I could scan it for you. Maybe somebody has the CD_ROM version and can send the pdf for those pages.

the gear tooth profile is described by an involute curve.:

http://www.abbeyclock.com/gearing4.html

http://www.cadquest.com/books/pdf/gears.pdf

Thanks, I was just researching the same thing, and I found these to respond to your post. How fortuitous.

My need is for a very small gear and rack to have a t handle drive a reciprocating shaft with a stroke of .670 inches. I am affraid that I need to define the profile, since we are doing this job in house.