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Member postings for Kiwi Bloke

Here is a list of all the postings Kiwi Bloke has made in our forums. Click on a thread name to jump to the thread.

Thread: releasing tapers
13/02/2019 10:45:36

Probably best not to add complication to the tang discussion by mentioning 'use-em-up' sleeves.

Wish I hadn't.

13/02/2019 10:03:41

OK Hopper, I'll bite...

'...a different kettle of fish...' Very good! Clearly a sly pun, alluding to the Poisson ratio, which is of central relevance to what I was rambling on about!

Clearly, following a whack on the little end, the outwards deformation of the inserted male member (can I say that on this forum?) in the female socket will be miniscule, but would be detectable with a strain gauge on, say, the outside of a tailstock barrel. A compression wave will indeed travel through the tool (and socket): (elastic) deformation will not be confined to the tang. And, of course, whacking the thing (usually) gets it out, so any transient increase in the friction holding the things together will be overcome. However, given Poisson's insight into deformation mechanisms, pulling things out of tapers should be easier than pushing - although perhaps less practicable. That was my message - for what it's worth.

Anyone who has used a Clarkson 2MT collet milling chuck, with its 'steadying ring', will know how readily tightening the ring can release the taper. Ideal geometry for release.

I'm not trying to labour a point here, nor wishing to disagree with anyone - just indulging in a bit of theoretical whimsy - but I always cringe when anti-friction-bearing-supported bits of machine get attacked by hammers. Unfortunately, often there's no sensible alternative.

12/02/2019 09:56:44

Clive Foster's Atco experience is fascinating - I must try to remember it for future use.

I've been thinking about releasing things stuck in tapers. I hate whacking the things free - it must do the bearings a power of no good. Self-ejecting arrangements, captive draw-bars, folding wedges and threaded collars at the nose end are so much gentler.

The trouble with thinking is that the more I think, the confuseder I get. When a bullet is fired, the back of the bullet starts moving before its nose. A compression wave spreads out through the bullet at the speed of sound (ie the speed of sound in whatever the bullet's made from). This causes the bullet to be plastically deformed - if it can 'go' anywhere - increasing in diameter, and contributes to the bullet being forced into the rifling grooves, and stops gas leakage. (Impressive and somewhat hair-raising experiments were done in the early 1900s by F W Mann, which involved the recovery of fired bullets without their suffering significant damage after they left the gun.)

Something similar (although elastic) presumably happens when the tang or small end of a tool in a taper socket is whacked. I would suggest that the whack will cause a transient increase in the radial forces between the tool and taper. Perhaps, if the whack is smart enough (not from a dead-blow hammer), the compression wave is followed by a 'tension' wave, which helps release. It would be better, (wouldn't it...?), if the blow could be applied at the large diameter end, so that there was only a wave of tension. Perhaps a slide-hammer puller, applied to the outboard end of the tool, or whacking a rod lying in a deep axial hole, bored from the small end, the end of the hole being beyond the wide end of the socket.

If this sounds crazy, just think about how you'd get a long rubber plug deep into a tube with an ID smaller than the plug's OD. You'd easily pull it in, but pushing would be impossible. I believe this is how the trailer 'Indespension' units were assembled (are they still going?).

This isn't meant to be a serious practical suggestion, just thought-provoking. Perhaps I should have gone to bed before now...

Thread: Myford tailstock ML7 / Super 7
06/02/2019 07:47:50

Just remember to check the centre height of a replacement tailstock. I don't think Myford held to specified dimensions too rigorously - it was easier to fit individual parts to each other.

Thread: super 7 headstock bearings
06/02/2019 07:44:17

Andy - it may just be loose terminology, but now I'm worried that you seem to be still fiddling about with changing the preloading of the angular contact bearings (set by the split, threaded collar, at the end of the spindle). Essentially, once all the 'slack' is taken up, increasing the preload will achieve little, if anything, in terms of axial rigidity, but will cause the bearings to have a harder time - or fail. Do not over-tighten them. The relationship of the spindle to its tapered nose bearing is what needs careful fiddling. This is set by the two rings, using C-spanners, patience and suitable language. It's easy, but tedious. I think you know that...

