How to reduce speed of Kress Router

[Fab6657]

Hello,

i have finish to build my first CNC with successful usage of Mach 3 (Nice Product)

So i use a Kress 800FME Router with rotation speed from 10000 to 30000tr/mn.

Do you know a system to reduce this speed to less, so that i can drill hole in the
table ?

Or i search also a shema for an command circuit for On-Off Spindle and for adjust
rotation speed.

Thank you if you can help me,

Fabrice

[Tweakie.CNC]

Hi

I have thought long and hard about your question and I have concluded that you should not try to reduce the speed of your Kress further than it's present minimum speed and here is why I think so.

AC motors which have brushes can be speed controlled by using a variable duty cycle of the applied voltage. The motor is slowed by applying full voltage for less than 100% of the time with the actual switching taking place at the zero crossing point of the AC waveform to reduce RFI (much the same as the system a microwave oven uses to reduce power output). Various speed control products are available to do this for electric drills etc. and they would work with the Kress.

This system works fine for relatively small variations in speed but there is a down side for large variations. Assuming the cutter consumes the same power at a particular feed rate then a reduction in the RPM will cause the motor to draw an increase in current to provide this same power. This occurs at a time when the airflow through the motor has already been reduced by the reduction in RPM. The result could be overheating of the windings and permanent damage to the Kress.

(Most of my stuff is made in low melting point plastics and I have chosen to use a 3 phase brush less motor running at 3000 RPM.)

Tweakie.