Controlling pin gauges & thread gauges in CNC shop – need advice

[ckk33]

Hi all, greetings, need some advice from you guys.

I’m working in a precision CNC manufacturing company as a Quality Engineer. Most of our parts have lots of holes and threaded holes. Right now, operators usually borrow pin gauges and thread gauges from QC and check the parts at their machines.

Recently we’ve had issues with gauges going missing, so management decided to stop operators from borrowing them. The new rule is: all gauges MUST stay in QC room, and hole/thread checks should be done in the QC room.

After talking to QC inspectors and operators, a few problems came up:

1. Operators normally check holes while the part is still clamped in the CNC.
   If a hole is undersize, they can rework it immediately. If they have to unclamp the part and bring it to QC, rework becomes slower and riskier because the origin has to be reset.
2. If parts can’t be brought to QC, QC inspectors are expected to bring gauges to the machines and monitor the checks.
   This increases QC workload a lot and isn’t very efficient, especially when multiple machines are running.
3. Some operators admitted they may skip hole/thread checks if gauges are not easily available.
   That’s obviously a quality risk.

So I’d like to ask those of you working in CNC shops:
How do you control pin gauges and thread gauges properly without:

• Increasing workload for QC or operators
• Slowing down production
• Operators skip checks
• Missing gauges

I’m trying to find a practical solution that keeps gauges safe but still works for the production floor. Any real-life practices or ideas would be very helpful.

Thanks in advance!

 

[ChrisM]

Your shop needs to have its own set of gauges - they may choose to have them uncalibrated "for indication only".
If necessary you should consider "partial first-off" inspection where the workpiece is taken into the Inspection facility, but it sounds like you are trying to avoid this and just want a confidence-building check by the operators.
The practice of lending out gauges from an inspection facility is a bad one - gauges may get dropped, mis-used (e.g. thread gauges used as taps by being forced into tight holes); ideally your set of inspection gauges should remain in the inspection area and only be used by your own "qualified" inspectors

 

[Michael_M]

Another way to look at gage pins, and to talk to management about it: A single gage pin is about $5.00 each (sets are cheaper). How much time (time equals money) does taking the part into QC cost? Gage pins can be 'calibrate prior to use' so there really is no extra calibration cost and I would think you would want to keep anything you need to measure the parts at the machine to measure a part (this is a company decision). I would think it's cheaper overall to have several gage pin sets on the shop floor to keep separate from QC gage pins as ChrisM suggests.

 

[greatwhitebuffalo]

The way we handle it (as others have mentioned) is to have separate sets for the floor. I made a quick spreadsheet that I use as a way to track them. Columns include operator, machine number, date, and nominal measurement, which ensures that the gages are indeed being verified before using (dedicated mics are placed at pin gage table). The system works well for us. Thread gages are stored in a central location with their own sign out sheet which records number of pieces manufactured in the lot the gage is signed out for. This makes it handy to track usage when reviewing for calibration.

 

[Watton1440]

I highly recommend dedicated gage pins and thread gages at the machines. In a perfect world, each machine/cell will have its own set. Using the same pin throughout the shop can compound your risk. Think about if you find an issue with a thread gage or a worn gage pin. If that gage is used on all machines then every product is suspect. If its only used on one machine, then you can isolate the containment to just parts produced on that machine.

On that same note, calibrating pin gages is cheap and easy. If you truly are a precision machine shop, then I would keep your operator's pin gages on a calibration schedule. One quality spill due to a worn pin gage could pay for years worth of calibrations of those same gages.

Also, I can't recommend the pin gage handles with sizes etched on the holder. Your operators will appreciate the handles instead of having to hold onto a small pin gage.

 

[Golfman25]

I would second each CNC having it's own set. All the better if you have standard sizes that you commonly use. Train operators to verify before use and you should be good to go.

Absent that, you could have a check out log which shows who took what and when.

 

[Jake with the Calipers]

Each of our parts have a "job bin" that moves with the parts from machine operation to machine operation. Each job bin has it's own set of gage pins, with spares, and operators are expected to check their gages for wear using micrometers at the beginning of the shift and at regular intervals depending on the work instructions and replace them if out of spec or bring the out of spec gages to QC's attention for them to replace. This check is recorded down on their in-process inspection sheets. We do not "calibrate" gage pins, we just do a quick verification with a calibrated tool, typically a micrometer.

For thread gages we have a similar idea except they are verified at regular intervals (parts ran) by our QC department that they are still in spec. That verification is a bit more involved depending on the type and size of the thread gage so we don't expect the operators to do that.

QC has its own final inspection bins for each part where their own gages are kept, operators from the shop floor very rarely use these final inspection gages.

 

[Maaran]

QC and CNC department has to be have their own sets. Gauges Specification has to be accepted by QA and then passed to CNC for perusal with indicated engraving *Acceptance by QC'.
Ensure QC to verify the gauges by monthly, quarterly to prevent rejection.

 

[Ron Rompen]

Are you a job shop, or do you run production parts (i.e. large quantities over extended periods of time). My common practice is to have a dedicated set of gauges (pin gauges, thread gauges, etc) for each different job - the cost of these gauges is estimated at time of quote, and is either a one-time cost to the customer (customer then owns the gauges) or is amortized into the piece price (customer does NOT own the gauges)