I need to counterbore some holes for fixings so they are flux or below
the surface.

The plywood will be pre-drilled with 6mm and 7mm holes and I wish to counterbore to widths of 15mm and 20mm with some sort of stop to define
depth.

I had hoped I might be able to get bits for a router with a 1/2" collet,
that had a pilot pin to ensure accurate placement of the counterbore.
And of course would have controlled depth.

Anything I've seen has either been unsuitable or of an extreme price.

Has anyone got any ideas?

--- SoupGate-Win32 v1.05
* Origin: fsxNet Usenet Gateway (21:1/5)

On 02/05/2025 19:55, Fredxx wrote:

I need to counterbore some holes for fixings so they are flux or below
the surface.

The plywood will be pre-drilled with 6mm and 7mm holes and I wish to counterbore to widths of 15mm and 20mm with some sort of stop to define depth.

I had hoped I might be able to get bits for a router with a 1/2" collet,
that had a pilot pin to ensure accurate placement of the counterbore.
And of course would have controlled depth.

Anything I've seen has either been unsuitable or of an extreme price.

Has anyone got any ideas?

Make a template with a hole in it from a scrap of ply, then use it to
guide your router with a guide bush fitted. You can put radial cross
hair lines around the hole to make it easy to line up with the centre of
the existing hole.

--
Cheers,

John.

/=================================================================\
| Internode Ltd - http://www.internode.co.uk | |-----------------------------------------------------------------|
| John Rumm - john(at)internode(dot)co(dot)uk | \=================================================================/

--- SoupGate-Win32 v1.05
* Origin: fsxNet Usenet Gateway (21:1/5)

Fredxx wrote:

I need to counterbore some holes for fixings so they are flux or below
the surface.

The plywood will be pre-drilled with 6mm and 7mm holes and I wish to counterbore to widths of 15mm and 20mm with some sort of stop to define depth.

I had hoped I might be able to get bits for a router with a 1/2" collet,
that had a pilot pin to ensure accurate placement of the counterbore.
And of course would have controlled depth.

Not sure what 'standard' sizes counterbores come in, I only have one.

I think what you want would be described as "M6, XXmm x 15mm cut
diameter", where XX is the total length of the bit, sounds like a long
bit isn't required in your case?

As for the larger size you're after, I mainly see even M numbers, so you
might be out of luck, unless a 1/4" shank by 7/8" cut diameter is close
enough? Might have to buy from USA?

--- SoupGate-Win32 v1.05
* Origin: fsxNet Usenet Gateway (21:1/5)

John Rumm <[email protected]> wrote:

On 02/05/2025 19:55, Fredxx wrote:

I need to counterbore some holes for fixings so they are flux or below
the surface.

The plywood will be pre-drilled with 6mm and 7mm holes and I wish to counterbore to widths of 15mm and 20mm with some sort of stop to define depth.

I had hoped I might be able to get bits for a router with a 1/2" collet, that had a pilot pin to ensure accurate placement of the counterbore.
And of course would have controlled depth.

Anything I've seen has either been unsuitable or of an extreme price.

Has anyone got any ideas?

Make a template with a hole in it from a scrap of ply, then use it to
guide your router with a guide bush fitted. You can put radial cross
hair lines around the hole to make it easy to line up with the centre of
the existing hole.

I recently needed to make some 65mm diameter by 17mm deep pockets for some castors. I 3d printed a template and then used a router bit with a bearing
on a 1/4 trim router:
https://www.amazon.co.uk/dp/B07PC71F35
to route out the hole - worked a treat, although I had to do several passes
to get the depth.

I could have also drawn a circle on a piece of scrap and jigsawed out the
hole, but I needed a friction fit so used the 3D printer to do it accurately (turned out I actually needed the pocket to be 66mm so I 3D printed a second template)

You can also do it with a Forstner bit - I'd draw a circle centred on the
hole and then ensure you get the Forstner started within the circle. But
you'd need to buy two bits, while you only need one router bit (and that'll come in handy for other jobs).

Theo

--- SoupGate-Win32 v1.05
* Origin: fsxNet Usenet Gateway (21:1/5)

Fredxx wrote:

I need to counterbore some holes for fixings so they are flux or below
the surface.

The plywood will be pre-drilled with 6mm and 7mm holes and I wish to counterbore to widths of 15mm and 20mm with some sort of stop to define depth.

I had hoped I might be able to get bits for a router with a 1/2" collet,
that had a pilot pin to ensure accurate placement of the counterbore.
And of course would have controlled depth.

