# Countersinking



## Heffalump (Jan 20, 2014)

Hi chaps, I *think* I have posted this in the right place, if I have not could someone move it?

On the plan I am about to build I need to drill a 3mm diameter hole and countersink it. There's no specification as to the size of the countersink. I'm assuming that most metric sizes use a countersink angle of 90 degrees? Are countersink bits sized according to the hole they are countersinking? Do I just pick a 3mm countersink bit and cut it in until I reach the edge of the angle? (I've never sunk before, can you tell?)

I have tried googling, but I'm sure this is such a schoolboy question that there's not much info around about it!


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## Sshire (Jan 20, 2014)

Machinery's Handbook has the head height specs. So with a 90 degree angle, simple trig to figure depth. 
There's probably charts for depth on the Interweb. Google that


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## MachineTom (Jan 20, 2014)

If the hole is 3MM, a 3MM countersink is NG.As the head is likely 6mm in diameter. When you measure the head you will likely find that it is not an even size, So the next size larger is used. If there are several holes to do then you can set the DP for the correct depth and quickly do them all the right depth.

Now if it is a counterbore those tools are often sold by the bolt size not the cutter size.


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## abby (Jan 20, 2014)

Hi , presumably the c/s is to take a c/s head screw , what I do is measure the diameter of the head then choose a drill a couple of thou bigger.
With the depth stop set on the bench drill I open up the screw hole and try the screw , adjust the stops and have another go at it until the head fits nicely in the hole.
If I have several to c/s I now do them all at the same setting.
Works fine for smaller sizes and no countersink necessary.


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## zimma (Jan 20, 2014)

abby said:


> Hi , presumably the c/s is to take a c/s head screw , what I do is measure the diameter of the head then choose a drill a couple of thou bigger.
> With the depth stop set on the bench drill I open up the screw hole and try the screw , adjust the stops and have another go at it until the head fits nicely in the hole.
> If I have several to c/s I now do them all at the same setting.
> Works fine for smaller sizes and no countersink necessary.



Standard Jobber drills are 118 degree point, whereas proper countersink bits are 90 degree points. Using standard drill bits to make countersink holes is just going to leave a gap underneath the head of the screw, with only a small contact patch at the base of the screw. It would work fine if you used a 90 degree spotting drill, or other drill bits that have been ground to 90 degree point.

Graham


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## zimma (Jan 20, 2014)

Heres some standard countersink bits for metric bolt sizes.

M3 -> 6.3mm countersink bit
M4 -> 8.3mm countersink bit
M5 -> 10.4mm countersink bit
M6 -> 12.4mm countersink bit
M8 -> 16.5mm countersink bit
M10 -> 20.5mm countersink bit

Graham


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## kvom (Jan 20, 2014)

I have a set of 4 countersinks of varying sized, and generally use the largest that fits the drilled hole.  I manually drill the first in small increments testing the depth against the screw.  When I have the correct depth I set a spindle stop to drill the rest.


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## Heffalump (Jan 20, 2014)

Hi all, you've successfully helped this to click into place in my head, thank you! Particularly Abby but I'm not sure about the angle with a normal drill bit.


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## Walltoddj (Jan 20, 2014)

If you go to this web site you can download a very handy book with bolt and screw specs. It cost nothing but has a whole lot of info. If you have a problem getting it let me know I'll send it to you in an email.

http://acfcom.com/ 

http://acfcom.com/fastener_handbook/fastener_specifications_handbook.htm

http://www.numberfactory.com/nf_metric.html

http://www.accuratescrew.com/Electronic-Fastener-Technical-Tips-Industrial-Links.aspx

Todd


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## abby (Jan 20, 2014)

On such small diameters the contact angles will not effect the efficiency of the joint , we are not building spacecraft afterall.
With c/s head screws I only buy the socket drive type and usually put a drop of loctite under the head.
A good many potential model engineers are put off the hobby by the quantity of tools and equipment others would have you believe you need.
Most of the recommendations are un-necessary and usually made by armchair engineers.


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## goldstar31 (Jan 20, 2014)

As a sort of follow on from Abby's take, the cheapest solution is nothing more than a depth stop made of a bit of round- metal or wood or plastic held by something- be it a grub screw or a dollop of glue of some sort.

 In the past, I had made up a set for centre drills and wall drills and ordinary drills and I went out and toted home a set of very cheap sh1te drills - and found that there was quite a nice set made up in steel/iron or something bright with a grub screw in each- tailor made by some inscrutable gentleman for a bowl of rice( grub screw, bowl of rice- never mind, it's junk!)

