Hi folks, I need to drill quite a number of 1mm holes in brass sheet. The holes are about 3mm deep. I consistently get trouble with the drill skidding- you can hear it, and the brass gets hot. The drills sometimes snap as they break through, leaving the broken fragment stuck in the brass stock. I assume this is due to the way the drill is ground, but I can't figure out what to do about it. I have enough trouble grinding large drills!
I'm using a Proxxon drilling machine at 8500 rpm.
I wondered about making a jig which would be a bit of round stock turned to the correct angle (which is what?) with a 1mm hole through the centre: poke the drill through and use slipstone on the tip, but I don't really know what I'm talking about here.
I guess you've been reading up on your recommended drilling speeds for various materials which for brass says 100-150 surface ft/min which equates to 10k to 15k rpm for a 1mm drill. These are all well and good but are designed for high speed production with everything optimised and still giving a compromise between metal removal and tool wear/breakage. I find the best thing to do is ignore them.
The right machining speed for you is whatever your machine is comfy at and which gives good results. When your only tools are a Colchester Student which runs to 900 rpm and a mill which runs to 1800 you just get used to machining at the machine's speed rather than what the book says. You can machine just about anything slowly without tool wear or breakage but if you go fast to save time you tend to lose more of it in the long run.
First off try dropping your speed right down. I've drilled brass for carburetor jets at 1mm ish on the lathe slowly and had no problem at all. At
900 rpm you belt through the stuff like it's butter. You also don't need coolant on brass at low speeds which save a bit of mess. Try 2000 rpm and work up if things go well.
As for small drills breaking on the way out of thin material, it helps to have something sacrificial underneath the stock to drill into so there isn't a trailing edge for the drill to snag on. Even hardwood ought to help. Aluminium or more brass would be ideal of course. You need to clamp down close to the hole though or there'll still be a small gap.
1mm drills are pennies so don't even bother trying to sharpen them unless you've got a really good eye. Buy plenty and change them when they start to squeal. If you run slow they won't go blunt in the first place.
Let us know how you get on.
-- Dave Baker Puma Race Engines
formatting link
Camp American engineer minces about for high performance specialist (4,4,7)
A bit long so get a coffee while I write the history of small hole drilling.
........................
Ready ?
I do a lot of small hole drilling in large numbers and know what you are talking about. For a while I used to buy good quality drills and re sharpen them from new. Contrary to popular opinion commercial drills even good ones like Guhring are machine ground in the most economically way which is the shape we are used to seeing, a sweeping curve from the leading edge is the best way I can describe it.
The reason I reground the drills was not being Jewish, but the cost effectiveness. I have a part costing less than a pound, a drill costing the same but two hours work invested in each part. A broken drill towards the end of the part after 1400 odd holes costs me two hours labour at commercial rates.
To this end I bought a small Meteor drill grinder that can handle drills in two collets from 0 - 3mm and 3 - 6mm. In my case the 3 - 6mm collet is missing and a new collet is over £1,000 - yes not a mis-print, £1,000. These grinder new cost about £12,000 to £17,000 and will fit into a shoe box.
The fact they still sell them and have a market for them proves there IS a need so it's not bullshit.
Christian also make one about the same price and quality.
These little grinders can't sharpen as a swept curve as we are used to but do 4 and 6 facet grinding, perhaps this tells us something. Since resharpening a brand new drill as a 4 facet I can get 2 to 3 parts per drill, before I could only get one most times.
Three months ago the rep from WNT cutting tools at Sheffield called round and offered some drills, stub drill, TiN coated that he said were very good and would do what I wanted out the box.
OK try anything once, ran these and kept going until it broke, I got 4 parts out of this and it didn't break but got very raggy on the 5th part.
On looking at this thru a glass it's a 4 facet grind but the cutting facet is only about 10 thou wide. It's a perfect bit of grinding, so smooth and even that it's obvious they have invested in state of the art CNC grinders to do 4 facet grinds economically.
The result is that I'm now using these WNT off the shelf drills, running 4 parts and chucking them in the general drill box after.
--Two tips: Try using cobalt drills: they make a distinctive "squeak" right before they fail, so you can swap 'em out in the nick of time. Also, I'm assuming these are *not* through holes and that indicating a replacement drill is a hassle? Make one of these:
formatting link
I call it a "drill depth presetter" but being as I can't sell 'em worth beans feel free to clone one. Sigh.
Thanks for all that, Dave. I've just tried lower speed with immediate improvement. I might be able to get something underneath but it's not that easy. I buy the drills in tens, usually Presto, happy to chock them away- it's the breakages which are a real sod. Cheers Richard
That's the kind of thing I was thinking about, but fairly difficult at this size!
Yes, I've used D-bits before, but not this small. Depends how long they take to make (I should say 'make correctly'!!) , there's precious little time to spare in the workshop. The smallest D bit I've ever seen was ground from a piece of banjo string, for a carb. jet.
This is the issue with me. These are musical instrument keys (think clarinet) with at least a couple of hours work before I drill the hole, which is to rivet on the spring.
Oooh noooo...anything but rivetted springs! Earn a place in heaven...tap the holes and use screws ( 9 or 10 BA is still used ). There's nothing like having to replace a broken rivetted flat spring to make your day go bad. Makes the punter mad too...when they see the bill for what is otherwise a fiver's worth of work.
No chance. These are Northumbrian Pipe keys (I just mentioned clarinet as an example). The keys are 2mm wide by about 2.5mm deep; 10BA requires a 1.45mm tapping hole, and seems to be 1.7mm max. diam. Cheers Richard
Phew, that's ok then...don't get many Northumbrian pipes in here! FWIW, leaving a generous ( tall ) rivet head will facilitate easier replacement of any broken springs...the head can be swedged at least once to allow the existing rivet to be reused.
Good point, Wayne. I always use stub drills for critical holes. One thing I can never understand is that although sets of normal length jobber drill are everywhere, I have never seen anyone offering a set of stub drills. A set of 1.0 - 6.0 x 0.1mm stub drills would be a very valuable addition to any workshop, but buying them individually is very expensive.
I'm a fan of 4 facet drill grind geometry and use a home brew grinder to grind small diameter drills. What diameter and material are you drilling and what RPM do you find most economical? Jim
Thanks, Richard! with JF Bryan( whom I never met) Was a member of his Youth Club which he ran for us raggy arsed kids. It does give me a write a long accolade but will make a Pigg of myself and talk of Cherries. GH Thomas writes " I imagine that the smallest drill that a model engineer would use in a drillin g machine is 1/16th***** and Cherry Hinds makes her own
1/64th split pins and drills suitable holes for them**** and Thomas concludes with account of one locobuilder drilled 1500 holes of 1/32 to do the tanks!
In fairness, the clear answer is using the right tools. As addition, I have just picked up the GHT Drilling attachment from next to where John was at the Midland Show.
Ain't got my 10mm Pultra now
When TWO of highest award holders(or 3) in the Society have more than demonstrated the successes- well,
One must look at just how good or bad tooling is
Kindest regards from the other side of "Cumberland Gap"
PolyTech Forum website is not affiliated with any of the manufacturers or service providers discussed here.
All logos and trade names are the property of their respective owners.