Manually machining a radiused pocket

[murpia]

Hi all,
Can anyone advise if it's possible to purchase a formed milling cutter with a radiused corner (but NOT a ball end) to make manually machining a pocket with a bottom corner radius as easy as possible?

I can't find one anywhere. Would need to be capable of some plunge cutting, although I planned to rough-out with a slot drill.

Regards, Ian

[murpia]

Hi all,
Can anyone advise if it's possible to purchase a formed milling cutter with a radiused corner (but NOT a ball end) to make manually machining a pocket with a bottom corner radius as easy as possible?

I can't find one anywhere. Would need to be capable of some plunge cutting, although I planned to rough-out with a slot drill.

Regards, Ian

[consig]

no problem, try MSC industrial supply and search 'corner radius end mill'

you will find many different popular brands and they will probably have the radius you're looking for.

[Conor]

Or take a standard end mill to a grinder... Just kidding, that's a terrible idea, although it'd probably work in a pinch.

[BrunoC]

The name of the tool your are looking for his a bullnose.

[murpia]

Thanks guys,
I'd tried a few combination of keywords but not 'corner radius' cutter. This looks to do the job (in slot drill form) but the corner radii offered are still quite small (all less than 2.0mm for what I could find).

Anyone know of a supplier of a corner radius cutter of approx. 20mm diameter with a corner radius of about 4 or 5mm? (or similar sized imperial)

Also FYI, 'Bull nose' cutters appear to be the same as 'ball nose' which as I said isn't what I was after as it's much harder to get a smooth pocket bottom.

Regards, Ian

[Boston]

A bull nose actualy is what you are describing, it's just not a name commonly used anymore.

[murpia]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by Boston:
A bull nose actualy is what you are describing, it's just not a name commonly used anymore. </div></BLOCKQUOTE>
OK, I think some catalogues (at least here in the UK) are calling ball nose cutters bull nose, then, sorry. Or else they are not dimensioning them properly on the drawings to allow me to see the 'flat' bit at the end.

Also I've seen cutters called bull nose which are designed to cut external radiuses, not internal ones.

Regards, Ian

[Composites Guy]

I have a half-inch diamter end mill with 0.125" corner radius. Its solid carbide and I bought it from MSC. I had previously tried to cut everything with a squre end mill and finish the pocket radius with a 0.25" ball mill, but the narrower ball tool chattered and left a mess on the wall of the pocket.

http://www1.mscdirect.com/ProductImages/7649131-11.jpg

[murpia]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by Composites Guy:
I have a half-inch diamter end mill with 0.125" corner radius. Its solid carbide and I bought it from MSC. I had previously tried to cut everything with a squre end mill and finish the pocket radius with a 0.25" ball mill, but the narrower ball tool chattered and left a mess on the wall of the pocket. </div></BLOCKQUOTE>

My experiences with using a ball end tool are similar - using a square endmill to rough out to within 1mm or so requires you leave a 'step' which must all be cut with the ball end tool as well as the sides. Either that or an insane number of rough cuts. Plus you need to carefully match tool heights to blend the base of the pocket cut with the end mill to the radiused sides cut with the ball.

Seems to me with the right tool form productivity will go up a lot - pocket tolerances can be drawn quite slack, -0mm,+0.5mm or something (you can leave a little extra material with no fatigue or stress issues just a tiny weight penalty). So you just plunge in with the right tool and spiral out using the machine readouts until you're done. Design for manufacture of course with rectangular pockets and side and corner radii to suit the cutter tolerances.

Problem is I just can't find the right cutters in the UK. Would have liked a slightly larger corner radius than 0.125" but at the price, maybe I'll mail-order a few from MSC...

Only thing I can't be sure of from the online MSC catalogue is whether they're truly capable of plunge cuts? Here in the UK we distinguish between slot drills (capable of plunge cutting) and end mills (which aren't). What's the US naming convention for that?

Regards, Ian

[Wes Johnson]

Ian,

A common nomenclature for your 'slot drill' is a center cutting end mill.

-Wes

[oz_olly]

You can plunge with an end mill provided that it isn't the type that has a hole in the centre of the bottom. When you try and plunge with those you end up with a little teet that fits inside the hole in the cutter and can break the cutter when it begins the move in the xy plane. We have plenty of four fluted end mills with out the hole and they plunge like a slot drill no worries.

Cheers

Olly

[Composites Guy]

Here's another alternative to ball mills for corner radiusing pockets... its from iscar (www.iscar.com) and it screws into a shank (they have all different shaped tips). Unlike the end mill that I mentioned above these come with corner radii greater than .125"

http://www.iscar.com/Ecat/datafile/PICTURE/1626.gif

[billywight]

Just drill a hole first and plunge with whatever cutter you want.

[Brian Evans]

I may well be a luddite, but I normally use two flute center cutting end mills in 5/8" (bought a lot on ebay once and haven't used them all up) for almost all my aluminium work. When I pocket cut in aluminium that's what I use. I have several that I have put radiused tips on by the simple method of grinding the radius by hand with a belt sander. I use a about a .100" radius, I have a gauge that I use if I need to. I know that if you send your tools out to be sharpened you can ask for any radius you want to be put on.

Brian

[murpia]

Thanks for all the tips guys. I'm going to try to grind my own 5mm radius on a two-flute slot drill as a starting point (going to make a little jig to do it right). If that cuts poorly then I like the look of that Iscar item - they have a UK office.

Have had some success with formed tools on the lathe, hope I can repeat it on the mill.

Regards, Ian

[Brian Evans]

Off-hand grinding of form tools is a skill that any old-school machinist learned before he was allowed to turn on a Bridgeport or run a lathe. Don't be scared of it, try it freehand and compare to a radius gauge if you need to. Sure, a jig is good if you need to make a dozen, or sharpen end mills in a production environment, but a machinist should be able to do routine tool sharpening of drills, end mills and lathe tools.

Brian

[murpia]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by Brian Evans:
Sure, a jig is good if you need to make a dozen, </div></BLOCKQUOTE>
Mostly I'm concerned about getting both flutes sufficiently equal in radius to avoid chatter, not whether my radius is spot-on.

Regards, Ian