 Regards

 Norman


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## Walltoddj (Jan 20, 2014)

I've always used 82 deg countersinks with no problems, only time I've had a problem is if someone get over big a gorilla when they tighten them then you try a center punch to break it loose or drill it out but I never use Loctite or glue of any type on flat head screws.

Todd


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## bazmak (Jan 20, 2014)

Drill a clearance hole thru say 3.3mm and use any size csk. Trial and error using the screw as ref
until the fit suits.Ie i like to have an exposed screw level but slightly lower if a part covers it
Use the screw to check as sotted hd and socket heads are different dias.I never measure
the screw hd/hole dia.I only use a depth stop when i want a large quantity all the same
CSKs are 90o but drills are 118o I have a quantity of drills ground to 90o so can can fit a csk screw
well below in a csk/cbore hole,i also use these mfor cbore for cap screws,which t machine
under the head to 90o.A csunk to a tapped hole gives a precision location fit in place of dowels
I usually mark out ,drill and fit 1 screw then do the rest while the items are fitted together
Its almost impossible to drill/tap and csk many holes by marking out


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## Walltoddj (Jan 20, 2014)

I forgot about one problem I've run into with flat heads, at times the head is thicker than the material your trying to hold. I've had to countersink the threaded hole a little deeper to get the screw to tighten. just a thought that might help!
Most flat heads are 82 deg go Smithfast.com. Lots of screws and specs

http://www.smithfast.com/toc.htm

Todd
http://www.fastenersuperstore.com/sockets. Shows 82 as well


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## Wizard69 (Jan 20, 2014)

Walltoddj said:


> I've always used 82 deg countersinks with no problems, only time I've had a problem is if someone get over big a gorilla when they tighten them then you try a center punch to break it loose or drill it out but I never use Loctite or glue of any type on flat head screws.
> 
> Todd




A good point here, flat head screws installed properly seldom need Loctite to hold them in place.  I'd be the first to suggest a proper counter sink for metric drills though.


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## Wizard69 (Jan 20, 2014)

abby said:


> On such small diameters the contact angles will not effect the efficiency of the joint , we are not building spacecraft afterall.


We may be building things that vibrate a bit.   


> With c/s head screws I only buy the socket drive type and usually put a drop of loctite under the head.
> A good many potential model engineers are put off the hobby by the quantity of tools and equipment others would have you believe you need.


Overall counter sinks are not that expensive.  


> Most of the recommendations are un-necessary and usually made by armchair engineers.



That might be going a bit too far.   Flathead screws properly installed are very nice and hold well.  Given that though it isn't too difficult to simply regrind a drill bit to 90°.   There are likely a number of ways to get the proper counter bore without actually buying something.  In the end if you are putting a lot of time into a project a few minutes to do the counter bores right isn't a big deal.


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## Walltoddj (Jan 20, 2014)

Wizard69 said:


> We may be building things that vibrate a bit.
> 
> Overall counter sinks are not that expensive.
> 
> ...



I agree counter sinks are not that expensive. Searching for info I find a lot on standard flat heads at 82 deg, I finally found a metric chart that showed 90 deg on metrics. I've got to tell you I've used 82 on all holes for over 35 years and have never had one come loose on any of the machines I've worked on at  GM so I'm sure what ever works best for you do it I'll keep with has worked for me.

Todd


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## zimma (Jan 21, 2014)

abby said:


> Most of the recommendations are un-necessary and usually made by armchair engineers.



I don't think the suggestions given warrant a reply like that.

The OP asked a question about countersinking using countersinking bits. Some useful information was given about countersinking bits in the replies, and there was also some alternatives given, which depending on the quality of output required may be adequate.

Not wanting to use the right tool for the job is your choice, but lets give the OP all of the information on how to do a job and let him make up his own mind up.

A new HSS-Co Sherwood M3 countersink bit can be had for less than the price of 2 pints of beer by the way.


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## abby (Jan 21, 2014)

Take the comment anyway you like Zimma and if you want to buy countersinks that is your choice , I prefer to spend my money on useful tools.
If I really did need a countersink then I would make one anyway , not because of the cost but because I don't want to wait 3 or 4 days for the post to arrive.


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## Tin Falcon (Jan 21, 2014)

First of all lots of good answers. 
If I am just countersinking a couple holes I grab my hand held deburing /countersinking tool and countersink the hole. put the screw in to check depth usually have to cut a little more and repeat until the top of the head is a few thousands below the surface of the plate. 






In the aircraft sheetmetal trade when one often has to countersink many holes and make them a precise depth there is  a tool for that. 




A micro stop countersink. Is great when you need to do lots of holes. 
the downside is you need a cutter for each size hole. These are availble on e-bay.
Tin


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## Walltoddj (Jan 21, 2014)

abby said:


> With c/s head screws I only buy the socket drive type and usually put a drop of loctite under the head.
> 
> A good many potential model engineers are put off the hobby by the quantity of tools and equipment others would have you believe you need.
> Most of the recommendations are un-necessary and usually made by armchair engineers.



