Member postings for Kiwi Bloke

Good grief! It's junk! Demand a full refund, including all out-of pocket expenses incurred in undoing the deal. You have the law on your side.

Let the forum know what happened. If retailers peddle such rubbish without shame, they need to bear the consequences, including adverse publicity.

Sadly, this illustrates the problem of unreliable quality control, which appears to extend all the way from manufacturer (rather an optimistic term in this case) to retailer. With so much stuff being imported from unknown sources, often sporting 'reliable' brand names, you just can't buy on trust any more. And it's probably going to get worse, before it gets better...

Oh, forgot to say that I have a Jacobs tapping chuck, which takes Rubberflex collets. These are axially aligned entirely by the chuck body's internal taper. The closer applies only an axial force to the end of the collet and mates to the body via a 'loose' square thread. Seems like a good design... Or is it?

Thanks MG for the link. I've read it all (phew!). Some interesting content, but sadly diluted by rudeness, mud-slinging and anti-intellectual attitudes. I'm not impressed by arguments that go like: 'I was taught to do it this way, as an apprentice, and have done it this way for the last 40 years, so it must be right', or: "Just do it, don't waste time thinking about it". Kiwi Bloke's First Rule: The heat under the collar is in inverse proportion to the quality of activity above.

From the linked-to thread, it seems that lack of concentricity of the closer can / will cause the collet nose to be deflected radially. I had assumed that the collet would make contact (well, several line contacts) all along the sides of the chuck body's taper, thus it would be the chuck body that aligned the collet. However, it seems that it's only really held at the narrow end of each taper, so the closer's radial alignment is critical. Without a register, the closer relies on the centring action of a V thread, and will also be deflected by off-centre spanner forces. This probably explains the need to tighten HARD - to maximize the not-very-good centring action of the thread.

These things (most things) are more complicated than at first sight. Clearly, in practice, the things work well enough, resisting sensible radial loading, even for holding work, rather than cutters, and for use with milling cutters. However, some people experience radial run-out. I wanted to start an intellectual discussion as to possible causes and especially whether the problems were inherent in the design. Perhaps, in view of the vitriol in the linked-to thread, I was unwise.

The thread 'Arc Euro ER16 runout' got me thinking. Thought I'd start a new thread, rather than hijack that one.

I've just looked at the Schaublin collet chuck that Emco supplied for the FB2 milling machine. I'd rather taken it for granted before - it just did its job, apparently accurately. But now I'm wondering... are these things designed optimally? Clearly, axial alignment cannot be taken for granted and the availability of 'forcing clamps' (dunno what they're really called) to tweak cutter alignment suggests that concentricity may not be as reliable as one would want.

I assume that the collet is aligned by the taper in the body of the chuck. If the collet collapses symmetrically (and is made concentric), alignment should be determined by the collet chuck's accuracy. But this assumes that the collet is not able to be deflected radially as it is tightened. Is this assumption valid, in practice? There are two complications...

Firstly, the short taper on the collet's nose mates with the taper in the closer (nut). The closer is threaded to the body with a 'normal' V thread, so it is 'centred' by the thread. If there is a malalignment between the closer and the body, the closer's taper and the centring action of the thread may fight each other, resulting in a radial force on the nose of the collet. Wouldn't a 'sloppy' square thread (large radial clearance) be better? There would then be no chance of the closer exerting a radial force on the collet. (OK, we really need symmetrical spanner work, but that applies to the conventional design anyway.)

Secondly, for collets with extractor grooves, it might be that, as the closer collapses the collet, allowing the collet to settle deeper into the closer's taper, the closer's extractor (half-) ring 'bottoms out' on the collet's groove, and contact between the closer's taper and the collet nose's taper is lost. Also, the axial force would be off-centre. Wouldn't it be better for the cap to be able to exert only a reliably axial force? Why have a taper in the closer, or is it to ensure the greatest radial force is applied to the cutter at the collet's nose?

Perhaps I should just continue to take it for granted...

Crikey! Lots of churches have lead roofs. Think of the volume of toxic water run-off when it rains. No wonder the surrounding ground is usually full of dead people...

Again, not quite the direct replacement you're after. 12V (3-5W) LED downlighter replacements for 50W halogen jobs make wonderful machine lamps, but don't have the hidden 'advantages' of heating the room or providing a sun tan because they run cool and AFAIK don't emit UV. Currently a bit pricey, but I got a load for about a quid each recently.

