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Member postings for Simon Williams 3

Here is a list of all the postings Simon Williams 3 has made in our forums. Click on a thread name to jump to the thread.

Thread: Interesting??
19/05/2019 12:34:53

"Earth Engine operates on the same principle as the ‘Slingshot Effect’ space travel phenomenon," (Quote taken from their web site, link above).

Which would be fine, except the sling shot effect to which they refer does NOT violate the Law of Conservation of Momentum, nor Energy. So much for that explanation!

And the fact that this has absolutely zilch to do with the hypothetical existence of a magnetic monopole simply compounds the felony.

At least snake oil might have had a placebo effect.

Rgds Simon

Thread: Drilling cast iron - where did I go wrong?
16/05/2019 09:00:19

Pilot hole is always a good idea, needs to be 1/3 to 1/2 of next drill size, not more. Give the next drill something to do or it will grab.

Drilling down a pilot hole in cast iron always needs the drill rake modified to be nearly neutral, a standard drill grind will always grab and chatter or rip the corners off the drill. Same goes for green brass. Standard 118 deg point jobber drill perfectly OK for CI if the rake is backed off. Negative rake not necessary, neutral or about +5 deg is OK.

Speed - 1000 revs is too fast as others have said. Drilling cast iron keep the speed low and the drill cutting. Chips should come out as discrete pieces - say half the size of a match head - not dust. Slowness not critical; to success (that's in the grind of the drill) but suggest anywhere below 500 rpm for 10 mm hole is right ball park. Slower the better, keep the feed going.

If drill wanders and chatters on entering the pilot hole (leaving a nasty serrated edge as it throws the work piece around) fold up a small scrap of rag (old jeans ideal) and wedge it in the pilot so the advancing drill touches it first. This is sacrificial, but will stop the chatter and grab as the next stage drill edge meets the face of the work.

HTH Simon

Thread: Bore micrometer
10/05/2019 15:55:24

This seems to substantiate the Law of Ladies Underwear.

"The less you want the more it costs"

Simon

10/05/2019 12:11:48

I've done some experimenting with telescopic gauges to see how accurate I am with them, and although it's not terribly scientific (I'm not working in a metrology lab with the resources to arbitrate on measurements to tenths of a thou) I would offer the following.

Firstly I measured a bore of about three inches with an internal micrometer. I could do this to a repeatability of about +/- 2 - 3 thou, as my ability to apply the same force to the micrometer barrel consistently was the limiting factor, though getting the micrometer straight across a diameter of the bore was also fiddly and variable. Taking successive measurements just taught me that I was a hopeless case and wasn't getting better.

I then tried telescopic gauges, in my case the Moore and Wright ones, though I do have some Starrett ones.

I found my measurement was immediately at least as repeatable, and with practice I got better in that the measurement I made with an external micrometer was also about +/- 2 thou repeatability initially, but I got better with practice which I didn't with the internal micrometer.. As the process of making a measurement with a telescopic gauge means making two measurements - one to set the gauge to the bore and another to measure the distance across that gauge - there is scope for more variation than a direct measurement. But using the telescopic gauge was more repeatable than the internal micrometer - at least in my hands. After some practice (I was boring a hole for a bearing) I was fairly confident my bore measurement was repeatable to about +/- 0.5 thou. Some of my gauges are in better nick than others, and it also depends to some extent on being well within the working range of the gauge, but that just taught me to be careful that my telescopic gauge was working properly.

Measuring the same bore with a digital caliper is revealing - the caliper may have a resolution of 1 thou but it sure ain't that repeatable.

I also have tried the same experiment with smaller holes within the range of a Starrett internal micrometer of the caliper kind (model 700) and find this is more repeatable, typically +/0.5 thou or may be a bit better, but of course this only measures the mouth of the hole and says nothing about the bore.

I've been careful to talk about repeatability, as I don't have anything I could actually say was calibrated to give an absolute accuracy.

HTH Simon

Thread: Larger VFD/Motors
08/05/2019 20:06:35

About this root 3 business, it depends on whether the line voltage (230V) is a line to line or a line to neutral figure.

To calculate the power drawn by a three phase motor load supplied with three phase 400 volts (line to line inferred) you need the root three factor. If the 230 volts figure is the same - line to line - then it follows that the root three factor is still needed.

If the supply is specified as 230 volts line to neutral then the root three factor has already been applied by dint of getting from 400 volts to 230 volts.

In each case the convention is that the line current in one phase is specified, and the other two phases carry nominally equal currents.

