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-   -   Drawing circular log scales? (https://www.vintage-radio.net/forum/showthread.php?t=158490)

mole42uk 30th Jul 2019 7:17 pm

Drawing circular log scales?
 
I need to make a circular log scale to replace the missing one on a signal generator but I can’t find any way of generating a software based version.

Is there something I’ve missed? Can anyone help?

ionburn 30th Jul 2019 10:56 pm

Re: Drawing circular log scales?
 
I am not aware of software, but have not needed or looked. It is something which may be not too difficult to do by hand. You only really need the length of circle perimeter (or length of the scale if not full circle) then calculate a normal straight log scale to fit that length. Then transfer over. I can see it would be tedious but with the right tools, practical.

Hopefully someone will have done this and know the tricks (or better still - software).

One other option would be if someone were able to take an accurate photograph of such a scale from identical model.

Terry_VK5TM 31st Jul 2019 5:09 am

Re: Drawing circular log scales?
 
1 Attachment(s)
Something like this?

Done with Abacom's Front Designer, all customisable.

Change text, rotation, line lengths etc within the program.

kalee20 31st Jul 2019 8:19 am

Re: Drawing circular log scales?
 
Hmmm... Can't have '0' on a log scale!

mole42uk 31st Jul 2019 9:48 am

Re: Drawing circular log scales?
 
That's right. The one I have is a photocopy of an original, it reads from 10 to 100 over an arc of 290° on a diameter of 4.25" (108mm).

I want to produce a drawing so that I can send it off to have one made in etched aluminium.

Terry_VK5TM 31st Jul 2019 11:44 am

Re: Drawing circular log scales?
 
1 Attachment(s)
Removed the 0 and changed it to 290deg scale.

mole42uk 31st Jul 2019 12:02 pm

Re: Drawing circular log scales?
 
Thank you! Please could you change it so the marks are on the inside of the arc and reverse it so that 10 is where 100 is? That would be an excellent solution!!

kalee20 31st Jul 2019 12:12 pm

Re: Drawing circular log scales?
 
Quote:

Originally Posted by Terry_VK5TM (Post 1164912)
Removed the 0 and changed it to 290deg scale.

I've just crudely put a ruler on my monitor face and measure chord lengths: 10-20; 12-24; 20-40; 30-60; 40-80; 50-100 all measure 72mm. so the angles are the same, exactly what would be the case for a log scale!

I like it :)

Herald1360 31st Jul 2019 1:20 pm

Re: Drawing circular log scales?
 
Quote:

Originally Posted by kalee20 (Post 1164843)
Hmmm... Can't have '0' on a log scale!

In principle, that's correct. A real life pot will jump to zero at the end of the track, though.....

Terry_VK5TM 1st Aug 2019 4:17 am

Re: Drawing circular log scales?
 
Quote:

Originally Posted by mole42uk (Post 1164922)
Thank you! Please could you change it so the marks are on the inside of the arc and reverse it so that 10 is where 100 is? That would be an excellent solution!!

Household chores to finish today so I'll change it around tomorrow for you.

Do you want the arc to remain where it is and the division marks come in from there

Or

Move the arc to the outside of the division marks as they currently are?

And do you want the lines slightly thicker?

Terry_VK5TM 1st Aug 2019 6:02 am

Re: Drawing circular log scales?
 
3 Attachment(s)
So much for the household chores, started raining and of course it was outside chores.

Attached as first pass depending on which way round you want the changes.

Also attached as a pdf as that is nicer than the jpg's.

mole42uk 1st Aug 2019 3:01 pm

Re: Drawing circular log scales?
 
1 Attachment(s)
Hi Terry, thank you, it's looking almost right!
I attach a photo of the dial I'm trying to duplicate, I don't know why I didn't do this before....

Alf 1st Aug 2019 3:44 pm

Re: Drawing circular log scales?
 
1 Attachment(s)
You might want to have a play with meterscales, I can't offer any help with the program.

mole42uk 1st Aug 2019 5:46 pm

Re: Drawing circular log scales?
 
Thank you, unfortunately I don't have a Windows computer....

Terry_VK5TM 2nd Aug 2019 1:41 am

Re: Drawing circular log scales?
 
Picture was a good idea.

I'll have a play a little later and see how close I can get it.

Are you able to measure the distance between the end of the division mark and the number and the lengths of the marks?

Radio Wrangler 2nd Aug 2019 3:00 am

Re: Drawing circular log scales?
 
There are ways round operating system issues.

This Mac has Oracle Virtual Box installed. This creates a number of virtual machines and I can load any operating system I want on each machine. so I got a legit copy of XP. I can open a window on the Mac OSX screen with XP running in that window, and run windows software on it.

David

Terry_VK5TM 2nd Aug 2019 11:13 am

Re: Drawing circular log scales?
 
1 Attachment(s)
This is about as close as i can get it from the picture.

Let me know if it needs any tweaks.

mole42uk 2nd Aug 2019 11:37 am

Re: Drawing circular log scales?
 
