Drilling! - small holes on the mill and centre drills

[raynerd]

Hi Guys
I need some advice if you will. I`m pretty useless at drilling but I have improved over the last year as I realised I was pushing the drill though too fast and it was causing my holes to wander. I have drilled small holes on the lathe and know to peck at the work piece. I really struggle drilling holes on the round surface of bar as of course my drill slides off. I want to drill a 0.8mm hole on a 3mm bar but with the work being so small, I can`t get in to centre punch without the punch sliding off. I`ve spoilt one part last night trying to do this, managed to get a small centre punch but it wasn`t enough and ended up chewing the surface of the bar rather than drilling the hole. Any advice welcome?

While I`m on the topic, although I own a large selection of centre drills I never really know when to use them. Are they really just to get the hole started with them being rigid (or is that is that a spotting drill and how do I tell them apart?) or are they for cutting the "cone" in the work piece to accept a lathe centre?

I know this is basic stuff but I`ve looked back at some of my old projects and really decided I need to think about my workmanship more, slow down with pace and eagerness to finish the project and take more time! I think it is fundamentals that are letting me down. My lathe turning is OK, my milling is getting better but it is the basics and setup inbetween that is letting me down when I move the work piece from one job to the next.

Chris

[Bluechip]

Chris

The apparently simplest thing turns out to be a PITA

You need to make a simple 'cross drilling jig'.

Plenty of ideas on the net, pick the easiest.

Dave BC

[Gauge3]

Hi Chris,

I use centre drills to make a good start on any hole I drill in the lathe, as they are more rigid than a twist drill (although you can get short 'stub' drills). They can also be used to make lathe centres as you mention.

There are lots of designs for drilling jigs out there. A quick (one off) way is to clamp a small square/rectangular bit of steel on the topslide, and 'square' it to the axis (e.g clock it or grip a bit of silver steel in the chuck and use a square of steel plate or a 6" ruler to align the block with the s/s). You don't want a huge piece as the drills will wander if too thick, so you may have to pack it up with a larger block underneath. For this I'd find a bit in the scrap box about 10mm square by about 25mm long.

Drill through the length of the block with the diameter of the rod you want to drill (e.g. 3mm). Then rotate the block 90 degrees (square it up again, using the chuck face this time. I have a bit of mild steel plate that I know is parallel to do this quickly and then carefully peck in your .8 mm drill (after 'dimpling' with a small centre drill - and you have just made a simple jig for this particular job. Leave the jig in the lathe after drilling it 0.8mm and shove you 3mm rod into the desired depth and then drill .8mm again.

Easier to do than to describe!

If you are going to do this regularly - then for small rod I think a finger plate with some simple round 'sized' guides, (easily made in the lathe as needed) is a good way to go. You can use it for lots of simple operations on small parts, so it's worth some time to get right and will last a lifetime once made.

Regards. 

[75Plus]

I use a similar method to the one posted by Gauge3 except I make mine with the drill press or mill.

Take a bit of flat bar and make sure the end is square. Clamp a stop on the table and, while holding the work piece against the stop, drill the larger hole through the wide side of the bar. Rotate the work piece 90 degrees and, using the smaller drill, drill the bar again while holding it against the stop.

The best part of this method is that NO measurements are necessary and can be accomplished faster than explained.

Edit: The picture shows a jig I made, using this method, for placing tension pins through the center of of 1/2" ali rod. The set screw was drilled through then case hardened to act as a drill bushing. It also holds the workpiece firmly while drilling.

Joe

[wheeltapper]

Hi
I see you are in the UK so you may get Model Engineers Workshop.
Harold Hall described a good cross drilling jig in one of his articles.

heres my take on it,

it fits on the lathe in place of the toolpost.

and here are two pins I crossdrilled, the pin is 6mm, the hole is 1 mm.


if you are interested I'll look up the issue No.

cheers
Roy

[Jasonb]

If I was doing it in the mill I would hold the bar horizontally in the vice, set the spindle over the centre - ruler trick if its not totally accurate or use an edge finder, then use a No1 center drill to get a start and then follow up with the 0.8mm drill.

Done this a lot on my current traction engine as there are a lot of 1/8" pins that are retained by 1/32nd split pins like this



Jason

[ksor]

--> craynerd
If the problem is centering the drill on a lathe - here is a nice solution - I found it the other day ... maybe here, maybe on HMEM - I can't remember ... as I remember there was a short video showing the trick on a drill press !

Mount your center drill
Mount the object in the chuck
Put some model clay on the end of the object
place a niddle in the clay so the niddle nearly reaches the cener drill
start spinding - but no TOO FAST !
With your finger you can now "center the niddle"
Now you just have to align the niddle and the centerdrill

But maybe it not the acuracy that you want - a simple and easy method anyway

 

[75Plus]

Hey Guys,

Look at the title of the thread


"Drilling! - small holes on the mill and centre drills"

[ksor]

I have ... but I can't read  !

[kvom]

Another idea:  use an end mill to create a flat area before using the center drill.

