Drill bits

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David B
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Drill bits

Postby David B » Wed Aug 03, 2016 2:50 pm

I have had a couple of duff lots of small drill bits from my local model shop and am desperately in need of some 0.3mm & 0.35mm.

Can anyone suggest where to get any? I have looked on the web but some prices are silly - £8 each ???? - others are £2 to £3 each. I have, up to now, been used to paying £1 a piece and they have been fine but the last couple of lots were just not ground properly.

garethashenden
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Re: Drill bits

Postby garethashenden » Wed Aug 03, 2016 2:59 pm

I've used these, or something very similar, with success. http://www.ebay.co.uk/itm/10pcs-0-3-to- ... SwfZhXM~ya

0.35mm isn't one of the sizes, I'm not sure how critical that is to you. Would 0.4 work instead? I like the 1/8" shank, it makes them very easy to hold. Just be aware that they are made from Chinesium, so they can break without provocation. Best to buy two boxes.

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John Bateson
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Re: Drill bits

Postby John Bateson » Wed Aug 03, 2016 3:43 pm

Chronos,
http://www.chronos.ltd.uk/acatalog/Engineering_Menu_Metric_Sizes_171.html
Seem to do most sizes in 0.1 mm increments

John

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David B
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Re: Drill bits

Postby David B » Wed Aug 03, 2016 3:51 pm

Thank you both. I don't know why I didn't think of Chronos - I have bought from them but very occasionally. I will look at them more often in future.

Size is important (!!), Gareth. I like wire (or any part) to fit as snugly as possible so I have drills going up in 0.05mm steps. Thanks for the link to Ebay, but I don't buy sets as I would accumulate some sizes and run out of others.

billbedford
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Re: Drill bits

Postby billbedford » Thu Aug 04, 2016 7:48 am

Try CNC Tooling Type N is a general purpose drill, type H is for brass and type VA is for Stainless Steel.
Bill Bedford
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David B
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Re: Drill bits

Postby David B » Thu Aug 04, 2016 4:37 pm

Thanks, Bill.

John Palmer
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Re: Drill bits

Postby John Palmer » Thu Aug 04, 2016 10:04 pm

I distantly recall an article in Model Railways or MRN, possibly by Colin Binnie, suggesting the use of piano wire with a suitably ground tip to provide you with 'drills by the yard'. The grinding involved the formation of a spade bit with appropriate angles at the tip; no spiral fluting involved. For drilling through sheet metal, might this be a solution worth considering?

billbedford
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Re: Drill bits

Postby billbedford » Thu Aug 04, 2016 10:48 pm

Not if you want the holes to be a specific size.
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Will L
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Re: Drill bits

Postby Will L » Fri Aug 05, 2016 10:35 am

billbedford wrote:Not if you want the holes to be a specific size.


Not necessarily. You can drill them small and ream to size, although that may not be practical for anything much under 0.5mm. Which I tends to be the way I do it anyway.

billbedford
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Re: Drill bits

Postby billbedford » Fri Aug 05, 2016 10:36 pm

Well, yes, but a badly ground drill will always give an oversized hole. As for reaming, I assume you mean broaching, as the smallest reamer I've come across would be 1.5mm.
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Will L
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Re: Drill bits

Postby Will L » Sat Aug 06, 2016 9:48 am

billbedford wrote:Well, yes, but a badly ground drill will always give an oversized hole. As for reaming, I assume you mean broaching, as the smallest reamer I've come across would be 1.5mm.


You'd be right.

Will

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Tim V
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Re: Drill bits

Postby Tim V » Sat Aug 06, 2016 4:52 pm

John Palmer wrote:I distantly recall an article in Model Railways or MRN, possibly by Colin Binnie, suggesting the use of piano wire with a suitably ground tip to provide you with 'drills by the yard'. The grinding involved the formation of a spade bit with appropriate angles at the tip; no spiral fluting involved. For drilling through sheet metal, might this be a solution worth considering?

D drill bits can make very accurate holes.
Tim V

Terry Bendall
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Re: Drill bits

Postby Terry Bendall » Sat Aug 06, 2016 8:03 pm

Tim V wrote:D drill bits can make very accurate holes


Yes but ...

The D bits that I am familiar with are mode from Silver steel and half the diameter is removed at the end leaving a semi-circular cross section to the end for say 20mm or so. The end is then filed to an angle from one side to the other, and some clearance provided. It then of course needs to be hardened and tempered. The design of this type of D bit means that there is no centre point so it cannot start the hole, only open up an existing one. I have not used one enough to be able to judge.

John Palmer wrote:The grinding involved the formation of a spade bit with appropriate angles at the tip;


According to L H Sparey in the Amateur's Lathe these are otherwise known as flat or tool post drills. In order to be accurate they must be symmetrical about the point, something that is nor easy to achieve.

For my money, standard twist drills are sufficiently accurate for the vas majority of what we need to do.

[quote="David B"] I have drills going up in 0.05mm steps

Each to his own of course. :)

I think this depends on what you are doing. Sometimes the use of number size drill bits will give a better range of clearance holes. To take a few examples:

0.33mm dia.wire is 0.0135 inches dia. which is the same size as a No.80 drill bit. I generally find this a bit tight so will use a No 79 drill although these are not easily available. A 0.35mm drill is 0.135 inches which gives sufficient clearance.

