By continuing to use this site, you agree to our use of cookies. Find out more

Member postings for Swarf, Mostly!

Here is a list of all the postings Swarf, Mostly! has made in our forums. Click on a thread name to jump to the thread.

Thread: ML7 questions
12/12/2018 20:42:42
Posted by ega on 12/12/2018 17:28:09:

This extract from an old Bedford catalogue may be helpful:

SNIP

Sorry about the bleed-through from the reverse!

A trick that usually works to stop bleed-through is to put the target document on the platen of the scanner or photocopier and then lay a sheet of black paper on top of it, then close the lid.

Best regards,

Swarf, Mostly!

10/12/2018 13:52:01

Hi there, Clive,

As nobody else seems to have commented on spanners (aka 'wrenches' ), here's my two penneth:

The rule of thumb on most ML7 machines is that all threads below ¼" are B.A. and all threads of ¼" or bigger are B.S.F.

Best regards,

Swarf, Mostly!

Thread: Horn Antenna for Radio Astronomy
04/12/2018 15:03:54
SNIP

Score so far - Swarf Mostly: 1 Duffer: Nil.

Dave

This type of antenna ... consists of a flaring metal horn with a curved reflecting surface mounted in its mouth, at a 45° angle to the long axis of the horn. The reflector is a segment of a parabolic reflector, so the antenna is really a parabolic antenna which is fed off-axis. ... It is extremely broad-band, has calculable aperture efficiency, and the walls of the horn shield it from radiation coming from angles outside the main beam axis. The back and side lobes are therefore so minimal that scarcely any thermal energy is received from the ground. The antenna has a gain of about 43.3 dBi and a beamwidth of about 1.5° at 2.39 GHz and an aperture efficiency of 76%.

Reference https://www.physicsforums.com/threads/qs-re-aspects-of-the-holmdel-horn-antenna-used-to-find-the-cmb.941032/
This type of antenna ... consists of a flaring metal horn with a curved reflecting surface mounted in its mouth, at a 45° angle to the long axis of the horn. The reflector is a segment of a parabolic reflector, so the antenna is really a parabolic antenna which is fed off-axis. ... It is extremely broad-band, has calculable aperture efficiency, and the walls of the horn shield it from radiation coming from angles outside the main beam axis. The back and side lobes are therefore so minimal that scarcely any thermal energy is received from the ground. The antenna has a gain of about 43.3 dBi and a beamwidth of about 1.5° at 2.39 GHz and an aperture efficiency of 76%.

Reference https://www.physicsforums.com/threads/qs-re-aspects-of-the-holmdel-horn-antenna-used-to-find-the-cmb.941032/

 

Dave,

Please accept that my post was not intended to be adversarial! You drew our attention to an interesting bit of hardware for which I thank you. My post was offered to broaden the discussion, nothing more.

If I remember correctly, the USA end of the Telstar trans-atlantic link used the same type of antenna as the Holmdel one, if not that actual one. (Perhaps it is time I took a Gribbin refresher! ) I believe that the UK end, at Goonhilly Down, used an alt/az mounted complete paraboloid, in a dome. It was an 'if at first you don't succeed' situation - the two teams had different conventions for the direction of polarisation. But it was 'alright on the [second] night' !!!

Best regards,

Swarf, Mostly!

P.S.: I apologise to the original poster for causing topic-creep!!  I think that horn is a splendid job.  How on earth did you hold the first two pieces in position while you fitted the fasteners?

S,M!

Edited By Swarf, Mostly! on 04/12/2018 15:08:14

04/12/2018 12:52:23
Posted by SillyOldDuffer on 02/12/2018 12:12:15:

Very smart!

This is the famous Holmden Horn in New Jersey that promoted the Big Bang to Theory status:

Story is the two guys experimenting with it were baffled by the unexplained noise it picked up and were slow to admit it really was cosmic evidence. Their efforts to eliminate the noise included climbing inside to clean out a gigantic quantity of pigeon poo. It seems Horn Antennas are the avian equivalent of a public toilet...

This is the fate of all engineering.

smiley

Dave

Edited By SillyOldDuffer on 02/12/2018 12:12:33

This episode is described in one of John Gribbin's excellent books - I recommend them.

I believe that the functional heart of the so-called ' Holmden Horn' is actually a segment of a paraboloid. That's the base of the 'scoop' on the extreme right-hand end of the structure. The focus is somewhere just inside the hut.

Modern satellite TV antennae have the same basic layout but don't have the enclosing pyramid (or the hut! ).

As I'm not an antenna guru, it isn't clear to me whether the Holmden pyramid is part of the feed to the paraboloid or a purely mechanical structure to hold the paraboloidal segment and the feed in the correct spacial relationship.

Best regards,

Swarf, Mostly!

Edited By Swarf, Mostly! on 04/12/2018 12:53:22

Thread: Require a .8 Metric Pitch Thread
26/11/2018 15:50:44

Hi there, all,

In discussions of screw-cutting, there is sometimes mention of the percentage error ensuing from the use of some combinations of change-wheels and/or quick-change gear-box, i.e. the percentage difference between the desired or nominal thread and the actual achieved pitch. (Though I notice that none of the posters here have quoted percentage error. )

I wonder whether a usable 'figure of merit' in such matters might be the number of turns required for the error to accumulate to 1 pitch?

