Imperial drill bits

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Dalboy

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Please pay good attention to this reply. There is very little engineering need today to buy imperial drills. The standard increment for metric drills is 0.1mm, or four thou' in freedom units. Unless you are into doing serious mental gymnastics over letter and number drills, that increment is finer than the standard imperial increment of 1/64" (roughly 16 thou'), so metric drils have four times 'resolution' of imperial.
The plans I am working from only state imperial fractions for hole sizes and also all other measurements are also imperial it is just a pain having to convert to decimal inch measurements. This also includes the reaming sizes
 

Vann

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...The standard increment for metric drills is 0.1mm, or four thou' in freedom units. Unless you are into doing serious mental gymnastics over letter and number drills, that increment is finer than the standard imperial increment of 1/64" (roughly 16 thou'), so metric drils have four times 'resolution' of imperial.
That's all very well, but every 'big shed' here has imperial sizes, however you have to find a specialist supplier (often at specialist prices) for drills in 0.1mm increments.

Cheers, Vann.
 

Kittyhawk

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Well inch/metric drill sizing is a problem for me.
In NZ metric drill sizes in 0.1mm increments will be available in specialized outlets but in general hardware stores metric drills come in 0.5mm increments and they don't stock imperial anymore. I use a lot of small gauge round bar in 1/16" and 1/8" diameter because for some reason small round bar is still sized in imperial. And you can't poke a bit of 1/16" rod in a 1.5mm hole nor a 1/8" into a 3mm hole. We have a big hardware store in my town and it kind of pees me off that I still have to order online, pay courier charges etc to get drill to suit. Why is so much engineering stuff still sized in imperial? This is a continual anguished cry from a lot of metal workers I know.
 

Yorkieguy

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As stated earlier in this thread, Imperial drills are readily available from UK Drills, either individually or in sets. EG a 29-piece boxed set ranging from 1/16th” to 1/2” in 1/64th” steps:


Drills from UK Drills are excellent quality in all types at very reasonable prices. I’ve used the company for years. I could also buy imperial drills from a local engineering supplier if I preferred, but not DIY stores.
 

ChaiLatte

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What about letter drills! They may be odd sizes but can give hole sizes that suit different metric fits.

I did try my best to exclude them (or perhaps treat them as a special case) in my original reply, but that is not reflected in the brevity of your quote.

Nevertheless, what could we usefully say about them?

There is a table of letter and number drills and their measurements in metric here: Drill Size Chart - Machining

In order to put some numbers onto your idea, please go through it and see what the biggest numerical difference is between a letter drill and a 0.1mm increment drill. Please then consider the significance of that difference in the context of the relationship between a drill's quoted diameter and the size of hole it actually drills (https://cdn.mscdirect.com/global/media/pdf/search/dormer/dormer-pramet-drill-tolerances.pdf). In that link Dormer say H12 tolerance, which, even for the smallest size (which is 50% smaller than a letter E drill), is 0.1mm (Tolerances for Holes and Shafts International Standards-APPORO).

Twist drills are not precision items: you can guarantee neither location, diameter, straightness, roundness or surface finish with them.
 

Seascaper

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Hi all,

Anyone know a good place to purchase imperial drill bits?

Specifically 1/2 inch?

Regards

Nick
I recently found a large amount of good quality imperial drills at our local car boot sale, many of which had never been used, new in their packets, made in England etc. 50p for the lot so a good find.
 

Spectric

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Twist drills are not precision items: you can guarantee neither location, diameter, straightness, roundness or surface finish with them.
If used in a handheld drill then the accuracy may not be precision but you get a hole, used in a drill press with the workpiece fixed down then you get a precise hole providing the drill bit is sharp and suitable for the material being drilled, for real precision then yes you will need a mill.
 

Dalboy

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If used in a handheld drill then the accuracy may not be precision but you get a hole, used in a drill press with the workpiece fixed down then you get a precise hole providing the drill bit is sharp and suitable for the material being drilled, for real precision then yes you will need a mill.
If you measure a drilled hole you will find that it will drill slightly over size to get a precise size would mean drilling very slightly under and reaming it
 

Vann

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...but in general hardware stores metric drills come in 0.5mm increments and they don't stock imperial anymore...

You've got me worried now. I'll have to go down to Mega and check, but last time I looked (2-3 years ago) they still sold both metric and imperial (I haven't had to buy any recently as they had a good supply at work).

...I use a lot of small gauge round bar in 1/16" and 1/8" diameter because for some reason small round bar is still sized in imperial...
...Why is so much engineering stuff still sized in imperial? This is a continual anguished cry from a lot of metal workers I know.

Nuts. I wanted some 1/4" round bar (to thread 1/4" BSW) two weeks ago and Fletcher Steel said they had none in New Zealand.

I'll send you some imperial drill bits if you send me some imperial rod...

Cheers, Vann.
 

sawtooth-9

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That's all very well, but every 'big shed' here has imperial sizes, however you have to find a specialist supplier (often at specialist prices) for drills in 0.1mm increments.

Cheers, Vann.
Yes, getting drills in 0.1 mm increments is more than difficult.
I run with standard metric increments of 0.5 mm, imperial, numbered and letter drills.
Still would like metric increments of 0.1 mm but sourcing these in Aus???
 

sawtooth-9

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Aus went metric eons ago, but still so many things have odd metric sizes that correspond to imperial dimensions.
If you can't get metric increments of 0.1 mm, then imperial sizes are very useful
I do a lot of work from stainless steel bar - which comes only in imperial sizes from local supply. I work with sizes from 1/8 - 2 inch dia. I usually turn these to metric size, but long shafts etc remain imperial.
Oh yes, and imperial reamers are a must !
 

woodwind

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All the recommended suppliers are very coy about their P&P charges, I was looking to replace a broken cobalt drill to keep the set complete but will not bother until I really need it, I already have all the drill bits I am likely to need so a £50 or £60 order to qualify for free delivery is unlikely to happen.
 

Kittyhawk

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You've got me worried now. I'll have to go down to Mega and check, but last time I looked (2-3 years ago) they still sold both metric and imperial (I haven't had to buy any recently as they had a good supply at work).




Nuts. I wanted some 1/4" round bar (to thread 1/4" BSW) two weeks ago and Fletcher Steel said they had none in New Zealand.

I'll send you some imperial drill bits if you send me some imperial rod...

Cheers, Vann.
We only have a Bumblings here in Whangamata and although they have good stocks of imperial and metric engineering, coach bolts etc there's not an imperial drill bit to be found in the store. Nearest place to source imperial bits would be Bay Engineers but thats in Tauranga, 100 clicks away.
What lengths and material did you want in 1/4" round bar? All that I would have is offcuts in stainless.
 

Stevekane

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Maybe your best bet is buying second hand,,drill bits are often two a penny at boot sales and here at least its easy enough to find imperial and metric,,I guess there is a used marketplace in NZ?
I fear us recommending specialist suppliers in the UK will just prove too expensive for you,,,thinking back I used to sell lots of old junk on ebay and was always happy to post off to exotic places,,a BSA ladies bike to Brazil comes to mind, and I was happy to do it at cost, unlike many new suppliers who seemingly want to charge you for buying from them! Maybe check out ebay private sellers and see if you can find a helpful one?
Steve
 

Sandyn

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Why is so much engineering stuff still sized in imperial?
Possibly because the US never fully adopted the metric system?, but having worked for an American company manufacturing in the far east, all drawings were metric.
It is a bit of a mess, but dividing imperial sizes in two is easier than metric.
 
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