#4 Countersink?

[Jasonb]

Would any of our American members know what is meant but a Number 4 countersink? It is suggested for use on the valve seats of the PiP radial.

I think it may be a specific dia for countersinking #4 screws and possibly piloted.

Thanks, J

[b.lindsey]

Jason, is this the one from littlelicos.com. ? If so a quick email to todd@littlelocos and he should be able to clarify this for you. I suspect the #4 refers to screw size as well.

Bill

[Jasonb]

That's the one. It's not actually for me and I gave away my copy of the drawings and notes that were in MEB mag.

[Lance]

Look here.
 http://www.carbidedepot.com/formulas-centerdrills.htm

[Jasonb]

Lance thanks for that but it is a 90degree countersink that is needed to suit the 45deg valve not a 60deg centredrill.

[Lance]

Jason
I cannot find a true 90 degree #4 countersink, they seem to fit in the category of hens teeth. The only thing I can find is 90 degree center drills and #4 all seem to be 5/16". Would that be the dimension of the valve head?

https://www.dansdiscounttools.com/?s=+%234+countersink&post_type=product

[Jo]

Countersinks come in many angles  for thin metal work you find 82 and 100 degrees also exist. 

A numbered countersink is combined tool designed for applications where a screw is to pass completely through the material without digging the threads into the material and have the head sit flush.



Sorry the numbers are in imperilious 

Jo

[Jasonb]

Jo as I said two posts above it is a 90deg that is needed.

I have found piloted ones with a 0.252" dia head, 90deg that would suit a #4 screw so think this is what is needed though they don't number the bits.

http://www.bsa-regal.co.uk/downloads/E-Catalogue.pdf

You will see head dia is a little less than your link which is really dia of the CSK hole if the angle were a knife edge on the screw but they are not so a little smaller CSK dia can be used if taken below surface.

[Jo]

Jo as I said two posts above it is a 90deg that is needed.

So best make sure you don't get a 82 or 100 degree one then: Careful they do 82 degree ones in that catalogue and a true numbered CSK will limit your depth to that which only takes the screw head flush 

Have you considered one of those really expensive 6.5mm Chinese Cone end mills? or do you need the lead?

Jo