First off they are flat head screws and if used properly you would never need Loctite to hold them.

You don't need any tools but if you are a tradesman you learn to to make or procure the tool you need to do the job right without cobbling it, to use a drill point would be a last resort to any true tradesman. So you want to think about what is because was an Engineer and a Tool maker for over 30 years!

Todd


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## abby (Jan 22, 2014)

"to use a drill point would be a last resort to any true tradesman. So  you want to think about what is because was an Engineer and a Tool maker  for over 30 years!"

Obviously rattled someones cage, only 30 years toolmaking ! not a time served apprentice then Todd ? a toolmaker does not consider himself a "tradesman"  that's for plumbers and electricians.
Like I said , this is model engineering , you know a hobby , we make toys .
http://en.wikipedia.org/wiki/Countersink


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## Heffalump (Jan 22, 2014)

I think this is getting a bit personal.

Thanks for the advice everyone.


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## Tin Falcon (Jan 22, 2014)

Gentlemen While Viper Venom is an excellent product for  cutting threading reaming ect it should not be used near the computer  keyboard and NEVER be applied to forum threads !!! Understood ??
Tin


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## goldstar31 (Jan 22, 2014)

From your new avatar etc, you seem to be within easy reach of one to one advice as there seems to be at least one active club . Whilst my membership of such things is no longer possible, I feel that it will be to your advantage to seek one to one contact with a club. 

Again, much of the information which you are presently seeking is contained in some or all of the classic books. I was thinking of Advanced Machine Tool work by Smith which is American, free on the net but contains graded exercises in machining. It may be 'full size' but the book is sufficiently old fashioned to include most beginners' needs. Again, I would commend the Amateurs Lathe by Lawrence Sparey who actually made 'model engines' From my copy, bought as an erk in Royal Air Force days, it does contain direct information on what were called Slocombe drills. Again, though a bit beyond what appears to be your present abilities, more information about more Slocombe drills than has been raised here is George Thomas's Model Engineers Workshop Manual which  was edited- wait for it- an expert on drills. Dr Bill Bennett has 52 years in since he qualified( with my wife) as a dental surgeon. 

So you have every opportunity to build up your skills.

Regards

Norman


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## Heffalump (Jan 22, 2014)

goldstar31 said:


> From your new avatar etc, you seem to be within easy reach of one to one advice as there seems to be at least one active club . Whilst my membership of such things is no longer possible, I feel that it will be to your advantage to seek one to one contact with a club.
> 
> Again, much of the information which you are presently seeking is contained in some or all of the classic books. I was thinking of Advanced Machine Tool work by Smith which is American, free on the net but contains graded exercises in machining. It may be 'full size' but the book is sufficiently old fashioned to include most beginners' needs. Again, I would commend the Amateurs Lathe by Lawrence Sparey who actually made 'model engines' From my copy, bought as an erk in Royal Air Force days, it does contain direct information on what were called Slocombe drills. Again, though a bit beyond what appears to be your present abilities, more information about more Slocombe drills than has been raised here is George Thomas's Model Engineers Workshop Manual which was edited- wait for it- an expert on drills. Dr Bill Bennett has 52 years in since he qualified( with my wife) as a dental surgeon.
> 
> ...


 
Thanks Norman, new avatar as this one contains less of me and perhaps less embarrassing! 

I think you may be right about my skills (or lack thereof) but I'm looking forward to improving. I will do some research on those books, they sound like a great resource.


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## goldstar31 (Jan 22, 2014)

Rest assured, you'll not be disappointed. In the meantime, you have a very useful offer on a PM.

 Regards

 Norman


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## Sshire (Jan 22, 2014)

With countersinking tools and techniques, as with anything else in this hobby and on this forum, you'll get much good advice.  A great deal if it from people who have been doing this professionally, or as a hobby, for many,  many years.
In addition, books, magazines and videos cover virtually every topic.
This is how I'm learning. Ask questions; use Google and YouTube.
As with so many things, if you ask a questions, you'll get 10 different answers. Interestingly, the majority are correct. Skinning a cat and all that.
The differences in correct answers is due to many things. Different apprenticeships, different vocational or military training, or the "I figured this out on my own and it works for me" school of experience.
When I started, I was on a few forums. The reason I stayed here and MEM, was that a few of the others were not very friendly to hobbyists. Instead of answering a question, they made one feel embarrassed for asking or were just plain rude. 
You shouldn't get that here. We want to help. Some of the more interesting and educational threads with the most responses, resulted from, what appeared to be, a simple question.
Make each engine you build a little better, a little more precise and a little more complex than the last one.


