Ball Nose End Mill / 10V Bearings Question

[Dr_GMJNParticipant @dr_gmjn]

Posted by Mick B1 on 14/05/2020 19:21:19:

Posted by Dr_GMJN on 14/05/2020 19:01:03:

I spoke to Ketan this afternoon about the cutter, and he assured me it was the correct geometry.

I might do a quick test on a differnent material later on, but since I should have ordered something smaller it doesn't really matter that much.

I really don't think so.

In your photo I can see a clear sharp breakaway between the radius end and the cylindrical portion of the slotdrill, and this is visibly matched in the profile of the slot you cut in your piece of alli. It looks to me as if the end rad is 1/4" or more when it should be 7/32" and run smoothly – tangentially as you said – into the cylinder part. I think it's clearly wrong – as I said, it looks like no other ball nose slot drill I've seen in 45 years.

Look up ball nose slot drill in Google Images and tell us if you see one with the clear edge between cylinder and sphere that you have on yours – I didn't..

Edited By Mick B1 on 14/05/2020 19:28:13

Mick – I know what you mean; you're making the same observations I did, although it's very difficult to tell the actual geometry of the cutter becasue the profile is projected on a helix. The geometry of the resulting cut is what it is, and plain to see.

Ketan told me the cut geometry may be different in other materials, but that the cutter geometry (or profile or whatever) was no different from any other manufaturer. At least that's what I understood. Seems like a very decent & helpful chap, so I'm happy to take his word on it.

If I was so inclined I could get the cutter geometry fully analysed and evaluated at work, but at the end of the day I've ordered the wrong thing anyway, so it would be a bit pointless!

[Mick B1Participant @mickb1]

Well, I'm even more surprised now to hear this from Ketan. Unless the material behaves weirdly, like perspex or something, closing up after the cutter's passed, the profile of the cut is within practical limits defined by the profile of the cutter. You'd think to get much the same result in Delrin, brass, steel or titanium. Even if there were significant spindle runout with a properly-profiled cutter, what you'd expect that to generate is an oversize slot with a flat at the bottom, not what you got.

Getting back to the fit of your bearing extrusion in the casting; if it's a sloppy fit, only the studs and nuts will be defining the location, and that's not normally regarded as adequate because of indeterminate clearances. Ideally you'd look for an accurate fit and line-drill the bearings square to the piston rod centreline to make sure there are no tight spots. I think I had a few on my 10V when I made it , but a minute or so's run-in with an electric drill chuck on the crankshaft end got rid of it completely. Now I can run the engine just by blowing into the inlet tube. I don't know, but I've a feeling the bearings just fitted the cast slots with minimal filing in my case.

Edited By Mick B1 on 14/05/2020 20:06:34

[PaulFParticipant @paulf49072]

I used an RDG Tools 11.0mm carbide ball nosed end mill with good results.

[Ketan SwaliParticipant @ketanswali79440]

I would just like to clarify what I have said…

First in an email reply I said: 'The ball nose endmills are correct and typical of the basic TiN coated endmills we supply. There is nothing wrong with them as supplied.' I followed that by saying that I have had zero complaint for this product… which is the case.

We have been selling this, as is, purchased from the same manufacturer, with the same 'shape' specification, for nearly 18 years. It is no different to what is available at the basic – budget end of the market for yellow TiN coated product. We are one of the smallest 'quantity' buyer. His main buyers are Americans, who buy a much larger volume from him than I do. The question over the shape being right or wrong has never been brought up to date. Either the buyers don't know, or they know, right or wrong for their application, and/or accept it for what it is in terms of shape.

How the shape compares to the 'premium endmills – HSS or carbide' which we sell, I also don't know, but I expect them to be better and different from the budget end end mills. Unfortunately we do not sell 11mm or 7/16".

In our conversation, it is also correct that I said that the TiN coating on the budget endmills will behave differently in cutting/finish when used on non-ferrous material such as aluminium (as what in this case), vs. ferrous material, purely because this ball nose end mill is coated, and for aluminium it is better to have un-coated.

Jason PM'd me with a suggestion for him to check the differences between the budget end ball nose endmill, compared with premium end mill. He has/may have a 7/16" Hertel ball nose end mill. So, I will send him the same ball nosed end mill for him to compare, on different materials.

[Anonymous]

Posted by Ketan Swali on 14/05/2020 21:02:23:

How the shape compares to the 'premium endmills – HSS or carbide' which we sell, I also don't know,…….

I can tell you that. This is a picture of the part I showed previously, but taken as near along the straight top edge as I could:

The cut was done on a CNC mill using an Arc carbide premium cutter. The curve looks to me to be pretty darn close to a perfect quarter circle, as it should be. So the premium cutters are correctly ground, the budget ones are not. I definitely won't be ordering any budget cutters.

Andrew

[Ketan SwaliParticipant @ketanswali79440]

Posted by Andrew Johnston on 14/05/2020 21:16:57So the premium cutters are correctly ground, the budget ones are not. I definitely won't be ordering any budget cutters.

Andrew

Thanks Andrew… I wouldn't expect you to either

Ketan at ARC

Edited By Ketan Swali on 14/05/2020 21:21:19

[Dr_GMJNParticipant @dr_gmjn]

Posted by PaulF on 14/05/2020 20:34:24:

I used an RDG Tools 11.0mm carbide ball nosed end mill with good results.

Thanks Paul, that's the kind of fit I was hoping for. I came to the conclusion I needed an 11mm cutter a bit too late though!

