Imperial counterbores?

[Andrew TinsleyParticipant @andrewtinsley63637]

I would like to have a few Imperial counterbores, as I often work on older equipment. The cheapest I can find seem to be at least £35 each and very much upwards of that figure. Does anyone know of a source of cheaper counterbores? I have been using my metric versions, but I am not too impressed with some of the results.

Andrew.

[Peter Cook 6Participant @petercook6]

Tracy Tools have them in 3/8 7/16 and 1/2 inch sizes at £8 each

[Michael GilliganParticipant @michaelgilligan61133]

Regrettably not, Andrew

This has long been a gripe of mine … Grrr!!

The proportions of the metric ones simply don’t do justice to Imperial cap-heads.

MichaelG.

.

Edit: __ Well-found, Peter

[VicParticipant @vic]

In my experience counterbores produce aesthetically over size looking holes for my liking. As a result I’ve made a number of them from silver steel.

Another way is to make a combined drill bit/counterbore by grinding a long “pilot” on a suitable size HSS drill bit.

This commercially available Pocket Hole bit shows the sort of thing. Easy enough to make with a battery drill and a bench grinder.

[Michael GilliganParticipant @michaelgilligan61133]

Our Tool-Makers used to grind their own, by modifying a drill-bit

MichaelG.

.

Edit: __ Like wot Vic illustrates !

[Nigel Graham 2Participant @nigelgraham2]

Another approach I have used, better on a milling-machine than a bench-drill, is to counter-drill the hole just enough to let a slot-drill or end-mill enter before it starts cutting.

The wall stops the cutter from trying to “dither” around the rim, spoiling the work, although this precaution should not be necessary on a milling-machine. It does need some care to ensure the twist-drill does not go too deep.

Obvously an end-mill will not act as a drill, but works here because the through hole already exists, putting the cutter’s centre in fresh air.

[duncan webster 1Participant @duncanwebster1]

I start the counterbore to nearly full depth with a normal drill then finish with a flat bottom drill, much easier to grind than the stepped arrangement

[Andrew TinsleyParticipant @andrewtinsley63637]

I like Duncan’s method, somewhat cheaper than a standard counterbore. It appeals to my miserly instincts!

I have ordered the 3 counterbores from Tracy Tools, even I cannot complain at the prices.

Thank you everyone.

Andrew.

[Paul LousickParticipant @paullousick59116]

Make your own custom size counterbore from silver steel.  These are easy to make and sharpen and suitable for occasional use.

https://gadgetbuilder.com/CounterBore.html

[bernard towersParticipant @bernardtowers37738]

Couldnt agree more with Paul, you can then make them with the clearance you are happy with. I have a set of comm metric ones they never get used as the clearance is huge.

[VicParticipant @vic]

Making a step drill.

https://youtu.be/wxrf4TJvygA

[noel shelleyParticipant @noelshelley55608]

Find someone with a proper drill grinder and flat bottomed or counter bores are easy to make.  Noel.

[Paul Lousick]

On Paul Lousick Said:

 

That’s quite an odd design for a countbore?

These are some of the four teeth ones I’ve made from silver steel. I harden but don’t bother to temper them, I just leave them glass hard. I’ve not had one chip yet. The angle of the teeth is easily cut for whatever material you intend to counterbore.

 

[John PurdyParticipant @johnpurdy78347]

I make mine like Vic’s out of drill rod ( silver steel). The top 5 have inter changeable pilots. The bottom 3 are for reverse facing castings for the seating of nuts or bolt heads where access is restricted. As can be seen I let mine down to light straw rather than leave them dead hard.

John

 

[Charles LamontParticipant @charleslamont71117]

I make my own too. For tempering silver steel tools, lately I have been giving them about 15 mins in the air fryer at 200°C. It hardly changes the colour or hardness at all, but does considerably improve the toughness.

[VicParticipant @vic]

I generally super glue the pilots in so I can change them if needed.

[Bill PhinnParticipant @billphinn90025]

On 5 January 2026 at 18:14 Andrew Tinsley Said:
“I would like to have a few Imperial counterbores, as I often work on older equipment. The cheapest I can find seem to be at least £35 each and very much upwards of that figure. Does anyone know of a source of cheaper counterbores?”

Andrew, I have two of these:

https://www.ebay.co.uk/itm/371695786775?var=640675509787

The name may be incorrect, but the items I received are counterbores like in the pic.

On 5 January 2026 at 18:43 Vic Said:
“In my experience counterbores produce aesthetically over size looking holes”

Look for the Chinese sellers selling 5 piece sets M3-M8. They are definitely not oversized. Many of these sellers give the dimensions. Don’t know what they’re like on tougher materials but they work great on alu, copper alloys and mild steel. I bought two sets for £8.50 each about three years ago. Still on the first set.

These are the measurements of a typical set:

M3: 5.9 (blade diameter) * 3.2 (boat) * 6 (shaft diameter) * 45 (full length)

M4: 7.4 (blade diameter) * 4.2 (boat) * 6 (shaft diameter) * 48 (full length)

M5: 9.5 (blade diameter) * 5.2 (boat) * 6 (shaft diameter) * 51 (full length)

M6: 11.0 (blade diameter) * 6.2 (boat) * 8 (shaft diameter) * 58 (full length)

M8: 14.0 (blade diameter) * 8.2 (boat) * 12 (handle diameter) * 67 (full length)

 

“Blade” =  bad translation of “cutting flutes” or similar.

”Boat = bad transl. of “pilot”

“Tracy Tools have them in 3/8 7/16 and 1/2 inch sizes at £8 each”

When I inquired about six months ago their site suggested they had them, but when I contacted them they said they didn’t have any, hence my purchase from Spalding Fasteners.

 

[BazyleParticipant @bazyle]

When is a spot face cutter a counterbore, and when did counterbore ‘reverse’ its meaning.

[JasonBModerator @jasonb]

I’d be inclined to say that a lot of the home made cutters being shown here are more in the style of spot face cutters. off the shelf Counterbores tend to have longer flutes so can clear the swarf at typical cap head depth or deeper. The cutters here would clog if not retracted several times and they are just like spot and back spot facers in this respect.

But in a hobby workshop the only real difference is how far in you feed them.

 

[John PurdyParticipant @johnpurdy78347]

To answer Bazyles question I have used mine as both spot facers and counterbores. As Jason says they just have to been withdrawn frequently to clear the flutes until the required depth is reached.

John

[VicParticipant @vic]

Probably the most useful commercial counterbores I’ve seen are those with replaceable pilots, they were quite expensive though the last time I saw them.

 

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