These unique tools, Harvey Tool's End Mills for Plastics - Square Downcut - 2 Flute, prevent fraying and chip-out on the top . . .

Home › Forums › Beginners questions › Counter sinking for Cap Screws This topic has 13 replies, 10 voices, and was last updated 15 June 2015 at 15:11 by Neil Wyatt. Viewing 14 posts - 1 through 14 (of 14 total) Author Posts 15 June 2015 at 07:49 #193471 Alan RawlinsParticipant @alanrawlins60482 i recently wanted to use some of the black cap screws on a component I was making that needed the head of the cap screws to be below the surface of the plate I was fastening to something else. The hole for the M8 cap screw was drilled initially to M8.5 .I sent to RDG for a suitable tool to counter sink the plate for M8 cap screws. When I used it to cut the counter sink, the cutter enlarged the M8.5 hole to M8.93 which isn't a problem. The countersink though, cut a hole to 15mm which is 2mm (1mm all round) larger than the head of the M8 cap screw and it looks awful The c/sk cut on parts of my lathe for an M8 screw were13.3mm which gave a much better looking clearance of 1mm (0.5mm all round) Is it now normal to have such a large clearance for the head of cap screws? is there not any standards that should be used by the manufacturers of cap screw c/sks? Advert 15 June 2015 at 07:49 #7670 Alan RawlinsParticipant @alanrawlins60482 15 June 2015 at 08:03 #193474 Michael GilliganParticipant @michaelgilligan61133 Alan, … am I right in thinking that you mean counterbore rather than countersink? I don't have the numbers to hand, but I do know that the standard clearances on Metric fasteners are 'generous to a fault' … more suited to IKEA than the toolroom. MichaelG. . Edit: Here is a useful chart … compare the dimensions specified for 5/16" and M8 Edited By Michael Gilligan on 15/06/2015 08:32:28 15 June 2015 at 08:26 #193476 JasonBModerator @jasonb Yes the standard clearance is quite large. You can use an end cutting milling cutter, grind a drill to about a 170deg point or ideally make a D bit to get a flat bottomed hole. For stressed items you need to make sure that the slight radius between screw shank and underside of the head has clearance which is covered by the large almost 9mm hole or by easing it with a csk or spotting drill if using a smaller clearance size. Edited By JasonB on 15/06/2015 08:30:00 15 June 2015 at 09:44 #193482 VicParticipant @vic I've used a variety of methods to counterbore holes including Bullet drills and hand ground drill bits with a flat bottom. As you've found, the recommended counterbores for metric cap screws is rather large and looks ugly. 15 June 2015 at 10:09 #193486 KWILParticipant @kwil I am not surprised by the "large" counterbore sizes, some sources of cap head screws seem to have lost the ability to make the heads concentric with the threads!! 15 June 2015 at 10:25 #193488 Paul LousickParticipant @paullousick59116 I have found that some counterbore cutters (especially the cheaper ones) vary in size for a particular size cap screw. Some were undersize and produced a hole which was too small. I now check the hole size that they cut before buying. Have not found a proper standard for counterbores but this seems to be what is recommended. Paul. Edited By Paul Lousick on 15/06/2015 10:26:22 15 June 2015 at 11:47 #193492 VicParticipant @vic In many cases the cap head diameter size in that chart must be the maximum recommended size as in practice they are somewhat smaller. I often counterbore to the "head" size in that chart! Am I right in thinking the counterbores for imperial cap screws are a bit tighter and therefore look better? Certainly the imperial cap screws I've seen have a smaller head in comparison to the thread diameter so that may have a bearing? Edited By Vic on 15/06/2015 11:48:18 15 June 2015 at 12:01 #193493 Gordon WParticipant @gordonw When cap screws were fairly new often the heads had axial grooves. The c/bores were quite tight, the heads were locked by deforming the material into the grooves. A special tool was available for doing this. May explain the variations in bore sizes. 15 June 2015 at 13:27 #193499 Michael GilliganParticipant @michaelgilligan61133 Posted by Vic on 15/06/2015 11:47:25:

The Harvey Tool End Mills for Plastics - Square Upcut - 2 Flute product offering features tooling with a slower helix, which . . .

Am I right in thinking the counterbores for imperial cap screws are a bit tighter and therefore look better? Certainly the imperial cap screws I've seen have a smaller head in comparison to the thread diameter so that may have a bearing?

If in fact you are using counter sunk screws, the bit should be a small clearance diameter over the head diameter, and a fraction of a mm of parallel hole to take the head flush.

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CNC ground in the USA from solid carbide, this fully stocked Harvey Tool offering of End Mills for Plastics - Square Upcut - 2 Flute features a slower helix (of approximately 20°) for minimized lifting forces, preferable for vacuum table setups.

This solid carbide, fully stocked offering of End Mills for Plastics - Finishers - Square Downcut - 3 Flute features a higher. . .

When cap screws were fairly new often the heads had axial grooves. The c/bores were quite tight, the heads were locked by deforming the material into the grooves. A special tool was available for doing this. May explain the variations in bore sizes.

In many cases the cap head diameter size in that chart must be the maximum recommended size as in practice they are somewhat smaller. I often counterbore to the "head" size in that chart!