The above instructions are correct, in principle (although be careful with the 12oz hammer...). Very small spanner angle adjustments are needed to get the best adjustment. In fact, you may find that you can change from a tightening spindle to a well-behaved one simply by bumping the spanner on the rear ring to make it a little tighter. I've always used the heel of my carefully-calibrated hand, not a hammer.

I suspect - but have no evidence - that the type of oil used in the front bearing may have a significant effect. Myford's recommendation may be rather old-fashioned. One day, I'll try something 'slipperier'. Any suggestions, anyone?

Thread: Hip replacement - End of live steam?
05/02/2019 21:17:22

The 'design' of the hip joint was discussed in an old anatomy text book I had. As I'm sure you all know, the socket's annular lip is orientated in an oblique plane. In discussing the functional implications of this, the book said that if one stood with legs straight and toes pointing in a bit, with back straight, but leaning forwards a few degrees, and a sack of potatoes happened to fall onto your shoulders, you would likely dislocate your hips. Armed with this knowledge, I've always been careful to avoid that...

Glad to hear of successful outcome!

Thread: super 7 headstock bearings
05/02/2019 21:00:38

I had exactly the same experience with my Super 7, when it was nearly new. I was trying to use a rather brutish 'carbide'-tipped tool - a negative-rake metal-shifter. The only way chatter could be (mostly) eliminated was to tighten up the front bearing clearance. The bearing continued to run cool at high speed, so I thought the spindle may have been not optimally adjusted previously. Then I needed to drill from the tailstock, and the lathe stalled at the slightest provocation. Unfortunately, this behaviour is a 'feature' of this lathe - others have experienced the same.

The problem may be because of a lack of stiffness in the thrust bearings themselves - perhaps the taper roller mod helps. However, IIRC, with a sensitive indicator, I satisfied myself that the part of the headstock casting which carried the thrust bearings wasn't very stiff, when the spindle was loaded axially - a few 'tenths' movement could be induced wrt the bed. I don't recall being able to detect movement between spindle and the rear of the headstock. Incidentally, my Emco Maximat Super 11 coped with the tooling perfectly.

As you've discovered (and it sounds like you fully understand what you're doing), setting the position of the spindle is either a compromise, or you adjust it for the job in hand. It's a very sensitive adjustment. I guess most users settle for a compromise setting, which is where the lathe doesn't slow down with the heaviest anticipated axial load applied. But then look at the axial movement of the nose of the spindle, when loaded radially, and don't be surprised to see a couple of 'tenths' of movement. Remember, it's a light lathe, designed more for versatility than heavy loads. Despite its worship from its die-hard fan base, it's a dated design with many flaws: better* lathes are out there...

* Of course, it rather depends on what you mean by 'better'.

Thread: Repairing a hole
02/02/2019 08:55:27

Thanks folks for all the suggestions. They've freed up the gummed-up neurones. I'd looked at the job and decided that it would be difficult - probably because of the small diameter - and then seemed to have just developed tunnel vision, seeing the only possibility as some sort of guided re-drilling procedure. I'd never considered what might be called a generation method (internal cylindrical grinding, boring, etc.). Now the neurones are free again, all sorts of alternatives present themselves.

Sorry for the unclear, rambling initial post. I tend to post after I should have gone to bed... The roll pin is out (not sure how it was done). It was in a blind hole, and punched below the surface, so there was nothing to grab. Why do designers do things like this? I wouldn't have thought hydraulic methods would work with roll pins, because of the large leakage path, but I've removed bushes hydraulically - very satisfying! Perhaps Plasticene and taking it by surprise would have worked. Must try to remember that idea for the next time...

01/02/2019 10:03:30

I'm not a beginner, but this seems to me to be a topic that beginners should know as much about as possible - as soon as possible. Clearly, I didn't...

The complicating issue in this case is that the hole is in hardened steel (a moving vice jaw). The hole diameter is perhaps 2.5mm (haven't got the thing here to measure), is about 10mm deep, and is blind. Apparently, it got chewed up by attempts to remove a roll pin. The first few mm are certainly no longer cylindrical, perhaps .5mm oversize, but it's probably as manufactured, deeper down.

I have access to a not-particularly rigid mill (Emco FB2). I have been asked to 'make the hole round again', so a removable dowel can replace the roll pin. Its diameter doesn't matter too much - it could be 1mm oversize, but the centre position should be retained as well as can be managed. I'm thinking of using a drill bush to locate the hole and constrain the cutter, as it will be cutting off-centre, at least to begin with.