JasonB - thanks for the pointer to the video. I hadn't found it because I searched specifically for 'Brian Perkins VW'. For some reason, it's the only thing I can remember that hasn't shown up correctly in this forum. Presumably it's because I run Firefox (on Linux) with cookies, scripts, trackers and ads controlled tightly. It's surprising how most sites still work OK with loads of scripts disabled. They must be trying to do something - but what?

Perhaps Jason B has answered, but all I see is a blank box.

A Brian Perkins (the Brian Perkins?) wrote up his BP 75 model in Strictly IC magazine, years ago. It was based on the VW flat 4, was 75cc and he flew it in a large scale model Colibri. Impressive. 'Fraid I can't provide more info. - my copies of SIC are in a box, somewhere...

You'll get a disappointing few hits from an internet search, but there's a little to whet the appetite out there...

As I suggested earlier, the spindle would benefit from being as large a diameter as the OP's application can accommodate. However, Belville washers are, IIRC, available in small diameters.

XD 351's comment about spring preload washers not controlling end-float is not strictly correct. They will not eliminate end-float, but can control it, to an extent that allows the design to be practicable. The force required to move the spindle axially can be designed to be higher than anticipated forces applied to the spindle by the cutter, etc. That this works in practice is borne out by the thousands of (fairly) satisfied Unimat users and its very widespread use in precision spindles.

The whole point of spring pre-loading in this application is because trying to set preload by screw-adjustment is difficult - you can't tell when it's correct and, in small sizes, the axial displacement required for reliably setting the correct adjustment is too small to be applied easily by a practicable-pitch thread, especially when a lock-nut disrupts the adjustment. If the adjustment of such a rigid set-up is such that the axial float is just eliminated, there will be minimal bearing preload - less than the 'correct' amount. However, setting the 'correct' amount is difficult - how do you measure it?

In much larger applications, opposed taper roller bearing-supported shafts are often set to a desired torque required to overcome the drag imposed by the preloaded bearing. Great fun, swapping shims, rebuilding, measuring torque with a spring balance pulling a string wound around a gear, taking it all apart and doing it all over again. And again. When, years ago, I rebuilt a Land Rover transmission, (LR service manuals detailed this method), I was surprised to learn that the local main dealer never opened transmissions - they just bunged in 'recon units'. The labour (and skill?) required was too much. Luckily, they carried boxes of shims for us idiots working for free, in our own time...

OK, enough of this counsel of perfection - don't be put off. You will probably get away with a screw-adjusted arrangement; make the thread as fine as you can and adjust it until there's just a little rotational drag, and there's no rattling on shaking the assembly. Spring pre-load makes life easier...

(Stupid emoji added to my previous post, apparently by 'auto-correcting' software built into this forum. Can't you just wait for self-correcting autonomous cars?)

Andy, I can only applaud your determination to repair this thing. I would do the same. Problem is, I wish I didn't spend so much time, effort and money trying to resurrect the dead or rescue the hopeless cases (even though they turn out to be not-quite dead or not entirely hopeless). I've got to the stage where this sort of battle is no longer a pleasure, but just an annoying distraction from doing what I really want to be doing. Also, I've probably spent more money on rebuilding machines and upgrading than I would have done by appearing extravagant and buying something really good in the first place. And the time spent and the aggravation along the way is incalculable.

As you get older, you realise that time's running out. If you're lucky(?) you may be able to predict fairly confidently that time will run out before the money does. If that's the case, put a load of beer vouchers into a VFD and a 3-ph motor, and enjoy the benefits.

Not telling you what to do, just the reflections of an old one. Good luck with the project, I'm interested to see how it turns out.

Er, regain control, dump Microsoft (and Apple) and use Linux! Enjoy Free software!

As DW above says.

Belville (cone) washers may be easier to find than wavy washers and avoid possible interference with the inner race. The washer contacts the outer race by the outer edge of its face only, and 'points' away from the bearing (towards the other bearing). Therefore install two, 'pointing' towards each other (><; the second one's OD contacts the step in the housing bore, as above. As used by Emco in the Unimat headstock - two, with angular-contact bearings in the early Unimat, 4 pairs, back-to-back*, with deep-groove bearings in the Unimat 3. You need a reasonably firm spring to resist the possibility of the spindle moving axially, should it ever be loaded towards the workpiece by, for example, a drill grabbing in brass.

* thus: >><<>><<

Ian, it was your suggestion earlier that the lock-nut order debate shouldn't be re-ignited, but then you did...

