Non standard feedrate while threading

[CommanderKeen]

I'm newish to machining, but I'm learning.

Here's the question: I'm tapping a bunch of 5/8-11 holes and having issues breaking tap teeth. Material is 1045 steel, using a 4 flute tap, lead drill is 35/64 with an 11/16 counter bore. They are blind holes. I blow the chips out thoroughly before tapping. And we hand apply cutting fluid before each hole, cleaning chips off the tap each time as well.
(We have the same issue with other sized holes as well)

Here's the question part: So on the first op,
G99 S100 F.0909 while threading

Second op (other side mirrored holes)
G98 S110 F10 while threading

Both run G84 for the cycle.

The second op cut way better than the first. Id like to know why? Of course I'm running an established program someone wrote a while ago.

Thank you for the help,
Keen

 

[CITIZEN F16]

I would use a spiral flute tap, to eject the chips. 4 fluters require a lot of cutting force.

 

[sinha]

The second command ix exact.
The first one is approximate because 1/11 = 0.09090909
Try F = 0.090909
Feed can be specified up to four decimal digits in mm mode and six decimal digits in inch mode, in G99 mode.

 

[706jim]

The second command ix exact.
The first one is approximate because 1/11 = 0.09090909
Try F = 0.090909
Feed can be specified up to four decimal digits in mm mode and six decimal digits in inch mode, in G99 mode.

Or just run 110 rpm. Feed rate is now 10.00000000000000000in/min