Hi Terry, that is fabulous! Thank you, I'll be able to finish rebuilding the signal generator...

mole42uk 2nd Aug 2019 11:39 am

Re: Drawing circular log scales?
 
Quote:

Originally Posted by Radio Wrangler (Post 1165409)
There are ways round operating system issues.

This Mac has Oracle Virtual Box installed. This creates a number of virtual machines and I can load any operating system I want on each machine. so I got a legit copy of XP. I can open a window on the Mac OSX screen with XP running in that window, and run windows software on it.

David

Hi David,
I have run Virtual Box on the Mac but I don't have a currently licensed version of any Windows system.

julie_m 2nd Aug 2019 3:02 pm

Re: Drawing circular log scales?
 
If you know how to write PostScript, it would take about a screenful of code to produce a scale like that!

If you are running any Unix-like system (i.e., Mac or Linux) then you probably already have GhostScript installed, which is a suite of programs for working with PostScript files including displaying them and converting them to other formats.

ajgriff 2nd Aug 2019 4:39 pm

Re: Drawing circular log scales?
 
As someone who has attempted this kind of thing with more conventional drawing/graphic design software I'm very impressed with Terry's work and Abacomb Front Designer. Unfortunatley, I don't think I could justify the cost of buying the package for the odd occasion it would be used. Having said that about €40 doesn't seem too outrageous.

Alan

Terry_VK5TM 3rd Aug 2019 2:51 am

Re: Drawing circular log scales?
 
Quote:

Originally Posted by mole42uk (Post 1165468)
Hi Terry, that is fabulous! Thank you, I'll be able to finish rebuilding the signal generator...

You're welcome.

Alan,
You'd be surprised at what uses you may end up using the Front Designer software for.

I've used it as above for various scales and dials, front panels (both custom and replacement), site plans for building and even A3 sized 'elf'n'safety signs for the Mens Shed, amongst other things.

As an aside, this sort of thing (the dial face) can be done (and is in industry) with ordinary CAD software, even the free ones. I just prefer Front Designer as it has much less of a learning curve than full on CAD packages.

Pamphonica 3rd Aug 2019 9:23 pm

Re: Drawing circular log scales?
 
The only freeware package I can recommend for this sort of thing is Galva, written by Jean-Paul Gendner, F5BU.
http://www.f5bu.fr/galva-about/
It's a script-based program so you just define things like start number, end number, log or lin, and you can draw scales for almost anything, including very complex multi-meter scales.
I have used it to restore the dial from a 1970 KW2000 transceiver, for instance, which has an irritatingly non-linear dial.
I highly rate it.
-Jeremy

PS, I also use Front Designer and have done some huge front-panel layouts with it. Much easier for entire front panels than Galva.

ajgriff 4th Aug 2019 6:00 am

Re: Drawing circular log scales?
 
I'll have a play with Galva. Thanks Jeremy.

Alan

tb10_flyer 19th Aug 2019 7:23 pm

Re: Drawing circular log scales?
 
2 Attachment(s)
I thought I'd refresh my old Galva skills my trying to replicate the OP's dial based on the photograph shown in Post #12. The first PDF shows a log scale in blue superimposed over the photograph. Clearly there are differences which indicate the original instrument scale is NOT logarithmic, and probably cannot be accurately represented by any mathematical function. So, using the 'measurement' technique suggested by Jean-Paul Gendner in his Galva Help file, by Jeremey <Pamphonica> in Post #23 and by myself in previous designs. the second PDF shows in red a perfect match. If Richard <Mole24UK> is still looking for a true restoration of the original scale, this will provide the art work. I have assumed that the '1' and '10' marks correspond to the full CCW and full CW rotation of the dial, through the measured 285 degrees.

Now, I wonder whether the empirical nature of the original dial may be because the resistance(?) of the control component was only an approximation to logarithmic progression as, I think, is usually the case with most log-law devices.

Mike

mole42uk 20th Aug 2019 6:12 am

Re: Drawing circular log scales?
 
That’s interesting, the designers at Radford must have made the dial to fit the log law of the Bourns potentiometer they used.

I’m away on holiday but as soon as I return I’ll pick this up again.

mole42uk 7th Sep 2019 8:25 am

Re: Drawing circular log scales?
 
The project progresses, not quite as soon as I wished, because work made huge demands after my holiday!

I have now 'borrowed' a Windows machine, used your Galva script and printed a version of your modified log scale. I also have the piece of 2mm anodised aluminium and the photo-resist film so that I can etch the scale.

Before I commit to the final version, I'm going to use the paper print on a dummy dial and measure the output frequency against the new markings. That should prove the theory about the variation of the Bourns pot logarithmic law against a genuine logarithmic scale.

I did not think that this dial would have taken quite so long to reproduce!

mole42uk 6th Oct 2019 1:24 pm

Re: Drawing circular log scales?
 
Right, more progress. I have used a paper copy and checked Mike's modified logarithmic scale on the actual machine, and it is accurate - well as accurate as my old test equipment and eyes can determine.

Now I need to get the scale etched onto the aluminium and the Radford LDO will be ready for action....


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