The confusion arises because while it is obvious that a single phase input/three phase output VSD is supplied with 230 volts line to neutral, to develop full power at the motor it generates three phase 230 volts line to line, not line to neutral. The motor rating plate assumes that the delta connected motor will be supplied with three phase 230 volts, just as the star connected motor requires 400 volts line to line to develop full power.

Of course the arithmetic changes with phase coverters that can generate 400 volts line to line three phase from 230 volts line to neutral single phase input.

HTH Simon

Thread: Removing Flux
02/05/2019 12:14:58

Hi Paul, this comes up every so often, and the perceived wisdom seems to be brick cleaner from your local builders merchant. I've tried it and it works a treat. Buy the one that actually says it contains citric acid, other formulations exist.

Good luck Simon

Thread: Bandsaw speed
01/05/2019 19:39:14

Let's do a bit of arithmetic.

I've got a bandsaw I bought second hand recently, I've been musing on the same question. For my bandsaw a motor of approximately the same speed and power also drives the blade directly. For the sake of a worked example I'll use the dimensions I took from my saw.

Drive wheel is 1 foot in diameter, and runs at 985 RPM. So linear speed of blade is 1 x 3.14 x 985 ft/min = 3000 ft/min in round numbers.

Recommended speed to cut mild steel with high speed steel blade is approx. 100 ft/min. That's a speed turn down well beyond the range of any variable frequency drive three phase or otherwise. Not to mention the problems of keeping the motor cool.

I pretty sure (though I don't know how to quantify it) that the torque requirement to cut steel will go up from that needed to cut wood. So we're into some pretty significant gearing here. I've been musing on whether to make a planetary gear reduction along the lines of the Dore Westbury mill, but it's a lot of work and it's never going to happen.

Having said that, Stefan Gotteswinter says he cuts steel on an ordinary (vertical) bandsaw, but it's not clear what speed the blade is running at. Have a look at the YouTube video of his basement workshop walk-around.

An HSS blade is going to cost £20 or thereabouts a kick, my feeling is that the teeth will come straight off it as soon as you show it a piece of steel. Cutting ally or possibly brass will probably be OK, though the cutting speed is still far too high.

So I decided that a bandsaw designed for cutting wood wasn't a good place to start.

HTH Simon

 

edit - Jason (as ever) beat me too it.

Edited By Simon Williams 3 on 01/05/2019 19:40:51

Thread: Hydraulic press or fly press
29/04/2019 09:42:21

Fly press is good at a high force over a short stroke, which is what it is designed for when used for punching or folding. The actual thread converting the handle motion into downwards force is pretty coarse, so it's not the best for use as a pusher in of bearings or a broaching press. You find your self pushing in successive "bumps" so it can be done but it's not ideal. It's big advantage is that the bolster (coming down on the tool) is located well by a dovetail so alignment and pushing square come easily and are built in. But its a big heavy thing that you can hardly put away after each use, so your space constraints may dictate that it's impractical anyway.

A hydraulic press will give you better control over a long stroke, but is much slower to operate. You could motorise it, but I'm assuming this isn't for repetitive use. Various sources of the components exist, the body press kit made by Clarke isn't expensive and gets you started. Enerpac is another option but tends to be pricey. Here's one I made earlier:

dsc_1627-1.jpg

This is a very controllable and versatile tool, I use it for pressing bearings, universal joint replacements, also folding sheet metal as you can see. Love it to bits but it's quite difficult making sure you are pushing square. The last broaching job I did with it went through crooked. It's relatively portable so it lives under the bench and comes out when needed.

HTH Simon

Thread: What Did You Do Today 2019
28/04/2019 12:03:27

It wasn't today, it was yesterday, but this is an object lesson in leaving well alone.

I bought a bandsaw from my local secondhand shop, did the insulation test and earth continuity, plugged it in, happy days.

The main lead had pulled through its cable gland into the motor terminal box, so yesterday I thought I'd while away 15 minutes putting that right. Simple enough.

Until I took the cover off the terminal box, and realised that the black bits in the bottom were broken insulation off the motor leads. Oh dear.

Can't leave that alone, so here's what I found when I took the end cover off the motor:

dsc_2028-1.jpg

Not the best photo ever, sorry about that. The green lead RHS of picture is one of the main winding leads, the two once-upon-a-time white ones are the starter winding on a 6 pole single phase capacitor run motor of about 3/4 HP. These wires are the original tails connected to the motor windings, and look as though they have been overheated though I can't explain why there is no evidence of damage to the windings themselves, and no "burnt" smell. The insulation is brittle and cooked, and the wire itself is tarnished and oxidised.

