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Member postings for Glyn Davies

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

Thread: Using a propane cylinder for partable compressed air.
04/04/2019 21:33:38

Many thanks to all those that troubled to reply!

I’ve just been examining the cylinder for any information marked on it. It is dated 1978 and a plumber gave it to me; there is no gas company mark on it, so I’m going to class it as mine!

It is marked TP 33.2 bar (481psi), SP 30.9 bar (448psi) and WC 9.2l. I assume SP is the Safe Pressure? The fact that propane molecules seem to embed themselves in the internal surface of the cylinder and then eke out over time did worry me a bit (the air coming out does smell a bit of propane, or whatever they add to propane to make it smell) and I see that the lower flammability limit for propane is just over 2% by volume at 150psi. That means that there needs to be 184cc of propane in the 9.2 litre cylinder when I fill it for there to be a combustible mixture and I just can’t see that much propane detaching itself from the steel interior. On the matter of condensation, I wonder if all the free water in the air will have condensed when it was first compressed by my shop compressor; I inverted the propane tank and opened its valve and no water came out.

I fully understand the views of those replies that urge caution (or cessation!), but having seen the test pressure value and lower flammability level of propane at high pressure, I’m fairly reassured that it won’t go bang. I think I’d be very wary of pressurising the 50 litre receiver of my Clarke compressor to 480psi, particularly after having regularly drained very rusty water from its drain tap over the years.

04/04/2019 14:59:01

I visited the US back in the 90s and saw some portable compressed air tanks for sale in Walmart. Never seen them here and often thought how useful one would be around the car and home. Anyway, I recently acquired an empty 3.9kg propane cylinder and thought I’d try it. It works a treat. When filled with compressed air at 150psi I can top up eight car tyres with ease before it empties. My question – can anyone see any safety issues with this that I’ve missed? I thoroughly purged any remaining propane from the tank before I filled it with compressed air and I see that the vapour pressure of propane is 150psi at 32 deg C, so the tank must be designed for this level of pressure. I tried unscrewing the valve on the tank so I could fill it with water and proof pressure test it to say 300psi, but the valve is too tight to unscrew.

Thread: broken calipers
04/04/2019 11:08:10

I would turn and file it from solid silver steel bar, hardened and tempered to blue.

I did a search on cheap calipers to see how much it would cost to buy one for the spring and came across this one from RS:


I'm not sure why it's listed as being metric!

Thread: DraftSight no longer free
25/03/2019 15:52:58

Just opened mine and cannot see a message - is it hidden somewhere?

Thread: AutoCAD substitute
05/03/2019 14:08:34

Just in conclusion - the more I play with Draftsight the more capability I find. Things like spline, rotate reference, scale reference, fillet are all there, just not on the main ribbon. So thanks again for the suggestion - life is good once more!

05/03/2019 09:32:03

Hmm.. The ebay listing gets seven glowing five star reviews and one one star review in Spanish that warns that you all get is a link to the free educational version of AutoCAD.

Ah well, as the atomic scientist said..

05/03/2019 08:58:05

Well, as usual with this forum, an absolutely brilliant response to my question. Many thanks for the replies. I've just downloaded Draftsight free and have been having a play. It imports my AutoCAD drawings, so that's a relief, and as has been said, the interface is kind of familiar.

But I sort of feel that having lost autoCAD, my life has taken a slight turn for the worse, so, in desperation, I did an ebay search and, behold! - Autocad 2019 full 3 years subscription for £8.95! I'll give it a go and report back.

04/03/2019 16:59:33


For about the last eight years I have enjoyed access to AutoCAD 2011 and have used it extensively for creating 2D drawings of parts to make, for importing images at scale and creating 2D drawings of from them and the odd bit of 3D modelling to create photo realistic images and to calculate surface areas to calculate anodising currents.

My access to AutoCAD has now been removed and I need something affordable that ideally is similar to use and at least gets me my 2D capability back. Are all CAD packages now subscription based (autoCAD 2019 is £1700 per annum!) or can I buy one for a one off price? Any help would be much appreciated! Thanks

Thread: Setting lathe top slide angle accurately.
25/12/2018 11:37:43

If I need to set the top slide to match an existing taper, such as a Morse taper, I hold some silver steel bar in the chuck and use a DTI to check that the top slide is set to zero by running it along the silver steel. I then slacken the nut clamping the Dickson tool post body to the top slide and bring the plain face of the body into contact with the silver steel. Then lock the tool post. I next fit the taper I’m trying to match into the chuck, release the top slide lock screws and bring the plain face of the tool post into contact with the taper. Then lock the top slide and turn my taper.

Thread: Cheap 3D printers
08/11/2018 19:40:42

Thanks for the replies - time to dip a toe I think!

08/11/2018 13:03:48

Hi Sorry if this is a question I could answer with a quick search, but - I just had a look on Amazon for 3D printers and couldn't believe how cheap they are, Some less than £200.

My question - if I buy a printer with a heated base plate, can I create prints in ABS or PLA from CAD models that I export as STL files? Is it really that cheap and simple? Will the printer come with software to slice the STL file and then print it?


