7MM Diameter Drills

[KEITH BEAUMONTParticipant @keithbeaumont45476]

Recently, while making a phosphor bronze bearing for a model engine crankshaft, with a finished bore of  9/32″and knowing the difficulty with reaming ph-bronze, I thought a 7mm drill would  be about right for the final size before reaming. I am well set up for drills, both metric and imperial, so when I found the 7mm drill being used, needed sharpening I thought it easier to use another drill. I have 5 sets of Aldi boxed sets,bought,(just in case), whenever they appear. However, none of them contain a 7mm diameter. Size jumps from 6.5mm straight to 8mm. Also, a set of mm drills, increasing by 0.5mm. stops at 6.5 mm. ( I found a 7mm drill, bought loose,at a show, so work continued) I then remembered that Hex key sets do not contain 7mm. Years ago, when I did all the servicing on my cars,I had to “special order” a 7mm hex key. I have several sets of Hex keys,not one with 7mm.

So, can anyone explain the reason for this apparent anomaly with 7mm?

Was it Napoleons unlucky number, perhaps?

To confuse the issue, I have a set of pointed drills  1-10 mm for  drilling wood, but this DOES contain a  7mm diameter!

Keith.

[bernard towersParticipant @bernardtowers37738]

The 7mm Allen key requirement for disc brake calibers was an attempt by the industry to look after itself and it is still done today. 7mm bolts are to be found on Jap bikes and Italian push bikes(usually with the finer thread). you didnt say how you got on with your reaming as I was thinking you didn’t leave much metal to be taken out, I would have thought the reamer would have rubbed more than cut!!

[Nigel Graham 2Participant @nigelgraham2]

Might those Aldi and similar sets be designed primarily with wood-screws in mind? I have a set of wood-bits (very shallow cone with central needle-point) and I don’t think that has a 7mm drill either.

[noel shelleyParticipant @noelshelley55608]

Then there’s 7mm X 1 bolts found on some cars – with an 11 mm head ! It is industrys way of trying to stop us repairing our own machines – never mind about torques / torkX, 6 point round flats, there is a 5 point type, then theres the one with the pin in the middle ! Plan B is the same shape BUT external – the list is endless ! Ah well, Keep smiling ! Noel.

[Nicholas FarrParticipant @nicholasfarr14254]

Hi Keith, I suppose it depends on what type of set of hex key set you are willing to buy. A bog standard set probably won’t include a 7mm key in most cases, as I suspect that a 7mm one is in a non-preferred category. I have Two sets of these, which do have a 7mm one and there are 3 that are under 1.5mm and 3 that are under 1/16″, that I don’t believe I’ve ever used.

There are plenty of sets around that do include a 7 mm one, including Magnusson 30 piece – B&Q  as an example.

As far as 7mm twist drills go, probably the same applies to a bog standard set. I have a set of Roebuck drills, with every size in 0.5mm increments from 1mm to 10mm, a set of Presto drills with every size in 0.5mm increments from 1mm to 13mm, and an unbadged set with every size in increments of 0.1mm from 6mm to 10mm. The larger sets of course will cost more to buy.

Regards Nick.

[KEITH BEAUMONTParticipant @keithbeaumont45476]

Bernard, It was a new reamer and reamed a perfect bore.

I do have a complete set of mm drills that include the 7mm. That was the one that needed sharpening.

It is still find it interesting that industry consider 7mm to be non standard on these products.

I suppose I was hoping for one of S,O,D Dave’s highly analytical essays, that would clear things for us!

(Tongue in cheek, Dave)

Keith.

[JasonBModerator @jasonb]

Maybe it is the same as metric stock sizes and fixing sizes

3, 4, 5, 6, 8, 10, 12, 16 Not that much use for 7mm

[Clive FosterParticipant @clivefoster55965]

Not forgetting the plastic wall plugs that specify 7 mm drill diameter.

Never seen a set of masonry drills with 7 mm in the box.

Or the one that says use a 6.5 mm masonry drill. Which has to be unicorn droppings. This antediluvian penguin knows they mean use a 1/4″ one, got plenty of those, but younger folk starting out on DIY may well be confused.

I actually emptied one box that said use 1/4 on the side and bought a new box of identical plastic thingies saying use 6.5 mm on the side.

Clive

[HuubParticipant @huub]

I live in metric country Netherlands and all bot one of my drill sets contain a 7 mm drill. None of my end mill sets contains a 7 mm version so I only have 1 bought separately. I also don’t have a 7 mm reamer and no 7 mm tap.

[David George 1Participant @davidgeorge1]

Dont forget to grind a flat on the front of the cutting edge. When you drill Bronze or brass a standard drill will grab and cause problems so unless you have a slow spiral drill you must grind a flat on to the cutting edge.

The drill on the right is a slow spiral drill and the other two have a flat ground on.

David

[David George 1Participant @davidgeorge1]

Dont forget to grind a flat on the front of the cutting edge. When you drill Bronze or brass a standard drill will grab and cause problems so unless you have a slow spiral drill you must grind a flat on to the cutting edge.

 

The drill on the right is a slow spiral drill and the other two have a flat ground on.

David

Sorry about double entry

[Nicholas FarrParticipant @nicholasfarr14254]

Hi Clive Foster, you can get 7mm masonry drills though.

Regards Nick.

[Clive FosterParticipant @clivefoster55965]

Nick

Yep I know, I’ve got both standard and SDS in short & long series. But had to get them individually. Never seen a set with 7 mm. So I have to remember to pack individually when I need that size plug.

Which mucks up my “Honey Doo” toolkit for domestic jobs something chronic. Clive likes kits with a marked space for everything so when he grabs the job box its all there an when he clears up nowt gets left behind. In my world the cost of duplicates is well worth the convenience and time saved from having appropriate full kits to hand.

Clive

[Nicholas FarrParticipant @nicholasfarr14254]

Hi Clive Foster, OK, misunderstood what you were saying. How about this box Erbauer 10 piece

Regards Nick.

[Nicholas FarrParticipant @nicholasfarr14254]

Hi David, I learned that many years ago, but I’ve only ever had to take the edge off.

Regards Nick.

[larry phelan 1Participant @larryphelan1]

Hilti supply a 7mm drill, which I use quite for wall plugs.

Quite a difference between 6mm and 7mm when drilling some walls !

[Clive FosterParticipant @clivefoster55965]

Hi Nick

Nice looking set with a sensible range of short and long. If I were 10 years younger I’d probably bite.

Larry is so right about the discrepancy between nominal size and hole size in certain wall materials. My place is brick, hard brick, downstairs and breeze block upstairs. Hafta remember to dill undersize, and clean out with the right drill if need be, upstairs.

Clive

[Howard LewisParticipant @howardlewis46836]

I have four sets of Metric Drills, one set from Aldi (1.5 to 13 mm x 0.5) Cromwell tools 1 mm to 10 mm x 0.5, and Cromwell 6 to 10 mm x 0.1.

All contain a 7 mm drill! (Obviously, the 1 to 6 mm x 0.1 set doesn’t!)

So far the 7 mm drills seem to be unused!

Howard

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