Renishaw OMP400 repair

[Milling man]

Hello colleagues.
On ebay we can find a large number of OMP400 probes at amazingly low prices - about $550 shipped from China. Of course, these are used probes.
We bought the first one about 3 years ago and it worked for 2-2.5 years. After that, he first began to show the "contact" state, when nothing acted on the probe, and then the LEDs began to glow blue - "I'm broken, send me to the manufacturer." We recently bought two more of these devices. One of them was immediately junk and showed a false positive, the second worked for about six months and also began to flash red when it should not.
It should be noted that the hMP x00 series is not a device with a classical circuit based on 6 balls and 3 cylinders. The stylus is based in them according to a similar scheme (3 balls and 3 prisms), but the signal does not come from the contact of cylinders and balls, but from strain gauges placed next to the balls.
When I began to think about how to fix this thing, I was faced with the fact that I could not even find photos of its insides on the Web! I think my experience will be useful to many who want to save money by buying a probe for 1/10 of the price of a new one.
And so, problem number 1 - how to disassemble this thing? There is a flat screw in the battery compartment. You need to unscrew it CW, if you look from the side where the probe is attached to the spindle. The screw is screwed into the body of the probe and the two halves of the probe are in your hands. To unscrew this damned screw, I made a flathead screwdriver on the end of a hex wrench using an angle grinder. I had to make two such "screwdrivers", each turns the screw in a certain sector.
After unscrewing this screw, further disassembly is not difficult. Here is what the strain gauge looks like:



Black "drops" cover the silicon strain gauges. I destroyed one such "drop", it hid two strain gauges.
This node was in the very probe that broke down completely and burned blue - so I didn’t stand on ceremony with it very much. I forgot to measure the resistance of two of the destroyed strain gauges, but the other two show infinite resistance. Measurements on working at least somehow instances show 4.6-4.8 kOhm. From this part to the board there is a loop of 8 conductors - 2 from each strain gauge. As you can see in the photo, the strain gauges themselves are silicon strips glued to a steel base. Thin conductors went from them to the contact pads.
What I have already found out: the electronic unit from one probe works with the strain gauge unit from another probe. At least it doesn't flash blue immediately after being turned on.
Now I want to solder the wires to the contacts of the block that I have already partially destroyed and replace the strain gauges with variable resistors. After that, I will try to get this Frankenstein to "work" with the electronic unit. If this succeeds, then I can replace the strain gauges with new ones, and solder a 100-200Ω variable resistor in series with each of them to match the resistance of the entire system.
I think this thing has some kind of service mode to calibrate the resistance of the measuring bridge at rest. There is a free connector on the board, apparently Renishaw can tune the probe through it.

 

[Vancbiker]

Last I knew, Renishaw had a reasonable repair exchange service. Hard to imagine that the time you’re spending is less costly than just sending it in for exchange.

One time I sent in an MP11 that had gotten crushed in a Z axis crash. They replaced it at the repair exchange price without a question. I was fully expecting them to decline that unit for exchange credit.

 

[Milling man]

Hard to imagine that the time you’re spending is less costly than just sending it in for exchange.

Oh, if only it were so.... We bought a probe for $550 on ebay for a reason Even such a waste is already significant for us.
But I, of course, will not spend a lot of time on this - I will dig for a couple of weeks for several hours a day. If successful, I will have a source of almost inexhaustible probes from China))))))

 

[Vancbiker]

Unless Renishaw have changed policy, you did not have to buy the probe new from them to utilize the repair exchange program. At least in the US that was the case. I too bought several probes and interface units from ebay to retrofit to machines that were not purchased new with probes. The heavily damaged probe I mentioned in my earlier post was an ebay purchase.

 

[escapethewrmhole]

Oh, if only it were so.... We bought a probe for $550 on ebay for a reason Even such a waste is already significant for us.
But I, of course, will not spend a lot of time on this - I will dig for a couple of weeks for several hours a day. If successful, I will have a source of almost inexhaustible probes from China))))))

Renishaw will replace any probe for about $1000 US depending on model with a new or refurbished one and you don't need to be the original purchaser. Not even worth trying to find broken ones to "repair" them

 

[Milling man]

Experiments continue:

I have already found out that the electronics of this thing is not at all critical to the nominal resistance of strain gauges.

