Thread: Daddy Drill Bits

Originally Posted by Brian Hjelm

You need to find a business that specialises in machine shop supplies. I can supply either solid carbide drills or LH helix drills but do not stock them. Near zero demand. They would have to come from the USA. I do stock sets of LH helix drills, 1/16" -1/2" in a steel index box. PM me if interested.

What you have done is drilled without a sufficiently heavy feed and the heat and pressure of the cut has turned the zone below the cutting edges into armour plate. When drilling work hardening steels the rule is to drill with a heavy feed and NEVER relax the feed. You have to keep the drill cutting on the softer area below the cutting zone. If you lift the drill to clear swarf, when you but it back down it is attempting to cut hardened steel.

If you had used a LH helix drill in the first place this may never have happened and the thrust of the LH cut may likely have just wound the broken bit out.

Ok so next time I have a go I should drill left hand at low speed with a good amount weight on the drill. If I stop it hardens? I was checking frequently to see progress (lack of progress) as I didnt want to overshoot (ha).

I would have gone out for a left handed drill bit but this bolt is as good as welded and I figured there was little chance of it unwinding from drill grip so I went to drill right through... anyway I have been schooled - I'll get it right next time!

I've used Dremal bits to grind off the hard face and start again with a new pilot hole.
Could be worth a try.

An end cutting solid carbide rotary burr in a die grinder may now be your best approach.

Originally Posted by Brian Hjelm

You need to find a business that specialises in machine shop supplies. I can supply either solid carbide drills or LH helix drills but do not stock them. Near zero demand. They would have to come from the USA. I do stock sets of LH helix drills, 1/16" -1/2" in a steel index box. PM me if interested.

What you have done is drilled without a sufficiently heavy feed and the heat and pressure of the cut has turned the zone below the cutting edges into armour plate. When drilling work hardening steels the rule is to drill with a heavy feed and NEVER relax the feed. You have to keep the drill cutting on the softer area below the cutting zone. If you lift the drill to clear swarf, when you but it back down it is attempting to cut hardened steel.

If you had used a LH helix drill in the first place this may never have happened and the thrust of the LH cut may likely have just wound the broken bit out.

Just as likely to have got the same result with a LH drill bit, it sounds like we are not making much headway. Slower speed, more pressure, cutting fluid etc, gets a bit difficult with smaller bits, shorten the length of exposed drill bit to restrict the flex and potential shatter of the bit.

what Brian Hjelm said.

i think you got the drill hot and burnt the end of it. IE going to fast easy to do if you are using a hand drill.

you are going to need to remove this hard facing that you have introduced, so grinding is the only way ahead i fear.

question what were you going to do once you have drilled your hole? easy out ??

Originally Posted by 85 county

what Brian Hjelm said.

i think you got the drill hot and burnt the end of it. IE going to fast easy to do if you are using a hand drill.

you are going to need to remove this hard facing that you have introduced, so grinding is the only way ahead i fear.

question what were you going to do once you have drilled your hole? easy out ??

I want to drill the bolt out. I will then enlarge the hole slightly for a helicoil.

I have a dremel, is there a dremel bit I can use to grind it? High Speed Cutters ? -> http://www.dremel.com/en-au/Accessories/Pages/SubCategories.aspx?catid=2070

Or carbide bur ball? -> http://www.mytoolstore.com.au/products/Carbide-Burr-Ball-3.2mm--%252d-2.35mm-Shaft.html

Originally Posted by manic

I want to drill the bolt out. I will then enlarge the hole slightly for a helicoil.

I have a dremel, is there a dremel bit I can use to grind it? High Speed Cutters ? -> http://www.dremel.com/en-au/Accessories/Pages/SubCategories.aspx?catid=2070

Or carbide bur ball? -> http://www.mytoolstore.com.au/products/Carbide-Burr-Ball-3.2mm--%252d-2.35mm-Shaft.html

so this is a bolt in an alloy housing correct??
i think it will be unlikely that you will end up with a hole suitable for helicoil. no offence but i dont think you are a fitter or ??? and if you are asking questions now i doubt you have the practiced skills to achieve what you want. now i mean that all in the nicest possible way, and good on you for having a go, even better for stopping and asking questions when you realized that things were not going to plan.

it may pay to take a step back, what bolt is this?? dia where is it? cap or hex etc can you take a picture.
is it snapped or just tight etc.

the reason i say this is drilling out a bolt in alloy is not the easiest to do, if you are not bang on center the drill will always want to move to the softer material, this is worse if you are drilling by hand, its bad enough when the job is solidly mounted in a press or radial arm etc.

Originally Posted by 85 county

so this is a bolt in an alloy housing correct??
i think it will be unlikely that you will end up with a hole suitable for helicoil. no offence but i dont think you are a fitter or ??? and if you are asking questions now i doubt you have the practiced skills to achieve what you want. now i mean that all in the nicest possible way, and good on you for having a go, even better for stopping and asking questions when you realized that things were not going to plan.

it may pay to take a step back, what bolt is this?? dia where is it? cap or hex etc can you take a picture.
is it snapped or just tight etc.

the reason i say this is drilling out a bolt in alloy is not the easiest to do, if you are not bang on center the drill will always want to move to the softer material, this is worse if you are drilling by hand, its bad enough when the job is solidly mounted in a press or radial arm etc.

No offence taken, I'm a complete amature. Bolt is M8, snapped inside aluminium timing cover plate. I'm pretty sure the only solution now, apart from sourcing another cover plate, is to carefully drill the bolt out from center out, stepping up sizes using good n sharp cobalt cutting bits and then enlarge for helecoil. I may also get a carbide burr in the dremel to break the hardended surface.

I've successfully helecoiled the other two blind holes in the cover plate which were baddly corroded and easily stripped, so I'm ok there. Its just this one has the added complication of an embedded bolt/stud to be cleared first.

In the pic you can see an outer ring scored in by a nut which was done by a previous 'mechanic'. He must have had issues with the thread because there was a stud and nut used in place of the usual 25mm M8 bolt. Its possible he wound a stud in and locked it in there good and proper, but unfortunatly for me the nut rusted on pretty solid, and undoing the nut snapped the stud.

Heat, slots and impact driver could not budge it, so I flattend it and drilled.. I've progressed about 5mm down but it was very slow progress and you may be able to see that the top of the hole has been enlarged.. I realise I need to drill right through the center with a smaller drill, hence the request for advice on drill bits that will pass through easily.