drillin' and tappin'


December 27, 2002, 06:54 PM
so i've got no choice to drill and tap this revolver if i want to scope it...

i'd do it myself but the frame is stainless, which of course is hardned steel.... what kind of drill bit and tap would i have to have in order to do the job?? is it worth the cost of the tools as opposed to having someone else do it?? not much chance i'll ever tap 6-48 in stainless after this...

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December 27, 2002, 07:09 PM
First off, stainless is not specifically hardened steel. In most cases the stainless alloys used for gun frames is the same or softer than the carbon steel used. It is "stickier" and requires a different technique.

Now as to the drilling...

Here's how I would do it. Figure out where the holes have to be positioned. Figure out how deep they need to be to hold (minimum 3 full threads). Put the frame in the mill. Make the holes with a carbide cutter so that they're flat on the bottom and not tapered. Use a starter tap to make the first pass. Use a bottoming tap to finish the holes. Take the frame out of the mill, clean and degrease (from all the cutting fluid). Install the mount, rings, and scope.

Cost $25 per hole & $50 for the mounting and zeroing. Parts extra.

P.S. I charge more to fix bad holes drilled by people who don't know what they're doing. And that's if they can be fixed.

December 27, 2002, 10:24 PM
i really don't know what you mean by "stickier" but i would assume that means cutting it too fast would be a problem....

why wouldn't you use a drill press as opposed to a cutting mill? what potential problems do you see using a press instead??

the holes will be through holes, i really don't see a way around that, plus it'll make it that much easier to tap...

and how about a resource for such a small fine tap? online that is....

thanks for the help

December 27, 2002, 11:24 PM
You usually pick up the turn rate on stainless, or slow down the feed rate. The optimum point is just different than carbon.

I use a mill because I can 1) make sure that everything is square, 2) make sure my measurements are precise, 3) easily put the taps into the drilled holes whithout changing the setup, and 4. because the mill will set up much more rigid than all but the most overengineered drill press. It's much more precise, and once the setup is done makes the job faster and simpler.

Through holes are easier.

You can get the tap from Brownells.


December 29, 2002, 10:58 PM
Think of stainless as tougher rather than harder. The "sticky-ness" quality is one more familier to machinists and smiths. These kinds of materials tend to load up the cutter with chips, and the loaded cutters cause galling in the work. Certain alloys of aluminum are considered sticky.
The mill also offers a more controlled down feed rate than the typical drill press.
My suggestion is if you like the gun, take it to a smith and let him do the job right. Your prize Pardinni is not the place to learn how to extract a broken tap.
Another source for taps & tools is MSC (MSC.com ?)

J Rhines
Seneca, MD

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