Anything I've seen has either been unsuitable or of an extreme price.

Has anyone got any ideas?

1. Does the counterbore need to be *accurately* centred on the hole? As
long as it's large enough to deal with a little offset then I suspect
that absolute accuracy isn't essential (presume you'll be plugging the counterbores ... ?) If the counterbore needs to be accurate than use 6,,
(and 7mm) pins to locate the router, fix or mark its position and change
to your 15/20mm bit, plunge to depth
2. A flat bit (the sort with teeth at the edges to reduce tear-out) in a
drill press?
3. Use a forstner bit to make a hole in a piece of ply and then use this
(held with double-sided tape) to guide it for the counterbores?
4. make a template and use a smaller bearing-guided router bit?

If 't'were me I would use a centring pin to locate and then use a
forstner bit.

--- SoupGate-Win32 v1.05
* Origin: fsxNet Usenet Gateway (21:1/5)

Fredxx <[email protected]d> wrote:

I need to counterbore some holes for fixings so they are flux or below
the surface.

The plywood will be pre-drilled with 6mm and 7mm holes and I wish to counterbore to widths of 15mm and 20mm with some sort of stop to define depth.

I had hoped I might be able to get bits for a router with a 1/2" collet,
that had a pilot pin to ensure accurate placement of the counterbore.
And of course would have controlled depth.

Anything I've seen has either been unsuitable or of an extreme price.

Has anyone got any ideas?

If you have not drilled the through holes yet then counterbore the hole
first with a flat bit if accuracy is not essential for the depth then a
piece of tape on the flat bit set for depth required will suffice. Then
using the centre point depression left by the flat bit drill the through
holes. If accuracy is important then use a forstner bit using the same
process.

--- SoupGate-Win32 v1.05
* Origin: fsxNet Usenet Gateway (21:1/5)

On 02/05/2025 20:52, John Rumm wrote:

On 02/05/2025 19:55, Fredxx wrote:

I need to counterbore some holes for fixings so they are flux or below
the surface.

The plywood will be pre-drilled with 6mm and 7mm holes and I wish to
counterbore to widths of 15mm and 20mm with some sort of stop to
define depth.

I had hoped I might be able to get bits for a router with a 1/2"
collet, that had a pilot pin to ensure accurate placement of the
counterbore. And of course would have controlled depth.

Anything I've seen has either been unsuitable or of an extreme price.

Has anyone got any ideas?

Make a template with a hole in it from a scrap of ply, then use it to
guide your router with a guide bush fitted. You can put radial cross
hair lines around the hole to make it easy to line up with the centre of
the existing hole.

Thanks, I hadn't thought of a template.

I have a total of some 40 holes to counterbore on a sheet and I feel
this would take an inordinate of time to clamp etc for each hole.

I could take a sheet with the counterbore holes all the way through and
use that as a template. The issue is I don't really want many large
sheets for templates and each design may undergo future changes.

--- SoupGate-Win32 v1.05
* Origin: fsxNet Usenet Gateway (21:1/5)

On 02/05/2025 21:37, Andy Burns wrote:

Fredxx wrote:

I need to counterbore some holes for fixings so they are flux or below
the surface.

The plywood will be pre-drilled with 6mm and 7mm holes and I wish to
counterbore to widths of 15mm and 20mm with some sort of stop to
define depth.

I had hoped I might be able to get bits for a router with a 1/2"
collet, that had a pilot pin to ensure accurate placement of the
counterbore. And of course would have controlled depth.

Not sure what 'standard' sizes counterbores come in, I only have one.

I think what you want would be described as "M6, XXmm x 15mm cut
diameter", where XX is the total length of the bit, sounds like a long
bit isn't required in your case?

As for the larger size you're after, I mainly see even M numbers, so you might be out of luck, unless a 1/4" shank by 7/8" cut diameter is close enough?  Might have to buy from USA?

Thanks for the idea.

I have been searching for similar and the closest I got was a set like this:

https://www.amadeal.co.uk/acatalog/21pc-HSS-Counterbore-Set-14.5-24.5-AMA_CT_HIPC02102SZJ.html#SID=54

Given what they are the price is not too bad. But it also has a Morse
taper from being intended for counterboring metals. I suppose I could
modify the holder.

--- SoupGate-Win32 v1.05
* Origin: fsxNet Usenet Gateway (21:1/5)

On 02/05/2025 21:55, No mail wrote:

Fredxx wrote:

I need to counterbore some holes for fixings so they are flux or below
the surface.

