I think it is normal, can you make sure --what do you mean "meter"

is there a analog meter or you see the spindle actual speed dispaly "796" on the HMI

AutoGen_7406247

Hi i don't know if it is a problem...i explain it....on my vertical centre with 808d advanced when i write S800 m3 and run the spindle, the meter on display has a wobble between 790-794-798,is not stable on 800 rpm ..is it normal this?on m4 mode go on 802-804

Hello.

It is in general normal that machines with direct encoder has a deviation like this, yor're controller should compensate the Z axis moving according the feedback and it should not cause and issue.

The machines you have seen online might have been configured only with the motor, or in some cases with analog spindle with no encoder feedback to the controller.

In these cases the feedback speed shown on the HMI almost never change. 

Best Regards

Riddersholm

 Can you check you machine specification book, find out spindle motor, to see it is Siemens spindle motor? I see you have ECO line, low cost. but if you use Siemens motor direct use motor encoder for spindle speed, as i know it will display less than 0.5% dev from setting speed (1000RMP--998 to 1003 ) you can find from NC Machine data 30240 , take picture of spinld page, I will know how many encoder are there, check if MD30240[1]=0 or 1

AutoGen_7406247

no,i look it on the hmi display...i see machine on youtube,are perfect,if they use s500 the hmi display show 500rpm fixed...i hope this  don't give me problem when i make a rigid tapping..my hmi display jumps between 790-796-798,is not stable,much time also 788..or is encoder very cheaper?

 You only have 1 encoder, maybe as you said from the spindle after transfer by belt --even that may be the timing belt the speed jumping cannot avoid 

AutoGen_7406247

Hi i check the parameter MD30240[1] ..it is =0