Reverse twist drills

[Guest]

OSH has left handed drill bits. If you are trying to do one of the centre ones you'll struggle to find small ones long enough to get in around the frame.... you might have to use a over length conventional one to start it & get in with the left hander when you get up near the 8mm so you've got the length.

When I tried it the bolt didn't back out so I just kept going & put a Helicoil in it...

It is the inner bolt for an outer cylinder, so access shouldn't be too bad.

The bolt seemed to have turned about a half revolution before it failed, so I expect that it will eventually come out without the need to retap or use a Helicoil.

 

[argonsagas]

For anybody watching: EZ-outs are a damn dirty lie. NEVER EVER EVER use these. Whether they're cheap or expensive, they WILL break.


Argon, if you've actually gotten an EZ-out to work, it's the first time in recorded history. Congratulations.

I have had very good luck, then, because, while admitting I have broken both types, I have twisted the screw-thread types apart quite easily, but the fluted ones worked well, once I figured out how to make them bite without expanding into the base metal, and how much torque to apply.
Lubrication and heat are great aids.

Of course, I also use what may be considered unusual methods of reverse-drilling, as I have sometimes used the standard CW drill bit to turn out broken bolts.

To do that you first grind the tip flat, then make the centre of the bit concave and sharpen it as needed. It will not take a lot of torque, but it will do nicely on bolts that are not stuck hard in place.

 

[Griffin]

Tom,

I have a set of left handed drill bits. PM me if you still need to use them.

 

[Guest]

Brett,

Thanks for the offer. I bought two reverse twist drills at Menards. The question is whether the Menards bits are tough enough for this particular job.

Friday, I tried to make a "fixture" to align the first bit when I start to drill the bolt out. Put a stubby M8 x 1.25 bolt in a lathe and tried to drill down the axis. (It's nice to get along with the HS shop teachers.) But the bit was only 1/16" and not designed for the hardness of the bolt, and it broke.

I'm going to try again with either a 3/32" bit or a 1/8" bit, either one designed for "hardened steel".

If nothing else, this excursion has taught me a little, before I go to work on the bolt remnant in the cylinder head.

I'll let you know if I need help. Thanks again.

 

[tom203]

Brett,

Thanks for the offer. I bought two reverse twist drills at Menards. The question is whether the Menards bits are tough enough for this particular job.

Friday, I tried to make a "fixture" to align the first bit when I start to drill the bolt out. Put a stubby M8 x 1.25 bolt in a lathe and tried to drill down the axis. (It's nice to get along with the HS shop teachers.) But the bit was only 1/16" and not designed for the hardness of the bolt, and it broke.

I'm going to try again with either a 3/32" bit or a 1/8" bit, either one designed for "hardened steel".
.

You want bigger left hand bits- maybe 3/16 inch if your exhaust bolt is 8 mm. Find a good quality nail set- small ones have a nice point (if they haven't been abused). Center nail set on bolt centerline and tap lightly till you feel it's centered- then tap harder to make a depression for the drill bit to start in. Not too fast- maybe 1000 rpm max. You're cutting, not abrading, so pressure needs to applied to drill ( this is why you don't want little drills).A little oil helps keep things cool and with a bit of luck, the drill bit will grab on bolt and back it out.