Drilling out an M6 bolt

[Simpo Two]

This may seem like a silly question but I'm not sure of the answer.

I need to drill out some M6 bolts that have rusted in, and replace them with new ones (to drop straight in, hole unthreaded). Do I need 6mm drills or 7mm to allow for the bolt thread?

[Simpo Two]

I just want new M6 bolts to drop straight through. There will be a nut on the other end to hold them.

[Simpo Two]

P924 said:

do you have both 6mm and 7mm? I'd just compare the drill to the bolt, and probably go with the 6mm anyway.

By the time you've gone through the bolt, you will probably have broken the friction/rust free anyway.

Edit: Which way through the bolt are you going? head first, or thread first? Is this on the garden bench?

Yes, this is the bench! Access in a straight line is impossible due to the design of the iron frames, so I'm getting a right-angle chuck, and ordered 6mm cobalt drill bits from eBay before thinking. Due to what an utter bd it would be to remove all the bolts I've decided to refurb the existing planks in situ as best I can; however there's one plank missing and the rusty remains of the bolts need to be removed. As for head vs thread, is there a best way?

[Simpo Two]

dickymint said:

It's going to be a bd doing that with a right angled drill!!

I know, but there's only about 6" clearance above and below.

Private Pile said:

Have you tried undoing the bolt? Can you add heat from a blow torch? If it's proper rusty and seized then it may well snap whilst loosening it.

WIth great difficulty I got about half the bolts off; the others sheared, and a few nuts are impossible to get a grip on as they're too close into an angle. Can't use heat with the wood there.

TooMany2cvs said:

If this is the kind of garden bench I'm thinking of, then wouldn't it just be easiest to cut the existing bolts off with a grinder, probably with the wood still in place, but destroying it if needed? They should just tap through the holes in the frame, which won't be threaded

That was the plan, but the bolts are rusted totally solid in the iron frame. Hence the plan to refurb the wood in place, but I just need to get the bolts out where the one plank is missing.

Worst case is that I cut/grind the bolts flat with the frame and stick the new plank on with Sikaflex!!!

[Simpo Two]

TooMany2cvs said:

Simpo Two said:

That was the plan, but the bolts are rusted totally solid in the iron frame.

Get the wood off, get some decent penetrating oil on for a few days, and then get some heat on. Tappity, tappity, they'll be out.

If the wood was disposable maybe, but I want to save it. And the holes through the frame are about 1.5" deep... can't use too much force or the iron frame could break. So I need to get the bolts out to get the wood off without destroying it...

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As a postscript, slightly to my surprise I managed to hammer one of the bolts out! Of the crucial ones, that's one down, two to go... WD40 stewing...

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mosstrooper said:

So, didn't my suggestion of 3 weeks' ago work ??

The 'screw' end of the clamp just tilts over at a silly angle and no force can be applied. I can't use the clamp the other way up as the fixed end won't go through the hole due to the curve of the clamp.

I have a number of situations. Some bolts have rusted through between the wood and the frame, some nuts have come off but others have sheared leaving no end, others are so close to the corner of the frame there's little room to work in. I think I could, using a combination of methods, get perhaps 25 out of 30 bolts out but it would involve a fantastic amount of effort so I've decided to restore the wood in situ and only remove the three bolts I really have to (to replace a missing plank). The left bolt has come out, the middle one has sheared off leaving nothing on either side and the right one has a thread underneath but no top. At least the middle one can be drilled out as I can get a drill in line!

I'll sort it out eventually somehow using either brute force or cunning!

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dickymint said:

With the best will in the World - some posters just don’t get it

This post was a simple question about diameters, but then lost focus with various people giving various helpful ideas on how to disassemble a structure. I have that structure in front of me, and so can judge whether those ideas will work or not.

I'mm a woodworker not a metalworker. As I said in more detail above, I will do the best I can with what lies in front of me and it will work out eventually. Thanks to everyone who posted ideas; some may work.

[Simpo Two]

dickymint said:

Saw this and thought of you.............

That's about right!

I hate metal, it's a bh. Just everything goes wrong or doesn't work. Already broke two special cobalt drills drilling 1.1 bolts out. The one in the right-angle chuck has gone in about 10mm but refuses to go any further. Hard to get any pressure on. And that's only 6mm, they need to be 8. More drills on the way...


Wood

[Simpo Two]

dickymint said:

That’s more than deep enough to get an “easy out” in it and use a ratchet.

Not sure now if that's real or you made it up...!