Member postings for Martin Dowing

@SillyOldDuffer,

Experimental evidence is conclusive in falsifying theory. Theories are models of reality, not reality itself.

Models are applicable within some ranges of conditions and less perfect ones are just special cases of those more widely applicable (eg Newtonian and Einsteinian physics).

Yes, non Euclidean geometries are there and applicable in GR for example, so I was wrong here. On the other hand, space in largest scales appears to be flat (Euclidean) base on up to date observations and gravitational curvatures are just local abnormalities.

I have heared that last Fermat theorem has been recently prooven after all but base on maths not available to Fermat himself. Did anyone undermine this proff?

Minus 2 apples means give away 2 and you will have zero (of course impossibility but yet a foundation of entire credit system).

A lot of terms (like word "number" mentioned by you) are some sort of natural truths, reasonably understood without further debate. For example word "life". What it really is?

There are many interesting proves in maths. Someone (Euler?) have proven that sum of all natural numbers is equal -1/12. This prove is not even difficult to understand and many interesting results are produced if it is accepted as true.

What about "renormalization"? Legitimate? Not? Illegitimate but we cannot produce many useful theories without it?

Finally I still do have troubles with peoples unable to divide 40 by 4 in memory. There is an overwhelming evidence that wealth is usually transfered from societies where such peoples are in abundance to societies where they are more rare. We are going to learn this simple truth a hard way.

Re. woman having 2.3 children... lets assume that she is living averagely 80 years (960 months) and pregnancy is 9 months long we can find out that at any given time she is 2.15625% pregnant.

Martin

Edited By Martin Dowing on 29/10/2017 18:48:45

Edited By Martin Dowing on 29/10/2017 18:55:09

@SillyOldDuffer,

Experimental evidence is an acid test of any theory and in Nature it is considered conclusive. You would have to wait far longer than Universe already exists (as per our believes) and convert all atoms within it into experimenters busy with nothing else than repeating experiment before any other result than 2 cropped up (it would entail exceedingly rare QM events before it have happened). So proposed method is sufficiently sound and not a guess at all.

Maths also relies on unprovable truths (axioms) which are nevertheless accepted without further debate.

So for example go and prove that only 1 straight line can be drawn by 2 points within Euclidean geometry.

Unprovable? yes

True? yes.

This does not imply that entire Euclidean geometry is just a guess. Why? Because we have plenty of evidence that it is realised in Nature.

And in theory is that possible for *other* geometries to exist? yes. Would they have some different sets of unprovable truths? yes. Are they realised in Nature? No, with possibility that at an extremely large scales comparable with size of Universe and larger some non-Euclidean factors crop up.

Regarding arithmetic - if you are mathematician you must understand that arithmetics (and entire maths) cannot be *both* complete and consistent. This was conclusively proven by Kurt Goedel in mid 20 century.

So *there are* statements in arithmetic which are proven to be unprovable but nevertheless accepted as true. Call them undecidable, if you wish.

Martin

@SillyOldDuffer,

Proving that 1 + 1 = 2 is not that difficult at all.

Place 1 match in box #1 and place 1 match in box #2.

Now throw contents of both boxes on the table and count total.

You will (hopefully) find two matches.

For higher numbers you may run separate proving experiments or use concept of recurrence if you wish. Many thousands of years *before* Bertrand Russell was born peoples knew that 1+1=2.

Heck, even chimps, ravons and parrots can be trained in simple arithmetics. Parrots can handle numbers up to 20 if I remember well. They can also be trained not to add pears to apples. Lets hope that children leaving our schools will not lose this ability because they are (together with their teachers) on the best track to do so.

What Bertrand Russel did is that he expressed said proff in mathematically correct language, within the cannon. One way or the other it looks impressive.

Martin

Neil,

Both, estimated and accurate formulas are comparably complex if one has access to trig tables or adequate calculator and wish to work in radians.

Extreme cases are used for checking only. I got alarmed because one extreme case where d1=2l and d2=0 would give a result which can be expressed as l = a x pi + b x sqrt(c).

However it is obvious that l = pi x d = 2pi x l.

It is *impossible* to get an accurate pi x d from the sum of a x pi and b x sqrt(c) if b x sqrt(c) is *not* equal 0.