0.45 dia. wire is 0.0177 inches dia. A number 77 drill is 0.0180 inches dia. and a 0.5mm dia. drill is 0.0197 inches dia. which would give a lot of clearance.

0.7 dia. wire is 0.0276 inches dia. A no. 70 drill is 0.280 inches and a 0.75mm drill is 0.0295 inches dia. The No 70 drill with give a better fit.

Note that with all of these we are only talking about one or two thousands of an inch difference which for the majority of applications does not really matter.

Moving up a bit, 1/8 inch is 0.1250 inches. a 3.2mm drill bit is 0.1260 inches which would give 1 thou of clearance and a no. 30 drill is 0.1285 inches giving 3 thou of clearance which might be just right for an axle. If it is a 3mm dia. axle, which is 0.1200 inches then a no. 31 drill, which is 0.1200 inches would give 2 thou clearance which would be about right,

The problem of course is that small size number drills are getting more difficult to find, and when you do they are more expensive. I tend to go for the nearest metric equivalent. How much clearance is needed in a hole will depend on the application but is something is going to be soldered or glued in place the amount of clearance in my view is not very important.

A table of decimal equivalents is a useful addition to the toolbox.

Terry Bendall

John Palmer
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Re: Drill bits

Postby John Palmer » Sun Aug 07, 2016 1:30 pm

For my part, I haven't found it hard to come by number series drill sets, though I've yet to encounter a set comprising the full range from 1 to 80.

A couple of years ago I picked up a nicely boxed set covering the 1 to 60 range at the BSMEE show at Thornbury for about £18.00, and a set covering the 61-80 range seems to be readily available either from Chronos Enginering or Tracy Tools for £5.00-£6.00. At a little more than 25p per drill bit, I wouldn't find that an unacceptable price unless I expected to suffer a high attrition rate of a particular size.

The worst problem I have found with the 61-80 set is the design of the plastic box that holds them. The sliding cover used to access individual drills relies on friction to be held in the closed position, and the frictional grip can be so tight as to make it impossible to move the cover without excessive force. All too easily you can either break the box or distribute the entire drill set in all directions - I've managed to avoid doing that yet, but the time is likely to come...

Wouldn't be without my Zeus tables, not only for tabulating both the metric and English sizes of drills but also for tapping/threading dimensions.

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45609
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Re: Drill bits

Postby 45609 » Sun Aug 07, 2016 8:49 pm

I've posted it elsewhere on the forum before but this IMHO is an invaluable reference.

Model Engineers Handbook

Drill tables on page 94

Morgan

Terry Bendall
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Re: Drill bits

Postby Terry Bendall » Mon Aug 08, 2016 6:52 am

John Palmer wrote: I picked up a nicely boxed set covering the 1 to 60 range at the BSMEE show at Thornbury for about £18.00, and a set covering the 61-80 range seems to be readily available either from Chronos Enginering or Tracy Tools for £5.00-£6.00.


Certainly a good bargain, but perhaps more for those just starting in the hobby, I have always felt that full sets of drill bits, just like sets of taps and dies, comes into the "nice to have but not essential" category. A friend from many years ago used to buy the drills he needed and kept them in a partitioned box, and taps and dies were kept in tins with the relevant tapping and clearance drills. Having said that, I do have a set of metric drills from 1.0mm - 5.9mm in 0.1mm steps which I bought about 30 years ago and at about the same time I picked up an empty wooden box for BA size taps and dies which got gradually filled up over a few years. Second hand stands at model engineering exhibitions are a good source of used tools in good condition and competitive prices.

I find that even with the 61-80 sets, there are quite a lot that I don't use. The plastic boxes with sliding covers are useful for keeping the drills in place, especially when the tool box goes to exhibitions and I have not found the sliding lids to be too tight - more often the opposite and a piece of tape is needed to keep the lid in place.

Terry Bendall

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Penrhos1920
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Re: Drill bits

Postby Penrhos1920 » Wed Aug 10, 2016 7:51 pm

garethashenden wrote:I've used these, or something very similar, with success. http://www.ebay.co.uk/itm/10pcs-0-3-to- ... SwfZhXM~ya

0.35mm isn't one of the sizes, I'm not sure how critical that is to you. Would 0.4 work instead? I like the 1/8" shank, it makes them very easy to hold. Just be aware that they are made from Chinesium, so they can break without provocation. Best to buy two boxes.


I've found these tend to break easily when drilling thin brass sheet as the drill snatches just before breaking through.
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jasp
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Re: Drill bits

Postby jasp » Wed Aug 10, 2016 10:00 pm

Breakages with small tungsten carbide twist drills are understandable.
They are much more brittle and, as these are designed for printed circuit drilling are intended to be run at 10,000rpm upwards.
HSS drills have, in comparison to TC, a degree of flexibility, hence reduced breakage with momentary stoppages like "breakthrough"
Jim P

allanferguson
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Re: Drill bits

Postby allanferguson » Wed Aug 10, 2016 11:22 pm

jasp wrote:Breakages with small tungsten carbide twist drills are understandable.

I would say "inevitable" in our usage. If I could get a perfectly rigid drill stand, and an equally rigid means of holding the work, then I would use them. Otherwise.......

Allan F


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