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Member postings for gerry madden

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

Thread: What does this circuit do ?
26/05/2022 13:22:16

Hi All,

I pulled this 'black box' out of my microlight which I installed in it about 25 years ago. I'd always assumed it was a small voltage regulator but when I now look inside I don't think it is. I checked this by putting my benchtop PS on the input side and voltmeter and load on the output side. Regardless of whether the output is open-circuit or given a 0.2A drain, the output voltage is the same as the input.

So what does it so ? I imagine the capacitor is there to smooth things. But the diode (I assume thats what it is) .... is it just there to protect for accidental polarity reversal ?


By the way, this 'device' would normally feed into the intercom system.


Thread: J & S surface grinder - refurbishment
13/05/2022 14:32:02

Thanks chaps. I'll give those ideas some thoughts.

Thread: Almost 4BA but not quite
13/05/2022 14:28:27

Michael G - thanks for posting the link to the comprehensive list of threads. I wanted to condense it and then print it but have a small problem. When I copy/paste into a spreadsheet the first column gets converted into a mixture of dates and other nonsense. If I then try to reformat that column to 'general' or something else, the content gets increasingly nonsensical. What am I doing wrong or what should I change to ensure that first column remains intact after pasting ?


Thread: Barograph 'stiction'
12/05/2022 17:32:23

David, I didn't know that about oscillating movements. Interesting. I had planned to use in a clock escapement, perhaps I wont now .

There is another material with similar CoF, called Vespel. Do you have any experience of this ?

Apologies if this is a thread hijack.


12/05/2022 14:32:41

One of the interesting characteristics of PTFE is that its static friction is the same as its dynamic. This helps avoid 'stiction' issues. Not sure if you would be able to work this in to your application... it might make things too big and therefore might increase friction to above what you already have, so perhaps the balance wheel pivot is better.


Thread: J & S surface grinder - refurbishment
11/05/2022 15:38:19

The refurbishment continues with lots of parts in for grit-blasting this week. So far only one unexpected surprise..... the oil pan. This was 'perfect' when I gave it to the master blaster but when he'd finished with it it was full of holes!


Well I say "full of" ...there are probably a hand full, but plenty of pitting which isn't far off becoming holes. There must have been some water sitting in the bottom of the tank for a long time.

So my question is: what would be the recommended repair for this ? I suppose welding some plates on would be the best, but are there other proven solutions I should consider ?


Thread: Which Collet Chuck?
29/04/2022 12:11:58

I think also if runout is a thing that worries you, the MT3 chuck is better. The flange mounted one's will tend to have more runout due to the spigot clearance adding to the eccentricity of the collet holder to the spindle axis.

With my 'Arc quality' MT3 collet chucks find I can turn one end of small parts, then turn the part around and machine the other end, with almost no perceptible step from the two operations.


Thread: Thread Cutting Change Gear Tables for Wabeco D4000
18/04/2022 16:28:03

Thanks for the info David. I have a D3000 and your info probably applies to this too. Its good to know the error on imperial threads.

The only issue I had with threading was when I needed to cut a LH thread and realised that one needed special gears instead of belts to do this in order to reverse the rotation of the lead-screw. I tried twisting the belt into a 'figure of 8' and much to my delight discovered that this worked perfectly.


Thread: J & S surface grinder - refurbishment
07/03/2022 15:30:04

Forget the question about the material for the seals. Further investigation shows that the ram seals are in fact proper 2-part hydraulic components which look like this:-


For the record the outer part has dimensions 9.5x 22.2 x 8.6 and back-up inner part 10 x 21.8 x 6.5. These should correspond to some imperial measurements of course and hopefully I should be able to find a cheap source somewhere on the net.


07/03/2022 12:43:47

I now have my table off and its being prepared for blasting and repaint. The ways look good, clear scapings cover the full surfaces and there is no damage or casting defects present. For the record the table weighs 55Kg.

I'm now cleaning and expecting the ram. Its all fine (apart from a obvious covered-up manufacturing error). Although the machine didn't have excessive leakage previously, I'm thinking that now its all in bits I may as well fit new seals. They are basically just simple bushes pressed into brass sleeves. as you can see below.