The first question is: what cutter, drill, burr, whatever, would be best? I have broken a few carbide twist drills, in the past, so am nervous about brittle, small-diameter cutters, particularly when cutting 'on the corners'.

...and the second question, the answer to which, had it been known earlier, would have saved all the trouble: how the hell are you supposed to get (small) roll pins out of blind holes?

Thread: Sliders too tight
01/02/2019 09:42:21

I would regard the use of abrasives as a last-ditch manoeuvre. There's always the risk of abrasive grains embedding themselves in the soft material and continuing to abrade for evermore. Also, you can't put the substrate back, after you've taken too much off. We've all done it...

If the thing is as sketched, I would expect that it was assembled by holding all bits tightly together, then tightening the screws. The through holes would have allowed a little movement, so the slide could be assembled rattle-free. With any luck, the screws are fixed with some form of Loctite-like adhesive. It would be worth cooking the assembly in the oven at, say 180C, to soften the adhesive, and then have another go at loosening the screws.

WD40 is a poor lubricant in some (many?) circumstances. When you've fixed the slide (by whatever means), there are specialised lubricants that increase their viscosity under shear - the opposite of thixotropic (can't remember the correct term. Was Kilopoise one trade name?). These make slow-speed mechanisms move beautifully, and are used in optical devices and things like rotary controls on hi-fi gear. RS Components used to sell them. I can't find any on the shelves here in NZ, but, for similar purposes (micrometer threads, etc.), use an 'assembly paste' (Molybond GA 50), which is a stiff grease containing 50% Molybdenum Disulphide. It's a pretty good substitute, and has the advantage that it's intended to prevent 'pick-up' and galling.

Thread: Ball bearing spindles
16/01/2019 09:27:49

Hmmm. My understanding of magneto bearings is that they are a sort-of hybrid: a deep groove inner track and an angular contact outer track. They can therefore take some axial loading, but little, if any more than a deep groove set. I don't think they are designed for high loading. Their purpose is to allow axial location of a shaft, rather than to react substantial applied axial loads, whilst being easily separable: the housing comes apart, axially, and the shaft can be removed without having to disturb the fitting of either track. I think angular contact bearings would be better for a milling spindle.

Re Neil's earlier post. Things ain't so simple. Angular contact bearings are supposedly available in different contact angles, to be selected depending on the ratio of anticipated radial to axial forces. IIRC, 3000 and 5000 series differ in contact angle. (Sorry, too lazy to go and look. Perhaps the indefatigable finder-of-information MG will search out more...). Dunno if the availability of different geometries gets as far as our usual suppliers.

CT. I agree about the radial clearance of angular contact beraings. I would assume that the 'steeper' contact angle necessary to react substantial axial loads results in decreased radial stiffness, compared to deep groove bearings.

I'm coming round to the idea that, provided axial loads arekept within the manufacturer's allowable range, C2 bearings will provide greater radial stiffness for a given axial load, but less axial stiffness. Thus they would seem better for, say, a small lathe headstock than C3 bearings, and perhaps also better than angular contact bearings, unless a lot of drilling from the tailstock is anticipated. However, this is all reasoning from first principles, rather than working from established fact - come on, we need a bearings expert to tell us!

14/01/2019 10:30:03

I'm a bit disappointed that no-one responded to the last para in my last post, above.

It seems to me that, counter-intuitively, in, say, a small lathe headstock, a properly preloaded pair of slacker grade deep groove ball bearings might be preferable to a pair of C2 bearings because the loaded slack pair will adopt a configuration more like a pair of angular contact bearings, and be stiffer in the axial direction. I suppose, however, this is at the expense of radial stiffness. Or am I getting old and stupid? (I know what my wife thinks...)

Thread: Small Milling/Drilling Spindle (again)
14/01/2019 10:15:50

Bearing in mind the 'inherent precision' aspect, I must concede that you've got a point there, MG.

...OK, I'll be off now.

13/01/2019 21:19:55

Re the cutting frame design: the bearing arrangement is OK, for the reason you suggest, but it's a pain to have to re-set preload every time the cutter is changed, isn't it? The design doesn't make it easy.

