End mill through pilot hole

[old mart]

The end size of the hole depends on several factors. I plunged straight in with a 1/4" HSS endmill and the hole was 0.270" diameter. Starting again with a different endmill, the hole was 0.253", much better for my purpose. I can only think that the second cutter was sharper and flexed less while cutting. Solid carbide gives the best hole size, probably due to the extra stiffness. The results I got in post #10 were no more than +0.001" in a 10mm diameter hole.

[Fasturn]

How and why? Is this any different than an improperly sharpened twist drill? Is there different geometry/whatever at play?

I dont know if you are kidding? The holders run out, the spindle is not ridged, tool pressure makes tool dance, chips get lodged in hole and so on. If the hole is not cleared first like you would for a reamer?

They did make Jig- Bore Reamers years back that looked a lot like end mills. Their is a skill level, knowledge to be a master Machinist.

[mickeyf]

Using an end mill as a drill will always make the hole oversize.

How and why? Is this any different than an improperly sharpened twist drill? Is there different geometry/whatever at play?

[Fasturn]

Dero- the original use of endmills was to plunge downward like you want to do. Thus the name " End Mill " They didnt sidemill. So yes it will work. As others said, it will make a hole .003-.007 oversize.

On a CNC machine I would peck drill with a 3 flute EM, then pocket with the same tool. No heilical entry for me, too slow!
If you are working with Aluminum, 3 fl endmills work very well.

[old mart]

I have just done this, I wanted a reasonable fit for an endmill holder I needed for long reach. I drilled the hole well undersize and then used a solid carbide endmill to finish the blind hole. The endmills that it will hold are a sliding fit with no slop, which is good news for me. As the hole is blind and only the depth of an endmill shank, a reamer would not do as even machine reamers have a lead in taper. I wanted the endmills to reach the bottom of the hole.

[mattthemuppet]

drill the hole first and then use an endmill for the counterbore if you don't have a counterbore the correct size. I've done that a bunch with good results, though typically I'm not aiming for a precise hole size, just clearance for a bolt head

[barracudajoe]

Use a piloted counter bore?

[Toolguy]

Using an end mill as a drill will always make the hole oversize.

[dero]

Thank you , I shall proceed .

[Lew Hartswick]

Does using an end mill where there is a pilot hole already drilled pose any problem ?

I'd put it this way; It not doesn't pose a problem, it's a GOOD idea. :-)
...lew...

[Doozer]

Even if I have a center cutting end mill,
I tend to drill a pilot hole anyways
just so the end mill does not "squirm"
when feeding down. If it "squirms"
and deviates from center, there goes
your size. If you are pocket milling,
I guess it does not matter much.
You know, zero radius in the exact center
so that means pure RPM and no FPM
(feet per minute, or what ever units you
tend to use).
If you are asking will an off center existing
hole drift an end mill off center as well,
the answer is no. Search jig borer reamers.
That's basically what they are, end mills
used to establish center of a previously
existing potentially off center hole.


-D

[dero]

I am thinking of using the end mill as a drill , to get a reasonably accurate hole with a shoulder at the bottom , with another smaller hole continuing through the bar .
Hope this makes sense .

[Toolguy]

Need more details.

[dero]

Does using an end mill where there is a pilot hole already drilled pose any problem ?