Applies to: Dental machines

Milling cobalt-chrome (CoCr)

How to mill non-precious metals? How to mill cobalt-chrome?

• Milling cobalt-chrome (CoCr)
• Introduction
• vhf machines suitable for milling CoCr
• Tools for machining CoCr
• Indications that can be machined
• Tool life
• Correct setting of bars
• Positioning bars in X- and Y-direction
• Positioning bars in Z-direction
• Correct positioning of objects

Introduction

Machining non-precious metals requires special attention to a few items if you want to achieve perfect results.

• The collet chuck of the spindle needs to be tightened firmly, otherwise the tool will be pressed into the collet chuck.
• The collet chuck of the spindle needs to be clean and without grease inside, otherwise rotational imperfections during machining will degrade the machining results and can cause tool breakages.
• The .stl-file must be free from design errors .

To be on the safe side, we strongly recommend to do the following:

• Activate the option in DentalCAM.
• Add at least 1 backup tool to the tool magazine in case of a tool breakage.

vhf machines suitable for milling CoCr

Machine	Wet /dry machining	Material	Supported holder
K4 / K4 edition	Dry machining	Blanks
K5 / K5+	Dry machining	Discs and prefabricated abutments	Abutment holder: MEDENTIKA PreFace ® DESS Pre-milled
N4 / N4+	Wet machining	Prefabricated abutments	Abutment holder: MEDENTIKA PreFace ® DESS Pre-milled DENRACLE Pre-milled ® MIT Pre-Mill ® nt-trading Preform ®
R5	Dry machining	Discs and prefabricated abutments	Abutment holder: MEDENTIKA PreFace ® nt-trading Preform ®
S1	Dry machining	Discs and prefabricated abutments	Abutment holder: MEDENTIKA PreFace ® DESS Pre-milled nt-trading Preform ®
S2 / S5	Dry machining	Discs and prefabricated abutments	Abutment holder: MEDENTIKA PreFace ® DESS Pre-milled nt-trading Preform ®

Tools for machining CoCr

Match code (4-axis except E4)	Match code (5-axis)	Cutting edge diameter	Tool geometry	Teeth	DentalCAM 7	DentalCAM 8
M060–R2-32	M060–R2–35	0.6 mm	Radius	2	Yes	Yes
M100–R2-32	M100–R2–35	1.00 mm	Radius	2	Yes	Yes
M120–T2–32	M120–T2–35	1.20 mm	Torus	2	Yes	Yes
M200–R4–32(-C)*	M200–R4–35(-C)*	2.00 mm	Radius	4	Yes	Yes

Indications that can be machined

The table shows all indications that can be machined from CoCr on vhf machines and the most suitable machines for these indications.

Indication	K4 / K4 ed.	K5 / K5+	N4 / N4+	R5	S1	S2 / S5
Coping and bridge framework	Yes	Yes	No	Yes	Yes	Yes
Fully anatomical crown/bridge	Yes	Yes	No	Yes	Yes	Yes
Abutment	No	Yes	Yes	Yes	Yes	Yes
Telescope crown	No	Yes	No	Yes	Yes	Yes
Implant bar	No	Yes	No	Yes	Yes	Yes
Secondary crown	No	Yes	No	Yes	Yes	Yes
Occlusal screw-retained bridge	No	Yes	No	Yes	Yes	Yes

Tool life

The maximum values for tool service life that you can actually achieve with your tools depend on many factors, such as the quality of the tools, the quality of the blanks, machine maintenance and cleaning, etc. Therefore, the maximum service life that DentalCNC specifies on delivery are standard values that must be adjusted until they correspond to the maximum values you can achieve.

The tool life depends on the bending strength of the processed material. Different bending strengths result in different tool life.

All tests were performed with a 4-flute cutter.

Material	Tool life
CoCr discs	> 8 hours
CoCr prefabricated abutments Dry machining	2 – 3 hours (approx. 4 – 6 blanks)

Correct setting of bars

Positioning bars in X- and Y-direction

Correct	Incorrect	Description
		Place bars evenly on all sides If you place bars on only one side, vibration during machining may occur. This can lead to the blank or tool getting damaged. Correct (left): Bars on all sides of the object Incorrect (right): Bars on only one side of the object
		Place bars with sufficient distance from each other If there isn't enough space between bars, the air nozzle of the spindle may not be able to blow off machining debris as required, which can damage the tool. Correct (left): Bars with suitable distances between them Incorrect (right): Bars without suitable distances between them
		Set enough bars You should at least set 3 bars for each object. Multi-unit-objects generally require 2 bars per unit. Otherwise, vibrations may occur during machining, which can lead to the blank or tool getting damaged. Correct (left): Enough bars have been set Incorrect (right): Too few bars have been set

Positioning bars in Z-direction

• Position all bars on the equator. If the equator is on the prepline, position the bar approx. 1 mm above the equator.

You need to position all bars completely on the object.

The bar in the figure below is positioned too high. Only a part of the bar is positioned on the object.

The bar in the figure below is positioned too low. Only a part of the bar is positioned on the object. Additionally, the bar is positioned on the prepline.

The bar in the figure below is correctly positioned on the equator.

Correct positioning of objects

The workspace of the objects must not overlap in CoCr blanks.