The design is, however, seriously flawed, for another reason. The weakest part of the shaft - the joint - is in the middle of the shaft, and under the cutter. It's exactly where it shouldn't be. It's easy enough to improve this aspect of the design, but why bother at all? I don't see any reason to bother with cutter frames these days. Perhaps I'm missing something...

My understanding is that they are a legacy of the days when you couldn't pop out and buy pre-made bearings. Early cutter frames had (I believe) conical-ended shafts, the cone running in a conical recess in the end of a screwed 'bolt' (for want of a better term) that screwed into the frame. (Hope that makes sense.) This is about the simplest bearing to make, and suitable for very light loads. The 'bolt' could be quickly unscrewed to free the shaft, and also facilitated bearing adjustment to eliminate end-float. One thing you really don't want, if you're cutting tiny gears, is any cutter end-float. With this design, the bearings were necessarily at the shaft ends, so the pulley and cutter had to be between the frame's arms. This can make things a bit cramped.

I can't really see why one shouldn't use a properly designed spindle, with the cutter at one end, and the pulley at t'other. Forget cutter frames - they're history!

Since you are laudably doing your own thing, rather than slavishly following published designs (which we now know to be untrustworthy...), bear in mind that you should only use sealed ball bearings if you are confident that you have sufficient torque to overcome the seals' drag, which can be surprisingly high. You can buy bearings with 'non-contact' or 'low friction' seals which are OK and shielded bearings are fine. Make sure your supplier understands your requirements - to some, a seal is a seal is a seal. Non-contact sealed bearings are no more expensive than 'conventional' sealed, but are perhaps not so readily available.

Edited By Kiwi Bloke 1 on 13/01/2019 21:25:07

13/01/2019 10:59:45

Enlighten you? I don't know - possibly add to your confusion. For the sake of what follows, can I assume you have a copy of the Spindles book and that you're a beginner, with little engineering knowledge? It's safer not to assume knowledge sometimes.

I've just rooted out my copy of the book and am very surprised. The author does not discuss bearings in any detail and most of his designs are faulty. OK, they will almost certainly 'work', but they can be much better and at the same time simplified: bearing 'slack' can be minimized by simple re-thinking. You really shouldn't have to tolerate any avoidable free movement that can be designed out, and it's particularly important to avoid it in a spindle intended for milling, grinding, etc.

The problem is that the type of ball bearing used in most of his spindles are 'deep groove' ball bearings. These always have a tiny amount of radial clearance built-in. Clearance may be designed into the bearing to allow for expansion when whatever the bearing is fitted to heats up. Hot-running and high-speed bearings are designed slacker. Bearings come in different clearance grades. These are numbered, typically, C1 - C5, tighter being lower numbers, and more expensive. I haven't seen C1 grade available in 'our' sizes, from usual suppliers. CN is 'normal' clearance and is somewhere between C2 and C3. Aftermarket bearings are often C3 grade, to suit a wide range of hopefully-not-very-critical applications. CM is also somewhere between C2 and C3, and is supposed to be designed for electric motors, where quietness in operation is desired, so very smooth tracks, for low vibration, but I don't think 'tightness' is a design priority.

If you shake a typical C3 bearing set, with seals and all lubricant removed (bad for the bearing!), it will rattle surprisingly, and the inner track can be felt to move, in all directions, with respect to the outer. Figures for radial clearance can be found, buried in the manufacturers' data sheets, but axial clearance is rarely listed (as far as I can recall).

As the inner track is pushed axially into the outer track, the balls roll 'up the sides of the grooves' a little, and can thus react the applied axial force. This loading has removed the slack, and you'll note that the radial slack has gone, too. High radial forces can still, of course, cause the built-in radial slack to reveal itself, but, as axial force is increased, radial stiffness does also. What we want is to load each bearing in opposite axial directions, so the slack is taken up in each bearing. This is known as 'preloading', and is often done by adopting a mounting like the book's author does for his taper roller spindle: the outer tracks are prevented from moving deeper into the housing by shoulders, and the inner tracks are GENTLY pushed together by the nut at the pulley end.