As Hopper says, it is (now) generally accepted that the half nut goes on first. The reasoning is only a few clicks away, should you choose to search out the science, rather than regurgitate dogma. The locking nuts to which you refer, sometimes known as Palnuts, are obviously much more elastic than conventional half-nuts, and compress and deform when tightened, rather than causing significant elongation of the stud. The deformation under compression 'bites' into the stud thread, thereby directly increasing nut-to-stud friction. They therefore work very differently from the conventional nuts being asked about. Stud elongation, resulting from tightening the upper (conventional) nut, unloads the lower nut, transferring stress to the upper nut, hence the upper nut should be the stronger one. When a Palnut is used, the lower nut remains the fully-loaded one.

Apart from any other considerations, if, as you suggest, you were to use a conventional nut on top, torqued 'just tight', it would tend to loosen more easily than a fully-torqued, non-locked, single nut, thereby defeating its intended purpose.

This whole subject is far more complicated than it seems at first sight, and it shouldn't be assumed that industrial practice is optimal at all times. I started the thread in the hope that it would get people to think.

Thread-locking compounds are probably the answer... ; )

Edited By Kiwi Bloke 1 on 26/10/2018 08:56:49

Half nut on first.

Bearing shields (metal) and seals (rubber) supposedly serve two purposes, although not necessarily at the same time - it depends on the situation: keeping the muck out and keeping the lubricant (usually grease) in. Metal shields are obviously more robust, thus better at excluding swarf and chips, but there is a small gap between shaft and shield, so dust and fluids can enter the bearing and lubricant can escape. Seals usually contact the shaft, thus will exclude liquid and fine solid contaminants and do a better job of containing lubricant. However, seals wear and also can exert so much drag on the shaft that low-torque drives may be unable to achieve desired spindle speeds. The drag can be quite surprisingly problematical. There are so-called 'non-contact' seals, which look identical to conventional rubber seals, but are drag-free. These are ideal for low-powered spindles, such as Unimat headstocks. Manufacturers' data sheets will give you the relevant identification numbers, etc.

Incidentally, for precision spindles, if using deep groove, rather than angular contact bearings, you should be looking for 'tight' bearings, with a small clearance rating. These may not be as easy to obtain as C3 or CN rated bearings (excuse me if I've got the wrong rating codes here - working from beer-addled memory tonight...). Lower numbers are tighter. Some manufacturers offer 'electric motor' bearings, which are designed to run more quietly, ie with less vibration, which is just what you want. They are not much more expensive than 'cooking' ones.

And, of course, buy quality, not cheapest.

Hey! Who defaced my post with a vile, smirking emoticon(?). I typed a closing bracket. What's going on?

Steve. Your proposed spindle's diameter is pretty small for its length. I'd guess that you want to be able to run the spindle up to, say, 20,000 RPM. I'd be inclined to make the spindle as large a diameter as you think you can. That would give you the possibility of a central bore, although you probably don't need one for your intended tooling in small collets. However, you never know, and building in versatility is often time well spent.

Angular contact bearings would be better than deep-groove bearings. In either case, setting the right pre-load with nuts on the screw-cut spindle might prove to be frustrating. Make it the finest pitch you can. Probably better to apply axial load with a Bellville washer (or a few). Plenty of spindle designs on the 'net and good stuff in Harprit Sandhu's book, No 17 in the Workshop Practice series.

I think Chris Gunn's point about an axially non-constrained bearing at the pulley end refers to the more complex, but better, design in which there are loaded, opposed bearings at the spindle nose end. It all depends on how 'good' the thing needs to be...

At the risk of being accused of stating the bleeding obvious, a 4-flute, end-cutting cutter is like a four-facet twist drill, but with a couple of extra cutting edges. So, if you can sharpen twist drills with four facets - or, better still, as split-points - you can sharpen these cutters. The extra two cutting edges will be conveniently out of the way, provided that the central arris is not normal to the 'long' cutting edges, as in Andrew Johnston's right-hand pic, and not as in Jason B's 'Rougher'. Nothing wrong with the latter, but far harder to set up successfully.

Link belts, with their high inherent losses, are good at damping vibration. Belt drives can vibrate horribly. Brammer or Powertwist belts make the primary drive on Myford Super 7s much sweeter, in my (and others' experience.

'Lock washers are not placed under the head of a bolt in a nut and bolt assembly because the shank of the bolt provides additional friction.'

I find that hard to believe if the bolt is in a clearance-diameter hole. Apart from that, I'm heartened to see that Robert Atkinson 2 shares the same ideas that I do.

Should serrated flange nuts be regarded as similar to nuts + star washers? They're popular these days.

I still suspect that common assembly practice owes rather a lot to dogma and questionable beliefs...