08-31-2011 05:20 PM

Tristan Lall

Re: pic: Cobra box version 2

Good work revising the design. Mind if I inquire about a few items?

Why did you put such a large radius on the gearbox plate corners? Anything more than a simple broken edge will require more machining effort. Big radii are good on inside corners when the stress concentrations matter due to the loads being transmitted through the plate. Only relatively rarely does that matter on an outside corner.

What does the output from this gearbox look like? Are the brackets going to be sufficient to take up any loads imposed by the things the gearbox connects to?

Do you need custom-bent brackets like those? Could you use a piece of angle, or maybe buy a bracket off the shelf that accomplishes the same purpose (e.g. from McMaster-Carr or a hardware store)?

What are the specs on the worm gear? How many starts (i.e. the helical teeth on the worm), material, angles, profile, etc.? Most critically, I'm interested in the efficiency of the worm gear—efficiency can vary enormously, depending on those parameters, and on the accuracy with which the gearset is assembled.

Are you using shaft collars? They're heavy, but can be good if you need fine adjustability. I'd generally prefer to use snap rings or shafts with fully-captured lightweight aluminum spacers (when thrust loads matter).

08-31-2011 05:39 PM

steelerborn

Re: pic: Cobra box version 2

Great questions.

I always like using shaft collars because they are just simple and are very reliable I have never had a problem with one, I have though with snap rings. And there is already aluminum spacers along the shafts (the blue).

The L brackets will be able to handle the transmission, but can be just bought off the shelf. And the rounds were to just minimize sharp corners but is really no big deal design wise.

The worm is a 1 in pitch diameter, and is made of steel. It has only one thread and has a pitch of 12. The worm gear is Cast Iron with 40 teeth and also has a pitch of 12. The pitch diameter is 3.33 inches.

09-01-2011 01:42 AM

Tristan Lall

Re: pic: Cobra box version 2

Regarding the worm gear and its efficiency, for now let me just point you to a couple references found in some old posts, here and here.

Also, see here for more general references about gears.

09-01-2011 01:26 PM

steelerborn

Re: pic: Cobra box version 2

Wow great post, I have already read the Martin Sprocket gear manual before I made the box. But thanks for all the other information on Worm gears.

09-01-2011 01:39 PM

AdamHeard

Re: pic: Cobra box version 2

Curious, what kind of machines do you have in house or available via sponsors. Edge tapping long thin plates on lower quality machines (like our mill) can be pretty imprecise for gear spacing. Hard to tell from the pic, doesn't look too long and thin but something to consider.

09-09-2011 01:33 PM

cseabury

Re: pic: Cobra box version 2

Is this design just a suggestion or canyou make available a bill of materials etc?