Romi Lathes

At the point on the cutting edge that is generally most susceptible to failure due to cutting speed (the corner or OD) - just like a turning insert (the tip of the insert).

Using the SS example provided he notching effects (if any) are not at the tip of the insert and the SFM at the OD is ~4 times that of the SFM at the tip.

Just as on a drill, some areas are moving much faster than others ..... in this turning example the tip of the insert is the SLOW bit, not the fast bit.

I think that I see a small problem ......

My point being, (and we don't do a lot of heavy roughing) I have never experienced notching or any kind of failure further up the cutting edge from the tip. Got boxes of worn inserts, and all of them have the tip worn off. We don't push our machines excessively though.

Understood.

Do whatcha gotta do. Industry standards are always a good place to start from. Running machines helps too.

So does understanding geometry .

You sound a bit like you are of the Bill Roberto school, at times .

Cliff wrote in news:fc9v21huffpelhjmf131kuqk2hard5cv3d@

So does understanding that a modern CNC lathe control can handle much of the math you're worried about.

Dan

Works better if you know what's going on. AFAIK almost all of the old CNCs could as well -- how long have you been doing this? Newbie?

I can remember when a hyperbolic pot and a clutch were connected to the end of the X axis lead screw to attempt CSS, sorta worked untill a better way came along.

Regards

Daveb

How was that supposed to have worked, if it did, whatever it was? I recall an old Bullard & an old G&L with manual change gears (for any taper cutting, IF you could get a pair that would work for the angle) with a GE 500 or GE 550 controls (one of each?) being used on them ....

Erm...... since it was pre 1970's as I remember you programmed an rpm required for the spindle centerline and that anlog voltage was applied to wiper of the pot and as the clutch was engaged and the slide moved in and out from center the rpm changed. I was in service when the control builder I worked for was using air type tape readers and tubes, ( Vickers Sperry Rand later named UMAC) so I have been around awhile. I dont miss the good ole days.

Regards

Daveb

I wonder where Hamei is? He'd LIKE this thread I suspect.

Cliff wrote in news:1k8131p75ut9u4lsuup8qcmj5v2kdb2ks2@

He's prolly busy teaching rocks to float. Last I heard he almost had 'em using dial calipers.

Dan

Dan:

Thanks to you and Bryce for pointing out to me the standard way that RPM is figured when calculating turned diameters.

Then perhaps the max SFPM envelope isn't being pushed as hard as it might be. Notching is always a problem lurking in the shadows when using inserted milling cutters in steel, but then I'm from the school of "push it till something fails - then back off a tad." IMO, if you don't fry a tool occasionally, you're not really testing the limits and efficiency of your process.

-- BottleBob

Bottl, perhaps that's standard on Jap-crap and pseudo-Jap crap like the Haas control but it is NOT a 'standard' on real controls.

Constant surface speed requires two things - a spindle speed constraint in the G92 block. That's to save yer ass from having a machine with a 15" chuck try to turn 60,000 rpm when facing :)

G96 has an S word. The S word defines the spindle speed in surface units per minute.

Then there's an R word. The R word defines the offset which you want to use for the calculations. The R word can be ANYTHING. You can choose the edge of the tool tangent to the part, you can choose the center of the tool, you can choose the point tangent to a surface parallel to the chuck face, you can choose a point in Montana if you like. The decision is left UP TO THE PROGRAMMER on a real control.

I used to choose a different r word depending on what I was doing. Since I never used CSS for heavy roughing there was no need to consider that the speed at the edge of the cut would be different than the speed at the tool tip - but if you were addicted to that crappy practice, you could. I did vary the R according to whether the use was facing or profiling - probably didn't make a lick of difference but it made me feel happier. On an 8" part with an .0312 radius tool tip what are we talking about - the difference between 830 rpm and 831 rpm ? Dan and moT and the other tiny-parts guys probably have to be more concerned about the exact surface speed they are using and where on the tool it is located but for normal parts it's not very relevant. If your process is so tight that .016" difference on a surface speed calculation is gonna wipe out your tooling, you're gonna have a lot more problems than newsgroup debate real quick !

Hamei:

Nice patented "Hamei Rant", but just what do machine specific programming procedures have to do with the way MMR formulas are calculated for turning?

-- BottleBob