Maintaining your Cerec Milling Unit

(Another Doc Hemp Web Site)

As per Doc Mike Birkhoff

(Developer of the now famous Cerec Birkhoff Effect
which has been incorporated into the new 3D software!)

5-21-13 ... A rare update, all is still well in Cerec Land ... In our 11th year now ..... still only about 3-4 fractures total so far ... Now as to a follow up on a problem ... A couple of weeks ago I went to turn on my Cerec machine and it was totally dead ... no power at all .... the patient and I were laying on the floor together looking for loose wires, fuses, etc. I did find the 2 Ceramic T 6.3A 250V Slo Blow 5x20mm at the lower rear ... These turned out to be okay .. I called The German Hot Line .. Mikey ... I was told there was another fuse on the very bottom of the unit AND An Air Filter down there too to clean along with the rear area that I cleaned periodically ... The fuse on the bottom is a T 1.25A 250V Slo Blow 5x20mm ... This it turned out was the one that blew out .. Maybe because of the dirty air filter? ... These are kinda hard fuses to find ... so I suggest you get and keep some of them on hand and PLEASE CLEAN THE AIR FILTER ON THE VERY BOTTOM TOO! 3/24/08 Doc Hemp UPDATE!! This morning I had 4 cerecs to do on a patient that flew in from Arizona ... Got all ready to mill the 1st one and got a "Milling Unit Not Ready" warning ... tried everything .... rebooted both main computer and milling unit ... It was working perfectly last Thursday and all I did was change the water. Then Called Mikey in Germany .... He suggested everything I already did first and then had me re - upload the software to the milling unit ... that was it ... He diagnosed that the battery in the milling unit motherboard was going bad ... lost it's memory over the weekend ..... Damn he's GOOD! ... here are his follow up instructions and photos ....


Also attached please find two pix of the little battery on the milling unit's care-control motherboard. This battery may lose it's capacity over the years, so over a long weekend the milling unit may "forget" the software, which results in the "milling unit not ready" error warning - thus requiring a new software download.

It' s a CR 2032 Li-Mn 3 Volt battery... (It comes in many brands, i.e. .. Sony, Varta, Maxwell, etc. and is in stock in all USA battery stores for around $3) .... maybe we should put this on our "how to maintain your milling unit" website?

Hope the big quadrant case worked out well! Hey, it was good talking to you!

I CC this to David Lawler, since he also has one of the early Cerec 3s.



A Doc Hemp Note
To open the motherboard compartment loosen the one screw at the top center
And Pull the outer edges of the 2 black plastic tabs toward you to slide the mother out. After you remove the CR 2032 Li-Mn 3 Volt battery and replace with the new one in the mother board you will have to download the software again from the aquisition unit.

- Start aquisition unit, but don't start Cerec program yet - milling unit must be turned off.
- Open the front flap on milling unit and press the little blue? button on the metal plate on the lower right side
- While holding the button, switch on mill. Keep holding button for 30 sec.
- Now start Cerec software on aquisition unit
- In the lower right taskbar it should now read "downloading software to milling unit"
- Wait until message disappears - can take a few minutes
- DONE! Please put procedure on Cerec maintenance website so we remember it in 5 years! ;-)) .... Mikey

10/09/07 UPDATE! .... More photos at the bottom of the page ... Doc Mike doing my milling machine service (and 3 wonderful Cerecs on me - Zero sensitivity!) The maintenance is very easy to do especially if you can actually see someone do it once.


please put this on your web site instead of my former "no service ever needed" statement! In fact, this grease job is the only thing that needs to be done on those older mills! And the service techs usually never do this!

Dr.Horst Michael Birkhoff

A few days ago a friend of mine who also has an older Cerec 3 told me that after milling his machine "lost a drop of oil".

Funny enough, my own machine also started to drop oil (well, so does my Harley and I don't care! ;-))

Both our machines have several thousands of millings on their belts. I checked with the hotline, secret agents and deep throats and here's what I found out:

1. it's not oil. It's water mixed with rust.