I would rather make something myself than buy new parts which cost around £50, but not sure about the material. I 'looks' like Tufnol, i.e. cloth impregnated, but its a little compliant, so its a kind of cloth impregnated with a hard rubber, as opposed to a phenolic. Would anyone know confidently what this material is or likely to be ?

Another puzzle is this. The spare parts manual shows gaskets between the central circular section tube and the two outer square section tubes.


The were no gaskets in mine, just spigots, and not particularly good fitting ones at that ! Could this be another build mistake perhaps ? Does anyone else have these gaskets here, and if so, are they fitted between the axial or radial surfaces of the spigots ?

Since there is no means of controlled axial clamping between these 3 ram cylinder parts its difficult to see how axial gaskets could ever be successful in this situation but what do I know


Thread: Precision ground flat stones in UK?
28/02/2022 10:46:24

When I looked at buying some from the US they were eye-wateringly expensive too. Once my J&S 540 is fully restored and tested, flat-stones are one of the first things I will attempt make


Thread: Metal Cleaning Using Vinegar?
20/02/2022 12:13:39

Graham, thanks for bringing some facts to the table.

A few years ago all the discussion seemed to be about the more 'passive' solutions for removing rust. I think even MEW did a piece on 'evaporust' telling us it was pretty good. Now, not a mention of such things.

I personally have used a lot of citric acid, it works but tends to etch the steel leaving it a bit dull. It can also produce some dreadful bad egg type smells if left too long doesn't go down well in the house, as you can imagine

For these reasons I also tried Arc's rust remover product which I imagine works in a similar way to 'evaporust'. It was totally hopeless. If you just let the parts soak in it for 24 hours nothing at all happened. If one followed the instructions and repeatedly scrubbed the part during the soak, one would eventually remove the rust. But after a few hours of this scrubbing nonsense one cant help thinking that it would have been a lot less mess to have got the rotary wire brushes and the flapper wheels out in the first place.


Thread: Front door locks
19/02/2022 12:29:25

+1 Keysafe.

Thread: workshop floor - strength question
15/02/2022 00:18:39

Yes Pete, I know concrete is often put on top of polystyrene foam, and thats exactly what I shall do if and when the time comes. But the concrete has to be thick enough to carry the load. Then the foam basically acts as insulation, not as load bearing.


14/02/2022 23:20:18


Edited By gerry madden on 14/02/2022 23:22:23

14/02/2022 23:19:22

Neil, in these situations it isn't only about the ultimate compressive strength, its about the compliance or stiffness of the materials as well.

Your polystyrene will only 'fight back' with any effort when it's considerably crushed. A hard brittle material like concrete, on top of soft material may crack well before the compliant polystyrene has built up any significant resistance to the load.

Imagine putting a large sheet of 0.1mm thick glass over a very large area of layer of sponge rubber. You wouldn't be able to walk on the glass without it breaking. So basically the stiffest material has to have sufficient strength to carry the load before it will be able to spread that load successfully into the softer more compliant material.


Thread: forum post display
14/02/2022 11:38:04

Thanks Jason, The strange thing is when I look in my 'grinder album' (that sounds bad doesn't it ) the picture is still there. Here's what I see right now....

snip 2.jpg

...and I can call it up again like this...



11/02/2022 20:11:59

Can anyone explain say why a picture inserted into a previous post has become an icon which when clicked on doesn't reveal anything ?snip1.jpg


Thread: workshop floor - strength question
11/02/2022 18:57:48

Thanks all for your input.

I think its clear now 50mm of concrete on a compliant base is quite risky, and especially so with electrical elements embedded in it. I will have to consider something substantially thicker, probably 100mm min. In a house this wouldn't be helpful as it just slows the warm-up time. But in the workshop it would only be a background heat just to keep the room a little above ambient, so perhaps 100mm is not a problem.

I had planned plenty of insulation and the calculations suggest it wouldn't take much energy to maintain a reasonable differential with the outside ambient. I already have solar panels on the house and they generate far more than I can use, so this would heat the workshop most days, and for free.

The real problem now is that the planning people want to reject the whole concept due to 'green belt' concerns. So all workshop design activities are on hold until this is sorted, ....if it can be sorted.


06/02/2022 20:31:45

Adiabatic heating of the air increases the pressure over that caused by the simple volume change.

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