Number drills

[Bill DawesParticipant @billdawes]

I have been following the Emma Victoria series with interest.

I notice on the drawings that number drills are frequently specified.

Is it advisable to stick with these or is there a good reason not to use nearest metric equivalent.

Why are number drills still used, authenticity?

Advise from the experts would be appreciated, i am seriously considering having a go at this project so just getting my thoughts together and compiling a list of materials/tools I might need to aquire.

Regards to all

Bill D

[Bill DawesParticipant @billdawes]

[Tony Pratt 1Participant @tonypratt1]

I have a set of number drills but haven't used them in years, I would suggest a decent brand metric drill set will be a better bet. Generally availiable in .05mm & .1mm steps so you can pretty well cover all options.

Tony

[Michael GilliganParticipant @michaelgilligan61133]

Here is a handy comparison table.

… and another, differently arranged.

MichaelG.

Edited By Michael Gilligan on 13/06/2013 22:29:06

[I.M. OUTAHEREParticipant @i-m-outahere]

If you buy a set of either number or metric fractional drills buy a known brand as i have two sets that are a bit dodgy from the eastern provinces .

Can't complain really for the price as 90 % are ok but i was looking through my metric set that is .1 divisioned and stumbled upon the 9.6 and 9.8 drills that are both stamped 9.8 and measure the same !

Have the same issue with number drills from 40 up but so far the bigger drills have been fine .

Suppose you get what ya pay for !

Most you will never use so maybe just buy what you need ?

Ian

 

Edited By SLOTDRILLER on 14/06/2013 07:24:29

Edited By SLOTDRILLER on 14/06/2013 07:26:15

[Chris HeapyParticipant @chrisheapy71135]

The problem with the 'buy what you need' method is that you end up not having it when you need it – so you then have to order it and wait.

Anyway, yes – some of these cheap drill sets seem to be made from high speed mild steel. Had one set that was so soft they would blunt on first use. I avoid them like the plague now. I'm still looking for a decent cobalt HSS set at something like an affordable price.

Chris

[I.M. OUTAHEREParticipant @i-m-outahere]

The sets i have are not too soft but rather brittle and the 5.0mm split up the middle !
If you look at a project and order what you need before hand there should be no hold up but i understand where you are coming from as everyone wants to use some wierd size drill for no rerason !

Ian

[roy entwistleParticipant @royentwistle24699]

Surely it doesn't matter whether you use letter, number, imperial or metric drills as long as you use the correct size or in a lot of cases near enough. You're only drilling a hole Use what youv'e got

Roy

[OuBallieParticipant @ouballie]

I think someone on the forum said " Buy cheap, buy twice!".

I've gone the eBay no brand cheap route, but never again!

I went through 5 x 4mm drill bits whilst fitting the roller shelves to my BH600G stand, and the remaining 5 soon after. They just snapped at the least provocation..

By comparison, I have a set of General number drill bits dating from the '70s and they are still going strong.

It's now name brand only, more expensive yes, but once only, unless I do something stupid.

Reminds me of a brand of metric sets I was selling in the '70s, from Taiwan, that I flung back at the distributor when a customer came into the shop, took a drill bit and bent it! I then did the same with another one, and everyone in the shop myself included, where goggle eyed before bursting out laughing, as this was up till then unheard off.

Nothing changes, except country of manufacture.

Geoff – Coffee time.

[MICHAEL WILLIAMSParticipant @michaelwilliams41215]

Hi Bill ,

For all general purposes in model engineering there is no reason to specify or use number series drills at all unless you already own a set .

For all normal purposes like tapping sizes , clearance holes for bolts and holes through fittings metric sizes are entirely satisfactory .

There is no authenticity issue . Almost all British locomotives were made using big imperial size drills – like 31/32 or 2 inch but these don't normally scale down to any exact size so metric drills quite ok . In any case drill sizes in models are usually chosen to suit a functional purpose rather than being strictly scaled down from full size . When it comes to totally freelance models I think anything is acceptable !

Always worth getting good tools no matter what . Rather than buying rubbish imports watch out for reduced price sets from makers like Dormer or get imported sets with some quality control from people like ARC .

