<Slider Name="slideMaxX"  Minimum="1" Maximum="50" Value="{Binding ElementName=txtMaxX, Path=Text, Mode=TwoWay, Converter={StaticResource RoundingConverter}}" SmallChange="1">

using System;
using System.Windows.Data;

namespace gol
{
    
    public class RoundingConverter : IValueConverter  
    { 
        public object Convert(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture) 
        { 
            if (value != null) 
            {
                double dblValue;
                dblValue =(double)value; //Fehler: Kann nicht konvertieren
                //dblValue = Convert.ToDouble(value);//Fehler:Convert ist Methode...Kontext n. gültig
                return (int)dblValue; 
            } 
            return 0; 
        } 
 
        public object ConvertBack(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture) 
        { 
            throw new NotImplementedException(); 
        } 
    } 
}