Calculating CSS values

[friolator]

I'm coming from a manual lathe so constant surface speed is new to me. My lathe is small (a Sherline 4000), and I am mostly machining Delrin on it, and working in metric. I've looked at a bunch of online calculators, but I'm not really clear on what to set here.

Manually, I would cut a 25.5mm diameter piece of delrin at 800RPM, 0.5mm DOC, at about 90mm/min feed rate. This gets good results. How do I translate this to the Feedrate (F/R) and Spindle Speed (CSS) numbers in intercon? can anyone point me to a good calculator where I can find this information? (most of the calculators I've found are in inches and the ones that let you choose metric still refer to inches so it gets confusing in a hurry)

[suntravel]

Camcut is a good APP for the mobile phone

https://www.camcut.fi/en/support-en-us/ ... obile-app/

The beauty of CSS and F/R ist you do not have to calculate, the CNC is doing it for you.

Just use the cutting and feedrates recommended for the tool/material

( on a small machine reduce them to the capability of your machine )

Uwe

[friolator]

thanks. I'll check it out. The tooling I have is generic from Amazon, no specs on the inserts. Once I'm through the last of these I'll get some that come with, well, some numbers I can go by!

So for now, I'm working backwards based on what I know works for RPM and feedrate on this machine. No matter what numbers I've put in though, it faults before it starts cutting. so obviously I'm not doing this right.

[Spartan117]

Manually, I would cut a 25.5mm diameter piece of delrin at 800RPM, 0.5mm DOC, at about 90mm/min feed rate. This gets good results. How do I translate this to the Feedrate (F/R) and Spindle Speed (CSS) numbers in intercon?

Your values give a CSS of 64m/s and a feed of 0.112mm/U (F/R)
Just to give a first starting point from your values

[suntravel]

ok, some guidelines vor sharp carbide inserts on very small lathes:

Delrine

100m/min 0.02-0.15mm/r Ap 1mm

Aluminium Brass

150m/min 0.02-0.10mm/r Ap 0.5mm

Steel

120m/min 0.02-0.10mm/r Ap 0.4mm

Stainless Steel

80m/min 0.04-0.1mm/r Ap 0.4mm

If the spindle stalls reduce Ap

For Ap <0.4mm use inserts with 0.2mm corner radius

Use sharp grounded Inserts highly positive for Delrine and Aluminium

Slightly positive for Brass and Steel like Kyocera CCGT 060202 FN-Z TN60

Formula:

V=D*Pi*n/1000 (62.8 m/min = 25mm*3.14*800min-1/1000)

Uwe

[friolator]

Your values give a CSS of 64m/s and a feed of 0.112mm/U (F/R)
Just to give a first starting point from your values

This confirms what I calculated as well. It faults before it starts cutting with these values or with even lower ones.

It's not the motor, because I'm monitoring the motor in Teknic's software and it's not even coming close to its limits, or triggering a fault. It's something else.

[friolator]

I think this is the same problem I was seeing in this thread: viewtopic.php?f=67&t=10263

Except I'm not getting the Spindle Slave Position Error every time (which was the case there as well, but it was coming up more frequently). Here It just fails but it's failing in exactly the same way at exactly the same position. The tool moves into place, the spindle comes up to speed, and then the Z axis moves slightly away from the part before failing.

[suntravel]

Belt slipping?

Max rpm on your lathe is 2500rpm, some encoders cannot count at this speed, whats the max rpm from your encoder manual?

Example:

100kHz/2500lines*60=2400rpm max.

Uwe

[friolator]

The encoder is a Koyo TRD-SHR2500V5D. Max RPM is 6000.

I don't think my spindle will ever go faster than 2500.

It's worth noting that I'm running this job right now, but with RPM and F/M instead of CSS and F/R. It's nearly done and is working fine. So this is something to do with CSS somehow. I'd just like to get CSS working so I can experiment with it!

[suntravel]

The encoder is a Koyo TRD-SHR2500V5D. Max RPM is 6000.

I don't think my spindle will ever go faster than 2500.

It's worth noting that I'm running this job right now, but with RPM and F/M instead of CSS and F/R. It's nearly done and is working fine. So this is something to do with CSS somehow. I'd just like to get CSS working so I can experiment with it!

6000rpm is the max mechanical speed.

Max. Electrical Speed** (max response frequency / resolution) x 60

In your case 200kHz/2500*60



Uwe