Hence it was immediately obvious for me that you have given an estimate where errors are produced by replacing lenghts of arcs with lenghts of chords or alternatively you have made a mistake. Because I have never done such calculation in the past and I am designing 2 step pulley system meant to work with *the same* belt, I was just wondering what sort of error might be there, just to make sure that fabricated parts (or one of them to be precise) would not go directly to scrap. Indeed, as you say, in normal situation the error is small enough to ignore. Just wanted to make sure.

For reference of this forum I will quote an accurate formula from discussed book:

l(belt) = pi/2 x (d1+d2) + *alpha* x (d1-d2) + 2 x l x cos*alpha*

where: sin*alpha* = (d1-d2)/2 x l and angles are expressed in radians, eg 360deg = 2 x pi.

*alpha* is an angle between "squared" situation, eg one where d1=d2 and "triangulized" one, where it is not the case and last point of contact of belt with pulley is shifted by an angle.

You do *not* need to know *alpha* a priori.

l(belt) means lenght of belt, d1 & d2 means diameters of pulleys and l is a distance between centers of rotation of pulleys.

Hope, I have written it clear.

Anyway, we have managed to convert something what looks trivial into quite lenghty discussion. It is interesting that an accurate formula is somehow well "hidden" on Internet.

Martin

Edit:

Hey, lets make it now more complicated, get rid of *alpha*, and put it into one final phrase:

It is known from secondary school that sin^2*alpha* + cos^2*alpha* = 1

so: cos*alpha* = sqrt{1 - [(d1-d2)/2 x l]^2}

so the final, one phrase equation devoid of *alpha* will read:

l(belt) = pi/2 x (d1+d2) + arccos*sqrt{1 - [(d1-d2)/2 x l]^2}* x (d1-d2) + 2 x l x sqrt{1 - [(d1-d2)/2 x l]^2}

where: *sqrt{1 - [(d1-d2)/2 x l]^2}* reads in radians.

Now I will go to do something useful

Martin

Edited By Martin Dowing on 29/10/2017 11:25:16

Peoples who need calculator to divide 40 by 4 cannot offend me, regardless what they do or say, and these are the peoples to whom such production is mainly addressed.

They are best left alone and need addressing only if *absolutely* necessary.

Regarding girlfriends - widely understood Western lot is of increasingly poor quality (don't last long and are expensive in maintanence) and very much like anything else they are going to be replaced by cheaper and better Asian imports. Older of you with useful Western wives are lucky. I have settled with Asian from Far East failing to find anything useful here despite of much efforts. Works for 25+ years, inexpensive to maintain, provides quality domestic services long time ago expected from Western wives as well, can think/read/walk 20 miles without fuss, very rarely watch TV and doesn't mingle with useless mob. Couldn't do without...

Regarding TV - within last 3 months I have watched it maybe 5 hours.

Martin

@Michael Gilligan

Many thanks, your formua seems exact. Had few goes at it and it invariably gives sensible results.

They are usually very similar to approximations discussed before but in weird cases approaching extremities there are significant discrepancies.

Martin

One source ( https://www.engineeringtoolbox.com/length-belt-fans-motors-d_872.html ) is giving following formua:

l(belt)=d1xPi/2 + d2xPi/2 + 2l + (d1-d2)^2/4l , the same what Brian have found elsewhere

Needless to say this formua is also an approximation. I wonder how the exact formua looks like? Cannot find it.

I wonder if Neils approximation or this one is better.

@Neil, spotted your ommission but still couldnt get correct result for extreme case regardless. Tried few combinations.

There must be an *exact* formua for this problem. These 3 parameters are determining exact lenght of belt.

Martin

Edited By Martin Dowing on 28/10/2017 22:55:57

Up to now no formua proposed by anyone here (including these proposed by myself above) doesn't work.

So how a correct one would look?

@Neil

When I substitute to your equation extreme case where l=1/2 x d1 and d2 = 0 I cannot get sensible resuls.

I am getting l(belt) = 1/2Pi x d1 + sqrt5 x d1

This cannot be true as obvious correct answer is Pi x d1. After some trials I can propose an alternative equation:

l(belt) = pi x d1 + pi x d2 + 2 x sqrt{l^2 - [(d1-d2)/2]^2]}

this works for both extreme cases, second is where d1=d2=0. Perhaps it will also work for all cases between too?

