Drilling SRBP F1 (Phenolic Cotton Rod) (aka Tufnol, Paxolin, Croylam )

[OJCar]

*Not sure this is the right part of the forum for this thread - Mods feel free to move*

I need to drill blind holes 6mm diameter 5mm deep in the end of SRBP rod 13mm in diameter.
Ideally the blind hole should be flat bottomed rather than the cone shape a drill bit will make.
I do not have access to a lathe, just a pillar drill.

The parts are guide buttons that go on the end of a modified 5/16 UNF bolt
as a part of a Classic Car braking system.
The original guide buttons made by Girling have not been available for many years.


What sort of speed should the drill be running at ?
Are there flat ended cutters that would be better to use than a drill bit ?
Cut dry or what lubricant ?

Some NOS

 

[Seadog]

Best to drill with a conventional drill, then finish off with a slot drill. A couple of hundred rpms will suffice. Make sure that your drill is sharp.

 

[oldbikedavey]

Funny old stuff to machine, is Tufnol.
Supposedly it has similarities to both wood and aluminium.
Give a few test pieces a whizz, and see what it tells you.

 

[KemppiFrog]

Best to drill with a conventional drill, then finish off with a slot drill. A couple of hundred rpms will suffice. Make sure that your drill is sharp.

Wot he said^
If no slot drill, just grind a normal one flat, then give it some angle to the edges.

I treat it like wood. Machines easily, but be aware of the dust, not good for you!
Made some boat winches out of 100mm dia stock from plasticsonline..

Oh, no lube needed.
Just curious, what classic motor?

 

[Seadog]

but be aware of the dust, not good for you!

But smells wonderful

 

[Kram]

Guide buttons for a braking system? Where are these used and what happens if they fail?

 

[OJCar]

Thanks.

I was told many years ago to cut Paxolin with no lubricant at all,
does that still apply?

Used to make prototypes on " Choir Strips " like this but with more tags.

 

[KemppiFrog]

But smells wonderful

True, but I have a slight aversion to cancer...
Actually the first reinforced plastic.

 

[Agroshield]

For me, a three flute centre cutting end mill and go straight in. Maybe a whiff of Henry to remove chips, but since 5mm deep is less than one diameter, swarf is not likely to be a problem.

There are very likely machining guidelines on Tufnol's own website or elsewhere:

How To Machine Tufnol

Every so often a Tufnol job will land on your desk and machining this old school dusty stuff can present its little challenges. Well recently we managed to get our hands on an old brochure made back in the 90's, now although the pages had now gone that slightly yellowy colour around the edges...

www.directplastics.co.uk

 

[OJCar]

Guide buttons for a braking system? Where are these used and what happens if they fail?

On the end of the brake shoe location adjuster screws in a Girling 2LS brake drum.
They bear on the sides of the brake shoe to resist the tendency of the shoe to twist sideways, so the shoe presents square to the drum.
If they fail the shoe will twist sideways, not be square to the drum, braking efficiency will be slightly reduced and the friction material will wear unevenly.
They are NOT a catastrophic failure item.

Item 3 in this diagram

 

[OJCar]

For me, a three flute centre cutting end mill and go straight in. Maybe a whiff of Henry to remove chips, but since 5mm deep is less than one diameter, swarf is not likely to be a problem.

There are very likely machining guidelines on Tufnol's own website or elsewhere:

How To Machine Tufnol

Every so often a Tufnol job will land on your desk and machining this old school dusty stuff can present its little challenges. Well recently we managed to get our hands on an old brochure made back in the 90's, now although the pages had now gone that slightly yellowy colour around the edges...

www.directplastics.co.uk

Thank you.

I'll drill them dry
( and breathe through my ears )

 

[Seadog]

True, but I have a slight aversion to cancer...
Actually the first reinforced plastic.

Whimp

 

[Onoff]

SRBP, the amount of PCBs I made as a kid using that as it was cheaper than copper clad fibre glass!

Smells like old tellies and valve radios.

 

[OJCar]

Smells like old tellies and valve radios.

I resemble that remark.

 

[Onoff]

I resemble that remark.

You've just reminded me I've a UV torch coming.

 

[brightspark]

a bit of silver steel the corect size and make a d bit easy to do and verry accurate you can buy them https://www.tracytools.com/product/d-bits/

 

[OJCar]

what classic motor?

Sorry, didn't see the question.

Series Land Rovers in this case.
There are quite a few other applications of these Girling Brakes such as Rover P4.

 

[Misterg]

I need to drill blind holes 6mm diameter 5mm deep in the end of SRBP rod...

I can't make out the 'grain' in your photo, but are you sure that the originals were made from rod?

The reason I ask is that we used to use something similar (but bigger) as electrical insulators on furnace supports. We got some replacements made out of (whale?) tufnol rod and the bolts kept pushing through them - the way the layers of fabric were oriented in the rod left the equivalent of 'end grain' for the bolt to push on, and this kept breaking away from the outer cylinder.

I think you should be able to tell from the originals whether the layers run parallel or perpendicular to the bolt (in which case, I think they would have been cut out of sheet).

 

[6ply]

Some tufnol is resin impregnated paper / cotton and other types were asbestos based. Many years ago I acquired some tufnol sheet from my dad and we were unsure if it were the latter type. I contacted the manufacturer for advice and they were very helpful, even offering to identify for me if I sent them a sample.

Tufnol stinks. When my dad came home from work I could smell it on him.

 

[6ply]

Thanks.

I was told many years ago to cut Paxolin with no lubricant at all,
does that still apply?

Used to make prototypes on " Choir Strips " like this but with more tags.
View attachment 480066

That image brings back some memories.