Countersinking

[freddo]

G'day all,

I wonder if there is a trick to determine how deep to make a countersink so that the head of the screw will be flush with the material - short of trial and error that is?

Freddo

[dickdastardly40]

I use a drill that is the same diameter as the screw head and plunge until it just begins to cut at full diameter. The drill angle is usually 118 deg and the countersink head is 120 deg so it is close enough for me. I sometimes find I have to go a little deeper than flush but doing it this way means that the screw head does not have a 'crater' surrounding it.

After the first one if doing a row of holes, I set the depth stop on the drill press and repeat, failing that you could trial and error the first with a countersink bit in scrap if necessary and then do the same with the depth stop.

Al

[houstonceng]

Hey Al. Where do you buy screws with 120 degree on the C/Sk heads. Mine are 90 degrees so, using your method, I'd have to regrind the drill.

Commercial C/Sk bits are available to do the same task. Of course, you need one for each size of screw and they aim't cheap. I've made a few like "D" bits with a guide-pin same size as the clearance hole for the screw. They work ok.

[freddo]

With the greatest respect to Al's 118 dgree drills, like you, houstonceng, mine screws aren't anything like 118 dgrees. I tried that on a piece of scrap, and piece of scrap it remained. 90 degrees seem to be the order of the day with my countersinks and screws (although, I do have a 60 degree one for nipples!)

I await the input from the maestros

Freddo

[dickdastardly40]

Mea Culpa,

You know what, I've countersunk a bazillion holes in both wood and metal over the years and generally always used the tip of a drill due to not having a countersink bit. Shows how much I know! I apologize wholeheartedly for giving bum advice.

I think the method of trial and error for the first hole using the drill press and depth stop will hold up, have you tried that?

Al

[russell]

I bought a set of cheapo metric drills for 2 euro at the local supermarket and reground them all at 90 degrees. No problems at low speeds.

Russell.

[Shawki Shlemon]

I must give Al some credit , I use his method but by resharpening drill bits to correct angle and keeping them for that purpose, after all I only use a few sizes of screws and drill bit are cheap . The difficult part is when you want to do it in a thin material , and in this situation it is a matter of compromise .The only other way I know how in thin metal is to stamp the screw into the metal and have the countersunk in the matching part if it is thick enough .

[abby]

I must admit that I use the same method as Shawki , but I rarely use countersunk heads exept for wood work , I use a bigger clearance hole so the screws don't "bottom" , main problem using this method on larger sizes is the countersink holes being - whats the word to describe a 50p shape ?

[gugger]

For countersinking just a bit of a rag under the drill and the holes will turn out perfectly round and clean. It is an old trick and works since generations.

Walter

[simonwass]

abby said:

I must admit that I use the same method as Shawki , but I rarely use countersunk heads exept for wood work , I use a bigger clearance hole so the screws don't "bottom" , main problem using this method on larger sizes is the countersink holes being - whats the word to describe a 50p shape ?

A slower speed and secure clamping down does the trick for me.
Countersinking bits are short & stubby so are rigid, its only the workpiece moving about which allows the multi-lobed cut.

[petercolman]

With thin stuff use the rag trick but back the job with some similar material and that will give the support you need.

[Smifffy]

"For countersinking just a bit of a rag under the drill and the holes will turn out perfectly round and clean. It is an old trick and works since generations."

Hi, Can you elucidate on this please - I'm not sure exactly what you mean, but if it'll give me clean countersunk holes, I'm going to try it

Mark

[gugger]

Smiffy,

What I do is, sharpen a drill of the required head size to 90º. Then feed the drill carefully to the approx. depth. Most likely you then will have some shatter marks and the hole will not be exactly the round shape it should be.
Now take a bit of fine rag fold it once or twice, but it under the drill and very slowly lower the drill to the required depth.
It was one of the first things I did learn when I started as an apprentice 51 years ago.
Try it and after some practise you will get the desired results. As petercolman said, for thin material use a bit hard wood under the material.

Walter

[freddo]

Thanks for all the various replies, but it does seem there is not a "look-up" table for countersink depths.

I'll continue with my trial and error methods.

Cheers

Freddo

[houstonceng]

freddo wrote :- SNIP "it does seem there is not a "look-up" table for countersink depths" SNIP

Problem I've come across is that a lot of C/Sk screws don't have a sharp edge to the head - more a small straight edge parallel to the thread. Consequently, these need the 90 degree drill method a bit deeper - so that you avoid the excessive surrounding groove that a "rose-bit" (or similar) C/Sk bit would produce.

Then, again, some C/Sk screws don't have the same sized heads as others. Two batches of 4BA, for example, from two sources = two different head sizes.

I, usually, do a trial and error for the first screw - or on a similar sized bit of scrap in preference - and then use the setting on the pillar-drill or mill to get 'em all the same.

[barryk]

Hi Freddo

Go to this url: www.myvirtualnetwork.com/mklotz/

It'll take you to Marvin Klotz's Home Shop Utilities and I can't recommend this site highly enough.

You'll find a list of mostly small, very useful, zipped applications & right down near the bottom of the page is an app 'csk.zip' which appears to be just what you require.

It's well worth a look at all the other apps too, there is some really excellent stuff here.

They are all dos programmes and all those I have downloaded will happily run in Windows XP - you just need to download the zip files & unzip to a suitable directory.

After unzipping, look in the directory and you will usually see the application 'csk.exe' and a text file. Do not run the app yet, right click on it, go to properties/program and un-tick the 'close on exit' box'

escape from properties, double click on the application, enter the data asked for and away you go.

BTW - hi all, this is my first post after lurking for a coupla weeks, I hope it proves to be helpful

Cheers
Barry

[freddo]

Barry, that's just what I was looking for - plus so much more. Very many thanks.

And I think this demonstrates what I have seen on this forum that too many members sit back and roast chestnuts on the fire instead of actually getting up and cracking the shells themselves.

I reiterate - folk like you Barry, making your first post, have probably contributed more to the real model engineers here than an awful lot of the long term members.

Thanks again

Freddo

[Noddy]

Thanks barryk,

That stuff looks really useful

Keith

[freddo]

Just a passing 2.00 in the morning insomniac comment.

I have to say from reading the posts in this thread, the some of the esteemed members here don't seem to read the question.

I've been given a few answers about how to get circular holes with countersinks - with the greatest possible respect, that wasn't what I wanted to know - that's easy - clamp the workpiece to a rigid machine ..... All this using pieces of rag is for worn-out old machinery.

G'day all (or should it be g'd yesterday), and many thanks again to Barry, I now know how to do it.

Freddo

[alanstepney]

freddo said:

Thanks for all the various replies, but it does seem there is not a "look-up" table for countersink depths.

I'll continue with my trial and error methods.

Cheers

Freddo

In fact, and from memory, there IS a British Standard which covers it.
Whether or not that is now an ISO standard, is metric rather than Imperial, is still applicable, or whatever, I have no idea.