Making an Undercut Tool?

[plasmator]

I am working on getting setup to do some gunsmithing, and one of the things I want to be able to do is machine a pistol slide. Pistols are are full of undercuts, and there are some tough ones on the slide, namely the lugs that the barrel locks into. Here's a picture for those who may not be familiar:


FN HP-DA Compact Slide and Barrel

To me, the only way to access the round, square-shouldered cuts for these lugs is to come down through the front of the slide (to the right in that pic) with a long-shanked tool.

So my question is, how can I go about fabricating such a tool? My grinding facilities are limited to a humble bench grinder. I do however have a Wabeco D2400 lathe on the way (roughly 9x20, ~2HP spindle).

I'm guessing that perhaps I could make this tool out of an endmill with a toolpost grinder on the lathe. That said, I've spent a lot of money setting up the shop already and would rather avoid the additional cost of a toolpost grinder at this point. Would there be any other way to make this tool on the lathe?

Finally, my apologies for asking what is probably a basic question, but I am just setting up my shop and am teaching myself as I go. Unfortunately I didn't have any machinist mentors growing up, and my day job doesn't allow for any formal machinist education.

Thanks...

[plasmator]

Really? Nobody?

[MikeZee]

At first glance it looks like there will be some fixturing involved, how much you wanna invest will depend on quantity, if you're just doing one or two then you can probably figure out a way to "knife and fork 'em off". Larger quantities better tooling. How far down are the grooves? Could they possibly be milled? Need more info.

[plasmator]

MikeZee, thanks for the reply.

I am pretty sure that I can work out the fixturing required, and have put some thought into that already. My question is more along the lines of how to make an undercutting tool - without a toolpost grinder or other 'real' grinding facilities. Do you have any suggestions along those lines? As for quantities, this is a personal project (It's legal to manufacture any firearm you can legally own, but I cannot legally manufacture firearms for sale - and have no interest in doing so). Thanks!

[MikeZee]

Get yourself a H.S.S. or Cobolt round tool blank and make it by hand on your bench grinder, the groove it self is not that deep and the distance from the entrance hole looks to be maybe a couple of inches. Get a large as posssible to get you through the first bore. Or you could get a woodruff key cutter the correct width and small enough to go through entrance bore, grind all the teeth off but one and use that as an undercutting tool.

[djr76]

An lathe id bore bar, thread/groove bar will do what is needed. Interpolate the grooves out with something like this. Kennametal will have what you need.

[universalfab]

Originally Posted by djr76 An lathe id bore bar, thread/groove bar will do what is needed. Interpolate the grooves out with something like this. Kennametal will have what you need.

I recommend the boring bar, works great. I use lathe boring bars for various jobs on cnc mills fairly often and get great results. We customize ours though.

[MikeZee]

That's an expensive option for one part.

[djr76]

Originally Posted by MikeZee That's an expensive option for one part.

You can try it the hard way with somewhat success or do it the right way with 100% success. Quality is my policy. Im sure you can find something used on ebay cheaper then a new tool.

[universalfab]

You could also let me know your dimensions required and for a price we can make you a custom carbide boring bar that will do the job. We have crates of carbide boring bars made in the U.S.A. Most of them are NOS and some have been re-sharpened. Doubtfull your going to find a boring bar that isn't going to need to be ground down and customized to fit your application.

[RICHARD ZASTROW]

djr76's boring bar makes good sense. You can use that tool on many other jobs as well. Just look at it as an addition to your tool library/inventory.

Dick Z

[MikeZee]

You CNC guys have no immagination!