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Member postings for DrDave

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

Thread: What did you do Today 2018
16/01/2018 21:54:07

I bought alength of 7075-T6 bar a couple of months ago because it looked like it had the block for a V8 engine buried inside. After making a considerable amount of swarf, look what I found. I have roughed it out to allow any built-in stresses to relax before machining to final size.

Rough Block

There is a lot more swarf still to be removed, but it is at least starting to look the part.

Thread: Arduino lcd display
14/01/2018 19:10:22

I bought my first Arduino & LCD display last year “to play with”. I also battled to get the display to do anything. Had I killed it? The only reference to screen brightness in the destructions was to change the voltage on one of the input pins. Being a bit shy to try that, I eventually thought that I would try adjusting the pot, on the basis that if I had killed it, a bit of fiddling wouldn’t hurt: it immediately worked. It was somewhat annoying that I had spent several hours trying to troubleshoot the blank display, all because the manufacturer had not said that screen brightness is controlled by the pot... Humpf!

Thread: What did you do Today 2018
14/01/2018 18:59:11

I managed to get a new pair of brushes for the DC motor in the mill on Friday. They were a tad thin (about 0.4mm thinner than the originals) so I was concerned that they might cause problems. Fitted yesterday & today spent milling a big block of ally into a small block of ally. No signs of trouble after a couple of hours work at near full speed. I’m a happy boy again.

Strangely, whilst the motor is German in an Austrian machine, the original brushes measured ¼” x 5/16”. Strange old world!

06/01/2018 21:48:05
Posted by Emgee on 06/01/2018 20:33:36:

Dr Dave

This was quoted in a mail to me some time ago but I believe your mill is an Emco F1 so should help with sourcing brushes, contact them directly at

ask for carbon brushes part no STL 0406



Thanks for the link: I will give them a try next week.


04/01/2018 16:08:08

After the motor stopped working on my mill, I started to troubleshoot it today. Before stripping anything down, and prompted by Neil's suggestion of the motor being at fault, I checked the resistance across the DC motor: open circuit. I looked at the motor and remembered that it has carbon brushes; clearly the next thing to check.


I hope that this is the problem. Now, where to get new brushes for a 20 year old German motor?

03/01/2018 20:26:14

In my last year at school, dad brought one of the new-fangled Hewlett Packard calculators home from the office. The RPN system seemed strange at first, but then I “got it”. Consequently I have used HP calculators through my professional life & have two on my desk at the mo. For anything more than the most basic equation, I find the reverse notation far quicker & easier than trying to use brackets on a “normal” calculator. Unfortunately, they are becoming hard to find now (but I have an HP calculator app on my ‘phone, just in case!).


Thread: 150cc Radial Engine - A restoration or new build...
02/01/2018 22:08:41


Thank you for that detailed response. I will look at A2 steel for my gudgeon pins: coming from an aerospace background, I am used to using 4340 for “everything “.

I had better start a new thread to avoid hijacking Michael ‘s buildblush.


Thread: What did you do Today 2018
02/01/2018 19:26:40

That’s an interesting point, Neil. I had assumed that, because it is a few decades old, the electronic bits would have gone geriatric, not the motor. This might take longer than I thought...


Thread: 150cc Radial Engine - A restoration or new build...
02/01/2018 19:10:57
Posted by Neil Lickfold on 29/12/2017 11:30:28:

A2 tool steel makes for great wrist pins/gudgeon pins. Harden and double temper to 58 to 60 Rc.


Is tool steel suitable for gudeon pins? If it needs to be hardened & tempered, would not a H&T structural steel such as 4340 (or European equivalent) be a better choice? Am I right in thinking that either would need professional heat treatment, or can this be done at home and would this require a decent furnace rather than a propane torch?


Thread: What did you do Today 2018
02/01/2018 19:01:19

Today’s plan was to spend some quality workshop time roughing out a crankcase. The plan worked this morning, but it has all gone wrong after lunch. I managed one cut in the mill, stopped to check a dimension, and now the spindle motor refuses to do anything.

To be fair, it has been showing signs of distress for some time, with the speed of the DC motor “hunting”, so the escape of some blue smoke was not unexpected. I have a spare controller board, but I would rather not have had to rip out the old wiring to fit a new, different board.


Thread: 150cc Radial Engine - A restoration or new build...
11/12/2017 14:47:37


This looks like it will be an interesting build: I am looking forward to your progress. Your use of 12.9 shoulder bolts for the gudgeon pins is interesting. I was going to use silver steel for the engine that I am making but a quick Google showed that I can buy suitable 12.9 bolts off the shelf, which will be far superior.


Thread: Magzine reader now not working?
04/12/2017 21:02:06
Posted by Neil Wyatt on 04/12/2017 19:24:02:

A HTML5 version of the archive is already 'served' by default to Mac users...

I wonder if that is why I am no longer able to print archive magazines from my Mac. It was useful to be able take prints of an article into the workshop, particularly drawings, but I lost this feature some time ago.


Thread: 2017 Christmas Challenge
24/11/2017 18:46:12

Well done, Rod. A worthy winner.


Thread: Aircraft General Discussion
18/11/2017 22:55:23
Posted by Andrew Johnston on 18/11/2017 22:47:55:

That's rather sad. The incident headlined on Look East this evening. It seems to be rather a mess - going to take a bit more than sticky tape to do the repairs. Given it was dead calm this morning I wonder if there was some finger trouble involved?

Sad indeed. It could be the death knell for the project. I hope not.


18/11/2017 21:43:31

It is not clear to me how the Airlander managed to break free from its mooring mast. It was nearly a dead-calm this morning when the crash (is that the correct word?) happened. I hope that it is insured against attempted escape. The last airship (the Gooyear blimp, I think) that escaped from RAF Cardington ended up in the nearby village of Cotton End. Imagine finding that in your garden. And the gardens of a few neighbours.


18/11/2017 16:56:09

Ooh,er: the Airlander is having more problems. It broke free from its mooring this morning & ended up, deflated, in the adjacent field.19372689-419f-4ad6-b3bd-37dd180e58b8.jpeg

Thread: 2017 Christmas Challenge
07/11/2017 10:19:17

As we are Model Engineers, I made a brace of model candlesticks...


Thread: Aircraft General Discussion
22/09/2017 20:17:07

Mrs Dave and I were sitting in the sun at Old Warden airfield this morning, when one of the staff called out "would anyone like to help push a Hurricane?". Well, it would have been churlish to refuse! A dozen of use Strolled over and gave it a shove out of its hanger & onto the airfield. They were going to fly four of their aeroplanes to Duxford for tomorrow's air show.

05/09/2017 22:11:09

Thanks for the definitive explanation of the source of helicopter blade noise, FF. My helicopter knowledge was learnt 30 years ago when I worked on the Puma. And it was not a young aircraft then! The technology of rotor blades has moved on a bit.

I still remember being "self-loading ballast" for an envelope expansion flight in one of the test Pumas: a maximum rate turn at low airspeed sure shakes your teeth fillings. Strangly, I didn't take the offer of a second flight....

05/09/2017 21:32:07
Posted by Fowlers Fury on 05/09/2017 21:14:54:

No doubt known to everyone, but I understand the "whump whump" as Andrew describes it, is because the tips of the rotor blades on most helicopters are travelling faster than the speed of sound i.e. mini sonic booms.

The tips do not go supersonic on a helicopter, it is the interaction between main & tail (or both mains, as Martin said) that causes the characteristic noise. When a helicopter is flying at a high airspeed, the retreating blade tip is often going "backwards" through the air: I thought that the "spades" were an attempt to improve the chaotic aerodynamics this causes.

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