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How can I drill a deep, non-standard, small diameter, hole?

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SillyOldDuffer08/07/2018 12:38:59
3742 forum posts
746 photos

My current project has me experimenting with a home-made pendulum clock driven by an electromagnet.

The latest pendulum consists of a mild-steel bob suspended on a 1mm diameter carbon-fibre rod.



The mild-steel bob has been drilled through 2.5mm and counter-bored to take the brass fitting on the right. The brass top-hat on the left takes the weight on it's shoulder. It's turned to be a sliding fit into the bob and is 10mm long. It's also been drilled through with a 1mm diameter hole to fit the carbon rod which is is super-glued in position.

No problem making the brass parts to fit 1mm carbon fibre rod because 1mm is a standard metric drill sturdy enough to cope with my heavy-handed metal bashing.

More challenging, I want to use the same configuration with 0.28mm diameter carbon rod and foresee two problems:

  1. Although 0.28mm drills can be bought, they're quite expensive and I can imagine me breaking several. Also I only want to drill two holes in brass, and might never need such a fine drill again.
  2. 10mm is deep for a 0.28mm diameter hole, and I can imagine the hole wandering and the drill breaking.

Can anyone recommend a way of doing this job without me spending a fortune and/or having a nervous breakdown? (Too hot & humid this week for me to do anything frustrating.)


Tony Pratt 108/07/2018 12:46:11
810 forum posts
2 photos

If I understand the use correctly the 0.28 mm drill would not need to be the whole 10 mm? How about drilling most of it say 2 mm & just say 3 mm at .28 mm dia.


Emgee08/07/2018 12:50:05
1015 forum posts
191 photos

Hi Dave

You could make 2 collars (top hat style) to keep the .28mm concentric with the 1.0mm drilled hole, so 1.0mm OD with a 0.28 hole drilled through, they could be brass or even Delrin or similar material.

Then fix the .28mm carbon rod with epoxy resin as opposed to cyno.


Edited By Emgee on 08/07/2018 12:50:38

Simon Williams 308/07/2018 12:52:10
338 forum posts
64 photos

I've never tried it for myself, but my first thought is to pick the brains of my local jewellery repair wizard. I bet he (she) knows how to drill exceeding small holes in hard things, pearls for example.


Hopper08/07/2018 12:53:04
3144 forum posts
52 photos

Precision EDM "spark erosion" process?

Make a piece like the one already made and fill the larger hole with something like epoxy. Then before it sets, poke your carbon fibre rod through it, covered in vaseline or similar release agent or kitchen plastic cling wrap or similar thin membrane material. Once the epoxy sets, remove rod, clean off membrane or release agent and you should have a hole just larger than the rod. You might have to set the job and the rod up in the lathe and tailstock chuck to keep it all aligned while the epoxy sets. Epoxy putty might be less inclined to dribble out in process perhaps?

Or make a toolmaker's reamer out of silver steel turned down to the .28 diameter and cut at an oblique angle on the end and then hardened and tempered. Good luck drilling a deep hole with that though. Maybe if you drill a standard .25 hole through first with a regular drill bit?

Michael Gilligan08/07/2018 13:01:46
12524 forum posts
544 photos


Have you considered bushing a larger hole with hypodermic tubing ?

A 24 Gauge needle is nominally 0.311mm bore.


JasonB08/07/2018 13:10:47
14613 forum posts
1452 photos

Does it really have to be 0.28mm as 0.3mm drills can be had for pennies. I recently did a gas just with one from those small 20 piece sets that was about the same depth. No fancy high speed spindles jigs etc.

I did use one of ARC's Micro Drill Adaptors but that was more because ketan had sent me one and I just wanted to try it out

not done it yet08/07/2018 13:15:05
2566 forum posts
11 photos

Diesel fuel injector engineering methods might be illuminating?

SillyOldDuffer08/07/2018 16:01:35
3742 forum posts
746 photos

My first attempt at turning 0.28mm diameter over 10mm ( 11thou over 3/8 "  failed:


This was with a new HSS form-tool at 2400rpm.

Depressed, I had decided that the best way to avoid wasting money on a twist drill was to order a collet chuck and collets, and perhaps make a jig.

Jason has saved my bank-balance. Now he's pointed out 0.3mm drills are available, I find they're cheap! (The 0.28mm carbide drills I found were £30 each...)

While waiting for the drills to arrive, I'll give packing a try. I may even have a suitable hypodermic needle.



Edited By SillyOldDuffer on 08/07/2018 16:01:55

HOWARDT08/07/2018 16:14:16
371 forum posts
14 photos

Why not drill the hole larger and bond (stick) the carbon fibre in place with a suitable filler. If you want to keep it central at one side of the part make a short bush, counterbore the hole in the bush to leave say 1mm thickness to drill 0.3mm.

jason udall08/07/2018 16:25:27
2000 forum posts
41 photos
Can I suggest
Wire of proper what is the diameter diameter ..expoxy fill bush..letting wire set.
Apply current to wire allowing wire to heat..pull wire free.. leaving hole..
Some experiment will allow wire selection to leave a hole of suitable fit

Edited By jason udall on 08/07/2018 16:26:00

Michael Gilligan08/07/2018 16:35:21
12524 forum posts
544 photos
Posted by SillyOldDuffer on 08/07/2018 16:01:35:

My first attempt at turning 0.28mm diameter over 10mm ( 11thou over 3/8 " failed:


This was with a new HSS form-tool at 2400rpm.



