CamBam
News:
 
*
Welcome, Guest. Please login or register.
Did you miss your activation email?
October 18, 2017, 15:40:36 pm


Login with username, password and session length


Pages: [1]
  Print  
Author Topic: best tactics to cnc mill an internal gear  (Read 915 times)
fourchette
CNC Ewok
*
Offline Offline

Posts: 4


View Profile
« on: April 17, 2017, 19:04:18 pm »

Hello,

I'm almost about to cnc mill my own planetary gearbox.



one question puzzles me.

For milling the outside ring, which is an internal involute gear (teeth are going "inside" the rind, not outside like a regular gear), I am faced with a classic "my endmill wont fit in the corners while later on another part must fit in there anyway" kinda problem (sorry for lacking the proper vocabulary but i'm pretty sure most of you must know what i'm talking about.


In general, when i face such issues, I design the part in CAD so that later on the end mill will always fit whatsoever.

A typical example would be


But for the involute gear ring, i would rather avoid weakning the part or do pretty much anything that might endanger the desired fonctionality.

Here my approach is different. I am making drawing the inside teeth slighly deeper so that the extra clearance is enough so that the part that will remain after the endmill has done its job cannot collide with the planet gears

screenshot below. the ring in green. the circle corresponds to my 1mm endmill. As you can see it should be fine (i hope so)

My question is : would you have better tactics in such a situation ?


Any idea is welcome.

thanks














Logged
lloydsp
CNC Jedi
*****
Online Online

Posts: 7109



View Profile
« Reply #1 on: April 17, 2017, 21:06:00 pm »

That works!  Another approach is to do a 'finishing pass' with a much smaller cutter.

Lloyd
Logged

"Pyro for Fun and Profit for More Than Fifty Years"
Bubba
CNC Jedi
*****
Offline Offline

Posts: 2225



View Profile
« Reply #2 on: April 17, 2017, 21:29:27 pm »

As Lloyd said. It not only will work but it is common practice to allow for little clearance.
Logged
kvom
CNC Jedi
*****
Offline Offline

Posts: 1384


View Profile
« Reply #3 on: April 18, 2017, 01:30:04 am »

Yes.  See definition of addendum and dedendum wrt gears.
Logged
kiwibrick
CNC Ewok
*
Offline Offline

Posts: 43


View Profile WWW
« Reply #4 on: April 21, 2017, 10:40:13 am »

Nice solution!
The thing I had a problem with with machining gears wasn't the tool diameter but the tool length, easy to get a 1mm end mill but not at 6mm doc, never did find any that long
Logged
fourchette
CNC Ewok
*
Offline Offline

Posts: 4


View Profile
« Reply #5 on: May 10, 2017, 10:33:25 am »

tool length is indeed a concern.

misumi has a pretty extensive list of tools. My hope was to find a tool that is long enough so that by machining on one side, and then machining on the other side (flip the raw material) => then i should be able to make it.

on the european dedicated website of misumi i see 272 models of 1mm flute diameter for square endmills
=> http://www.misumi-europe.com/en/catalog/vona2/fs_machining/T0101000000/T0101010000/

I hardly see them not having a someone cheap+long+strong_enough endmill that works for you. And they have a USA version (never tried it though)

My 1mm square endmills are 4mm long, so for a 6~7mm deep internal ring i should be ok.

I do have to master the flip-your-work technique because at the moment i am still unable to perform it without "visually trying to be at the right place", which for such tiny work simply can't work i guess. any idea is welcome here. i have not searched at all at this point. i guess it's something very basic for most of you guys

Well i do know that at least for Z, estlcam does it with a simple detector Tongue
 dunno for XY
there's gotta be something simple for that, even with cambam. just my ignorance here


Logged
kvom
CNC Jedi
*****
Offline Offline

Posts: 1384


View Profile
« Reply #6 on: May 10, 2017, 11:50:25 am »

For a gear I would set the center at the center of the stock so that flipping on the X axis while using a vise stop would retain the center point.  With an even number of teeth the gear would be symmetric as long as one tooth pair is centered on X.  With an odd number you'd want to mirror the part in CB along the X axis.
Logged
EddyCurrent
CNC Jedi
*****
Offline Offline

Posts: 3135



View Profile
« Reply #7 on: May 10, 2017, 12:58:07 pm »

What about something like these cutters? www.ebay.co.uk/itm/u-MKEAF-1-1-5-or-2mm-solid-carbide-TiaLn-long-SLOT-MILL-General-use-to-60HRC-/171065877758

« Last Edit: May 10, 2017, 14:58:52 pm by EddyCurrent » Logged
Garyhlucas
CNC Jedi
*****
Offline Offline

Posts: 1001


View Profile
« Reply #8 on: May 10, 2017, 14:22:34 pm »

Those are drills not mills, no side cutting.
Logged

Gary H. Lucas

Have you read my blog?
 http://a-little-business.blogspot.com/
Garyhlucas
CNC Jedi
*****
Offline Offline

Posts: 1001


View Profile
« Reply #9 on: May 10, 2017, 14:26:57 pm »

You know a better approach for this project might be a different type of gear reducer. You might take a look at a cyclo-reducer design. It has roller ramps not gear teeth and would likely be way easier to machine.
Logged

Gary H. Lucas

Have you read my blog?
 http://a-little-business.blogspot.com/
dwc
Wookie
****
Offline Offline

Posts: 489



View Profile WWW
« Reply #10 on: May 10, 2017, 14:38:02 pm »

You know a better approach for this project might be

Or why not redesign it so there are no internal gears?
There are lots of possibilities.
Don
Logged

EddyCurrent
CNC Jedi
*****
Offline Offline

Posts: 3135



View Profile
« Reply #11 on: May 10, 2017, 14:59:44 pm »

Those are drills not mills, no side cutting.

Gary, Well spotted, I put the wrong link there but it's correct now.

Also as suggested by Gary and Don, have a look at these threads;

http://www.cambam.co.uk/forum/index.php?topic=4640.0
http://www.cambam.co.uk/forum/index.php?topic=3497.0
http://www.cambam.co.uk/forum/index.php?topic=4610.0
« Last Edit: May 10, 2017, 15:09:42 pm by EddyCurrent » Logged
Garyhlucas
CNC Jedi
*****
Offline Offline

Posts: 1001


View Profile
« Reply #12 on: May 11, 2017, 00:13:10 am »

Internal gears are where broaching comes into its own.  I have broached key ways in cast iron on my home built CNC and they came our great.  Mill out the material the cutter can reach, then a fourth axis or even a manual rotary table could rotate the gear under a formed cutter.
Logged

Gary H. Lucas

Have you read my blog?
 http://a-little-business.blogspot.com/
Pages: [1]
  Print  
 
Jump to:  

Powered by MySQL Powered by PHP Powered by SMF 1.1.19 | SMF © 2013, Simple Machines

Valid XHTML 1.0! Valid CSS! Dilber MC Theme by HarzeM
Page created in 0.158 seconds with 19 queries.

Copyright © 2008 HexRay Ltd. | Sitemap