[HopperParticipant @hopper]

It may be that as a budget cutter in a short production run for oddball (today) imperial diameter of 7/16 the ball radius was machined in the standard 12mm radius fixture to save production costs. Results in a rounded end suitable for most work but not a perfect complete hemisphere.

They couldnt use the closer 11mm radius fixture because it is slightly too small and would leave a tiny but noticeable step.

Or not. Pure speculation of course. But i have never seen such a cutter so have to think there is a reason for the large radius. Production cost wpuld be the most obvious.

Edited By 

Edited By Hopper on 15/05/2020 00:59:59

[JasonBModerator @jasonb]

As Ketan said the main buyers are American they would not regard 7/16" as oddball even today!

I've had one of the Tin ones from ARC for a number of years in 1/4" so will take a closer look at that too but not noticed any problems with that but would be harder to see.

[HopperParticipant @hopper]

Posted by JasonB on 15/05/2020 06:57:26:

As Ketan said the main buyers are American they would not regard 7/16" as oddball even today!

True. But possibly to a manufacturer in, say, China churning out millions of metric milling cutters for their own huge domestic market, the declining post-industrial US market would be peanuts. It's getting harder to source imperial sized cutters direct fron China via Aliexpress etc. Sometimes impossible. I get the impression they are becoming a bit special for export only.

 

Edited By Hopper on 15/05/2020 08:32:14

[JasonBModerator @jasonb]

While waiting for one of the 7/17" cutters to come from ARC I thought I would try out the 1/4" one that I have had for some time, it's showing it's age but good enough for a back to back comparison with a 6mm HSS one from ARC's premium range.

As you can see the vertical face flows nicely into the curved so it may well be just the 7/16" cutter that may have the odd shape and I can't imagine that being a fast seller so could explain the lack of others having an issue as I expect 1/4, 3/8, and 1/2" are far more popular.

regarding the Doc's other post where it has been suggested that his cutter may be blunt it is worth comparing teh cut straight out of the mill and how they cut. The ARC one is as I said past it's sell by date and with the 8mm approach (height) it tripped the X3's cutout trying to take 0.5mm DOC so had to use just 0.25mm and it did not sound happy. On the other hand the nearly new ARC Premium was happy taking 1mm DOC and would have done more. The tell tale burr thrown up by the cutter is another indication of it's blintless compared to the clean edge left by the sharp cutter.

[Dr_GMJNParticipant @dr_gmjn]

Trying to replicate your test with my 7/16" cutter (in aluminium).

For me, personal non-expert opinion, the cut shouldn't look like that.

But…I don't want to get into some arguement about it. That's just my opinion. I will be interested to see your results.

[Mick B1Participant @mickb1]

Posted by Dr_GMJN on 15/05/2020 14:38:37:

…

But…I don't want to get into some arguement about it. That's just my opinion. I will be interested to see your results.

I don't believe any legitimate argument is possible. Ball nose means what it says – it should sweep out half a sphere plus any tolerance of cutter diameter and runout, and that implies that the radius should blend to the cylinder without sudden corner. There are plenty of conditions where ball nosed cutters are required to generate such a radius-bottomed slot, of which the 10V's bearing mounts are just one clear example.

Looking at your first cut, that isn't what yours is doing. Vertical deviation or movement would only put the corner at a different height, and horizontal would only make the slot wider and create a flat or shallow inverted vee at the bottom without effect on the corner. Your most recent pics don't show that condition so clearly – are you using the same cutter?

[Martin ConnellyParticipant @martinconnelly55370]

I have had a look at ball nosed cutters I have got, some unused some used. If you look at the cutting edge as you rotate it there is one point where the silhouette is perfect. In all other positions the relief behind the cutting edges show up as in the earlier photos making it look like a badly ground ball cutter. I think there is an argument going on about an optical illusion and there is no problem with the cutter profile.

Martin C

[Dr_GMJNParticipant @dr_gmjn]

Posted by Martin Connelly on 15/05/2020 15:33:32:

I have had a look at ball nosed cutters I have got, some unused some used. If you look at the cutting edge as you rotate it there is one point where the silhouette is perfect. In all other positions the relief behind the cutting edges show up as in the earlier photos making it look like a badly ground ball cutter. I think there is an argument going on about an optical illusion and there is no problem with the cutter profile.

Martin C

Martin , I alluded to this in a previous post. Surely, the fact is it’s the resulting cut that tells you if the cutter geometry is correct. Assuming of course there isn’t some gross error in technique!

[Martin ConnellyParticipant @martinconnelly55370]

Ball nosed cutters are a bit of an oddity. The cutting edge on the axis of rotation has an effective speed of zero and so to some extent scrapes its way through the material like a plough. Any lack of stiffness in the set up will result in unwanted movement from the forces involved. I think you are trying to do some cutting operations that will test your experience. If you get a cutter with the equivalent of a four facet grind on it the forces are lower but I think the cost will be higher.

This photo shows the difference between a simply ground ball nose and a more expensive type.

Marin C

[Dr_GMJNParticipant @dr_gmjn]

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.

[Jeff DaymanParticipant @jeffdayman43397]

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.

[Mick B1Participant @mickb1]

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.

[Dr_GMJNParticipant @dr_gmjn]

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.

[JasonBModerator @jasonb]

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

[Dr_GMJNParticipant @dr_gmjn]

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.

[JasonBModerator @jasonb]

Posted by Dr_GMJN on 20/05/2020 21:22:11:

Is there any chance you could check runout on the ARC tool, above the flutes?

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.

[Dr_GMJNParticipant @dr_gmjn]

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.

[JasonBModerator @jasonb]

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.

[Author]

Posts