Tapping on a lathe - unexpected feedrate

[gina68ABR]

I am getting unexpected feedrate trying to use a thread tap on the lathe.

I've attached some screenshots: 

• The first shows the tapping tool, set to inches, with a thread pitch of .05.
• The second shows my post configuration with the post processor being 'HAAS ST-30' and with the units set to inches.
• The final shows the post output, which shows the post version is 43833 and the tapping cycle on line 23, with a feedrate of 0.002.

What am I missing?  Shouldn't the feedrate on line 23 be .05?

[leo.castellon]

The way I always verify that my feed rate is correct on the Haas Sl20 that we use, is to divide 1 by the posted feed rate and multiply that by the spindle RPM, that should give you the thread pitch. See attached for reference, this is for an 18 pitch thread.

LeoC

[gina68ABR]

What post processor are you using to generate the nc program you attached?  I don't see the G99 that tells the lathe to interpret feedrates as feed per revolution.  The HAAS ST-30 post processor I found does output the G99.

- Gina

[gina68ABR]

OK. I have tracked this down to using an expression to specify the thread pitch in the tool library.  If I specify the thread pitch as 1/20, fusion appears to do the right thing and shows it to me as .05, but the post processor outputs F0.002.  Then if I go back to the tool and set the thread pitch as .05 (i.e. not asking fusion to do the division for me), the post processor does the right thing and outputs F0.05.

This seems like a bug to me and I'm seeing similar behavior elsewhere.  For instance I specified a drill with a cutter diameter of 25/64 and in the tool library it tells me the diameter is .39063 but when I try to use the tool to drill, the toolpath thinks the drill diameter is ~.015.

[leo.castellon]

By your statement, 

 "For instance I specified a drill with a cutter diameter of 25/64 and in the tool library it tells me the diameter is .39063 but when I try to use the tool to drill, the toolpath thinks the drill diameter is ~.015." That tells me something is in metric units. If you divide .39063 by 25.4, you get .015.

LeoC

[obrienm · Accepted solution]

Hi @gina68ABR ,

We believe this is kind of miscalculation is related to the 'Tool Library - User Expressions' preview feature. If it's disruptive then we recommend turning the option off for now.

See this related post: https://forums.autodesk.com/t5/fusion-360-manufacture/created-a-chamfer-mill-o7-16-quot-tool-is-only...

[gina68ABR]

Thanks Mark!

I had already forgotten it was a preview feature.  I've turned it off and I hope it will be fixed and I can turn it back on again sometime...I find it very useful.

- Gina