Am I correct, or some rots have been proposed?

@Brian Sweeting

Formua given in your reference would read as follows:

l(belt) = 2 x l + pi/2 x (d1+d2) + (d1-d2)^2/4l

This cannot be true for l=1/2d1 and d2=0 because it delivers value higher than pi x d1, which is correct answer.

Alternative equation l(belt) = 2 x l + pi/2 x (d1+d2) - (d1-d2)^2/4l would be correct in both extreme cases. I wonder, what about cases between?

@oldiron,

Must know algoritm to trust calculator.

@Muzzer,

Good practical considerations. Regarding mentioned or other similar software - do not have access to such a luxury.

@ Robin,

No access to CAD etc. I also tend not to believe online calculators until proven correct for variety of inputs.

@Those who are suggesting "measure broken belt" etc.

I am designing 2 steps pulley system which is intended to work with *the same* belt. Do not want to fabricate parts which are not mating correctly.

Anyway, it seems that question is still not resolved. Any other ideas?

Martin

Edited By Martin Dowing on 28/10/2017 20:35:45

Lets approach this subject from mathematical perspective and forget allowances for belt streatching etc.

So we have 2 pulleys of diameters d1 and d2. Pulleys are rotating on 2 separate shafts and centers of rotation are separated by distance l, eg distance between centers of shafts is l.

What is exact mathematical formua for lenght of transmission belt?

It must be somewhere between 2l (in hypothetical situation of d1=d2=0) and 2"pi"l for d1=l and d2=0 or the other way. What is general equation for all cases between these theoretical extremities?

Martin

Edited By Martin Dowing on 28/10/2017 12:14:03

Perhaps it is good idea to ask wheel distributors about possible troubles with cooling, to begin with.

Edited By Martin Dowing on 26/10/2017 11:18:51

Many thanks for your ideas and advice.

@jon - At least it is good to know that small throw is acceptable. In practice I have also noticed that dressed wheel cuts better and not much deleterious effects related to any remaining eccentricity are noticed.

Yes, it is dressing, not actual grinding, what produces most of dust.

@Peter Krogh - My grinding rest would obstruct area where hosepipe to hoover need to be fitted. On the other hand modification of wheel shield might allow for this idea to be tried - will have to have a look.

@David George - I am actually using something comparable but your approach seems more straightforward. Will try. Easy enough.

@Rik Shaw - I am not an owner of surface grinder or cylindrical grinder. Regarding cooling, I wonder if some sort of arrangement can be made for bottom of grinding wheel of my bench grinder to be immersed in bath with water. Is it in your opinion a legitimate idea or something daft?

Yes, I know, cooling *is* important. and now my machine (means ML 7 lathe which also serves as a makeshift miller with aid of vertical slide) is devoid of this luxury very much like offhand grinder. However mid next year I will get a proper miller (total mass of this machine is approx. 1 ton) and she will have cooling system installed.

@Hopper - That is very much what I did. My grinder is also at the garage door, about 15 feet from lathe. Still this dust is annoying. Taking it outside for dressing would be tedious. It is bolted, it would need bolting outside etc.

@John Reese - Didn't try this one. May try in the future. Sad truth is that Chinese stuff is competitive in price but also increasingly in quality. Sometime ago I have kissed goodbye to European carbide inserts. Chinese are coming at 10% of European price and recent batch ex Mitsubishi (still sent from China) is doing miracles at price of 1 USD each. European versions are simply a ripoff.

Martin.

Subject may well be boring but there are few issues related to that.

1. I have found procedure of trueing grinding wheel to be a messy one. To begin with, every aluminum oxide/silicon carbide grinding wheel, even a new one, needs trueing after installation and occassionally during use, when got dull or groved. Procedure, regardless how done, produces considerable quantities of fine dust which fly around shop and likes to settle on slides of other machines. These need covering to prevent later damage and floor of shop needs good hoovering later. Looks tedious and probably some dust will still find its way to machines and contribute to wear.

What remedies could be offered other than an obvious one to move all grinding equipment to another room?

2. How to proceed with "trueing" correctly? I have found that even new wheels are showing 1mm of "throw" and sometimes even worse than that. Despite all efforts I am finding it difficult to reduce said "throw" to less than 0.25mm or so, even with use of some simple guides etc. It seems that grinder vibrations and resonances with table are responsible.

