Print

Please login or register.
1 Hour 1 Day 1 Week 1 Month Forever
Login with username, password and session length

[SMD]

If I need to drill out sheared cat bolts?

Thanks

[Andy H]

I have got a set of HSS drill bits in 0.5mm steps.

Start small (say 4mm) & drill larger & larger until the thread can be seen.

From memory the bolts are 8mm so you want to stop before you get bigger than the tapping size, possibly less if the drill wanders off centre so probably about 6.5mm

You need to use sharp drill bits and keep them cool.

You might be able to pick the bits of thread out but using a tap to clean up the threads is easier.

If all else fails just drill it out to 8mm and fit a longer bolt and a locking nut (not Nyloc, they can't take the heat)

[SMD]

Thanks Andy.

I'll look into the sizes you mention, but I'm thinking of drilling out the thread using an 8mm bit and using a nut & bolt to make future removal easier. Just thought it would be easier to start small and work up or shall I just skip this stage and start with the 8mm bit?

[feeutfo]

All of them probably, as starting with the most desirable size inevitably means thats the most likely to snap off in the bolt. ...steady as she goes.

[Andy B]

as above, bear in mind that the tapping drill for a M8 thread is 6.8mm which is near as damn 17/64" (amazing what you remember from being an apprentice  ) 

[Keith ABS]

4mm carefully then 6mm and 8.5mm for a little bit of clearance.
Keith B

[Andy B]

I'd suggest that you drill the 6.8mm hole in one go without going up in stages, maybe use a small 3mm pilot  . Reason being that the drill has more chance of snagging & snapping if it only has a millimetre or so to drill, it's all very well if you're drilling on a proper drill with the job clamped down to the bed, but not if you're lying down under the car using a portable drill.