Seeking assistance to cut a slot for a shaft collar

[auto.pilot]

I made a shaft collar out of mild steel and need to cut a slot in it. This is part of a bending jig with the following dimensions: 1.5 inch OD, 5/15 ID and 3/4 inch thick. The slot needs to be 1/8 inch wide. I attempted to cut the slot on the mill using a 1/8 inch 4 flute end mill, but broke 2 of them. Spindle speed ~ 230, feed was very slow and depth of cut was only a couple thousands each pass. The first end mill broke after I got about 1/4 inch deep. The second one broke on the very next pass. I suspect that they were binding on the 'walls' of my cut. I'd like to try a slitting cutter, but have no idea what to buy. Would appreciate any thoughts.

Thanks

Jim

 

[Bob Korves]

If you have a band saw or access to one you could use it to rough out the slot, then file it to size. A hack saw also works for that. Your spindle speed was way too slow for a 1/8" cutter. Around 2800 rpm would have been better. Learn about surface feet per minute (SFPM), mild steel likes about 90 SFPM. Also learn about chip load...

 

[darkzero]

Yup, a slitting saw would be best, they cut slow but you can cut the entire depth of the slot in 1 pass. It would be possible to do it with an endmill though if that's all you have accessible. As Bob sated, your RPM is way too slow. I don't know what mill you have but assuming it's a manual mill, spin the endmill as fast as your spindle will go.

5/15" is a weird fraction to use. Assuming it's not a typo & by the OD you stated, you need to cut just over .58" depth. 2 flute end mills are better for slotting. What will happen when you get deeper, the chips will pack up in the flutes & in the slot. A 2 flute endmill will be better at evacuating chips but they are also not as strong as a 4 flute, so in that small of a diameter you'll have to be very careful.

It can be done though. I had to make a slit in a boring bar bushing that I made, I didn't have a slitting saw but I did have 1/16" carbide endmills. I spun it as fast as my mill could go & fed slow. As I got deeper, I took lighter cuts & made sure to clean the chips out as I was making the cut. No broken endmills & the cut came out clean.

 

[auto.pilot]

Thank you for the helpful of replies. If I ramp up the spindle speed I guess I still don't understand how deep the cut should be. Do I attempt to make this all in one pass? The ID is 5/16

 

[Technical Ted]

Everybody had different rules of thumb based on their personal experiences and the equipment/materials they work with. My rule of thumb for depth of end mill work is not to go with a deeper depth of cut than the diameter of the end mill in mild carbon steel. This works for me but YMMV. As others have said, crank that RPM up and also use some cutting oil or coolant to help the chips clean out as your cutting. This is especially useful when you get in there deep and the chips don't have as much room to clear out.

Good luck,
Ted

 

[auto.pilot]

Success! Thank you