 

[Milling man]

Renishaw will replace any probe for about $1000 US

When I changed a sensor I bought from them, they charged me about 50% of the cost of the new sensor. For OMP400 it will be about $2.500

 

[PROBE]

When I changed a sensor I bought from them, they charged me about 50% of the cost of the new sensor. For OMP400 it will be about $2.500

Why do you mess with OMP400 ? OMP40 will do exactly same job (sorry, its repeatability is 1 micron only comparing to 0.5). Even better, if sizewize acceptable, use OMP60. Much more sturdy, more switch on options, adjustable trigger force, and tons can be found on eBay.

 

[PROBE]

When I changed a sensor I bought from them, they charged me about 50% of the cost of the new sensor. For OMP400 it will be about $2.500

Why do you mess with OMP400 ? OMP40 will do exactly same job (sorry, its repeatability is 1 micron only comparing to 0.5). Even better, if sizewize acceptable, use OMP60. Much more sturdy, more switch on options, adjustable trigger force and tons can be found on eBay. And of course new unit price is just half.

 

[Milling man]

Why do you mess with OMP400 ?

Initially, I bought OMP400 because it was cheaper than all other types
Now I bought an OMP40 for replacement (new, in a box) - and I am unpleasantly surprised by its repeatability and uneven actuation force. Or rather, of course, I'm not surprised - in another workshop we have OMP60, and it shows approximately the same results. In reality, the repeatability of OMP40 was about 3-5 µm.
Therefore, I want to continue repairing the OMP400. Moreover, it has already become clear that repairs are possible, and will not be very difficult. Most likely, the problems occur in the very thin wires that connect the load cells to the contact pads. Now I'm looking for someone who professionally repairs strain gauges, and I will give them this thing to replace these thin wires, or entire strain gauges.

 

[Areo Defense]

Initially, I bought OMP400 because it was cheaper than all other types
Now I bought an OMP40 for replacement (new, in a box) - and I am unpleasantly surprised by its repeatability and uneven actuation force. Or rather, of course, I'm not surprised - in another workshop we have OMP60, and it shows approximately the same results. In reality, the repeatability of OMP40 was about 3-5 µm.
Therefore, I want to continue repairing the OMP400. Moreover, it has already become clear that repairs are possible, and will not be very difficult. Most likely, the problems occur in the very thin wires that connect the load cells to the contact pads. Now I'm looking for someone who professionally repairs strain gauges, and I will give them this thing to replace these thin wires, or entire strain gauges.

You should call Renishaw to verify the authenticity of the products. OMP40 probes should work better than you described and certainly closer than almost every machining center. There are a lot of fake products on the market, especially from china, and personally I never purchase anything that important from them. A men's dress shirt from china? Sure. Sensitive electronic inspection equipment? Nope. No. Never.

 

[Milling man]

You should call Renishaw to verify the authenticity of the products. OMP40 probes should work better than you described and certainly closer than almost every machining center. There are a lot of fake products on the market, especially from china, and personally I never purchase anything that important from them. A men's dress shirt from china? Sure. Sensitive electronic inspection equipment? Nope. No. Never.

China has only recently begun to make a semblance (poor semblance) of OMP60-type probes. I am sure that they will not be able to make OMP400 soon.
As for OMP40, which I have now installed - I am also sure of its originality. I bought it from a person I trust.

 

[Billy_C]

OMP40s are noticeably inaccurate probing 3d surfaces compared to the OMP400. Try probing the center of a calibration ball a few times with each and compare the results.

The last Renishaw repair quote for one of our OMP40s that got coolant in it through a leak somewhere was over $1000.

 

[Milling man]

Some more experiments
I tried to greatly upset the balance of the measuring bridge without batteries in the device, then I inserted the batteries. And..... It works!!!! I want to note that the Renishaws do not get their money in vain - this thing is designed very cleverly.
I was finally convinced that even the strongly unequal resistance of the strain gauge is not a problem for this thing. The main thing is that it does not change after the batteries are in place.

