Straight bevel gears with 90? shaft angle but shallower profile angle

[thinkntink]

Hi Art,

I pray that you are well.

I am still feeding my Gearotics addiction, but am actually getting ready to do some cutting. WHHOOOPPPEEEE!

A problem that I am running into is that I need to fit the wheel and pinion into a fairy cramped space. I can do this if I can make the pinion look more like a Torx screw driver (with a 20? to 30? taper) with matching teeth on my wheel. I have been playing with the various parameters in GM by cannot seem to change the bevel angle. This same type of wheel / pinion setup is used on the tightening ring  / key on a drill press (Jacobs style chuck).  Any suggestions?

Be well.

[ArtF]

Ron:

  I "think"  I understand your question. ( These things are always hards to explain arent they? )

SO basically youd like a normal spur gear, but with the face beveled. So one gear woudl be placed
facing outwar on its bevel and the other facing inwards so the two bevels mesh at 45degrees making
it look like two normal spurs meshing together? (I can picture it, but Im not sure why it'd be done. :) )

    Sounds like two bevels with 90 degrees shaft angle, giving each a 45 degree tooth angle.
Wouldnt that work?


Art

[thinkntink]

Hi Art,

If you have a drill press out in the shop with a key tightening Jacobs style chuck, you will see that, while the spindle axis and key axis are at 90?, the angle of the bevelled teeth is shallower than 45?. On my old Craftsman, the key bevel angle is about 30? relative to the axis of the key. This type of geometry is pretty handy if you need to implement a right angle drive in a system where you are space limited in one direction but not so in the other.

I tried to capture some pictures from GM to show you what I mean but the .JPS seem to be blank (see attached). The same thing occurs with the AVI no matter which flavor (codec) I select or which viewer I use (MP, MC, VLC...). Any idea what I might be doing wrong?

[thinkntink]

Hi Art,

I used the snipping tool to capture some images to show you what I meant. Please see attached.

[ArtF]

Ahh, I see nbow. BAsically, GM splits the shaft angle in two and assigns each gear that half.. ( ie.. 2 45Deg bevels make a 90 degree shaft angle. ). You want to split in differently, like 30/60 to make 90.

  I guess youd hav to set it up for a 60 degree, ( it will give you two 30's) place the wheel, then set it up for a 120 to get 2 60's.. and use one of them..

  I dont think GM at the moment will do more than 45 degree on the bevel.. I will look into it though to see if I can make this possible,,

Art

[thinkntink]

Hi Art,

I tried experimenting with shaft angles over 90? but the program ignored me. I had previously thought of doing the 30/60 (shaft angles: 60/120) trick but could not get GM to kow tow to my wishes. Maybe a good future enhancement.

Any insight as to why I cannot capture AVIs or JPGs?

[ArtF]

Hi Ron:

  Might not be that long before I can give you various angled bevels and helicals..Ill keep you posted.

As to the jpgs and avi's.. thats a strange one. Every once in a while someone reports no capability to record, or they record
blanks. Im not sure why. For a few, downloading a codec pack and then selectin gon of those codecs has worked, for others
nothing seemed to. The recoridn is done with Video4Windows calls into the Windows kernal. It reports no failure to my konwledge, it just for some reasons gives a few systems blank output. I will investigate that when I redo those routine as well..

Art

[thinkntink]

Thanks Art.

Be well.

[thinkntink]

Hi Art,

The current version already does what I need it to. I was being stupid.

The way that you control the face angles is by the ratio of the number of teeth between the wheel and the pinion. If both have the same number of teeth, the pitch cone angle is 45?.  As soon as the pinion starts getting smaller (or the wheel larger), the pitch cone angle of the wheel (relative to the central axis) increases and the pitch cone angle of the pinion (relative to the central axis) decreases to compensate. It's obvious once you think about it. In any case, the only caveat is that both the wheel and the pinion tooth counts (gear ratio) MUST be specified before either is created. You probably list this in the manual but I did not see it.

Ole dopey me!

Could you clear up a couple of terms for me? You show  "bevel outside diameter" and "gear diameter" listed on the Project Control screen . The gear diameter is larger and I assume that it is the maximum projected diameter. I also understand "pitch diameter" and "root diameter" (at least in the case of simple spur gears). But, what does the "bevel outside diameter" and "base diameter" refer to. The reason that I ask is that I am getting ready to have some pre-forms turned and bevelled and I want to make sure I specify the correct diameter.

[ArtF]

Hi Ron:

  Bevel outside diam is the full outside diameter at the large end of the bevels cone. ( The true outside edge of the teeth.)

As soon as next update you'll be able to use GT to get stats such as outside diam, inside cone diam..and various other stats not presently shown, the bevels will be getting huge upgrades in the future..

Art

[thinkntink]

Hi Art,

Thanks.  But what is the "gear diameter" (the biggest of the 2)?

[ArtF]

Hi Ron:

  Sorry about that, the Gear Diamter is the diameter the Gear would have been if the teeth werent beveled in . In other words its the virtual gear the bevel was created from. In the new
software I actually show that beveling in on the creation screen so the user gets an idea abut how such a gear is derived. Bevels and helicals use "Virtual" spur gears based on normal
spur gear math, and then are modified in various ways. For example in a bevel the teeth get
twisted inwards to the cone angle, but if not twisted inwards they would have had a diameter of
"Gear Diam".  "Bevel outside diam" is then simply from a formula based on the cone angle and the original "Outside Diam".

  In future that stat will be shown as "Virtual Gear Diam.". Facewidth is another similar thing, in future youll see "Facewidth" and "Axial Facewidth" to show the difference between the requested facewidth, and the resultant "Axial Facewidth" which is the facewidth twisted to the bevels cone and how wide that is in the axial plane.

  In future Ill try to show as many stats about the gear as I can, and how they get formulated.


Thx

Art

[thinkntink]

Hi Art,

Thanks for the clarification. I suspected as much as soon as I took a look at "unfolding" a bevel gear.

By the way.  VERY clearly explained. I am slowly, but surely, developing some facility with gear terminology. Which is a good thing, since we are getting ready to spend a fair amount of money on a pre-pilot run of a new gear set and I have found that a lot of "gear folk" seem to be a clannish lot. If you don't speak the lingo, or at least a passable patois, you must be from out of town and worthy of suspicion.

[ArtF]

It IS very hard to get accurate information in this area. Gears are rarely discussed as to how or why they are designed as they are,
doing the math for the program, I daily think "Ahh..thats why...:), such as why helical must be larger than spurs, yet bevels are the same size.. .

  Usually, the answer is in that math.

art

[thinkntink]

That is probably it.

I was led to believe, after talking to a couple of gear manufacturers that it involved lots of magic sauce and chicken blood in the hands of high-paid "Priests of Gear Lore".

Thanks for clearing it up for me.

I will send a picture of what we are making as soon as the simulation is done.

BTW.  Is this the best place to put a short tutorial on a usable process for going from Gearotic to full fledged 3D CAD files?