Member postings for SillyOldDuffer

Yup, some people will do anything for a cheap thrill!

Cheers,

Dave

PS +1 for the serious part of your post.

Edited By SillyOldDuffer on 05/07/2016 14:00:18

Is that meant to be a serious suggestion? Creosote and old Engine Oil are both carcinogens. Of the scrotum.

Hi Ian,

Sorry about the delay replying, I missed your post.

Well it's hard to tell who's got the finest paper when our sheets are a world apart!

I think I've got the real McCoy though, what I've bought turned out to be ultra-fine grades. Here's a link to the Starke Brochure, unfortunately it's in German, but it includes this graphic:

True these are ISO sizes and your system might well be different. Our P1200 has 15 micrometre grains. Do you know what your 1200 grain size is?

The US has a different system and you might well have that. CAMI 1000 is the same as ISO P2000: they both have a 10.3 micrometre grit, which makes a very fine paper.

Part of the fun of model engineering is deciphering the various metric, imperial, gauge and other systems!

Cheers,

Dave

Edited By SillyOldDuffer on 04/07/2016 21:42:09

Having thought about it over a glass of wine, it's clear that a good model engineer will need to commit all seven deadly sins:

• looking for easier ways to do things (sloth),
• getting cross with mistakes (anger),
• showing off the model (pride),
• wanting tools you don't need (lust),
• wanting that other blokes workshop (envy),
• generally wanting more and more stuff to play with (greed),
• ignoring the budget when buying tools at shows or on the web (gluttony).

Cheers,

Dave

Hi Martin,

Good timing - you got rid of the smileys whilst I was away logging in.

Re: 'On a question with your sized pulleys Dave would the bigger pulleys give better torque than the 2" to 1"

Well, in theory no. The torque conversion simply follows the same ratio as the speed conversion, only the other way round. (So a 2:1 ratio would halve the speed and double the torque whereas a 1:2 ratio would double the speed and halve the torque.)

It's not that easy though. Theory is fine and dandy but in the real world belts slip. And they are much more likely to slip on a small pulley than a big one. Slip costs both torque and speed, wears the belt and might overheat. Therefore for a given load and speed it's unwise to go below a certain minimum pulley size, which is why some of the other posts questioned your 1" pulley.

I'd give it a try and see what happens. If you get slip that you can't control with a jockey wheel or other way of adjusting belt tension, try bigger pulleys.

Trouble is, if you double the size of the driver, you have to double the size of the next one too.

It's a bit of a balancing act.

Cheers,

Dave

Too late, I've got my slide rule out!

Judging by this afternoon's iffy efforts I'm a confirmed recidivist. Today I starting by failing to read the instructions and finished by losing a part. At one point I drilled a hole in the wrong place after failing to divide 38 by 2 with a pocket calculator.

A sense of humour has got to be one of the essentials.

Dave

Looking back I think you had it right early on in the thread Martin.

1 on the motor and 5 on the counter-shaft would reduce 3000 to 600 rpm. Then to get from the counter-shaft to the 4 on the lathe, you need a 1:1 ratio, which would be provided by another 4.

So 3000 x 1/5 = 600

and

600 x 4/4 = 600

I think anything between 350 and 650 rpm would do for most general purpose work. Ideally you would have three of four speeds available between 100 and 1000 rpm. The extra speeds make it easier to do a wider range of jobs.

Cheers,

Dave

Now I'm confused! I thought we were all joking...

Cheers,

Dave

Hi Martin,

Second attempt to get the diagram right!

Cheers,

Dave

Hi Martin,

Yes if you mean this way

Edit

Whoops I got the diagram wrong.  Will try again in a minute!

Dave

Edited By SillyOldDuffer on 02/07/2016 20:46:17

Hmmm, tricky one. Might be an earth leak...

I'd come at this problem from another direction, that is how to get useful speeds from the ratios provided by a standard step pulley set. The advantage of using a step pulley pair is that only one belt is needed to change speed, with the drive-shafts arranged so that the belt is also a standard size.

For example a pair of these with 2", 3" , 4" and 5" diameters would give you:

3000 rpm x 2" / 5" = 1200 rpm

3000 x 3" / 4" = 2250

3000 x 4" / 3" = 4000

3000 x 5" / 2" = 7500

As these ratios driven direct from a 3000 rpm motor are far too fast, the motor should be geared down first with a fixed ratio pulley or gear pair. Of these:

2:1 in front of the step pulleys would give you 600, 1125, 2000 and 3750 rpm

3:1 would give you 400, 750, 1333 and 2500

4:1 would give you 300, 562, 1000 and 1875 rpm - this starts to feel reasonable for your Drummond

5:1 might be better with: 240, 450, 800 and 1500 rpm.