All this is absolutely standard stuff, and I'm disappointed that the book got published, containing as it does so many poor designs. The Ch5 design allows the cutter in the chuck to 'see' all the slack in the bearing nearest to it: preload is impossible. The Ch6, 7, 8, and 11 designs are bad: the only thing holding the spindle into the housing is the friction fit of the outer tracks of the bearings (and the rear one should be free to slide with a bit of effort). The spindle might easily vibrate out of its housing under the influence of milling vibration, until the outer track of the rear bearing abuts the shoulder in the housing. Also, again, no preload provision. The Ch9 &10 designs have no provision for adjustable preload - both inner and outer tracks of both bearings are fully constrained - so incredible precision of manufacture would be needed for real success.

The design in Ch 13 is fine, and also the simplest. It embodies what I've been trying to explain, albeit with taper roller bearings. Note that the inner tracks are constrained at their outer face only - there is no spacer tube between them, so they can be moved together by tightening the nut outboard of the pulley. The outer tracks are constrained at their inner faces by the shouldered housing. If deep groove ball bearings (or angular contact bearings - but that's another subject...) are substituted into this style of design, you have a design in which bearing clearance can be miminized. You can also go for C2 bearings, if you can source them (I can't, in NZ).

Someone may post that I'm being over-fussy, but the 'proper' design I've described is the easiest to make and employs the bearings to their best advantage. Hope this is enlightening, rather than baffling...

09/01/2019 19:29:29

Forgive me if I have misinterpreted the drawing, but the design illustrated in JasonB's post is seriously flawed. Both inner and outer races of the nose-end bearing are constrained. The pulley-end outer race is not constrained. This means that the bearings are not pre-loaded and therefore there is nothing 'taking up' the built-in clearance of either bearing, but particularly the nose-end bearing. The clearance is small, but enough to cause problems with milling.

A better design, and standard practice, is to have each outer race fitting into a stepped housing, with the nose-end bearing's inner race abutting an 'outboard' step on the spindle. The inner race of the pulley-end bearing is then located by the pulley hub, screwed and locked to the shaft (there is no shaft step at this end). Thus, bearing clearance can be removed.

There are other ways of taking up axial clearance, but the essential point is that the illustrated design has none.

Thread: Posh washers
01/01/2019 19:44:38

Have you tried asking your local nut & bolt supplier for 'T&C' washers (Turned & Chamfered)?

Thread: Measurements from the past
31/12/2018 21:57:30

...and units for the future? The minimum possible length is the Planck length, so speeds can be expressed as multiples of it. The maximum possible speed is the speed of light, so speeds can be expressed as fractions of light-speed. The unit of time is then the time taken for light to travel one Planck length. Useful in physics, but far too many zeroes to deal with, for everyday use.

Don't worry folks, after Brexit, there may be sympathy for rods, poles and perches again. As long as beer still comes in pints, it's OK...

Thread: Ball bearing spindles
31/12/2018 19:46:25

Spring-loaded ball-bearing spindles have a long and noble history. Precision grinding spindles have often used such a method to pre-load the bearings, to ensure stability, although rather better engineered than Emco's circlip abutment scheme. Prof. Chaddock used one such design (copied from Hoffmann) in his Quorn. Angular contact bearings may be the most commonly used in this application, but a deep-groove bearing, when axially loaded, is behaving like an angular-contact bearing. However, this is where I start wondering about bearing clearance grades...

An axial force on a deep-groove bearing causes displacement of the inner race wrt the outer, which causes the tangent at the ball contact points to 'swing round', so that the line of reaction force, normal to the tangent, swings towards the axial direction, to oppose the applied axial force. The geometry of a 'tighter' bearing will (presumably, all other things being equal) restrict the amount by which the tangent can swing round. Thus, for a given axial force, it seems to me that a greater radial force is induced in a 'tighter' bearing, and the resultant of the axial and radial components will be greater, i.e. greater forces at the ball contact points. Perhaps, if a deep-groove bearing has to resist axial forces, it should be a 'slack' grade, so it can approximate more to an angular-contact bearing when loaded. Or are the forces so far within the allowable range that 'tight' bearings are OK? They should provide greater radial stability in any case. Or have I got myself completely confused?

Edited By Kiwi Bloke 1 on 31/12/2018 19:50:58

Thread: Emco Compact 5
31/12/2018 19:15:31

The capacitors will probably be rated at 400V, so no problem. Individual households' UK mains voltage may be lower than you think - it depends on how far 'down the line' you are. However, even at full nominal voltage, the slight added heating would be most unlikely to be a significant problem.

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