OD calculation

[bruce]

I see to calculate the OD gear blank one uses the formula OD = (number of teeth + 2) / DP so far so good but
I have some gear cutters labeled M1 and I read that is the reciprocal of DP, is this correct?
They also talk about this being metric but I am confused on how to use the OD formula using M1 ( or other M #'s)
in this calculation. Could someone please enlighten me about this difference between M's and DP?
Thanks,
Bruce

[ArtF]

Hi:

  Mod ( or whats labeled M) is the number of teeth per mm over the circumference.

DP, is the imperial equivalent, so its the  25.4/Mod and Mod is DP/25.4.

On the circular gear page, enter a DP, the equivalent Mod is instantly shown. Works
the other way as well..

Art

[bruce]

Thanks Art, that clears things up on that calculation.
So I am running Gearotic and have circular gears selected and it is displaying a pinion and wheel. I changed the DP to 25.4
and module is showing 1 now.
My next question relates to number of teeth and cutter # (1 thru 8) for this Module 1 set of cutters. I changed the pinion
to 10 teeth and the wheel to 30 teeth but cutter number 8 shows 12 to 13 teeth, there is no cutter for 10 teeth unless I make my own
but didn't want to do that right now. So I am limited to make the pinion to 12 teeth or more because of the available cutter number?

I see under the tools tab a print button, will that print out all the gear parameters for the pinion and wheel only? If I want to create
the G-code I would click on the 4th axis button to generate the code  using the A axis with a rotary head?

Sorry for the DA questions but I have never made a gear before ( your software did help me make a sprocket a couple of years ago.) and
this is something I have wanted to do for a long time now.
Oh and I see one could spend a fortune on cutters given there are 8 for every DP or Module!
TNX,
Bruce W7BCW

[ArtF]

  Hi Bruce:

    When they make cutters, they they tend to make them suit a certain
number of teeth. Your Mod#8 for 12-13teeth for example. This is because the
curvature of the pitch circles affect the tooth shape, but not so much it matters
for every tooth count. So they make them in a range.

If you have a gear and send it to the 4th axis, yes, you use the A ( or any axis letter
you define) as your rotary. But you dont need to use a cutter. Gearotic will crate Gcode
for a fluted mill of any size that can fit in the tooth space , you dont need a
tooth cutter, ( though that is an option ). When using a milling flute, the gear curves are
shaved into spec, where the module cutters just do multiple passes getting deeper each
time till that shape is cut. Module cutters are faster, but shaving works well...

  Theres a video on doing it in the list of video's on Gearotic..

Art

[bruce]

Art,
I was successful in creating the G-code for 4th Axis but I find the 4th axis setup a bit confusing since
I am not familiar with some of the terminology you use there. It seems more for using an end mill but I chose
a formed cutter and then slitting saw but even that shows an end mill for some odd reason in the description
but the graphics show a saw. I used a value of 0.1 inches for flute length which is more cutter thickness
for a slitting saw. There are other parameters in that window that seem more for end mills than slitting saws or formed cutters like
I am using. Oh and one other thing I am going to make my gears 1/8 inch thick but defaults 1/4 inch, how do I change that?
I updated gearotic to 3.03 to make sure I had the latest for 4th axis use.
TNX,
Bruce

[ArtF]

Bruce:

  If the tool is listed under slit saws, the flute length becomes the thickness of the blade.
End thickness of the gear is set by the "FaceWidth" box. This will be the gears thickness.
 
    If your module cutter is the slitsaw type, then select slitsaw and set the flute length to anything
that will fit the tooth space. Then use the "Shaped Tool" toolpath selection. Its important to
unselect and reselect it if you were experimenting with another tool. What you will see is a
single position per tooth with multiple cuts down to "Final Depth" using "Z-Dn per pass" increments
and using a "Final Pass" run for the last pass.

  In the end the simulation should show what your setup looks like. You can adjust that a bit in the settings for which axis your A axis is on.


Yell if confused.
Art

[bruce]

[img]http://pinion_12_pix.jpg[/img]

Not sure this picture of the 2 gears i made using the 4th axis. I used aluminum since i didn't have the right brass stock.
I need to go over the parameters for the g-code generation since i was cutting more air than material.

[ArtF]

Bruce:

  Shaving does cut a lot of air depending on parameters, or was this
a shaped tool? If shaving tangentally, try fewer segments, usually 7 or so is fine, also check the safe_z to make sure it isnt raising too much. Other than
that it is pretty typical to cut lot of air as the technique is all about positioning..

  They look pretty good from that distance though...

Art

[bruce]

I used a shaped cutter, the mod 1's set I purchased a year ago. I used a G0704 mill converted to CNC with Flashcut
hardware and software. The g-code generated by Gearotic worked with out making any changes. Sometimes
Flashcut doesn't like the way some g-code commands are setup but not in this case.
The gears shown seem to mesh ok but I really need to either cut some thin slices off each to make a set that i
can put shafts in and see how well they do run by hand or cut up some brass blanks and make them over again
now that I have proven out the g-code.

The gear teeth are a bit coarse and I am wondering if there is/are DP or Mod's that are used more so than others?
I guess that depends on the application but just curious for now.
Bruce

[bruce]

I would use the tangentially method for larger gear tooth sizes that are higher Mod numbers where
a shaped cutter might be too expensive to buy.

[ArtF]

Bruce:

  No, I dont think any particular mod is the most common, its all
pretty application dependent. I suspect youll be fine, they look good
at any rate. :)

Art

[bruce]

Art,
I have another question about Gearotic on Projects window. Should I create a different subject? Not sure so will
ask here anyway.
Using the Tools tab I am able to see 2 gears (pinion & wheel) that are meshed together and when I send each
to the Project window the gears end up on a common shaft. How do I keep the gears on separate shafts like I see
on the Tools window?
I haven't been able to see on the Projects tab window under properties a button to do this separation.
Thanks,
Bruce

[steve323]

The gear teeth are a bit coarse and I am wondering if there is/are DP or Mod's that are used more so than others?
I guess that depends on the application but just curious for now.
Bruce

Yes, tooth size depends on the application.  I like 10DP gears for wooden clock gears because they can be cut with a 1/8" router bit.  A 60 tooth gear has a 6" diameter at the pitch circle with about 0.15" tooth width and 0.16" space between teeth.

I am not sure what sizes are appropriate for brass gears, but I would probably prefer large coarse teeth.  If you are going to spend the time to make your own gears, then they should be visible when you are showing off your creation.

Steve

[ArtF]

Bruce:

When you add the first gear, it is placed on a shaft. When you add the second, it wont appear till you click the thing you wish to attach to. If you click
the shaft, the gear will share the shaft, it you click the gear, it will roll around the first gear till you again click to set it. To make it easier, click "Add Pinion", then when the project screen appears, click on spur#1 in the tree instead of on the graphics screen, the gear will then be ready to roll on the first one.

Art