I have tried both diamond and abrasive block meant for the business.

Is it accptable to settle with such small throw (0.25mm on 200mm wheel), or I should struggle to get better than that? How to improve situation?

Martin

Many thanks for feedback up to date. It seems that issue is an interesting one.

@Clive Foster, I would prefer tailstock location. Seems neater. Alteration at headstock could easily hamper smooth changing of changewheels for screwcutting. If done on tailstock, I would replace leadscrew handwheel with an appropriate toothed pulley or gear, coupled to motor by toothed belt or something alike. Would try to make it as compact as possible.

@ega, he says, he did it but no details are disclosed.

@Nick Hulme, Saving leadscrew this way will be offset by frequent need to replace handwheel pinion gears.

I would rather install telescopic springs as swarf guards on my leadscrew, if objection is to reduce wear. Nevertheless idea is interesting, it didn't come to my mind while analyzing problem.

@Hopper, Search results from your link do not deliver any output. Maybe I do not know yet how to use it correctly.

Planetary gearbox with normal motor seems to be a good way forward, but clutch is a necessity as such gearbox is not "reversible". During screwcutting it could be damaged.

@Martin Kyte, thanks for reference to mod, but my leadscrew is still 5/8 inch (machine is from Dec.1968), so the kit sold would not be suitable and it still would need to be altered to incorporate motor drive.

Interestingly I had ideas about incorporating thrust bearing on leadscrew of my ML 7, particularly because it will be replaced with new one which I am free to modify. Sometime ago I had a daft engineering idea with modifying screw press with thrust bearing. Press got damaged.

By profession I am chemist and I am not well versed in electronics beyond basic concepts, albeit I have designed and made simple few V @ 300A DC power supply based on 6 diode rectifier of 3 phase input. I went for 3 phase version to get rid of problems with 10F or so "smoothing" capacitor which would be needed otherwise, at 50Hz at least. This machine and dangerous buzzing sound it produces as well as diameters of wiring there is causing fear in my wife but it is useful also for other things. Nevertheless I would have considerable difficulty with programming controller of driver of stepping motor.

Anyway, don't you worry that stepper motor will jerk, possibly adding to chatter during turning? I understand that so called microstepping is only applicable to a very low power stepper motors.

@Douglas Johnston, Regarding automatic carriage stop, I am now testing very similar device, but this one trips relay in 3 phase power supply in my main motor. Inertia of 3 phase motor, pulleys and a chuck spoils a fun at open speeds, though my stop has buffering spring incorporated and system will work without causing damage to machine. For screwcutting to shoulder or screwcutting of blind holes on backgears it works well.

Btw, congratulatios. You have made device discussed here. Did you notice any problems related to jerking by stepper motor? How much power or torque your stepper motor gives?

Martin

From time to time I am doing various upgrades to my ML7.

Of course the best upgrade would be to buy Hardinge lathe but lets see what can be done on machine which I already have.

I found it very inconvenient to meddle with changewheels while going from turning to screwcutting and vice versa. On the other hand I do not mind at all to rearrange gears for different screwcutting operations, as long as fine feeds are always available.

S/C gearbox is usual solution for this type of issues, but it is also carrying its own troubles (limited number of pitches, troubles while going from imperial to metric and vice versa etc). This gearbox also cost about thousand pounds on ebay and there are better ways how to spend these money.

My idea is to fit some sort of drive on tailstock end of machine.

Very slow motion motors with planetary gearbox (which allows gearing ratio in range of 200:1 or so are sold as nice compact units. Such motors coupled with frequency modulators could provide very convenient means of such arrangement, eg providing fine feeds. Unit could be integrated with modified bracket for tailstock bearing of a leadscrew (holes for mounting usual bracket would be used to house discussed assembly and there is a chance that they would be sufficient for the task).

Did anyone attempted with success something like this?

What power motor should have to provide adequate torque, assuming 200:1 gearing ratio via planetary gearbox. Lets assume that my ML7 is expected to make up to 1/4 inch @ 4thou/rev cut in MS. How much power such geared motor would need? 50W enough? It is important to get this power right - will provide for idiotproving as well, in case of crash assembly will just stop without causing unforeseen destruction here or there. A clutch would also be needed to disengage this drive at any moment during normal turning and also during screwcutting.