Best regards,

Swarf, Mostly!

Thread: Lead Bearing Solder is Banned
15/11/2018 16:02:24
Posted by Tim Stevens on 15/11/2018 15:30:30:

SNIP

And the comparison between a field of ordinary earth and a modern rubbish tip is equally questionable. Spring Water - so popular that it sells for more than petrol - filters through the earth. There is no sale for water that drains through land-fill, in fact you can be charged to get rid of it.

Just trying to keep the discussion balanced in scientific terms.

Tim

PS how much does my wife need to pay me before I count as 'professional' so I can use up my stock of lead solder?

Edited By Tim Stevens on 15/11/2018 15:32:05

I'm no expert on landfill sites but such acquaintance as I did have told me that the modern sites are separated from groundwater by impermeable membranes.

Best regards,

Swarf, Mostly!

14/11/2018 09:35:47

Hi there, all,

I've recently replaced three electrolytic capacitors on one of the printed boards in my computer monitor. (It didn't cure the fault so trouble-shooting continues! )

The boards were manufactured using lead-free solder. In order to free the joints to enable the old capacitors to be removed, I first had to flood them with 60/40 solder. I know I wouldn't have had anything like the same struggle if the boards had been assembled using 60/40.

As a microscopist of my acquaintance says 'if lead-free solder were any good, the Romans would have used it!'!

My reel of fine-gauge 60/40 Ersin Multicore is down to the last layer on the spool. I have several wooden reels of 60/40 Ersin Multicore in stock which would 'see me out' except that it is of the gauge we used to use to solder the tags on Octal valve-holders!!!!!

Best regards,

Swarf, Mostly!

Thread: Myford Super 7 quick change gearbox fitting
04/11/2018 21:22:01
Posted by roy entwistle on 04/11/2018 19:34:42:

Doesn't the Super 7 have a larger diameter leadscrew than the ML7 ?

Edited By roy entwistle on 04/11/2018 19:45:04

The ML7 lead-screw is 5/8" diameter, the Super Seven lead-screw is 3/4" diameter.

However, the left-hand end of the 3/4" lead-screw for use with the gearbox and Super Seven is reduced to 5/8" diameter so it passes through a bore in the gear-box casing. The coupling sleeve between the 3/4" and the 5/8" sections is secured with two roll-pins - it fouls the lead-screw guard attached to the saddle so one of the instructions is to shorten the lead-screw guard. I had to shorten mine by about 3/4" more than specified to avoid losing saddle travel.

Later models of the ML7 lead-screw (non gear-box version) have two Woodruff key slots so you still have one after you've shortened the lead-screw. Early lead-screws only had a single Woodruff key slot.

Best regards,

Swarf, Mostly!

04/11/2018 13:44:27

Hi there, Kevin,

Do you have the installation Instructions for the gearbox? If not, I suggest you obtain one and read it. (I believe they are available on-line, maybe from the 'Files' section of the of the Yahoo Myford group. )

Does your lathe have the necessary tapped holes (¼" BSF ) in the front shear of the bed? They are between the two holes that have the push-screws that push the head-stock against the back shear. Some early lathes didn't have them, mine included, so I had to drill and tap them. Beeston Myford used to offer a drilling jig for this purpose, though they denied all knowledge when I phoned until I was connected to the late lamented Malcolm - he found me one. You temporarily remove the push-screws and use their tapped holes to hold the drilling jig.

The gearbox has a third screw at a lower level - that fixed into an existing tapped hole, from memory, one that previously held the left-hand lead-screw bracket.

Best regards,

Swarf, Mostly!

Thread: Gear cutting
19/10/2018 16:39:07

It might be a good idea to practice on a piece of tidy scrap (but the same as the real job) material first?

Best regards,

Swarf, Mostly!

Thread: ML7 clutch repair/overhaul
10/10/2018 19:13:22

Hi there, Bill,

Do you mean ML7 or Super 7? The two clutches are very different!

The ML7 clutch should respond to treatment without any nasty surprises (though you maybe need to be careful not to lose the two small bits of red fibre that ride in the brass spool on the right-hand end of the push-rod! )

Best regards,

Swarf, Mostly!

Thread: What bearings for a submersible wheelchair?
05/10/2018 17:13:15

My choice would be a fabric reinforced grade of Tufnol, with the grain going the right way. There used to be a material trade-named 'Ferrobestos' used for propellor shaft stern tube bearings but I guess the 'bestos' bit makes it a No-No nowadays.

On the strength of many years experience, I'd say that metal items don't have to be immersed to suffer corrosion in a chlorinated swimming pool environment.

However, I thought 'the modern thing' with swimming pools was ozone or ultra-violet sterilisation.

Best regards,

Swarf, Mostly!

Thread: Three flute drills
05/10/2018 16:59:11

I have several three and four flute core drills. I use them in the lathe to open up smaller drilled holes but I don't think I'm getting (or needing) their full benefit.

