View Full Version : Need Help..! Generate an alarm signal, during an improperly placed workpiece..!

20-07-2016, 05:44 AM
Hello, I am Govind from Bangalore, India.
I have a production related issues on our CNC machines.

When the CNC operator does not keep the work-piece material properly on the machine bed or worktable, the machine simply runs and the time get wasted. After realizing the mistake, the operator keeps it properly and re-run the machine. It happens especially during night shift, and the production capacity affects.

Is there any solution (programming or sensor related) to avoid such mistakes?
If the work-piece material is improperly placed on the machine bed or worktable,
the machine should give an alarm signal (warning) to the operator, so that he can immediately rectify it. How to achieve this? Any practical solution for this problem? Thanks in advance.

20-07-2016, 01:14 PM
Using fixtures which eliminate the ability of the operator to place the work incorrectly would solve the problem.
Operator training would also help.
You could spend a lot of money with more technical solutions but adequate fixturing will eliminate positional operator error.

- Nick

20-07-2016, 01:16 PM
The workpiece is normally located with a fixture / dowel pins for repeat work to make sure the workpiece is always in the same position.

Assuming you are at least doing that, and you are cutting metal, then using microswitches and prox sensors might be possible but it is difficult due to contamination from metal swarf and coolant.

Another option is to monitor the current from the spindle supply and if the part is loose or falls out of the fixture and you are cutting air, then the current will be low. You would probably need some sort of interface device to check that the current stayed low for a certain period before feeding a fault signal into your controller and pausing the machine.

A picture of the problem, and the cnc machine you are using may for further ideas.

20-07-2016, 01:16 PM
Get better operators?

20-07-2016, 01:57 PM
Get better operators?

+1 ;-)

22-07-2016, 07:25 AM
Hello magicniner & routercnc,

Thank you & very kind of you for your swift reply.
Let me put my issues, very precisely now.

We use Manford CNC Bed Type Milling Machine - Tontec Technology.
Model No : Manford - VM1100 / VM1000.
You can view its specifications in the below URL.


We run 3 shifts in a day. When the tool bit looses contact with the workpiece,
the CNC machine simply runs. During this time, we want to generate an
alarm (alert) signal & stop the machine automatically, if possible.

We would like to monitor or measure, how much time is wasted in a day for this?
Looking to improve the production capacity with best cost-effective solutions.

How can this be achieved. Can it be done with program alone or any
external hardware is required? Thanks in advance.

22-07-2016, 11:20 AM

broken tool detection is something you can program into your tool changes as long as you have a way of identifying the broken tools. Renishaw are the first company that springs to mind for this. You can also get the same hardware from japanese companies such as Metrol:


With your machine you can write macros or other routines such that before a tool is used or after it is used, the machine will test it:


I hope this helps you

26-07-2016, 10:51 PM
Deduct the Operator a days wage every time he forgets and your problems with poor fixturing will soon go away.

Broken tools are another issue and easily taken care of with simple tool length check at regular intervals during the cycle. But again if the operator is awake then this shouldn't happen or be required.

Boyan Silyavski
27-07-2016, 05:08 PM
How could not the material be fixed properly by fixture on a VMC? What exactly are you doing?

There is sth wrong from what you say that does not fit in the picture:

-Fit sensors on fixture and i don't see how that could happen. Or just a couple of fixed DTI.

-Or the material that is fed is smaller / thinner sometimes? Then adjust all so a sacrificial material is milled from top.

-if the bit is damaged, fit a simple Z zeroing DTI and make sure every start of program the bit touches it for a check.

And teach them to clean the fixture beforehand, and hammer down the pieces using plastic mallet, then fix. Cause that is what causes usually discrepancies when machining. best would be to hire a good machinist so he teaches the other.