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## Swifty (Jan 22, 2014)

Coming back to the original posting, countersink bits cover a range of holes, a set of 4 would cover most fasteners used by the home hobbyist, for example the smallest might cover 2mm to 5mm, the next 4mm to 8mm etc. If you think that you will be staying with your new hobby, purchasing the counter sinks as required will last you a lifetime. And of course, countersinks are also used to remove burrs from straight holes as well, so you will use them all the time.

I always use metric screws, so the countersink angle is 90 deg. Keeps it simple.

As to how deep to go, I always make them so the screw is just a bit under the surface, check with a few screws as the manufacturing tolerances may see some heads slightly thicker than others. Nothing looks worse than the head still being a bit proud of the surface.

Paul.


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## bazmak (Jan 22, 2014)

Good one swifty as you say csk angles can be 82-90o and head dia varies between slot hd and HSocket
I always use 90o and multi touch until the head height suits the application.I also self grind suitable size drills
to 90o if the screw is required to go well below surface.Nothing wrong with that.Model engineers will do lots 
of things (not proper Eng) to get jobs done.I also highly dislike people being arrogant in their replies
when answering someone who does not know what he is doing now but trying to learn
WE WERE ALL AT THAT STAGE AT ONE TIME,lets not forget it.I like to browse many threads for an 
interesting read,and try only offering positive advice.This is a very informative forum,even with
subjects i have no interest or knowledge of, but i still like to browse


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## Tin Falcon (Jan 22, 2014)

> As with so many things, if you ask a questions, you'll get 10 different answers. Interestingly, the majority are correct. Skinning a cat and all that.


And that is only if 6 guys answer the question.
Tin


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## kvom (Jan 22, 2014)

Most of the SAE flat head fasteners that are most common in the US seem to be 82 degree, so that's the set I bought.  I used a lot of 8-32 flat head screws in the loco build.

I generally run the countersinks at fairly low RPM.  400 seems to work well in HRS.


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## Swifty (Jan 22, 2014)

Unless absolutely necessary, I try not to use flat head / countersunk screws. The sockets are shallow and easily damaged by over tightening, and the heads want to pull around the plate being clamped. If the countersink favours one side of a hole, the screw won't contact all around and looks odd.

Paul.


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## bazmak (Jan 23, 2014)

As previosly stated,csk fixings are used when a flush surface is requ ie when a component fits over the top.I like to use them if a part needs to be removed
and replaced fairly accurately.As stated previosly a tapped hole and a ssk screw
will replace dowels (up to a point) as a precision location fit


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## Heffalump (Jan 23, 2014)

The reason I'll be using a countersink in this instance is to attach the frame of an engine to the base plate. The screw will go through the bottom of the base plate, so needs to sit flush or the base plate will not sit flat!


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## kvom (Jan 23, 2014)

Heffalump said:


> The reason I'll be using a countersink in this instance is to attach the frame of an engine to the base plate. The screw will go through the bottom of the base plate, so needs to sit flush or the base plate will not sit flat!



For cases where the screw head is not visible, it can be just as easy to counterbore and use a socket head.


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## bazmak (Jan 23, 2014)

Thats true but csk bits are more readily available and cheaper than c,bore bits
I use std drills as cbores but have to machine the uside of the cap hd to 118o
usually when the screws are exposed,again the tapped hole and csk give a 
precision location fit but sometimes flush cap heads look better than hex hds
I also like hs button hds.I specifically dont like slotted csk screws on models
They dont seem to look right for scale.The problem with multiple csk screws to
tapped holes is that you cant mark them accurately,so have to fit 1 then assemble and drill/spot thru.Its a lot easier for multiple stip downs and 
accurate reassembly.Best regards barry


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## barnesrickw (Jan 23, 2014)

DeWalts brad point bits work well.   Except for in brass, because it's the Devil's drilling metal.


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## kvom (Jan 23, 2014)

For counterbores of small screws I use an endmill.


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## Omnimill (Jan 24, 2014)

I (mistakenly) used countersunk screws on some archery equipment many years ago as it was easier for me to countersink than counterbore at the time. I found the screws self tightened in use, to such an extent that on one occasion I had to drill the screw out to remove it. I try to avoid them now if I can as a nicely seated cap head socket screw looks so much nicer to my eye at least. I also avoid slotted or cross head screws in favour of hex and Torx but that's a personal thing.


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## Walltoddj (Jan 27, 2014)

Found so information on Loctite web site that might be of use.
Todd 

View attachment 166733_LT4985_Threadlocking_Guide_032010_Web.pdf


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