[Jonny]

Chris a centre drill is mainly used on mills and lathes to aid the centring of a twist drill after. If tailstocks out the drill will probably start off centrailish and cut large.
Normally used as you say to cut a cone but in your case 0.8mm you will struggle with a BS1 centre drill just touch the round leaving an indent. Swap for twist drill and get a feel for whether its cutting or not, no good just forcing it, it will blunt the drills quicker plus generate heat.

Nearly forgot, mount the round in mill vice on a suitable parallel packer and centre the X and Y to suit, even lock the beds, easy.
If its wandering off after indentation it will suggest a mill problem/s somewhere whether that be quill play, lack of torque, other mill flex some where, too fast as in motor speed or drills bending and not cutting, etc.

What else   sounds like your twist drills are not sharp and scrap unless you can sharpen at correct angle and equal else it will cut large.

[raynerd]

Well thanks for the replies. I didn`t think about using a jig, that could be useful and is perhaps the way to go although I did except that I could get the job done with just an indent and dilling directly in that.

Kvom - milling a flat is what I end up doing but what annoys me is that I then either need to mill a flat, drill and then turn it down to diameter with the hole already there. I have now had a few situations where it has been at diameter and me needing to put in the hole and hence why I decided to post but yes, a flat is what I have been doing.

OK, well some good tips and I`ll let you know how I get on, certainly a lot here to think about.

[Lew_Merrick_PE]

There are really two problems here.  (1) Locating your position dead center on your round part; and (2) drilling a small hole without wandering.

(1) There are several ways to get to dead center over your shaft.  If you have a DRO or TravaDial (yes, I am still in the dark ages), an edge finder used from either side of the bar will get you within .0002 (0.005 mm) without too much trouble.  In the days before TravaDials (long before DRO's), we used to have a widget that was a piece of v-block (about .100 inches or 2.5 mm thick) mounted in a round bar.  The v-block had spot for a test indicator to "touch" on and the shank had a collar that would hold the indicator.  When both sides of the v-block read the same on the indicator, you were dead center on the shaft.  I found my "center indicator" a while back -- and packed it up in one of the 3000 or so boxes still in storage, so I don't have a picture to post.  The drawings for making it were in one of my apprentice milling books, but I have probably "passed that along" quite a while ago (they used to be really common).

(2) The first problem with small diameter drill bits is being sure that you have them properly sharpened and centered.  Most drill bit grinding units stop at 3/32 inch (2.3 mm).  There are several "hand honing jigs" floating around.  The one described in Guy Lautard's The Machinist's Bedside Reader (#1) works.  There are several variations on this design that were in various apprentice handbooks in days of yore.  The one I like best uses a bushing with a guide pin so you can have several for different diameter and twist rates to locate the tip.  The "point" being that you hone one side of the drill and then spin it 180° to hone the other side.  Typically, by the time you have 1.5 diameter of the drill (past the lips) in the hole, it should be self-guiding -- so long as you do not collapse the column of the drill bit with too much force.

As noted above, centerdrills are shorter and stouter than equivalently sized drill bits.  Anytime you need accuracy of placement with a drill bit, a centerdrill should be your first step of operation.

Finally, beware of cheap drill bits.  They are almost never straight and even less likely to have been ground correctly.  You are far better off going to some major manufacturing facility where they "surplus" dull drill bits and dig through the bins there than to buy the cheap sets.  My "take" is that China is at least a decade away from being able to make a good drill bit.  The Indians are nearly there (and their prices reflect this).  I do have a set of (relatively) cheap Polish-made bits that are what I keep around my shop for "visitors" to use.  (You will pry my Chicago-Latrobe drill sets out of my cold, dead hands!)

[BK]

I've had this problem making hubs for spoke wheels (5"), I couldn't for the life of me get 6 centres on a piece of round brass, so I used hex, marked, drilled, turned it down to round. 2 of these made a 12 spoke wheel.

[John Stevenson]

Centre drills are a throw back to the days of using dead centres in lathes.

They have a small pip at the front to aid starting and breaking off in a part that already has 10 hours thrown at it and a 60 degree cone for the centre to be supported.

The pip's main purpose was to start the drill, provide clearance for the point of the centre and provide a reservoir for white lead as a lubricant.

Unless you are drilling a support hole for a centre forget the centre drills, times have moved on but unfortunately no one has updated any of the books, everything is repeated ad nausuem.

Industry today uses spotting drill which are a very stiff, short fluted drill made for accurately spotting holes. Stub drills do virtually the same thing at a quarter of the cost.

A tip for using centre drills when you have to is to take a new one and grind the short pip back to half it's length.
This will make it stiffer and less liable to snap in a hole, true it will reduce it's life but so will snapping a brand new one in a part.
Seeing as we mostly use revolting centres nowadays that reservoir isn't needed and you only need the bare minimum for clearance.

John S.

[Lew_Merrick_PE]

Centre drills are a throw back to the days of using dead centres in lathes.

They have a small pip at the front to aid starting and breaking off in a part that already has 10 hours thrown at it and a 60 degree cone for the centre to be supported.

The pip's main purpose was to start the drill, provide clearance for the point of the centre and provide a reservoir for white lead as a lubricant.

Unless you are drilling a support hole for a centre forget the centre drills, times have moved on but unfortunately no one has updated any of the books, everything is repeated ad nausuem.