MikeW

[Ian S CParticipant @iansc]

I remember dad being most disappointed, Via his woodworking magazine he bought a set of imperial twist drill, advertised as top class English made(he thought they would be better than the NZ made drills, they were cheaper). He put a drill in the Black & Decker, and started into a bit of wood(fairly hard), things did'nt feel right, pull the drill out of the work, the twist had reversed in an area about half way up the drill!! Ian S C

[KWILParticipant @kwil]

Stick to Dormer brand A002, Greenwood Tools (usual disclaimer), just a satisfied long term user.

[Nigel BennettParticipant @nigelbennett69913]

Another vote for Greenwood's Dormer drills.

Going back to the OP, it's not intended that you use drills to obtain an exact size hole. Generally if you want accuracy, ream it. If you're tapping, then the tapping size drill is open to quite a bit of latitude – very often you can get away with 50% thread engagement. Usually (it depends on the material and depth of tapping) you would go for 80% – 90% thread engagement, so just choose the nerest drill you have. The 0,1mm steps between metric drills will usually geive you what you want. Charts will show you what's needed.

Number drills are often useful to open up a hole "by a few tenths" to give you a better fit with a mating part, so it's good if you have both sets.

[Chris HeapyParticipant @chrisheapy71135]

Apart from giving you more options on size, my number set(s) are old – meaning they are much better quality drills than currently imported items. I still use them for that reason if no other. Also, I had reached the point where I had memorised the tapping/clearing sizes for all the threads I commonly used so could easily reach for the correct one without having to look it up.

Chris

[magpieParticipant @magpie]

Many years ago at the Harrogate show, I bought a 115 piece set from Arc Euro. 1/16"- 1/2", plus a set of number, and letter drills. When i bought mine at about 10.30 am on the friday, they had two pallets full of these sets. Having got my bargain, i went back to find my mates in the cafe to tell them. The conversation was overheard by lots of others sitting nearby all of them got to their feet and headed to the Arc Euro stand. When walking past the stand a few hours later they were down to a single layer on one pallet. Up untill that time i had never used either number or letter drills, however i now use them very often. If i need a hole to be spot-on size, i use one to drill a few thou under then ream to finish. Cheers Derek. P.S. They are still in use every day.

[Sub MandrelParticipant @submandrel]

I have a full number set (very nice from Tracy Tools) and one of the 115 piece sets (cheaper but most drills OK, a few badly sharpened). Both have done sterling service. If I break a drill or sharpen one away, I replace it with a single of good quality.

That way all the ones I use a lot gradually become good quial;ity ones without the spend of buying a fuill set at top price.

Neil

[magpieParticipant @magpie]

I forgot to say that the reason for the big rush to buy the 115 piece set from Arc Euro **** £15.00 **** Cheers Derek.

[Chris HeapyParticipant @chrisheapy71135]

I've seen a nice set of Cobalt HSS drills, although the point grind is a bit odd – looks like 6-facet split-point? Is this normal for these type of drills? Might be tricky to sharpen.

Chris

[MetalhackerParticipant @metalhacker]

Chris,

those look good! Do you have a link? The narrowed chisel point will make them easier to start on a centre punch mark. If it wears too much they can be gashed in again from the side with a very narrow wheel or perhaps with a Dremel in a jig.

[Chris HeapyParticipant @chrisheapy71135]

Link is here: **LINK**

Chris

[Anonymous]

Posted by Metalhacker on 15/06/2013 08:45:40:

Chris,

those look good! Do you have a link? The narrowed chisel point will make them easier to start on a centre punch mark.

I find that quality (Dormer) 4 facet drills start quite accurately without centre pops being needed. If I need better accuracy (less than a thou or so) then I start with a carbide spot drill.

I have a set of number drills that must be at least 40 years old, but hardly use them, I rarely use threads below M3, so I don't often need small drills.

For thread engagement I normally use 60-70%, may be a bit more for fine pitches. Of course that's another reason for using quality drills, they tend to cut on size.

Regards,

Andrew

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