Serious Crash

Can anyone help please
I forgot to change the tool on my Beaver cnc mill with manual tool change and Heidenhain 155 control and the Z axis smashed into the vice on rapide.it has
now gone wierd on me.. when the Z axis should be going to +80mm at the end of the program it goes to +57.241mm but at the tool change it (there is only two)goes to +80mm.
using MDI with +80mm it goes to 57.241, but if I switch off the machine and home it and before running the program the MDI will take it to +80mm.
I have checked the toothed belt for broken teeth and it is ok and the pullys appear to be ok. at the start of the program I have added an extra line to move the Z from 57.241 to 80 and after 5 runs it has moved out of position by 0.04mm in the "-" direction. the program and the machine was ok before the crash.I am right in the
middle of a rush job and need some help.
thanks

That is about 20mm difference, it is not a shear pin or key gone somewhere and there is roughly a 1 turn error between directions?
Do a Dial Gauge test in both directions to see if any dead band of movement, load the z up with as much weight as possible to do the test.
With the Z, you need to also put a heavy duty spring under the Z when you jog it down to diagnose any shear condition.
Al.

It might be necessary to actually check for sheared keys beneath your pulleys. Setscrews on couplings may also have loosened. Check couplings for sheared keys as well.

Same goes for encoder connections. Although keys are seldom used to drive encoders, the momentum of the shafts during the crash could cause a setscrew to score a shaft and loose its grip.

Brian,I was in Dundee until 8pm.I saw your missed call on the mobile and called back but you must have gone home.As Hu and Al say it has to be something gone on the pulleys or possibly the encoder slackened to give you this fault.Did you check the motor pulley like I told you?The encoder is easy to check,if you look at the end cap of the motor that the encoder is on you will see a plastic plug with a screwdriver slot in it in one of the sides of that flange.Take the plug out and with a torch you will be able to see the clamp screws of the encoder coupling,you may have to turn the motor shaft to bring them into line with the hole.Check they are tight.
I still go for the sheared key as it`s quite a big motor on that axis and there would be a fair bit of inertia when it came to a sudden stop.To give you a bit of hope I had a loose encoder on a Beaver mill last week.I am busy tomorrow but you will get me on the landline at Broxburn if you have any questions.
Mark.

thank you all for the replies I will have a go tomorrow
Mark I will give you a call
cheers
Brian