 

[snowshooze]

Here is your guy:
Mike
https://www.metrologyparts.com/

 

[Dale_P]

I have an OMP400 that the probe shaft seal deteriorated and let coolant into the electronics. It immediately drained new batteries and only flashed red, or red, blue, green (sometimes purple) then repeated... I removed the batteries and did a water flush, blow dry then an alcohol flush and dry. Let it dry over the weekend and it worked again, but exposed to any dripping or splashed coolant. So I decided to take it apart and clean it as well as try to replace the seal with one from china on e-bay. As there aren't any other photos of the disassembly online I'll share here. Careful of the ribbon cable on first separating the halves. Carefully pop out the bit in the pocket, it seems to be attached with silicone or a soft glue. Pull the glass ring, then carefully work the electronics out. Pop the latch on the ribbon cable in the 3rd photo. Pull up the sheet metal cover by the 3 locking tabs. Unscrew the 6 bolts. The spring will pop the center up, be careful to guide it around the ribbon cable. Part orientation is shown in the 4th and 5th photos. The ribbon cable comes out over an extra hole and the bolt pattern is not symmetrical. The load cell is just set in and will slip out freely. Lastly where the seal goes, and the reason for this... umm DON'T press the insert out, I destroyed mine trying. The circlip is captive and inaccessible and I don't know if there is a way to remove it. Perhaps a thin shim in the gap worked around, but I doubt that will work. It will spin, so trying to machine on it to access the circlip will cause it to move. Perhaps I didn't try hard enough to dig out the remnants of the seal after the load cell was removed, I don't know yet. Waiting on the new seals to arrive and making a new cover pc.
It seems this is a LOT easier with the OMP40 as it seems to just screw off the front to give access to the seal. Last 2 photos are some parts available on e-bay. Mostly OMP40 and made in China but since you can't get these from Renishaw...
Hope this helps someone else.

 

[Milling man]

А few more results of my experiments. I tried setting the variable resistors to 1kOhm. The device is working again! This finally confirmed my assumption that this thing +- does not care about absolute resistance of the strain gauge.
And one more piece of news - I finally found a new strain gauge bridge for this Renishaw on TaoBao - https://item.taobao.com/item.htm?spm=a1z0d.6639537/tb.1997196601.4.28317484v58jym&id=697229459698 1,100 yuan I have already ordered one piece.

 

[Milling man]

I recently received a new strain gauge bridge and tried to assemble Reni - it works! Now I'm waiting for new rubber protective membranes so I can assemble the entire device and put it in the machine.
Here it is in the Chinese warehouse of the intermediary, immediately after receiving it from the seller:


And a few unpleasant surprises. The lid that covers and holds the rubber membrane is absolutely non-removable. I turned it into shavings on a lathe)))) Below are a couple of photos of the front part of the frame with the cover and membrane removed - and only with cover removed:


A radial groove can be seen in the housing opening. The lid also has a groove at the same level. During installation, a spring retaining ring is inserted into this groove; during assembly, the ring fits into a groove on the body, opens, and that’s it. It's impossible to make out.

 

[Milling man]

I finally had time to put this thing together. The retaining ring is not quite right, but I was too lazy to wait for the right one. So far we have only tested this Reni in the machine and put it on the shelf as a spare. Overall, it looks like I've found a source for cheap ( about 600-700$ on Ebay), high precision Renis with a little work and patience.

 

[Alo machine]

А few more results of my experiments. I tried setting the variable resistors to 1kOhm. The device is working again! This finally confirmed my assumption that this thing +- does not care about absolute resistance of the strain gauge.
And one more piece of news - I finally found a new strain gauge bridge for this Renishaw on TaoBao - https://item.taobao.com/item.htm?spm=a1z0d.6639537/tb.1997196601.4.28317484v58jym&id=697229459698 1,100 yuan I have already ordered one piece.

Hey guy
Thank for your sharing!
I am using OMP400, when one of them was broken, I disassemble it and store good components to replace to other probe. It worked again.
But sometimes, strain gauge on bridge was fail, I could not reuse strain gauge bridge.
I think to replace NG strain gauge by another, but can not see the it's specification.
Do you think that the probe can work if we replace other resistance strain gauge?