Member postings for Kiwi Bloke

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?

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.

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!

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...)

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

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

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

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...

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.

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

...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...

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

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.

Mil is still used for 0.001" in that most backward ex-colony across the Atlantic. Mille, French for 10^3, but used as 10^-3, as in mm, mg, etc.

Edited By Kiwi Bloke 1 on 31/12/2018 18:53:01

I'm jealous of you lot! I'm 'between workshops', so most of my equipment is inaccessible. This morning, I sprayed (back-pack) 100 litres of glyphosate, but was stopped by the breeze getting up. Job only half-done... This afternoon, I took pity (again...) on neighbour and chainsawed up the big lumps of the poplars recently felled on his land. Two-foot diameter trunks, but easy going, for a big saw and a beer-refuelled old man: there was just rather a lot of it (I mean the timber, not the beer). One day is much like another, really...

Edited By Kiwi Bloke 1 on 30/12/2018 09:13:33

Several small lathes and milling spindles are supported by a pair of deep-groove ball bearings, often pre-loaded by 'wavy washers' or Belville spring washers. I don't know what grade bearings are generally used. If the bearings are to be replaced - but not by converting to taper roller bearings - is it worth the expense of C2 bearings?

OK, it's a 'how long is a piece of string?' question, I suppose. However, it's worth knowing the answer because C2 grade bearings seem to be made of Unobtainium in NZ. Upgrading just for the fun of it can get quite expensive...

Well, I never expected there to be so much discussion about this machine. Thanks everyone for all the information and opinion. It all sounds quite encouraging.

An apparently very little-used example, complete with milling head, collet chucks, collet set, 3-jaw, 4-jaw, topslide, steadies, change wheels, dividing unit, and a few other bits and bobs recently sold here (NZ) for about NZ$2,500 (divide by 2 for pounds) - the same as a well-equipped, little-used, Cowells 90ME made. Emco gear is fought for here. Just out of interest, what would these machines go for in UK?

Quick question - it's not uncommon to see Cowells equipment sold in almost new condition: what's going on?

I've been wondering about a small lathe. The Emco Compact 5 looks attractive, and is about the right size, but is it a dressed-up toy or an accurate machine, capable of sensible work (in steel)? A certain G Meek uses one: should that be recommendation enough? Any available will be fairly old by now - how do they wear? Also, is the milling unit worth considering?

The restricted speed range, alloy headstock, saddle and tailstock, and the rudimentary fine feed for the milling unit's quill don't inspire confidence. What do users think?

A friend in Oxfordshire told me the following, which happened to an unpopular 'know-it-all' builder, who had moved into the area, into a large, expensive pile in the country, which he was 'improving'. I think it was just before Christmas.

Said builder had installed one of those glass-fibre septic tanks that look like a monster onion. He knew better than to follow instructions, so didn't bother with the heavy concrete collar around the top of the unit, having buried the 'onion'. The outflow field turned out to be unwisely sited, in a low part of his land. It rained. And rained. The ground got soggy. The septic tank stopped draining, and overflowed. (OK, you know why, but he didn't).

Reasoning that the best thing to do with an overflowing tank is to empty it, that is what he did. The water table being unusually high, the back-fill around the tank being not properly compacted, and lacking the mass of the concrete collar that should have been there, the now empty tank did what physics said it must, and what the displaced volume of water compelled it to, and promptly popped right out of the ground. My, how the locals larfed.

Big changes in the last 50 years? TIG, MIG, tipped tooling - all more-or-less affordable. The demise of Myford and the popularity of oriental equipment of dubious quality. CAD/CAM/CNC. The internet, where information and mis-information compete for your attention and where fora like this enable idiots like myself to appear authoritative and reach an audience we don't deserve.

I may be missing something, but heating things with a flame is thousands-year-old tech, even if the fuel has changed. I still occasionally use a meths wick burner and a blow-pipe.

Predictions for the next 50 years?

Edited By Kiwi Bloke 1 on 26/12/2018 09:11:33

Aargh! Just noticed brain fart in 3rd line of 2nd para of my first post. Of course, I meant 'radial alignment', or making sure there's no radial displacement: i.e. making sure everything is co-axial. Confusing innit?