# Today's "What is it?"



## hman (Jul 9, 2020)

Here's what looks like some kind of milling cutter or counterbore.  It was mixed in with a bunch of cutters and other stuff I got a couple years ago.  Both or them were in wax when I got 'em.

There are 5 cutting edges on the face.  A 1/4" hole extends through the cutter (possibly for a guide pin?) and through the cutting face.  Note that the flutes are only sharpened along the last ~1/4" next to the face, and that they are tapered a bit.  Not easy to see in the photos, but there's a radius, about 1/32", between the side and face edges.  The hexagon is 1/2" across the flats, and the shank between the hex and the spiral flutes is slightly tapered - not suitable for a collet!

How the heck this is supposed to be held in a machine tool is a puzzler.  And though it does resemble a counterbore, it looks kinda large for use with a 1/4" guide pin.  Spotface cutter???  But again, how would it be held?


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## Alcap (Jul 9, 2020)

Kind of reminds me of tools used in automotive/engine work on the top of the valve guides when upgrading the factory valve stem seals , can you post a picture of the face ?


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## hman (Jul 9, 2020)

OK.  Here it is ...


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## MikeWi (Jul 9, 2020)

is that really a 1/4" straight hole, or is there a taper?


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## pontiac428 (Jul 9, 2020)

Valve spring seat cutter?  Most valve guides are a bit larger, but maybe for small engines.  It's definitely meant to be turned by hand.


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## mmcmdl (Jul 9, 2020)

I always figured them to be shell reamers and have a few of them down the basement . I have never located just what would go thru the hole ( if anything actually does ) . The ones I have , have a very small step in the bore up front which I thought could be used with a threaded adapter or something . Once again , I''ve never found such adapter , but I have quite a few more junk drawers to go thru .   

Hope someone can figure this one out !


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## hman (Jul 9, 2020)

The ¼" hole goes all the way through, with no lip at the cutter face.  Matter of fact, the diameter is slightly enlarged (clearance?) between the hex end and about halfway in.  No threads anywhere along the length of the hole.  I didn't try to measure the diameter exactly, but a known accurate ¼" shaft passed through with what appeared to be a slip fit.


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## kd4gij (Jul 12, 2020)

Valve seat cutter, for cutting the recess for the valve seat to press in.  old flat head engines, or small engine


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## Aukai (Jul 12, 2020)

It looks similar to this








						machinist tool lathe mill lot of Gairing Counterbore Cutters  | eBay
					

Gairing A-1 holder - tapered shank with 1/2" 90 deg cutter Gairing A-2 Holder - straight shank. 7/16", 1/2", 9/16", 5/8" counterbore pilots for A-2 holder. All bits are in really good condition. 1-1/8" - W (2 of these - still in original cover).



					www.ebay.com


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## hman (Jul 12, 2020)

I see the similarity, and originally thought mine might be countersinks.  But the tapered shank and tapered side cutters make it a bit doubtful.  Guess I'll have to go with valve seat cutter (for small engines).  I jst haven't ever had any interest in messing with gas engines, so it's brand new territory for me.  Thanks to all for your responses!


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## Superburban (Jul 12, 2020)

hman said:


> I jst haven't ever had any interest in messing with gas engines, so it's brand new territory for me.


Now you have a reason, start looking for a small engine to rebuild.


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## Lo-Fi (Jul 13, 2020)

Yep, valve seat cutter. You put a mandrel in the valve guide bore and the cutter rides on that. The machine drives the cutter via the hex with a flexible coupling. Means you don't have to faff setting the machine lined up perfectly central or concentric with the valve guide.


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## hman (Jul 13, 2020)

Makes a lot of sense.  Thanks!


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