Breaking end mills 80% lower

[ryanr24]

Hello I keep breaking end mills on my modulus arms jig I feel like in following directions, first one broke in half at the bit, the other broke at the very tips have 1 of 4 left.

[edgerly779]

Are you using router or mill?

[glockman19]

What type of end mill? What is your drill speed and feed speed?

[Eddbot]

Are you using the Modulus Arms bit? I broke that one pretty quickly, got another from McMaster Carr, broke that too. Got ANOTHER from M/C designed for cutting aluminum, has 3 flutes instead of 4. Haven't had a problem since.

http://www.mcmaster.com/#8829a72

Length of cut is 1/4" longer than the Modulus Arms bit though so I have to be careful near the edges of the jig for the first few passes.

Also, I was following the instructions as far as pass depth goes, decided it was too much depth per pass for the speed of my router. Now I go like 1/16" or less at a time. Takes forever but it works, the final product looks good and I don't break bits anymore.

[sonofeugene]

Using routers or drills for milling is just plain nuts. For many reasons.

[baih777]

are you using cutting oil ?

[ryanr24]

What type of end mill? What is your drill speed and feed speed?

using a router, set at 3500, as per modulus instructions, and Ridgid R24012 as per modulus as well

[ryanr24]

are you using cutting oil ?

Yes i am

[liber]

using a router, set at 3500, as per modulus instructions, and Ridgid R24012 as per modulus as well

I've never used a router for a lower, but Holy Moly Batman, 3500 rpm on a HSS cutter ?

[glockman19]

using a router, set at 3500, as per modulus instructions, and Ridgid R24012 as per modulus as well

You should go here for feed and speed calculations...

http://www.endmill.com/pages/training/spdfeed.html

and here:

http://www.harveytool.com/cms/GeneralMachiningGuidelines_17.aspx

Check the metal you are cutting, Don's by a cheap foreign tool bit.

Call Mike at drillbitwarehouse.com He'll make sure you are buying the correct tool for your application and running it at the proper speeds for the metal you are cutting.

I think you are turning way to slow.

[liber]

Glockman,

I think the OP is doing as recommended by Modulus. Just seems crazy to spin HSS at 3500 RPM.

[762x39]

I've never used a router for a lower, but Holy Moly Batman, 3500 rpm on a HSS cutter ?

Glockman,

I think the OP is doing as recommended by Modulus. Just seems crazy to spin HSS at 3500 RPM.

Modulus end mills are carbide, not HSS

[762x39]

using a router, set at 3500, as per modulus instructions, and Ridgid R24012 as per modulus as well

HSS

RPM = (SFPM * 12) / (PI * Cutter_Diameter)
RPM = (~400 * 12) / (~3.1415926536 * .250")
RPM = (4800) / (.7853981634)
RPM = ~6112

FR = FPT * #Teeth x RPM
FR = .002 * 3 * ~6112
FR = .006 * ~6112
FR = ~36.7 IPM

Carbide

RPM = (SFPM * 12) / (PI * Cutter_Diameter)
RPM = (~800 * 12) / (~3.1415926536 * .250")
RPM = (9600) / (.7853981634)
RPM = ~12,223

FR = FPT * #Teeth x RPM
FR = .002 * 3 * ~12,223
FR = .006* ~12,223
FR = ~73.3 IPM


3500 RPM is not so far-fetched... a little slow really.

Modulus recommends starting about midway on the speed setting. Since most trim routers run in the 25,000 rpm range, halfway should put you around 12,500 rpm

[liber]

Modulus end mills are carbide, not HSS

Wow, how much do they charge for them? The OP broke 2 of them...

I'm sticking with my mill...you guy's can have the router and do the dance...

[scarydog]

I Used this bit from amazon KCT136475. $25 with free ship on prime.
I broke one because it came loose in the chuck. Make sure it's right and recheck it every time you adjust your cut depth. I also recommend not going more than 1/8 inch adjustment at a time.
When you cut through the wall of one hole to the next, make sure you "egg" the hole open so the bit doesn't catch on both sides. This will help stop the "chattering grab" that will cause the bit to make you tip your router and subsequently break the bit.
Focus on cutting against the rotation of the bit.
Hope this helps.