Industry today uses spotting drill which are a very stiff, short fluted drill made for accurately spotting holes. Stub drills do virtually the same thing at a quarter of the cost.

1) Center drills are about 3X as stiff as a spotting drill because less material is removed for the flutes.

2) Here in the U.S. the "cost equation" for center drills versus spotting drills is reversed.  A good quality spotting drill costs slightly more than double the cost of a good quality center drill.

The main thing is to provide a very accurately placed "start" that places the initial cutting of a drill bit near to the lip (where the grinding is likely to be more accurate) and prevent the center chisel-edge from being used until at least 1 diameter of the drill lip is bearing on the circumference of the hole.

[John Stevenson]

1) Center drills are about 3X as stiff as a spotting drill because less material is removed for the flutes.

So why don't you see CNC machining centres using them? Less material removed isn't correct, if you take to pip that always breaks off then it's very weak in comparison to the main body.
a spotting drill is the larger diameter all the way.

2) Here in the U.S. the "cost equation" for center drills versus spotting drills is reversed.  A good quality spotting drill costs slightly more than double the cost of a good quality center drill.

Same here but now compare a stub drill to a spotting drill, hardly any difference and a fraction of the price of both.

This was yesterday afternoons work.



Believe it or not there is a 10" chuck under that lot and that is all done from drilling 8,500 holes in a series of 6mm thick steel plate with a 1/8" stub drill, nor pilot or centre drill first.

I wouldn't offer advise unless i know it works.

John S.

[Rob.Wilson]

1) Center drills are about 3X as stiff as a spotting drill because less material is removed for the flutes.

2) Here in the U.S. the "cost equation" for center drills versus spotting drills is reversed.  A good quality spotting drill costs slightly more than double the cost of a good quality center drill.

I am with John here ,,,,,,,,,, spot drills are stiffer ,,,,,,,,,,,,,,,allot stiffer

Yes they may be a tad more expensive,,,,,,,,,,,but they can be re-sharpened  ,, ever tried re-sharpening a centre drill ?

Rob 

[JimM]

John / Rob can you recommend anywhere that sells (small) spotting drills at a sensible price ?

Cheers

Jim

[raynerd]

John Stevenson, thanks for the reply, I`m now much clearer.

Chris

[jim]

centre drills are only realy used when a centre is needed.

spot drills tend to used for HSS drills and to provide a start for thin (say up to 4mm dia) or long carbide to prevent wandering.

a centre drill is no where near as strong as a spot drill! in fact we often run an M00 (stop in program) to check centre drills

[Rob.Wilson]

John / Rob can you recommend anywhere that sells (small) spotting drills at a sensible price ?

Cheers

Jim

Hi Jim

I get mine off Ebay ,,,,,,,,,,,, about a fiver each ,,,,,,,,,sometimes you can pick up some good deals ,,,,,,,,,,, cheap as chips
http://cgi.ebay.co.uk/6MM-NC-SPOTTING-DRILL-90-DEGREE-COBALT-SPOT-DRILL-NEW-/140418151078?cmd=ViewItem&pt=UK_Home_Garden_PowerTools_SM&hash=item20b192f2a6#ht_1259wt_1137

Regards Rob

[AdeV]

Fascinating stuff... I learned my early machining knowledge (before I found this forum) from Darrell Holland's videos on how to run a vertical mill; and he used centre drills, just as Lew describes.

As a result, I bought a set of 8 centre drills - in various sizes - for 20 quid, not long after I bought the Bridgeport. And yes, I've snapped 3 nibs off, so far... usually because I've plunged into the work too fast for the drill.

I'll definitely be looking at spotting/stub drills from now on, & will keep the centre drills for lathe work.

Qs: Why are spotting drills so much more expensive than stub drills, and - seeing as I'm only an amateur machinist - is there any reason to buy a spotting drill in preference to a stub drill?

[John Stevenson]

Personally I don't think so.

On those dividing plates I do there are literally 1,000's of holes, one has a 127 row right on the outside and it's just possible to fit this row in with 12 thou between holes.

If you get a drill wandering it stands out like a sore thumb two holes will be broken together and another two will have a large gap between them.
I buy good quality stub drill, usually Guhring, from J&L in quantity and change the drill every 4 plates, that's about 2,000 holes, if I do this I get no problems, any more and it's pushing it.

I do regrind drills but I have a precision Swiss drill grinder that fits in a shoebox and cost £9,000 when new and no I didn't pay that. I only do this not to save money but a correctly ground drill will do 6 plates, remember drills are produced on production equipment to the best economical shape, not the ultimate shape.

This is why Meteor and Christian are still making drill grinders that cost up to 15K and fit in shoe boxes. If there were no demand they would go out of business.

John S.

[AdeV]

This is why Meteor and Christian are still making drill grinders that cost up to 15K and fit in shoe boxes. If there were no demand they would go out of business.

Do you have a piccie or model number of your grinder? I've been a'googlin', but nothing jumps out as being super-exceptional & shoebox-sized (let alone £15k...).

Would your machine deal with a 5/8" x 600mm bit....?