Countersinking – guidance please…?

[SpurryParticipant @spurry]

Axminster Tools sell chatter-free countersinks…and several other types.

 

Pete

 

 

 

[Ian S CParticipant @iansc]

To make a neat counter sink, have the counter sink bit the dia of the screw head, take the sink down a short way below the surface so that the srew head is flush with the surface. his is where home made cutters come in handy,silver steel is quite OK. Just keep the rpm down, and use cutting oil. Ian S C

[Sam StonesParticipant @samstones42903]

If you like your work to look good and/or have a professional appearance, here’s another idea which removes the hassle of counter-sinking. Drill the counter-sink first!

It’s a technique I’ve used for many C/S situations, and which provides a near perfect looking result whether or not the C/S screw is in position.

It assumes however, that you are both unperturbed by altering the tip of a twist drill AND that you are capable of sharpening drills by hand.

Select a drill which is only just bigger than the head diameter of the C/S screw. Sometimes there are drills which sit in the drill stand that hardly ever get used. Even if the selected drill has to be used in a hurry later, it will still work.

Instead of the usual 30 degrees, grind the tip of the drill to 45 degrees to match the underside of the screw head. A further improvement which I alway use is `pointing’ the drill tip on the corner of the grinding wheel, effectively thinning the drill web. Some practice is needed to get this right, but it’s worth the effort. Go easy with backing off (lip relief angle), a reduced angle goes towards improving the finish. When you get the geometry right, it’s almost impossible for the drill to chatter.

There’s more good news. It’s easier to see the drill tip, you can use normal drilling speeds, and you can still drill into virtually any normal workshop material.

On the down side (there has to be one!?), a little care is now needed with a normal 30 degree drill when starting to drill the clearance hole for the screw body.

By the way, if I want a quick means of de-burring a hole, a large drill given the 90 degree treatment comes in very handy too.

Another tip if you happen to be drilling brass, is to remove the sharp cutting edges of the drill so that it has a negative `top’ rake. Because of the `nature’ of brass, this reduces the tendency for the drill to snatch or dig in.

[TerrydParticipant @terryd72465]

You should be able to obtain a high quality csk using any of the types mentioned above.  I have single flute and multi-flute csk cutters and use whatever type is at hand at the time or is suitable for the size.

 

The secrets, if there are secrets about this operation, are to use slow speed as mentioned and a quality cutter, they are not expensive, and cut steadily but with sufficient pressure to keep cutting, don’t let the tool rub. You could always use a cutting fluid, although I don’t, except with ‘difficult’ materials. Ramon’s ’emery cloth’ tip is an old and well tried technique, if things start to go wrong, if chatter starts, stop cutting and use the emery cloth.  Why that works I don’t know but I think G H Thomas has something to say about it in one of his books but I can’t remember the reference.

 

I tend not to buy ‘sets’ except drills but prefer individual tools as necessary, that usually guarantees better quality.  Ian’s tip about cutting below the surface with an appropriately sized csk is an excellent one, it makes a very neat looking job.

 

My countersinks are many years old now and are mostly made by Record Ridgeway, who don’t appear to exist any more, however I would love to be proven wrong on that one.

 

Here’s a picture of a typical Countersink, this one is about 14 mm across.  

 

 

[Ian S CParticipant @iansc]

Some timeswhen using counter sunk screws it is apppopriateto reduce the dia of the head, and by using the method I described makes a neat job, with little difference in strength, and it some times makes the difference of getting a screw in a tight spot(a muck up in the design dept), and not. IAN S C

[Sam StonesParticipant @samstones42903]

Not sure if this text has arrived in the forum thread twice.

 

Anyway, the idea of using a bit of emery cloth when countersinking was around when I was a kid in the toolroom c.1950. It was mentioned to me by one or two of the older chaps, some old enough to retire.

Tucking a bit of emery cloth under the drill/cutter probably works by sitting under the back rake, and both damping the vibration and rubbing off the chatter marks.

I like Ian S C’s idea of modifying the head of the screw. With a counter sink (drill) the same dia as the screw head, and thus forming a step, the screw can be made to sit flush with the work piece. When using Allen screws for laboratory instrumentation, besides adjusting the head size, I often rubbed and polished off the blue finish.

 

Good luck.

Sam

[TerrydParticipant @terryd72465]

Hi there,

 

I’m not sure why the image I posted is ‘Non Disposible’, it showed up ok on the original while writing, so I’m posting it again as a test, Please bear with me,

 

Terry

 

 

[the artfull-codgerParticipant @theartfull-codger]

I have used my ”home modified” countersink bits for years, especially on aluminiun which tends to build up on the cutting edges, I use broken twist drill bits found in the scrap bin, I turn the shanks down to fit in the drill chuck & then grind them to 90 degrees & the secret is to round off one of the cutting lips off so only one lip cuts & the other just rubs round, after a little”fine tuning” on the grinder they cut with no chatter, run at a slowspeed & I use ”rocol” on steel or ”trend” cutting wax on aluminium, you can use any diameter & the best bit is ”they are free”.

 

  slan go fol

[jomacParticipant @jomac]

Hi, I have had to make a number of dovetail slides, and at that stage had no mill, or a milling attachment for the lathe, making them  all out of different pieces of steel, (cutting the angle with a 9″ grinder then fileing and lapping) so after lining everything up, drilled and bolted each ends, I pilot drilled numerous holes, and as mentioned in previous threads, I counter sunk with a modified drill bit,  (10mm in this case)  and let the countersink in, a set distance below the surface, then clear drilled for the threaded section. The benefit of  machining the heads down for a snug fit in the countersink was that, I now did not have put in locating pins/dowels, and everthing stays rock solid. I did not get chatter or squealing when countersinking, and found a good use for old drills. It was a pain in the butt to do but  Im”e Happy with the result.

Bye, it’s late and frosty and Im’e too tired to stay up to watch the Footy. have a good day.

John Holloway

[alfParticipant @alf56185]

Hi

 

Your answer is to buy a set of countersinks from Greenwood Tools (advertised in ME and at shows).  Expensive about £56 a set (usual disclaimer) but they are fantastic.  Run them slowly with lubricant and your troubles are over!  I tried other types for years before evenually forking out for Greenwood set!

[Sub MandrelParticipant @submandrel]

I have a countersink I  made like a d-bit from 1/2″ silver steel. Works OK.

 

I also have some of the ‘cone with a hole’ ones, but don’t like them – I think they are better suited to deburring.

 

Neil

[Billy MillsParticipant @billymills]

One good use for the cone and hole type is in countersinking thin sheet- especially in thin soft materials. Because the hole type cuts with very low feed pressure you don’t get  a dome on the back side of the sheet.

 

Like others, I’m a convert to the single hole countersink. The cut is always chatter free, you can use higher speeds and de-burring could not be neater. This is a tool that seems to convert most users.

Regards,

Alan.

[Author]

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