I cut the damage out, grafted some PTFE insulated wire in with heat shrink sleeving and threw it all back together. Not the best job ever, but better than it was.

I could have made a better job if I knew how to withdraw the stator lamination stack from the motor outer housing. Any clues anyone? The only thing I can find on the internet assumes the windings are already toast, and you can pull the whole thing to pieces by brutality. In my case there seemed to be nothing wrong with the windings and I'm reluctant to get it rewound when it still works.

So it runs, takes a sensible looking load current, insulation at 500V is 85 megohms. I've put it back together and it'll do.

Rgds to all

Simon

Thread: Dol starter or just a plug is it really worth it?
26/04/2019 14:48:31
Posted by Grant Allen 1 on 26/04/2019 14:32:07:

So, do I get a nvr switch or a single phase 240v dol starter with overload 2.3- 4 amps both are the same price both will have a 5amp plug on. So running a .37kw motor maybe wishing to add to an e stop and motor reverse switch would determine which one

Kedu nvr switch

Or

240v dol starter overload 2.3-4amps

For the same price go with the extra protection and adaptability of the single phase push button starter with an overload device and the option of a remote E Stop. I take the point from an earlier contributor that it's a bit anachronistic, but not as much so as the yellow pushbutton thing. Either way, that's the price you pay for bringing modern day safety technology into a 60 year old environment.

Besides, if as you say the Kedu type switch would have a cable to a 5A plug, (which won't be locally fused?) where is your overcurrent protective device and what rating would it be? And what else would it have on the same circuit?

Rgds Simon

26/04/2019 14:14:08

Er...

One of those yellow pushbutton kedu type switches is by definition a direct on line (DOL) connector (switch) though the convention is that the word "starter" indicates that an appropriately sized overload device is included. As several have said, yer gets yer no volt release (NVR) function either way.

The IET wiring regs (BS7671) determine that a overload protection device must be fitted to automatically disconnect the supply to a motor in the event of overload (usually overcurrent) if the motor is over a certain size. From memory that size is 0.375 Kw (1/2 HP). A motor thermal overload relay is a far more sensitive device than any of the usual types of MCB in that it is designed to imitate the thermal characteristic of a motor and monitor its recent service history as well as the presence of an instantaneous fault. An MCB - even of the various different types (A, B, C or D) - is a different beast entirely..

Small overloads do exist, but below 0.375 Kw it's a bit of a lottery, as the current/load characteristic of small induction motors is a black art, and needs to take into account the phase angle of the load current. So protecting a small (sub 1/2 HP) motor with a plug top fuse isn't ideal, but is probably as good as it gets without major complication.

Using DOL starters on single phase is easy enough, provided the coil voltage for the maintain/NVR function is 230 volts not 400 as it might well be on a starter designed for three phase use. Remember to double back the load current through the spare poles of the overload on a three phase starter used on single phase so all three poles of the overload see the same current, as most are sensitive to current imbalance and will trip if one pole is left unused.

HTH Simon

 

 

Edited By Simon Williams 3 on 26/04/2019 14:15:37

Thread: DIY Bed Gap
24/04/2019 13:35:07

Hello Terry, good afternoon.

It's your lathe --- but.....

I'm in the no don't do it camp, though not because I wouldn't buy a lathe which had been modified so drastically. I might look at it and marvel at the bravery, but I suspect the resale value of said machine has just plummeted. I'm also not too bothered by the argument that you will have affected (detrimentally, but how much I know not) the stiffness of the machine.

I'm anti because I don't think you're going to be able to resurface a disc even after chopping a bit out of the lathe bed. Firstly I don't rate your chances of mounting the disc in a three jaw chuck (run out and grippability) but I don't think you'll get a surface finish worthy of the name. It's a big flat disc and the tool surface speed at the outer periphery is going to be off the scale and chattering (screaming) like fun. As I understand it a 290 is inverter drive, you need low speed torque for this job, not speed.

The finish on the disc would be much better ground, and frankly I think you'll get better results with a linishing disc on a hand held angle grinder!

And how certain are we that there is enough meat on a modern brake disc to allow for a re-surface anyway? What's the thickness lower limit?

There, that's put the kibosh on it! Sorry!

Best rgds Simon

Thread: Z Axis-Support
22/04/2019 20:29:33

SOD - Dave - thanks for the explanation, but it still doesn't wash. There is no torque applied to the strut, only a force acting to compress it. The strut of course provides a force reaction to this compression; the magnitude of this force can be measured in Newtons, lbf, Kg (wrongly, but at least it's understood), poundals (if we must) etc. etc. All are dimensions of force, not torque.

