A question about figuring out what size end mill to use for a given gear

[Rhett]

I have access to a pretty nice cnc table, but the smallest end mill we have for it is a 1/8 inch and I'm trying to make gears as small as possible. I would like to know if there is anyway within gearotic to tell what the biggest size endmill that could be used to cut a given gear profile would be. As of the moment, I'm just zooming in and guesstimating the radius of the inside corners while trying to keep them greater than 1.6mm. I'm still a newbie to this, so I wouldn't be surprised if the info I'm looking for is staring me in the face.

Any help would be appreciated :)

[ArtF]

Hi Rhett:

  Once a gear is ont he project screen , click it to select it. In the text shown, ( near the bottom left), is a line "Max Tool Diam:".

  This is true for gear types where the program figures it knows the maximum as a result of its calcs.

Hope it helps,

Art

[Rhett]

That's great! Thanks for such a quick reply art. Your program is amazing

[Rhett]

I noticed that the max tool diameter seems to be pretty closely related to the spacing in between the teeth and not so much the fillet at the bottom of the tooth. Some of the gears I've designed that are stubby have almost no fillet at the bottom and I am certain they would probably bind if they were cut with the max tool size. Is the max tool size meant for gears with no mods?

[ArtF]

Rhett:

    Its a calculated value, so yes there are times it will be tight, its always smart to look and see what you think. In 2.5D workshop you can simulate it to see if it looks
right after the cut. In 4th axis module you can slowly simulate against the actual gear outline to see if it looks like its hitting the actual gear during the cut. I add such
methods of checking because I dont always trust what programs tells me and I believe in verification. NC code generation is like an arms treaty, you can trust, but should
always verify. Run the sim, or watch the sim and if it looks wonky, curse me and try a smaller diameter.


:)
Art
 

[David Morrow]

I'm a little late to this discussion but I'll tell you some practical results from my gear making...

As unscientific as this sounds, I'll bring up my gear DXF file in my CAD program and create a 1/8" circle and move that into the tightest spots of a part. If it fits, that's what I usually cut with. Why use anything larger and cut away more material than necessary; more stress on the machine, more chips to vacuum and sweep.

I have a Sherline CNC mill with extended X and Y axes. My first big project was a fairly large clock designed for wood but which I built out of brass and aluminum. I never did gt it to run but I did experiment a lot with end mills. So, for cutting metal, I always use 2 flute 1/8" diameter end mills. I could have used 1/16" end mills but they break too often when running at reasonable feed rates. I would cut at a depth of about .015" and a feed rate of about 10-12 Inches per minute IIRC.
This is that project :  http://ldrider.ca/cnc/garysclock/garysclock.htm

More recently, I decided that I liked making clocks and so I designed and built a CNC router large enough that I could make larger clock parts and make parts out of either wood or metal. I have been building Clayton Boyer's "Simplicity" clock, still in progress, using 1/4" and 1/2" Baltic Birch. I bought some 1/16" carbide end mills on eBay and use these whenever possible as there is virtually zero tearout of the plywood. Due to their short flute length, they are only practical on depths to .250". I run these at 15-20 inches per minute at a depth of .10" They cut beautifully.

The flute length of the 1/16 end mills is a bit too short for 1/2" plywood so for that I first used 1/8" Onsrud router bits. They worked great for a short time but then started to blacken due either to resin in the wood or, more likely, the plywood glue. Then I started getting a lot of tearout. They were awful in no time. So, I went back to the guy on eBay and bought a couple packs of 1/8" two flute, down cutting, carbide end mills ( $75 for 20 end mills ). They cut brilliantly through the 1/2" plywood. And, because they are 1/8" shank ( held in the collet with a 1/4" - 1/8" adapter - cost about $5 ) I can cut a little deeper than the 1/2" maximum flute length of the Onsrud router bits. I started running the 1/8" router bits at 30 inches per minute in an attempt to minimize the burning. So, I keep up that speed with the carbide end mills and run at a very shallow .050" depth. The feed is so fast that the time to cut gears is extremely quick. I'll probably bring that up to .100"

Here is a quick video cutting a very small pinion with the 1/8" end mill:
https://onedrive.live.com/?cid=DE1BA0F71D977DAB&group=0&id=DE1BA0F71D977DAB!96308&parId=DE1BA0F71D977DAB!85578&o=OneUp

The guy on eBay is Drillman1 and he has a great selection, great prices, and great service. I'll keep buying from him but I don't think my new carbide end mills will ever get used up.

[John T]

For really small pinions in my projects they are never more than 1/4 inch thick and for the smallest pinions i'll go down to 1/32" mill. As long as the cut depth per pass is small (0.003)  I don't have any significant problem but it also depends on the wood.  Teak is nice because there is oil in the wood and it helps lubricate things. 

[ArtF]

I do love the teak.. makes a strong gear too I find...

Art

[JustinO]

"Teak is nice because there is oil in the wood and it helps lubricate things."

Teak is also self sanding -- it takes the edge right off HSS.

[David Morrow]

For really small pinions in my projects they are never more than 1/4 inch thick and for the smallest pinions i'll go down to 1/32" mill. As long as the cut depth per pass is small (0.003)  I don't have any significant problem but it also depends on the wood.  Teak is nice because there is oil in the wood and it helps lubricate things. 

John, I'd love to see some pic's of your small gear projects.

David

[John T]

Hi David,

Probably the best example of "small gears" from my works is:

http://jtwoodenclocks.com/Learning_Agai ... hua_2.html

If you take the time to read through all the developmental steps in this clock you'll see that the final clock is quite different from the first trial.

In the end the clock works fit in a space of 5" by 7" by 2" 

John

[David Morrow]

Not sure if it's a passion or obsession but you're about as serious a clock maker as I've ever seen. I just love your work. I saw the Canadian penny and checked your profile and see you're from B.C. Same here; I live in Vancouver ( Kitsilano- Dunbar area ).

David

[ArtF]

THAT is some serious clockmaking.

Art