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

[OJCar]

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).

Difficult for me to photograph clearly.
The "grain" of the cotton layers of the Girling NOS runs parallel to the bolt.

(I had the magnifying glass out to examine the NOS ones)

 

[Keith 66]

Standard twist drills tend to bite & dig into tufnol, similar to acrylic, Grind (or file with a diamond file) a small slight negative rake on the cutting edges of the drill bit & it will cut much easier with no chance of digging in.

 

[dave h 2]

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/

You can also take the 6mm drill used to drill the hole, then turn it round and grind the butt end to look like a 'D' bit and use that in the chuck to flatten the bottom of the hole.
Saves you time, money and you still have a 6mm drill that can be used normally.

 

[Ian X]

I used a 6mm router single flute "upward" helix bit with a large pedestal drill, it left a clean edge, a flat bottom too., material was coloured acrylic sheet.

 

[Robotstar5]

Useless fact: Tufnol was invented here in Birmingham in the 1920's and are still going today - Link

 

[OJCar]

Useless fact: Tufnol was invented here in Birmingham in the 1920's and are still going today - Link

And there was me thinking it came from Tufnol Park, London ...

 

[Agroshield]

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).

With something like that, made in large quantities, is there a possibility they could have been made to their finished shape rather than produced by cutting down/out of something larger?

I can imagine cutting the layers to size, pressing them into a mould and squirting in some glue. It is something you might do with fibreglass resin and fabric, so is the same thing possible with tufnol?

 

[OJCar]

^ Looking at the Girling originals under the magnifying glass you can see the machining marks.

 

[OJCar]

Following on;

The SRBP rod I ordered on Sunday from Direct Plastics
( Rother Valley Way, S20 3RW Sheffield, United Kingdom, also on e-bay as Direct Plastics Outlet )
arrived yesterday evening, extremely well packed.
Included in the package of the 1metre length was the offcut from when it was a 4 foot length.
Looks like the rod has been in stock for many a long year.

Very pleased with Direct Plastics.

Ironically the offcut will probably provide me with more than enough material to make the guide buttons from.
( I might put a point on the end of the 1m and use it to prod Mad Wife in the Attic. )