Another tapping problem. (burrs)

[bakerbj]

I've got a 55 mm circular part, notched on the OD in 4 places, with a 40.6 mm hole threw the middle. The hole requires a M42 x 1.5 D9 thread. The tap I tested is 6 flute (straight), TiN coated.

I may be running about 100 RPMs fast as the machine only has two speeds.

I keep getting a rather large burr (0.5mm-0.8mm or so) on the bottom of the part when the tap comes threw. The part has a 0.8 mm chamfer on each side before tapping.

Any suggestions are appreciated. Thanks.

 

[CoryPad]

What is the thickness?

 

[bakerbj]

Sorry 4.5 mm.

 

[CoryPad]

Are you doing this on a lathe? Milling machine/drill press?

What is rotating at 100 rpm?

Regards,

Cory

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[bakerbj]

Basically the machine works like a drill press. (its a custom machine) The part sits in a fixture on a 4 station rotating table. Load, chamfer, tap, unload. The Chamfer on the one side is stamped in the press. The OD is has four 4.5mm radius slots for a spanner wrench, also keeps the part from rotating during tapping. The tap manufacturer recommended a tap speed of approx 165 rpm. The lowest we can currently run is approx. 265/270.

 

[CoryPad]

What is the workpiece material?

Are you sure the burr isn't there after drilling/chamfering?

Regards,

Cory

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[bakerbj]

The material spec calls for 1008-1010 hot rolled, descaled and oiled.

Actually, I havent checked for a burr after chamfer. I'll look into it next time I run a trial. (prob Monday) We currently run 3 other similar parts on this machine with diameters from 32-36mm though.

The center hole is stamped out, so there is a little burr on one side. That burr side is the one that gets chamfered though.

Thanks

 

[btrueblood]

Can you find a spiral-flute tap in the size required?

 

[bakerbj]

That is one option I have been looking into. I have a straight flute tap that I haven't tried yet. If it doesn't work I will try the spiral flute.

What are the advantages to spiral flute? Chip removal?

 

[btrueblood]

Due to helix angle, the cutting edge is advancing at an angle to the workpiece, and this helps to reduce burrs. Also, you can usually run a spiral flute tap at higher speed than straight flutes.