Maybe it's just a typo. (Occam's razor!)

Thanks as always

Simon

22/04/2019 17:05:10

I don't understand the force indicated on what I take to be the plastic wrapping for the strut in Nm? Am I missing something?

Rgds Simon

Thread: Thread confusion
21/04/2019 16:23:05
Posted by Roderick Jenkins on 21/04/2019 10:52:34:

I have no problem fitting the 34t gear on the unmodified banjo on my 70s S7B.

And, credit where credit's due, this is really the Reverend David Hoskins' method back in ME 3955.

cheers,

Rod

To my shame I'd couldn't remember the gent's name, let alone conjure up the correct reference. So thank you Roderick for giving credit where it is properly due.

Rgds Simon

21/04/2019 09:47:56

Hi David, good morning. Sent you a PM just.

Brian correct me if I'm wrong but I believe on a Mk2 S7, and with 33 or 34 Teeth your new drop arm isn't needed? If you want to go bigger you need it, my recollection is that a 34T mandrel gear just fits in place and the slot in the standard banjo is just long enough to drop the banjo and line up the transfer gears with a smidgeon of clearance.

I seem to remember you might need to tickle the slot in the standard banjo with a round file, but it should fit together. I've not tried this experiment - mine's the earlier MK1 S7 where it doesn't fit at all and anyway it's irrelevant.

Best rgds Simon

20/04/2019 22:52:07
Posted by David Canham on 20/04/2019 22:19:08:

I then had a proper look at the gearing set up behind the leadscrew drive gear guard and noticed the metric pitch chart pinned to the inside of the guard as the photo. So one question that comes to mind, the gears on the diagram - 60T and 63T plus the 50T and the 45T, are they both one piece items and do they mesh together across via the 63 and 50T.

No doubt Brian will be along shortly, but here is my three penn'orth for the time being:

To deal with the questions you ask one by one:

Firstly you can set up the change wheels any way you like so long as the maths works out and the bits go together, so the set up as per the label you have included is perfectly valid, but does require (obviously) that you not only have those gears identified but also the banjo onto which they are mounted. This is NOT the same banjo as the standard one with fixed centre spacings which is included with the standard quick change gearbox. So your expense factor is obvious.

The gear pairs are splined together by the centre sleeve, which has a key way machined into it. So the 50 and the 45 tooth gears are fixed together and rotate as one assembly, hence giving the ratio change you need. The same is true of the 60 and 63 t gears, they are two separate gears fastened together and rotating as one complete assembly.

What we will call "Brian's" method, as described in detail in his book, has a simpler solution and works just as well as the approximation represented in the gear set Myford drew out in the label you have noticed. However it has several advantages over the "standard" metric kit as you only need a couple of extra gears to do most of the commonly used metric pitches, you don't need a new banjo nor do you need the centre keyway boss. Whole lot of financial happiness there, however the biggest advantage isn't about cost at all, it's that you don't forfeit the fine feed system of the reversible 19/57 gears cluster because you use it as part of the gear assembly. Brian's book has the details.

However you do need a 33 and/or a 34 tooth gear to fit on the first mandrel spindle (below the tumbler gears). Again, Brian;s book describes the details. Now the snag of this is that these two gears are not the easiest of things to find, indeed the 34 tooth one seems to be in national shortage mode at present. But then neither is the metric set, and the special banjo is shades of unicorn poo...

With due deference to the proprieties of advertising on the forum (which is out of order, and I'm not going to do it) I have been making a batch of 34t gears (proceeds to charity) in response to similar questions elsewhere, so if you want one send me a PM and I'll explain further.

And no, I'm not making a profit - I'm not even covering my expenses making them the old fashioned way but if it helps someone try out "Brian's" elegant and simple adaptation, and makes a contribution to charity no-one's the worse for it, so I hope that's Ok with the moderators.

Hope this helps

Simon

Thread: Does anyone know where I can source a Myford 34t change gear?
18/04/2019 22:23:48

Karl (OP), Nigel(mgnbuk)

Gents I have sent you a PM.

HTH Simon

Thread: Myford Super 7 screw cutting gears (metric)
18/04/2019 22:12:54

Bob (9fingers) - I have sent you a PM.

Rgds Simon

Thread: Help to identify a tool that came with a Centec 2A
11/04/2019 09:00:25

Ah Hah!

At last someone's invented a gismo for correcting the effect of chopping a bit off the end of the rule in the guillotine.

Rgds to all

Simon

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