The plywood will be pre-drilled with 6mm and 7mm holes and I wish to
counterbore to widths of 15mm and 20mm with some sort of stop to
define depth.

I had hoped I might be able to get bits for a router with a 1/2"
collet, that had a pilot pin to ensure accurate placement of the
counterbore. And of course would have controlled depth.

Anything I've seen has either been unsuitable or of an extreme price.

Has anyone got any ideas?

1. Does the counterbore need to be *accurately* centred on the hole? As
long as it's large enough to deal with a little offset then I suspect
that absolute accuracy isn't essential (presume you'll be plugging the counterbores ... ?) If the counterbore needs to be accurate than use 6,,
(and 7mm) pins to locate the router, fix or mark its position and change
to your 15/20mm bit, plunge to depth
2. A flat bit (the sort with teeth at the edges to reduce tear-out) in a drill press?
3. Use a forstner bit to make a hole in a piece of ply and then use this (held with double-sided tape) to guide it for the counterbores?
4. make a template and use a smaller bearing-guided router bit?

If 't'were me I would use a centring pin to locate and then use a
forstner bit.

The counterbore is intended to keep the fixture flush with the ply. Not
much depth is required.
Accuracy isn't that important except for aesthetics. While it won't be
visible, it will be from a QA POV and obviously my view!

This needs to be a quick operation and I have 20 in each size.

I did come across these flat bits with pilot:
https://mudhole.com/products/flexcoat-pilot-drill-bit

--- SoupGate-Win32 v1.05
* Origin: fsxNet Usenet Gateway (21:1/5)

On 03/05/2025 09:53, Tricky Dicky wrote:

Fredxx <[email protected]d> wrote:

I need to counterbore some holes for fixings so they are flux or below
the surface.

The plywood will be pre-drilled with 6mm and 7mm holes and I wish to
counterbore to widths of 15mm and 20mm with some sort of stop to define
depth.

I had hoped I might be able to get bits for a router with a 1/2" collet,
that had a pilot pin to ensure accurate placement of the counterbore.
And of course would have controlled depth.

Anything I've seen has either been unsuitable or of an extreme price.

Has anyone got any ideas?

If you have not drilled the through holes yet then counterbore the hole
first with a flat bit if accuracy is not essential for the depth then a
piece of tape on the flat bit set for depth required will suffice. Then
using the centre point depression left by the flat bit drill the through holes. If accuracy is important then use a forstner bit using the same process.

It is important that the holes are made with relative precision.
Therefore the holes must be made first by a CNC machine.

The reliefs can be made by the CNC machine, except due to long file
lengths the machine can't cope with the relief has to be made in 2
passes. I thought the quickest way would be to manually make the
counterbore using the hole as a reference.

--- SoupGate-Win32 v1.05
* Origin: fsxNet Usenet Gateway (21:1/5)

On 02/05/2025 19:55, Fredxx wrote:

I need to counterbore some holes for fixings so they are flux or below
the surface.

The plywood will be pre-drilled with 6mm and 7mm holes and I wish to counterbore to widths of 15mm and 20mm with some sort of stop to define depth.

I had hoped I might be able to get bits for a router with a 1/2" collet,
that had a pilot pin to ensure accurate placement of the counterbore.
And of course would have controlled depth.

Anything I've seen has either been unsuitable or of an extreme price.

Has anyone got any ideas?

These are the closest I've got in style I was thinking:
https://flexcoat.com/shop/reel-seat-arbors/arbor-pilot-bits

Also this gives some inspiration:

https://www.amazon.co.uk/Woodworking-Various-Perfect-Improvement-Projects/dp/B0CS6PYPQK?th=1


https://www.amazon.co.uk/Carbide-Woodworking-Router-Buddha-Milling/dp/B08KFY3NDW/258-3443561-4449913?th=1

Both the above would be ground flat. The only issue is the puny sized
drill and would have to make a plug with a 2mm centre hole.

Perhaps braze a plug on the end end of one of these:

https://www.amazon.co.uk/XFLYP-High-Carbon-Design-Reaming-Accessories/dp/B0CLD7SJ28

--- SoupGate-Win32 v1.05
* Origin: fsxNet Usenet Gateway (21:1/5)

Fredxx wrote:

On 02/05/2025 21:55, No mail wrote:

Fredxx wrote:

I need to counterbore some holes for fixings so they are flux or
below the surface.

