Counterbore cutters?

I

imagineer

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Does anyone have info on these cutters? Each has 3 cutting edges on the bottom face. There’s a pilot hole thru as well as a set screw to tighten a pilot.

The boxes for the larger ones stated “Counterbore”. There are 3 sizes, ¾” diameter w/ .250” pilot hole, ½” diameter w/ .188” pilot hole and 3/8” diameter w/ .156” pilot hole.

What is installed in the pilot hole, a dowel pin, a drill bit or another endmill?

Would these be used at high or low spindle speed?

Thanks.c-bore end.jpgc-bore top.jpg
 
Those are for cutting recessses for Socket head cap screws. You use a pilot in the hole that is a close fit to the clearance hole of the bolt hole you are trying to counter bore. They will follow the location of an existing hole if the pilot is close in diameter.

Go slow. Speed is for metal removal rates. You aren;t removing much and they aren't cheap. Low speed, last long time.
 
I figured they were for counterboring for socket head screws, but the diameters of the cutter and pilot don't seem to match. For example, a 1/4-20 SHCS has a head diameter of 3/8" (so a 1/2" diameter counterbore would be sufficient) but the counterbore that uses a 1/4" pilot has a 3/4" cutter diameter.

I'm guessing the idea is you drill the pilot and counterbore 1st, then final drill the hole for the fastener?

I googled "interchangeable pilot counterbore" and found them, and yes, they're pricey.
 
Not specifically for SHCS, general purpose counterbores. That's why the interchangeable pilots. They do make counterbores specifically sized for SHCS with fixed (integral) pilots, some with .015" oversize pilots and some with .030" oversize. I have the latter, wish I had the former. In theory they can be run as fast as a HSS drill of the same size, but are generally run much slower since they're harder to sharpen.
 
The pilot parts are stepped. diameter to fit cutter, step to desired diameter for pilot.
I put the fastener hole in first, using the mill. Then I often setup the drill press to put the counterbore in to the correct depth.
slide part until pilot enters hole, secure part with C clamp, Counterbore.
 
As mentioned, they can be used for counterboring or spot facing for hex head or other top clamping style bolts or machine screws. I much prefer this style over those with a permanent pilot. That's the only style I've purchased. I like the fact that the tool has multiple uses. Over the years I've amassed a fairly large collection of pilots from one of the used equipment dealers.

Originally, I only purchased the "close tolerance" (.015") style. They worked fine as long as the fasteners were held to tolerance. Now that most fasteners are made offshore, I often find they either won't fit, or are tight in the counterbore. Still in most cases I start with a close tolerance counterbore, but many times have to go to a "standard tolerance" (.030") one to get the fastener to fit properly.

I used to try to purchase fasteners exclusively from Rockford Screw Products in Rockford ILL. They always had high quality products and were generally available at the local hardware and farm stores. Unfortunately, they were driven to close in 2016 by the influx of cheap offshore fasteners.
 
Still looking through the boxes and bins, but haven't found any pilots yet.
Since my new lathe was delivered yesterday, maybe take a stab at making one?
 
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