Did anyone think about such solutions?

Any othe Idea, how to resolve this fine feed problem?

Martin

At the same time clean, replace or make out of felt (if absent) oil filters. Bearing will be grateful for that.

Also dont break these oilers. If you do, you will face a lot of troubles. These ex Adams are expensive but good and cheap imports sold by RDG do not work. You will end up making new or at least making some parts new, unless you get them from Adams.

Matrin

@ Martin Kyte,

In chemical company where i was working there were 2 opinions.

1. Don't you ever put any cap on it - may go bang if iced around.

2. Put the cap on it very lightly, in loose way. This reduces air access to liquid nitrogen.

This air access may be dangerous for entirely different reasons - oxygen from air will condense in liquid nitrogen and upon evaporation of nitrogen can concentrate itself to 80% or so. If there are there some organic impurities, what is often the case, it may then go bang for entirely different reasons.

I was puting this top very lightly, some others did and some others didn't. There was about 15 workers. Nothing have happened to anyone during 20 years. Nitrogen was handled nearly every day.

So from my perspective it seems that risks are largerly theoretical albeit from time to time accidents (like everywhere) *are* reported.

Martin

Highly polished shafts and holes might not be good candidates for adhesive joint.

Recently I have tried something like that:

Tolearances for interrupted fit were machined. Part with a hole was warmed to modest 100*C. Shaft was immersed in liquid nitrogen for 10 minutes (hospitals and higher end pubs have it, pubs are using it for making icecream - just smile to manager and come with suitable 2- 4 pint household Thermos flask - do not tighten it too much - there must be a way to escape for boiled off gas). You can store it for few days before is gone. Liquid nitrogen is cold (-196*C) - take care. Spilling it over hand usually does next to nothing as it boils off before contact with skin but touching metal cooled to -196*C guarantees nasty frostbite in no time at all. Now , with aid of thermally insulating gloves, insert/press shaft into hole and let it expand upon warming. Do your job reasonably fast, before shaft warms itself. You may pour liquid nitrogen to wide mouth thermos or thermally insulated thin walled pot for the job.

You won't disassemle it easily...

Martin

As an long term owner of ML 7 I may advise following:

#1 Lock backgear, insert key into socket and tap the key using reasonable strenght, but with *bare hand*, not a mallet or hammer. This works in 90+% of cases and would not strip teeth of your gears because your hand is going to hurt badly well before you get there, unless you are training of karate or something similar - then be reasonable. If doesnt work, proceed to #2.

#2. There is an accessory for ML7, very useful for example for tapping, which is a handle which can be installed on journal from the back. It works by means of split pipe and a cone which expands pipe upon tightening screw. So install it on your lathe, disengage belts, etc. Mandrell must run freely. Now open jaws of youch chuck and on motor side stuff under one of these a wooden block, in such a way that jaw would hit this block and stop when mandrel is turned. Now, with an aid of your handle turn journal rapidly, so the jaw will hit wooden block. Try to gain some momentum. This nearly always helps, if not proceed to #3

#3 Leave wooden block like in #2 but drive jaw of chuck on it *under power, on slowest speed and on backgear (this speed is 35rpm). You must reverse direction of motor rotation. I have 3-phase motor, so it is easy, using 3 position switch, if you have 1 phase motor, which turns only one way, you may try to cross v-belt, one which drive countershaft (longer one would be needed around for this occassion). Didn't try trick with v-belt, it is just idea.

#3 never, ever failed.

Martin

Others have summarized it already very well.

Check battery contacts as that is about the only bit which you can repair, if electronics/electrics have failed.

By myself, I am positively avoiding electronic micrometers, calipers etc.

Verniers last for life and grandkids life, if not abused badly, Electronics are IMHO "use few years and throw away items" and sometimes phrase "few years" will read "few months".

@Mike Poole,

Recently I got scientific calculator with trig functions working good enough. My older version at one occassion have driven me banana, while finding a sine or a tangent of very small angle. Problem was like this: If you mill 5 or 10 thou of side of 2 inch bar, how wide flat area would be?

Reading from calculator were taken as a gospel and then delivered results were complete nonsense. I got scared, that my brain have stopped working correctly and I forgotten rather basic trig. calculations, but at the end I have realized that it is calculator what plays jokes on me.

Martin