The plywood will be pre-drilled with 6mm and 7mm holes and I wish to
counterbore to widths of 15mm and 20mm with some sort of stop to
define depth.

I had hoped I might be able to get bits for a router with a 1/2"
collet, that had a pilot pin to ensure accurate placement of the
counterbore. And of course would have controlled depth.

Anything I've seen has either been unsuitable or of an extreme price.

Has anyone got any ideas?

1. Does the counterbore need to be *accurately* centred on the hole?
As long as it's large enough to deal with a little offset then I
suspect that absolute accuracy isn't essential (presume you'll be
plugging the counterbores ... ?) If the counterbore needs to be
accurate than use 6,, (and 7mm) pins to locate the router, fix or mark
its position and change to your 15/20mm bit, plunge to depth
2. A flat bit (the sort with teeth at the edges to reduce tear-out) in
a drill press?
3. Use a forstner bit to make a hole in a piece of ply and then use
this (held with double-sided tape) to guide it for the counterbores?
4. make a template and use a smaller bearing-guided router bit?

If 't'were me I would use a centring pin to locate and then use a
forstner bit.

The counterbore is intended to keep the fixture flush with the ply. Not
much depth is required.
Accuracy isn't that important except for aesthetics. While it won't be visible, it will be from a QA POV and obviously my view!

This needs to be a quick operation and I have 20 in each size.

I did come across these flat bits with pilot:
  https://mudhole.com/products/flexcoat-pilot-drill-bit

That prompts a revision to idea #2: cut some short lengths of metal tube
to go into the holes and then use standard flat bits with the centre
spike sitting in the tube. The tube will help with centring and prevent
damage to the hole.
Alternatively, buy one of the cheap CNC routers (but from another reply
I see you may already have one).

--- SoupGate-Win32 v1.05
* Origin: fsxNet Usenet Gateway (21:1/5)

No mail wrote:

Fredxx wrote:

On 02/05/2025 21:55, No mail wrote:

Fredxx wrote:

I need to counterbore some holes for fixings so they are flux or
below the surface.

The plywood will be pre-drilled with 6mm and 7mm holes and I wish to
counterbore to widths of 15mm and 20mm with some sort of stop to
define depth.

I had hoped I might be able to get bits for a router with a 1/2"
collet, that had a pilot pin to ensure accurate placement of the
counterbore. And of course would have controlled depth.

Anything I've seen has either been unsuitable or of an extreme price.

Has anyone got any ideas?

1. Does the counterbore need to be *accurately* centred on the hole?
As long as it's large enough to deal with a little offset then I
suspect that absolute accuracy isn't essential (presume you'll be
plugging the counterbores ... ?) If the counterbore needs to be
accurate than use 6,, (and 7mm) pins to locate the router, fix or
mark its position and change to your 15/20mm bit, plunge to depth
2. A flat bit (the sort with teeth at the edges to reduce tear-out)
in a drill press?
3. Use a forstner bit to make a hole in a piece of ply and then use
this (held with double-sided tape) to guide it for the counterbores?
4. make a template and use a smaller bearing-guided router bit?

If 't'were me I would use a centring pin to locate and then use a
forstner bit.

The counterbore is intended to keep the fixture flush with the ply.
Not much depth is required.
Accuracy isn't that important except for aesthetics. While it won't be
visible, it will be from a QA POV and obviously my view!

This needs to be a quick operation and I have 20 in each size.

I did come across these flat bits with pilot:
   https://mudhole.com/products/flexcoat-pilot-drill-bit

That prompts a revision to idea #2: cut some short lengths of metal tube
to go into the holes and then use standard flat bits with the centre
spike sitting in the tube. The tube will help with centring and prevent damage to the hole.
Alternatively, buy one of the cheap CNC routers (but from another reply
I see you may already have one).

I just tried a search for "forstner bit with pilot" and several appeared
- if you replace the pilot drill with a pin you (I think) have what you
need.

--- SoupGate-Win32 v1.05
* Origin: fsxNet Usenet Gateway (21:1/5)

No mail <[email protected]> wrote:

I just tried a search for "forstner bit with pilot" and several appeared
- if you replace the pilot drill with a pin you (I think) have what you
need.

I've just drilled a trial hole with a 20mm Forstner: https://www.amazon.co.uk/dp/B084KCWKZD

There's enough of a point on it to locate in an existing hole, and it's dead easy to then drill as deep as you need, using a nice slow drill speed.

Theo

--- SoupGate-Win32 v1.05
* Origin: fsxNet Usenet Gateway (21:1/5)