reverse countersink source and design

[pipemakermike]

I have been asked to find a way of countersinking the holes for welding in new stays into an old loco boiler.  Now, I have made reverse countersinks and counterbores for myseof in the past but this is a bit bigger than I am used to.  I have measured up the quill of the huge drilling machine (the pink bit in the picture) and I think that by using a drill blank with a No. 4 morse taper already done I should be able to do what is needed.  The picture shows a Ø16 drill blank and a couple of removable keys, not to drive but to protect the drill shank from pulling out or falling out.  I don't know where to source the actual cutter and would welcome any advice.  I would think that a bespoke inserted tooth carbide cutter would cope with the scaly and abrasive surface inside a loco firebox.  Thoughts etc

[Jasonb]

I would have thought a large HSS dovetail cutter or even an indexable one would be an option though that would give you a 60deg chamfer. You can also get whats called a double angle cutter that would give you teh 45deg but thats HSS.

Take a look through the MSC/J&L catalogue starting around page 224 and the chamfer mills on page 321

http://www.mscjlindustrial.co.uk/CGI/INPDFF?PMCTLG=00

Is there no way of getting a mag drill into the firebox? may be easier.

You could also ask on somewhere like Traction Talk forum as there are plenty there that have repaired or replaced fireboxes and whole boilers.

http://www.tractiontalkforum.com/

Whats the size of the stay hole you have to work with as one of the facemills that have the tips set at an angle may be another option.

J

[Fergus OMore]

Mike

I'd have thought that you would have followed the way that clarinet tone holes were undercut.

Again George Thomas ( and his followers) did some fancy undercutting on his small versatile dividing head.

F O'M

[Lew_Merrick_PE]

Pipemaker -- A standard back countersink has the cutting tip on the end attach to the shank using a 1/4-turn latch mechanism.  I would assume that a cobalt HSS insert end would be better than carbide given the drilling machine usage rather than a milling machine usage (rigidity of cut is the question).  Whomever is the equivalent of Manhattan Supply Company (MSC) or McMaster-Carr on your side of the pond would be a good starting point as you may be able to get what you need off the shelf.  ???