Thread: Small Carronade model - 68 pdr.
15/09/2018 13:18:50

As regards bluing the metal - I think you'll find that the sodium nitrate is now classed as an explosive precursor so that, for our safety, the freedom we once had to buy it has been removed.

An option is to rust blue it. You can still buy ammonium chloride (sal ammoniac) on ebay and if you dissolve 2 grammes into 100 grammes of water, you have an effective rust bluing solution. I'd try on scrap steel first and see if you like the result. Method is to swab the solution sparingly onto the degreased steel and leave supported above a dish of water for a couple of hours until a light grey/brown rust forms on the surface. Then immerse the item in boiling water for a few minutes, let it cool and rub off the loose fine rust with 0000 wire wool. Repeat the swabbing, rusting, boiling and wire wooling five or six times until the metal looks a sort of grey colour after the final wire wooling. The last step is to rub in some linseed oil, which will give some corrosion protection and turn the colour from grey to blue/black.

You can actually use sodium chloride at a pinch(!) in place of ammonium chloride but the process might take longer to get to a good blue.

Thread: Painting anodised aluminium
05/09/2018 08:58:42

I thought the last step in anodising after the oxide surface had absorbed the dye was to seal it by boiling in straight water. Anodising is easily removed by immersing in caustic soda solution for only a few seconds. You can tell if the anodising is gone (apart from the colour disappearing) by touching the surface with an ohm meter. The anodised surface will be non conducting, if you have conductivity, the anodising is gone.

I don't see why anodising would prevent paint adhering though.

Thread: Peace Flame
13/08/2018 16:46:00



Thanks for the replies. Following Jason's suggestion, I took the burner off a butane stove and lit the jet. The control knob is just what I want. But how to get it apart to see how it works without wrecking my stove?

I assume the valve is seeing the full vapour pressure of the butane (about 30 psi or 2000mb).


Edited By Glyn Davies on 13/08/2018 16:55:05

13/08/2018 15:31:03


I could do with some design help, please.

I'm tasked with producing a propane fired peace flame for the village. The enclosure will hold two 3.9kg propane tanks with an automatic changeover valve that switches to a full cylinder when the first is empty. The valve incorporates a 37mb regulator. We have been given a ruby pilot jet from a portable gas heater.

When fed from the 37mb regulator, the flame from the pilot is too large and will consume too much gas. So I produced a manifold with a tapered screw to throttle the gas flow and reduce the flame. Here's the drawing of the manifold:


The problem is that the adjuster has to be screwed in tight to get the flame down to what it needs to be. I was disappointed that screwing the screw in tight does not completely shut off the gas flow and it is very sensitive. Screwed fully in, here's the flame produced:


The flame size is about right but I want a finer adjustment. Can anyone suggest a better design for the throttle that will completely shut off the gas and allow fine adjustment at the very low pressures and flows pertaining?


Thread: Zeus book download
28/07/2018 17:59:37

Thanks Bob - what a gem that Presto book is!

28/07/2018 13:09:06

Thanks Vic!

28/07/2018 11:31:12

Thanks for the replies. I've been given the job of designing and making a burner manifold for an eternal peace flame for the village. I'm trying to figure it all out in CAD and it has numerous metric and UNF screw threads and it would have been nice to have the screw thread data that's in the Zeus book on my PC.

Gosh - I have two Zeus books in the workshop - a 1980 one that I use all the time and a 1995 one that I bought as a spare. I've just bought the 1995 one in and see that the table of BA thread data has been replaced by a metric fine one. What's the world coming to?

28/07/2018 08:51:59


Does anyone know if the Zeus data booklet is available as pdf download. A google search takes me to sites that ask me to create an account before I do anything and ebay just lists the booklet itself. I'd happily pay the price of the booklet for the pdf file.

Thread: Myford Super 7 Clutch
26/07/2018 19:10:33


The clutch on my S7 started slipping under heavy load (maybe it was a mistake to oil it to stop it squeaking) so I decided to dismantle it and clean it.

I decided that making a simple compressor wouldn’t be too hard, so I set to with some 4mmx30mm hot rolled bar, 6mm screwed rod with four M6 nuts and an M8x60 bolt from B&Q.

I cut two pieces of bar 56mm long, bored a 7/8” hole in the centre of one and drilled and tapped two M6 holes on 41mm centres. The second piece had an M8 hole in the centre and two 6mm clearance holes on 41mm centres. I then cut two pieces of M6 screwed rod 180mm long. Using my mandrel handle, I centre drilled the end of the M8 bolt in the lathe.

Here are two pics of the compressor:



To use it, I split the compressor and slid the bar with the 7/8” hole past the circlip groove in the countershaft spindle, fitted the circlip and then assembled the compressor. I then screwed the M8 bolt until it contacted the ball bearing and used a screw driver to unscrew the push rod off the driver plate.

Here are some pics of the pushrod and spring.



I hope this is of some help to others contemplating dismantling the Super 7 clutch.

Edited By Otley on 26/07/2018 19:23:08

Edited By Otley on 26/07/2018 19:32:39

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