End mills break when making a dog clutch

Forgot to say, I always limit the depth of cut to 1/3 of the end mill diameter.

if it breaks after 1/2 hour, that means either that you are doing something different 1/2 hour into the program, or that it is getting a little dull - maybe less depth of cut would help it

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Sounds like too narrow an end mill for the depth of cut, Iggy.

Advise use a 5 mm endmill.

--Winston

Ignoramus17758 fired this volley in news:rcKdnWDeYd58avzQnZ2dnUVZ snipped-for-privacy@giganews.com:

Ig, you can probably hear what the problem is.

When the bit's tip starts to deflect and "orbit" about center, rather than cutting true, you'll hear those little bits start to "sing" as they make a cut. When you hear that "zzzziiiiiiinnnnnnnnnggg" sound, they're chattering at enough amplitude to rapidly fatigue the metal.

I know you want to get familiar with small detail work... well... small detail work involves hogging out all the excess stock you can with drills and larger bits, then using lighter cuts for the finishing.

Tiny bits were never intended to remove large volumes of stock.

LLoyd

Ignoramus17758 wrote in rec.crafts.metalworking on Sun, 20 Feb 2011 23:28:01 -0600:

So your chip load (per rev) is 1"/2000rpm = .0005"per rev. /4(flutes)=0.000125.

I think that is too small of a chip load. Increase your feed, or decrease your RPM. I would aim for .002 per tooth.

.002load * 4flutes = .008/rev. * 2000rpm = 16ipm

I would also slow down(feed) on inside corners, where extra load is encountered.

BTW, I once saw what you are making in a catalog some ware. It was to use in a 1/2" drill to crank the knee up and down.

Seems pretty high for a puny 1/8" end mill.

I now also suspect that the unknown steel bar was not 1018.

First thing that strikes me is that the feed rate is extremely low. It sounds like you're dulling the tool with a way too conservative DOC.

Carbide or HSS end mill?

What depth of cut are you using? What is your chip load per tooth? What is your cutter SFM?

You should never use an end mill smaller than you need, and from memory, the knee crank "crown" could be milled with at least a 1/4" end mill which will be stronger, have a higher SFM at your spindle speed and have more chip clearance.

Remember, too low a chip load = rubbing and dulling = eventual breakage.

Chip load, not DOC. Agree, the tool is rubbing more than cutting and as a result is rapidly dulling, deflecting more and more as it dulls and eventually snaps.

BTW Iggy, that "dog clutch" will introduce tremendous backlash if you are thinking of running your servo drive through it. For a servo connection you need to use a "hard" connection. Note that in a manual mill, the feedback from the dial or from a scale is after the handle clutch and thus the handle clutch backlash is not a factor.

"Pete C." fired this volley in news:4d62907a$0$1855 $ snipped-for-privacy@unlimited.usenetmonster.com:

So long as you mean "tight", not "hard" I agree.

A lot of stepper-drive machines use a Lovejoy coupling between motor and ball screw, with a very tight (even very tightly compressed) spider.

LLoyd

By "hard" I mean any connection that does not introduce appreciable backlash. This could be a low-backlash version of the Lovejoy type connector, a helicle coupler, flex plate coupler or a rigid coupling as used in most commercial CNC machines where the motor has a precision mount.

If I make it precisely, there will not be much backlash.

So something like this would be better?

-- The more passions and desires one has, the more ways one has of being happy. -- Charlotte-Catherine

You already have inherent backlash in the right angle gear drive from the hand crank shaft to the Acme screw, as well as backlash in the screw itself, though the screw backlash should not be an issue if the table isn't over counterbalanced. You don't want to introduce any more backlash if you can avoid it.

I agree with you.

My first suggestion would be to use a 2-flute. The 4-flute is getting dull and then loading up and breaking.

Can you rough it out with a larger diameter 2-flute?

Dave