6:1 gives 200, 375, 666 and 1250

Hope I got the maths right and that this makes sense!

Cheers,

Dave

Good question. I dunno, and this won't help much either!

Not so unfortunately - they are too predictable. Whilst it's true that the bad guys won't know the names and ages of your particular friends, they do know that's a very popular way of making a memorable password. Therefore they have lists like this one and a computer program to methodically scan possibilities.

Attacks based on typical passwords are easily confounded by long random passwords (8 or 9 characters) but these are difficult to remember.

One way of generating memorably "random" passwords is to use a phrase or book title to create a character stream, and then perhaps add a few numbers to make it at least 8 characters long.

For example, using the first letter of each word in the title of the book "Down and Out in Paris and London" would give you the stream "DaOiPaL" . As I'm 21 years old (ahem), I would use that to create the password "DaOiPal21", which is extremely hard to guess.

Another example: "My first lathe was a Dean, Grace & Smith", would give you the password "MflwaD,G&S"

Note that passwords made this way can contain mixed case, punctuation and numbers. This massively increases the number of permutations that have to be searched.

Let's be careful out there...

Dave

Edited By SillyOldDuffer on 02/07/2016 13:29:27

Gorgeous!

Hi Duncan,

Your modification pretty much eliminates the mains risk inherent in the lamp as bought and I'd be happy to use it as is. So we're only worrying about the possibility of a low voltage short in the goose-neck if your lamp happens to have the same fault as suspected in MikeP's unit.

Where the fuse or fuses go depends on how your 40V stepper supply is configured. If you have a voltmeter, all you need to do to find out is to check if there are any volts between the machine ground and the plus and minus 40V stepper power wires.

If the 40V+ wire shows volts relative to machine ground, you need a fuse in the positive wire.

If the 40V- wire shows volts relative to machine ground you need a fuse in the negative wire.

If both + and - shows volts relative to machine ground, you need a fuse in both wires.

If neither shows volts relative to machine ground, the one fuse should be fine.

Does the Duffer know what he's talking about? My understanding comes from a lifetime interest in Amateur Radio where there are different earth requirements for Radio Frequencies, Mains Safety, lightning protection and signal isolation. Professionally I know a bit about electrical practice in computer rooms and data centres but note all that's theoretical and not particularly deep. Therefore I'm quite happy to be corrected about the advice I offer - several people on the forum are better qualified than me.

Cheers,

Dave

Hi Duncan,

Your pictures are causing another mystery. I can't see them in your original post but as you see they appear when I quote it!

Anyway, looking at Bandersnatch's post and Mike P account of his blue flash moment, Sherlock Duffer concludes that MikeP's lamp must have had a bare wire inside the metal goose-neck. As the lamp circuit floats, it could have been either the plus or minus wire that shorted.

I wonder if you might need in-line fuses on both plus and minus? Depends on your stepper motor supply, which could be floating, or negative ground, or positive ground.

The extra fuse isn't a safety feature - it further guards against the possibility of a short damaging your stepper motor supply. (Perhaps!)

Dave

I wonder if the "ball bearing" was actually the bullet-shaped trigger cam wotsit. In my version of the punch, it's the silver cylinder with one end rounded and a hole drilled in the other. (Component is top left in both pics.)

When I took the punch apart yesterday bits flew about. Today it's completely tame. Very strange.

Dave

Just to tidy up the discussion about the power output of humans, this is what Wikepedia says as part of their horsepower entry:

"In 1993, R. D. Stevenson and R. J. Wassersug published an article calculating the upper limit to an animal's power output.^[15] The peak power over a few seconds has been measured to be as high as 14.9 hp.^[15] However, Stevenson and Wassersug observe that for sustained activity, a work rate of about 1 hp per horse is consistent with agricultural advice from both 19th and 20th century sources.^[15]

When considering human-powered equipment, a healthy human can produce about 1.2 hp briefly (see orders of magnitude) and sustain about 0.1 hp indefinitely; trained athletes can manage up to about 2.5 hp briefly^[16] and 0.3 hp for a period of several hours. The Jamaican sprinter Usain Bolt produced a maximum of 3.5 hp 0.89 seconds into his 9.58 second 100m dash world record in 2009.^[17]"

So my school-day experiment that showed 14 youths to be roughly equivalent to a horse wasn't too far out. 1hp/14 is 0.07, which is within spitting distance of the official 0.1 I'm not sure I could have kept going indefinitely at that rate though - I was a 7-stone weakling who often had sand kicked in his face.

To the workshop - I need to find a spring.

Cheers,
Dave