Proper counterbored holes are not a close fit on either the shank of the screw or the cap – alignment should be by a dowel or some other form of register as screws a can be made to wide tolerances and only the underside of the head should bear on the part being fixed. Hence the generous clearances.

We offer a comprehensive selection of more than 28,000 miniature and specialty cutting tools that are all fully stocked. The breadth and depth of our products help solve the industry’s toughest machining challenges.

Harvey Tool is committed to designing unique geometries that optimize cutting performance for a variety of materials and applications. We introduce hundreds of new tools to the market every 6 months, offering our customers the solutions they need most.

Ideal for deburring on the back side of a small hole and tight pockets, this offering of End Mills for Plastics - Finishers -. . .

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The hole for the M8 cap screw was drilled initially to M8.5 .I sent to RDG for a suitable tool to counter sink the plate for M8 cap screws. When I used it to cut the counter sink, the cutter enlarged the M8.5 hole to M8.93 which isn't a problem.

With its slower helix of approximately 22°, lifting forces are reduced for fiber-reinforced applications and vacuum table set. . .

Harvey Tool is committed to designing unique geometries that optimize cutting performance for a variety of materials and applications. We introduce hundreds of new tools to the market every 6 months, offering our customers the solutions they need most.

I've used a variety of methods to counterbore holes including Bullet drills and hand ground drill bits with a flat bottom.

Great in Heavy Radial Efficiency Milling (HREM) applications of Titanium 6Al4V and other titanium alloys, these fully stocked, square profile Variable Helix End Mills decrease chatter and harmonics.

We offer a comprehensive selection of more than 28,000 miniature and specialty cutting tools that are all fully stocked. The breadth and depth of our products help solve the industry’s toughest machining challenges.

Add products to your Harveytool.com shopping cart and then submit the cart to a participating distributor to place your order

Our fully stocked inventory is ready to ship the day of its purchase. We offer second day delivery at ground pricing, and any overnight orders ship until 7 p.m., EST.

The countersink though, cut a hole to 15mm which is 2mm (1mm all round) larger than the head of the M8 cap screw and it looks awful

I have found that some counterbore cutters (especially the cheaper ones) vary in size for a particular size cap screw. Some were undersize and produced a hole which was too small. I now check the hole size that they cut before buying.

For stressed items you need to make sure that the slight radius between screw shank and underside of the head has clearance which is covered by the large almost 9mm hole or by easing it with a csk or spotting drill if using a smaller clearance size.

In the past if I have made counter bores from old drills by grinding the tip away on an old drill leaving a centre parallel pilot section the same size as the hole, in your case to fit an M8 clearance hole. once this is done I just grind in to cutting edges at 90 degrees to cut the bottom of the counter bore hole. Maybe you have one. The shorter the drill is the better as the web will be thicker and you will get a more complete pilot. I guess 14mm is an odd size but worth a try if you have one. I keep a box of broken cutters and worn out or broken drills "Just in case" for this sort of job. Do tests on a piece of scrap until you get it cutting nicely.

Yes the standard clearance is quite large. You can use an end cutting milling cutter, grind a drill to about a 170deg point or ideally make a D bit to get a flat bottomed hole.

Am I right in thinking the counterbores for imperial cap screws are a bit tighter and therefore look better? Certainly the imperial cap screws I've seen have a smaller head in comparison to the thread diameter so that may have a bearing?

The c/sk cut on parts of my lathe for an M8 screw were13.3mm which gave a much better looking clearance of 1mm (0.5mm all round)

Add products to your Harveytool.com shopping cart and then submit the cart to a participating distributor to place your order

First introduced in Harvey Tool’s Spring 2020 Catalog, this line of End Mills for Plastics – Square Downcut – 2 Flute, featur. . .

I don't have the numbers to hand, but I do know that the standard clearances on Metric fasteners are 'generous to a fault' … more suited to IKEA than the toolroom.

New to Harvey Tool, Machining Advisor Pro (MAP) is a cutting edge resource for generating customized running parameters for Harvey Tool end mills.

I am aghast at Mattel/Fisher Price New motor/esc for mill? Brake caliper windback tool and stiff caliper Water tank Spring material advice needed Horizontal mill cutter runout Steam Model Days in the Industrie Museum in Lauf an der Pegnitz Penny-Pinching Trapezoidal tap drill size ? Machining 1050 Grade Aluminium

Is it now normal to have such a large clearance for the head of cap screws? is there not any standards that should be used by the manufacturers of cap screw c/sks?

I am not surprised by the "large" counterbore sizes, some sources of cap head screws seem to have lost the ability to make the heads concentric with the threads!!

New to Harvey Tool, Machining Advisor Pro (MAP) is a cutting edge resource for generating customized running parameters for Harvey Tool end mills.

i recently wanted to use some of the black cap screws on a component I was making that needed the head of the cap screws to be below the surface of the plate I was fastening to something else.

Great in Heavy Radial Efficiency Milling (HREM) applications of Titanium 6Al4V and other titanium alloys, these fully stocked, square profile Variable Helix End Mills decrease chatter and harmonics.

Also, spot facers often have greater clearance than counterbores (being intended for nuts) but the line between a counterbore and a spot facer is a vague and indistinct one.

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