Questions about Gears

[diarmaid]

Hi all,
This is actually a few questions and hopefully someone will be able to shed some light for me. the 3D drawing below is not an exact representation for machining, just a diagram to show what Im talking about.

1) In the diagram below, what would be the best way to secure the gear wheel onto the smooth drive shaft?

2) Likewise if the driveshaft was splined along its length?

3) Is there any CAD program either specifically for creating gears or one that is exceptionally good at this?

4) Are gears difficult to machine correctly either with a manual or cnc mill and what are the considerations (Im thinking metal fatigue would be a major factor in metal choice)?

I added in the bolt because this is my only idea for attachig the gear so far and I think is common in non load bearing applications, but there will be a lot of torque on the gear and I need to secure it better than this. The bolt is not to scale with the rest of the drawing!

I also dont think I will have the capability to cool the gear with liquid nitrogen and shrink it onto the shaft.

Thanks.

[ironDigit]

if you look well just in your neighbourhood you should at least be able to come up with some dry-ice with any lukk real life liquid nitrogen


hint : fish shop(were they sell fish) or isn't the dry ice cold enough ?

just my 2cents you can have for free

[diarmaid]

Thanks IronDigit. Thats a good idea, at least it wouldn't cost anything to try.

[lakeside]

[QUOTE=diarmaid]3) Is there any CAD program either specifically for creating gears or one that is exceptionally good at this?
4) Are gears difficult to machine correctly either with a manual or cnc mill and what are the considerations (Im thinking metal fatigue would be a major factor in metal /QUOTE]

gears can be machined on a mill depending on the form of the gear you are looking for.If you only need one cad file for a gear I can do it in Bobcad. Below are some screen shot to give you more info. Note the screen shot of gear profile, each color is an angle cut. Most gears are cut with form tools on a gear hobber.

[Owain1602]

Erm..........its Alec Stokes that wrote the book. What is the purpose of your gearbox then? or is it not a gearbox, more of a gear on a shaft? how much torque is going through the gears.
There are many different ways really, but it depends on a few things.
You could use a key-way on the shaft, splines, taper, interfearance fit, splines with circlips, your idea of a bolt to the shaft but i havent seen many like this. what sort of side thrust is the torque gonna create on your shaft.
I'll try and help you from what i know of gearboxes for cars but i can't help at all really with designing, materials and all that because im a total newbie by melf im affraid.
PS. Im determined to make my own gears, if it doesnt meet all requirements first time, then strip down, re-asses, re-design and try again. sorry if i sound quite cocky but i really really want to do it eventually.

[diarmaid]

Not cocky at all m8. Thanks for the advice. Im thinking maybe if I could cool the gear to fit it onto the shaft I could use a rod through the gear, shaft, and back into the other side of the gear. The rod could be shrunk using cooling the same way, but Im worried this might weaken the shaft. I have plenty of time to figure this out but I need as much advice as possible. I'll post some more detailed drawings as soon as possible.
Its not a gearbox at all, simply a gear on the shaft so that I can change the direction of rotation to operate a second drive at the same rate but they will rotate with opposing force. Its to run two propellers and I need one rotating clockwise and one counter clockwise for balance.

[diarmaid]

Here are some more detailed drawings. Please note that the two gears dont fit together, this is why I need a good gear modelling program! Also, ignore the dimensions, they dont matter at this point and are not shown clearly. All advice is appreciated. Thanks.

Im also not sure if this is a good method of connection to run propellers but thats for another day.

[Owain1602]

Ok, um....from what i see, the best way i think i would do it is;
Spline the shaft wherever you want the gear to sit, then at the lower side of the splines, lip the shaft so the gear can not get off that way and maybe circlip the upper edge?
I dont know about the vibrational forces involved but maybe a pin would shake free? But then again they uses roll pins to lock car drive shafts in.
Maybe a combination of both?

[diarmaid]

Thanks Owain. Thats sounds like a fairly solid way to go about it.

[franchesco]

aqui dejo una paguina interezante para quienes quieran hacer cosas en 3Ds yo lo probe, digo que con respecto a los diseños la idea de la paguina es interezante, nos fasilita un catalogo muy bueno, los nc cuestan algo de 25 a 40 usd. reguistrensen y les regalan unos nc.
http://www.vectric.com/

Una cosa mas, como un gran necio que soy dejo aqui tambien una paguina que por ahi les interece, este hombre que hace estas cosas ama al cnc, creo sus propias piezas con moldeldes, ahi muestra como corto los moldes con hilo y luego funde, tambien tiene COMO CREAR un CAMBIADOR DE HERRAMIENTAS , eso si es algo grandioso,

http://www.buildyouridea.com/cnc/atc/atc.html

[RICHARD ZASTROW]

diarmaid, There are many keyless connectors and clamping sleeves commercially available. Spieth & Ringfeder are both from Germany, Fenner drives in the USA. These make a more secure and stronger coupling than key/keyway fit. As for gear mfg., if you can specify commercially available gears you will save time & money. Otherwise if you prefer to diy, obtain the appropriate single tooth cutter and the gear can be cut on a mill with a dividing head. or a wire EDM. or a gear shaper. or a gear hobber.
Good Luck

[Cory]

I'd use a keyway.

If you had access to a hex broach, I'd broach the gear and use a hex shaft.