Bevel Gears 5

[CarlosEstinos]

Hi all,
I have been tasked with 3D modelling a bevel gear... I am slightly confused as the design includes minor details which are very difficult to measure. Can any one help me with this/ are there any standard dimensions of Bevel Gears.

 

[handleman]

Yes, there are standards. Why are you modeling it? For FEA? For Rapid Prototype? For CNC? If none of these, (in other words, you just need a visual representation) there is no need to model the tooth profile geometry accurately. Specify on the drawing that it is to follow the standard and a gear maker will make it.

-handleman, CSWP (The new, easy test)

 

[CorBlimeyLimey]

Gear models can be downloaded from

http://www.rushgears.com/?referrer=GoogleGeneralGears&gclid=COCRl9Tn7awCFeQCQAodIXvWIg

 

[SnowCrash]

The form of a gear tooth is an involute. On a bevel gear it tapers as well. I found an excellent example on GrabCad: 'Pinion gear By Robert Harvey' has the sketch. You will have to adapt it to your tooth pitch and taper details, but it will show you how to draw the tooth form.

--
Hardie "Crashj" Johnson
SW 2011 SP 4.0
HP Pavillion Elite HPE
W7 Pro, Nvidia Quaddro FX580

 

[Updraft]

Handleman is correct. The accurate detail is only required for certain situations. If you do not need an actual involute then there are many ways to provide a suitable simulated shape as is done with the models from RushGears (in CBL's link).

- - -Updraft

 

[CarlosEstinos]

Hello all,
Thanks for the replies, there is some very relevant and useful information there. I need to be able to solid model them for a few reasons. Number 1 is for a CNC operation, number two, is because I'd like to know out of my own intrigue, and number 3 would be to produce an accurate drawing.
Ultimately I would like to carry out FEA. CAD I'm fairly competent in but CAM is a new world to me, currently using bob cad/cam with great difficulty! I use solid works for CAD.

Id like some pointers or tips on what or where I need to start in terms of solid modelling a bevel gear.

I've got the machinists handbook, which has excellent references on the geometric aspects of gears, so I understand the basics!

Any advise would be gracefully recieved.

 

[Updraft]

CNC machining a bevel gear? Bevel gears are usually made with very specialized hobbing machines. You can check out the files from SnowCrash's link for an accurate involute, but if you want to explore CNC machining I suggest you work with something simpler than a bevel gear such as a cam, or even a domed surface.

As far as an accurate drawing goes, you need to research how gears are specified and have been for many years. Typically the blank or non-gear features are dimensioned and the gear tooth is "detailed" in a list of specifications, i.e., DP, T, PA, AGMA Class, etc. Usually just a representation of a gear tooth is shown with no direct dimensions applied to it. The Machinery's Handbook (not Machinist's) show diagrams to indicate how these specifications physically relate to the tooth form; they are not intended to be examples of drawing dimension schemes.

- - -Updraft

 

[CarlosEstinos]

Thanks for that,

Opologies I meant the machinerys handbook!

I have a bevel gear which I want to model, so physically dimensioning it is something that appears to be tricky.

I do have an accurate gear to work with that has been made by a gear cutter. I wish to manufacture 20 of these gears.

Regarding computerising machining of such on object, I'm open to all suggestions, relatively speaking this is a new world to me. I have access to a slotting machine various milling macnines and one 3 axis CNC I dont however have acsses to a "hobber" I'll post some photos and rough dimensions of what I wish to model tomorrow when I'm in

Id like to think I could solidmodel a bevel gear and in turn program a machine using CAM to cut it.
Even if it meant justifying to the company I work for to buy a particular type of machine

I want to explore wether it's worth putting the effort in to model this particular bevel gear , my interest drives me more then anything!

 

[Updraft]

If you are dead set on machining your own gears with a CNC then you can start with a simpler file to see if you can even get it through your CAM system. The attached file is a bevel gear I downloaded from RushGears as CBL had suggested. The tooth profile looks good, but is not a true involute, but that won't matter. I will be very surprised if you can get your CNC to do this part. If you can then machining one similar with an accurate involute should be possible.

I cannot fathom buying a special piece of equipment to machine these gears instead of paying someone to make them for you. RushGear is even in that business and must have the right equipment to do a better job and faster/lower cost than you could with piece of CNC equipment.

Good luck.

- - -Updraft

 

[CarlosEstinos]

I'm not nessasarily dead set on machining them, but Accuretly solid modelling is something I'd like to be able to do, for a variety of reasons. The cam system I'm using is bom cam ( which I don't like!) I'm open to new suggestions on cam software!

As for buying certain machinery, this is potentially a huge buisness area for the company I work for. People who manufacture gears for the industries I work in are a dying breed. I work mainly in the water and gas industries so The gears im trying to manafacture are quite large(weigh approximetly 20kg) they would normally be used to drive valves and will have been normally made out of cast iron so they are not precision gears in terms of tolerances.

Where are rush gear based? From what I can gather they are in the US based, I am UK based.

I really appriciate your feedback, do genuinely find it very useful, I wont be able to open your link till tomorrow as I'm currently on my iPad and I've got a really bad Internet connection,and I wont have access to my computer till tomorrow morning.

Thanks

Carlos

 

[Updraft]

The size of gears you mention are not really a problem. There are many vendors out there that can make your part. In this global marketplace they would not have to be in the UK to serve your needs.

Do not confuse cast iron gears as low tolerance gears. Cast iron is a perfect material for gears depending on their application. The precision of the gear is more a function of the manufacturing method than the material.

We use FeatureCam and realy like it. It does a great job of using our SWX part files directly.

- - -Updraft

 

[ArtL]

Carlos I don't know what a gear hobber costs, but I beleive it is in the 1/4 million dollar price range. You need 20 gears, that translates to 40 hours at the most. what are you going to do with a $250,000.00 investment the rest of the year. Plus you need a machinist that knows what he is doing, plus hobbs, inspection equiptment. I feel its really a bad investment on your part.Gear hobbing is one of those areas that is highly specalized.The rest of the machine area is nothing like gear hobbing. I have had special gears (one and two gears) made for quite a reasonable price. Explore your options a bit further.I have a hard time beleiving there no gear hobbers in England or the main Land!! Best of luck. Art L

 

[SnowCrash]

BobCAM for Solidworks takes some effort to get working, but the newest revision has improved it a lot. I suggest you search out the tutorials on YouTube and

http://www.bobcad.com/forums

.
To actually create a bevel gear on a milling machine will be a challenge. I would suggest a lathe turned conical form placed in a rotary index head and generating a tool path to mill the space between teeth.

--
Hardie "Crashj" Johnson
SW 2011 SP 4.0
HP Pavillion Elite HPE
W7 Pro, Nvidia Quaddro FX580

 

[Bugie]

Most modern lathes have a hobbing function

http://www.youtube.com/watch?v=lJ_S1CzMsbw

CNC machining large gears is common practice

http://www.zakgear.com/

Regards
Greg

 

[Bugie]

Also here

http://www.spiralbevel.com/

Regards
Greg

 

[SnowCrash]

Here is a very odd gearset:

http://www.youtube.com/watch?v=-1Gfc1Iq0GY

--
Hardie "Crashj" Johnson
SW 2011 SP 4.0
HP Pavillion Elite HPE
W7 Pro, Nvidia Quaddro FX580

 

[kellnerp]

So why not rapid prototype them in wax and have them investment cast?

Or just rapid prototype them.

Machinery's handbook and any modern CAD textbook will tell you how to create the profile and what dimensions are critical.

TOP
CSWP, BSSE

http://www.engtran.com

http://www.niswug.org

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