Now, If I were machining a casting that had cored holes I think that would show their full benefit. A cored hole could, as cast, be slightly out of position but the lateral rigidity of the core drill will cope better with cutting more on one side than on the other - a common two-flute drill will try to follow the path of least resistance resulting in a hole of correct size but (slightly) in the wrong place! Of course, the context here is use in a machine that can position the drill axis in the right place by some means other than needing a centre punch mark.

The core drills I have do not have a point but have an almost flat business end.  They cannot start a hole on their own.

Best regards,

Swarf, Mostly!

Edited By Swarf, Mostly! on 05/10/2018 17:01:28

Thread: Rocol RTD shelf life
04/10/2018 11:47:42

Posted by Howard Lewis on 03/10/2018 22:54:20:

SNIP

Many years after Shackleton's expedition, someone brought back one of the tins from their supplies. The College lecturer opened the can in the morning, and put the contents onto a plate. When he returned after lunch, the plate had vanished. the lab assistant said "I thought that you had put out for my lunch"

As I keep saying, "Common Sense is no longer that common".

Howard

Hoping, as usual, that the following isn't too far off-topic:

At very low temperatures, tin can change from a shiny metal to an amorphous grey powder. (I suppose that, strictly, it remains a metal but you know what I mean.)

It was my understanding that some of Shackleton's supplies had suffered this - maybe it was Scott's. Loss of the tin coating opens the steel of the can to rust.

My chemistry text book contained a story that the Russian government bought a consignment of tin ingots and stowed them in an unheated cellar. When the cellar was opened sometime later, there was considerable consternation!!

Best regards,

Swarf, Mostly!

30/09/2018 14:55:51

Again, I hope this contribution will not be too far off-topic:

When my late-wife was shopping in preparation for entertaining guests for dinner, she would attempt to arrive at the cheese counter and intercept the shop assistant when she was removing cheese from display because it was 'best-before date-expired' - she (my late wife) reckoned that was just when the cheese was ripe!

But her best story was of a visit to the food hall of an up-market department store in High Street, Kensington:

Shop assistant: 'May I help you, madam? '
Wife: 'Yes please, I want some Brie. ' (It might have been Camembert).
Shop Assistant: 'And when do you plan to eat it?'
Wife: 'Tomorrow.'
Shop Assistant: 'Lunch or dinner? '

Best regards,

Swarf, Mostly!

Thread: Marine Plastic
28/09/2018 09:42:34

Two contributions, meant to be helpful:

Regarding plastic identification - Delrin (acetal) burns with an INVISIBLE flame.

Regarding Tufnol - a good material but you need to get the right grade. Fabric reinforced rather than paper and with the grain going the right way for the application.
See the Tufnol web-site, **LINK** .

Best regards,

Swarf, Mostly!

Thread: Hut Consumer Unit & MCB Question
27/09/2018 14:01:26

Slightly off-topic (but not too far, I hope) :

I read somewhere that the current rating of a twin 13 amp socket is 13 amps, TOTAL.

That is, if I'm drawing 10 amps from one socket, I mustn't draw more than 3 amps from the other one! And likewise for other share ratios.

Best regards,

Swarf, Mostly!

Thread: Another workshop insulation question
19/09/2018 12:49:29

Plus one for: 'For insulation material, look on the Secondsandco website (https://www.secondsandco.co.uk) '.

Best regards,

Swarf, Mostly!

Thread: What has happened to fly spray?
17/09/2018 15:10:52

I have noticed that what I take to be first generation worker wasps are smaller than later generations. I always thought that this was because that first generation have to be raised by the queen wasp on her own.

Best regards,

Swarf, Mostly!

Thread: First Thoughts on Anodising
17/09/2018 11:33:01

Re HARD anodising:

Many years ago I had visibility of a project that employed many aluminium alloy parts that were hard anodised. So, the following from memory:

It was found that hard anodised parts 'grow' by an amount that will prevent close fitting of parts but is not always easy to predict. It was also found that the hard anodising film is vulnerable at sharp corners and sharp edges. So sharp corners and edges had to be rounded.

Best regards,

Swarf, Mostly!

Magazine Locator

Want the latest issue of Model Engineer or Model Engineers' Workshop? Use our magazine locator links to find your nearest stockist!

Find Model Engineer & Model Engineers' Workshop

Latest Forum Posts
Support Our Partners
Advertise With Us
Eccentric Engineering
Eccentric July 5 2018
Warco
Ausee.com.au
ChesterUK
Meridienne Sept 2019
TRANSWAVE Converters
Allendale Electronics
emcomachinetools
Subscription Offer

Latest "For Sale" Ads
Latest "Wanted" Ads
Get In Touch!

Do you want to contact the Model Engineer and Model Engineers' Workshop team?

You can contact us by phone, mail or email about the magazines including becoming a contributor, submitting reader's letters or making queries about articles. You can also get in touch about this website, advertising or other general issues.

Click THIS LINK for full contact details.

For subscription issues please see THIS LINK.

Digital Back Issues

Social Media online

'Like' us on Facebook
Follow us on Facebook

Follow us on Twitter
 Twitter Logo

Pin us on Pinterest