Have a look at how watchmakers work, Dave

... No need to follow them religiously, just understand the spirit of what's going on.



This is promoting Eternal Tools' carbide gravers ... but it illustrates some standard processes rather well:


Edited By Michael Gilligan on 08/07/2018 16:52:31

JasonB08/07/2018 18:35:15
14613 forum posts
1452 photos
Posted by SillyOldDuffer on 08/07/2018 16:01:35:

My first attempt at turning 0.28mm diameter over 10mm ( 11thou over 3/8 " failed:


This was with a new HSS form-tool at 2400rpm.

Dave someone has to say it, why a form tool and what an earth did it look like? Forgetting the small dia even the larger one looks as rough as a badgers, I think my dogs could have got a better finish if I had given them the metal to p

So while the BBQ was warming up I quickly put a bit of 1/8" silver steel in the chuck, ignoring the old gits tale that inserts tools can't be used for fine work I stuck the tool holder with a CCMT tool in the QCTP, wound up the speed but did not bother to select high ratio so only about 1100rpm and got this. No fancy form tools or having to buy gravers and diamond wheels to sharpen them with just one of my usual tools, does not look too shabby to me.


Sorry it's a bit out of focus but this is the part and a 0.3mm drill bit. Part is actually 0.012" rather than 0.011" as I just quickly touch off on the 1/8" dia and used the handwheel dial rather than measuring until it was out of the lathe.


mark costello 108/07/2018 20:03:03
477 forum posts
11 photos

Perhaps We should start a thread seeing Who could turn the smallest diameter. Lots to learn.

Michael Gilligan08/07/2018 20:21:35
12524 forum posts
544 photos
Posted by mark costello 1 on 08/07/2018 20:03:03:

Perhaps We should start a thread seeing Who could turn the smallest diameter. Lots to learn.


Nice idea, Mark

But I think we must have a 'standard material' to work with.

... Dave is presumably using Crumbly Cheshire, which is doing him no favours.


SillyOldDuffer08/07/2018 21:19:27
3742 forum posts
746 photos

I wish I was using crumbly Cheshire, then I might have an excuse!

Inspired by Jason, I just tried again using two different rods in case the metal was suspect.

The 'Form Tool' is a knife, not one specially shaped to cut a profile.


You can just about see in the photo that it's blunt.

Rather than sharpen it in my unpleasantly warm workshop, I switched to carbide inserts and failed again with two different types. The tools aren't keen to cut, and the work breaks when the cutting point digs in.

I think my problem could be insufficient sharpness plus tool height not set accurately enough for fine work.

Jason and I have much the same lathe. He made this:

I did:


Possibly one of us knows what he's doing and the other, ahem, doesn't!

This has turned into a challenge. Fingers crossed I'll do better tomorrow when it's cooler.


Edited By SillyOldDuffer on 08/07/2018 21:20:38

Meunier08/07/2018 21:23:35
177 forum posts
Posted by mark costello 1 on 08/07/2018 20:03:03:

Perhaps We should start a thread

Poor Old Duffer is having enough difficulty without trying to thread the piece !
(sitting in front of computer making comments - Sorry Mark 

I like MichaelG's suggestion of a hypodermic needle, ID a close match, a reasonable OD for drilling and easy to insert (no pun intended ).

duncan webster08/07/2018 23:45:57
1856 forum posts
36 photos

A different approach. Epoxy the carbon fibre through a small bead (jewellery type), then when the epoxy has setpass it up through the 2.5m hole and with the bob resting on a flat surface, arrange a pulley above, pass the fibre over the pulley to a small weight to keep it under tension and shift the bob around to get the thread central. Then fill the 2.5mm hole with potting resin. It's a bit permanent, but could always be drilled out

JasonB09/07/2018 06:57:10
14613 forum posts
1452 photos

Dave, I'll have a word with Neil and get him to add thin turning to his beginners series, I'm sure he would like to show how it is donedevil

Main thing is not to pussy foot about, I did that in two cuts first 60thou off dia and then the remaining 53-54thou. Did half the length that way and then the remaining so 4 cuts in total.


PS Only on ME can a question about forming a hole morph into one about turning something

RichardN09/07/2018 07:09:43
102 forum posts
9 photos

Apparently drilling small holes can create a Japanese game show- I was watching this the other week...


(For those who don’t want to watch 30minutes subtitled with far more drama than necessary- a contest between drilling on lathe vs EDM- but drilling a hole up the middle of a 0.5mm mechanical pencil lead).

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