Minimum Helix Diameter

[jparamo4546]

What is the recommended minimum Helix Diameter for say, a 2D adaptive strategy? 

Hole diameter is 7mm and tool di is 6.35mm at a 0.025" diameter for helix motion which is close to nothing so might as well plunge into the piece. Is there a rule of thumb to determine a minimum EFFECTIVE helix diameter? knowing this value would help me determine the cutter diameter in cases not so obvious as above.

Cheers!

[seth.madore]

That's an awfully small difference between the tool and the hole size. I favor no more than a 75% difference between hole and tool size. With that, you can still have enough motion to allow for chip evacuation

More importantly than helix diameter is ramp angle. Most tools do not really allow for more than 3 degrees or so of ramping motion. SwiftCarb is an exception to that, for sure

[fdboswell · Accepted solution]

If you'd like to think of it as a "rule of thumb", the Fusion built in default for 2d adaptive helix diameter is "Math.max((tool_diameter - 2 * tool_cornerRadius) * 0.95; tool_diameter * 0.25)", which for a flat end mill is pretty well just the end mill diameter. So, figure an end mill of half the diameter of the hole. But, of course you can often get away with as little as half that, so an end mill of 75% of the diameter of the hole can work reasonably under favorable conditions (good chip removal -- flood or air through tool, conservative speeds & feeds). Probably good to think about predrill if the end mill is bigger than 50% of the hole size, and think even harder about predrill if greater than 75%.

Also, remember to subtract twice the radial "stock to leave" from the hole size when ball parking the helix diameter and minimum cutter size.

[jparamo4546]

Ramp angle? Yet another variable to consider. This is overwhelming for beginers lol

is there a formula or rule of thumbs for that?

[fdboswell]

Comments on ramp angle: 2 degrees is pretty conservative although not a guaranteed safe value. However, your cutter supplier will generally specify the max ramp diameter in the cutter specs, along with whether or not the cutter is capable of plunging (center cutting). It is pretty critical not to exceed the ramp angle spec, as the results can get notably ugly with larger inserted cutters.

[fdboswell]

Sorry, make that "supplier will generally specify the max ramp angle..."

c/diameter/angle