2. The problem was partly solved 2 or 3 years ago when Sirona changed the tank lid to a tupperware-style design. Now the tank does not leak any more.

3. The motor and block shafts run thru a thin white teflon bushing which again is encapsuled in a metal/plastic housing. These pieces cost about $ 2.- or $ 3.-.
They are the same like in Cerec 2. But with Cerec 2 the block shaft was vertical so when the teflon bushing got bad water would run into the electronics and destroy them. So, part of the yearly service for Cerec2 was to exchange that bushing.

Now comes the funny part: With the motor and block shafts now all mounted horizontally in Cerec 3, Sirona engineers relied on that these bushings would NEVER have to be replaced (because no water would get into a horizontally mounted shaft bushing). They designed them to be non-replacable! BIG mistake. They do deteriorate and leak over time. What Sirona will do then is sell you a completely new milling unit insert... costs several thousands of bucks plus labour.

While a new milling unit insert MAY make sense after the warning at 30000 minutes of milling appears (because of worn-out parts that affect milling precision and fit), it is no a joy to have this kind of expensive fun on relatively young machines. So here is what you (or your technician) should do - in both scenarios - if a) machine leaks or b) to prevent leaking:

Open machine at least once a year. Put a little new grease*** on the shafts. This little bit of grease is only used to thin the old hardened black grease and then rub it all off. Now put some new grease on the shafts, especially in the area between the big toothed wheel and the milling chamber bushing (see red arrows on pic # 978).

Actually this IS part of the yearly service plan, but it's often neglected. In fact, it's the ONLY thing that is REALLY important in the service plan! (all the other small things like rubber stops, new tank etc. is just b.......!)

On heavily used machines, this should be performed more frequently. It's the old hard grease that makes the bushings leak. New grease will seal them for a certain time.

On pic # 985 you can see what happens if you or the tech don't properly spread the grease over the shafts: water will leak from the milling chamber down to the motherboard housing. Will give you trouble sooner or later!

*** The grease you need is:

Chesterton's 622 White Grease. This is a pure mineral oil grease with Teflon* added designed for applications where a clean, nonstaining, food grade lubricant is required.

It is a superior, multipurpose product that conforms with FDA regulations 178.3570 and 177.1550 for food machinery use. It is certified by NSF as an H1 lubricant and can be used in federally inspected meat and poultry plants. It is a long lasting, non-hardening lubricant that withstands washout from water, steam, food or fruit juices.

Chesterton 622 White Grease is virtually tasteless and odorless. When used on food processing equipment, users can be assured that the lubricant will not contaminate finished products.

NSF Certified
Food Grade, H1 Lubricant
Excellent Water Resistance
Teflon* Fortified
Kosher Certified
*Teflon is a registered DuPont trademark.


Picture # 978

Picture # 985

all you need is some torx bits and a screwdriver that holds them. For those of you who want to do it themselves, please make sure

1. to switch off the unit before opening it, pull the plug! Be careful not to damage the thin door magnet switch cable that is attached to the front plastic flap (when taking it off)

2. be extremely careful not to let dirt or dust or grease get on the back of the timing (=big toothed) wheels where they meet the light barriers! (and of course the light barriers themselves)

See attached pic: The little black square is the upper part of the light barrier, and the back of the wheel runs thru it!

3. Of course this will void your warranty... so if your machine still has warranty call your service tech and ask him to bring the white poultry grease for service! ;-))


Hempster .....
This last photo shows the position of the light barrier... to make sure that people do not place grease or other dirt there! Otherwise the shaft would not find it's "zero" position any more!


More photos added here below

Flushing Your Milling Unit with Water
(another important maintenance item)

(1) Periodically when the tank is emptied to be re-filled with water and Dentatec solution first fill with plain water.

(2) Then go to start->all programs -> Cerec -> service -> maintenance only -> start water pump. Now let run until it stops (about 3 minutes).

(3) Empty tank again and then re-fill with water and Dentatec.

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