Ball Nose End Mill / 10V Bearings Question

Thanks for that Martin.

I take your point that since I'm a novice at this, it could be a problem with technique. However, I still fail to see how.

I've managed to generate two idential cut geometries - a full slot, and now a half slot, with exactly the same stepped side profile.

Lets assume the cutter is correct, but my machine vibrates massively in all three axes, and the spindle bearings are knackered. As far as I can see there is no way that any cutter intended to create the orange edged profile below could possibly also create a profile with step in it:



Conversely, it would be possible for the white central profile (stepped) to create a rounded profile, but that would mean simultaneous, and consistent movement in x and z as well as feed and rotation. This is clearly not the way to do it!

Can you draw me a diagram of what you mean?

Thanks.

Your pictures seem to show a ballnose cutter that has not been ground correctly with the start of the radius exactly tangent to the side of the cutter. That could be the problem. I would suggest looking for a better quality cutter with start of rad tangent to sides.

I'm sure Doc's right - this ain't no optical illusion - it's the profile swept out by the cutter.

And the cutter's named as an extremely well-established variety - informally a tulip (two lips, geddit?) of a sort I've been using since 1975, and it can't have the correct geometry if it produces a slot like in the OP's first post.

I'm ducking out of this now. I can't put it any more clearly, and if anybody ever sells me a ball nose slot drill that cuts like that, it's a false trade description and it goes straight back.

I can't seem to edit my post - but to clarify I meant "any cutter intended to produce the orange edged profile - not including the hatched area ie with tangential radii."

Thanks.

The Results are in!

While waiting for the sample cutter to come from ARC I did a test cut using what turned out to be an 11mm Hertel one though marked as “Select” which is an MSC brand.

Cut taken to depth required for the Stuart extruded bearing, possibly a very slight “step” where the curve meets the sides.

This measured 10.86mm wide

I cut a little more off each side so that the bearing would fit and this is the resulting slot and cutter which looks to smooth transition from the curved end to the sides though the slot still shows that slight “step”

On opening the package from ARC it was easy to see that the cutter looked to have a more prominent “step” just like the one the Doc posted so I had not been sent a special one.

A test cut confirmed that the cutter produced a slot with a marked “step” in comparison to the one cut previously

Though it did cut bang on width

A closer shot of the two slots and the cutters

So in conclusion the 7/16 Tin coated one from ARC does not give the shape one would hope for and even the other make has a slight Step. Ketan said to me that it looks like others in the range are likely to show a “step” to some degree.

It is interesting to think that ARC have sold a good number of these and the US market considerably more yet this is the first time the issue has been raised, I certainly did not have any issues with the smaller ¼” one that I have had for quite a while, maybe it is just a bit more noticeable on the larger sizes.

J

Edited By JasonB on 20/05/2020 20:14:24

Thanks for doing that test Jason. Is there any chance you could check runout on the ARC tool, above the flutes?

I got another mill from Cutwel (11mm), and that is also ground differently, with a tangential radius-flat. There is no change in profile as you turn it and look in the region of the transition. The ARC version always has the step no matter how it’s viewed; I thought at first it might be an effect that might not translate to the workpiece when rotated, but apparently not.

At least I now know it wasn’t some effect caused by my technique (or lack of it!).

Cheers.

Don't think I could have got much better even if I invested in super precision collets and a high spec holder and mill to run it in.

I would say 0.003mm tir which is in teh region of 0.0001" or 1/10th thou

What you can't see out of shot is that I start off with the stylus on the high point then move to one side and back across the high point to he other just to show I'm not fudging the reading.

OK, thanks very much for your time - and thanks to Ketan for helping out with supplying another end mill to you for testing.

With my new 11mm tool, my intention is to set the casting up and move the cutter back and forth through the housing, incrementing downwards after every pass. If the brass casting fits, I'll do the depth by trial and error, if not I'll cut the slot slightly shallow, and then take equal depth side-to-side cuts, as you did, until it's a good fit. Then I'll increment downawards again until I get the depth right.

I'll obviously do a quick check in aluminium first to get used to it.

Thanks again all.

Sounds liek a plan

Just make sure you knock the corners off the slot when test fitting the bearing as there is a very slight internal fillet. Also When doing the tests I noticed on mine that the two lugs are not totally flat on the underside. Mine was too tarnished to see if id filled a bit off years ago or whether the actual extrusion was slightly distorted, you can see here that only the end of the lug makes contact and I have my doubts that the curve is perfect.

Understood. Thanks.

Wish me luck..

This is the new 11mm tool, as tested in aluminium:



Pretty much perfect - it didn't need any more side cutting on mine, so with some trepidation, on to the real thing:







Went through the cast iron beautifully. Unfortunately I centred the casting on the inner edges of the standard flats, double checking it with the insides of the cast bearing housing prongs. Result is that the brass is slightly offset to one side (obviously the right on the image above), but centred on the inside edges of the base. I should have thought more, and used the outside edges of the bearing housing prongs.

Anyway a few passes with a fine file and it’s not really apparent, but lesson learned. I'm still waiting for the silver steel for the spot facing tool. BTW I put a thin coat of red oxide on the casting becasue I find it much easier to see where I'm marking or initially cutting that way.

As ever, thanks for your help. Any comments welcome. Onwards...

That's a nice piece of work, Doc - can't see how it could be any better.

Thanks very much Mick!

Last post moved to the build thread.

The chances of anybody noticing that the end rad did not match the shank are very small. The need to fit two parts together with such a good match is a very demanding and rare thing. Ball ends are usually used for rads in corners or channels which don't matter so much.