Countersinking

[Heffalump]

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!

 

[Sshire]

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

 

[MachineTom]

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.

 

[abby]

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.

 

[zimma]

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

 

[zimma]

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

 

[kvom]

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.

 

[Heffalump]

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.

 

[Walltoddj]

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

 

[abby]

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.

 

[goldstar31]

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

 

[Walltoddj]

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

 

[bazmak]

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

 

[Walltoddj]

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

 

[Wizard69]

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.

 

[Wizard69]

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.

 

[Walltoddj]

We may be building things that vibrate a bit.

Overall counter sinks are not that expensive.


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.

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

 

[zimma]

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.

 

[abby]

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.

 

[Tin Falcon]

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