Simple spur gear design

[wildcat]

Likely I am being dense but I am having a heck of a time deciphering the gear section in the Machinery's Handbook. What I would like to do is cut some simple spur gears out of aluminum using a vertical CNC mill. I'm not looking for super precise gears... this is a hobby for me. Looks like it should be pretty straight forward as gears are a circular pattern of a feature pair (the tooth and the valley) but I missing something. Would someone point me to a layman's explanation of gear design or a freebie program that can at least provide the necessary parameters or preferably export a DXF profile?

Thanks

[wildcat]

This is the sort of instruction that I can get my head around. If someone knows of a better way, e.g. one that does not involve the piece-mill generation of the involute curve please share.

http://www.cartertools.com/involute.html

Thanks

[greg b]

Im not quite sure what size gears you are planning to make but they will need to be blanked out and set up properly .When i have mucked around doing this in the past,i have used a horizontal arbour arrangment with a right angle head attached to my vertical mills quill.You will need to use a rotary table or indexing head to accurately space the gear teeth with the correct calculations,I am not sure that you will be able to do this in a cnc vertical mill because if its like mine it does not have the facilities to use a horizontal attachment.However if the gears were big enough and had the right size teeth i guess you could use a small end mill and set up a program that could cut them while the blank is laying down flat.

[RICHARD ZASTROW]

wildcat, Try www.sofengsvc.com

[NC Cams]

The HOME SHOP MACHINIST magazine has shown a number of times how to cut a gear using DIY processes, a dividing head and a simple gear cutter blade and a vertical mill. I don't recall which issue but they definitely had some how-to's.

[kenbo0422]

How about a 'tap' with your desired pitch held in a lathe. The gear blank is held onto the tool post, but allowed to spin. The idea is that as the blank is fed into the homemade tap, the tap itself moves the blank around. Feed it until you reach the desired/correct depth into the blank. As the blank turns, the changing angle on the cut from the tap produces a nice gear tooth profile. Probably good enough for most hobby uses.

[NC Cams]

A tap won't wonk - think about it - for aw while. The "lead" of the thread is what will pretty much cut all the teetho off of the gear blank.

YOu'll need to cut each tooth without "lead" in order to make a gear.

[RICHARD ZASTROW]

See'n as I spend a lot of my time with gear processing, I'll have to agree with NC Cams. I am a bit extreme for a DIY forum, so bear with me.

The easiest way for a DIY gear cutting expedition is to buy a gear form cutter and mill the gear (hopefully the gear is a simple spur gear) and have some method of indexing the blank to the number of teeth (actually you will mill the gaps).

This can be accomplished on a vertical or horizontal milling machine whether CNC or not. I know, 'cause as I've often mentioned, I'm older than Older Than Dirt. Also, I've dunit.

There are many other ways to accomplish the same thing, but it's like re-inventing the wheel, not really required.

You can buy the cutters on e-bay for peanuts, so why do the wheel thing?

Smile, I'm never very serious It's too painful

[Ken_Shea]

This may be of help to you. The low precision is free to down load.

http://www.hobbing.com/

Look for the horizontal menu bar toward the top of the page, click on the "spur gears"

Ken

[kenbo0422]

Normally I would agree that a tap won't work. The channels are too wide to keep the blank engaged and turning properly. The mysterious 'tap' is cut from scratch, or a bolt that has been modified with cutting channels small enough to handle the blank. If a blank is too thin, either stack them or sandwich it between two layers of metal/plastic. This will give the blank some rigid support and allow the cutting tool to stay engaged. The jig clamps to the tool post. The post is gradually fed into the cutter to allow at least a full turn of the blank until the correct depth is reached.

The stacking and/or sandwiching helps keep the rough edges down. GRANTED this isn't precision gear cutting for the space shuttle fuel feed system, its a hobby cut i.e.- (at least in this case) hobbing.