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Vintage Test Gear and Workshop Equipment For discussions about vintage test gear and workshop equipment such as coil winders.

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Old 4th Jul 2018, 12:44 pm   #1
David G4EBT
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Default 'Red Nose Day' for a Heathkit probe!

In a recent thread I mentioned that I'd been stopped in my tracks from being able to get into my workshop due to having had a knee replacement operation (five weeks ago today). However, this last few days I have at least been able to tackle a little project on my lathe. It's another example of how useful a small and basic lathe can be in the hobby. They can often be had quite cheaply and indeed, sometimes appear on the forum.

I've just turned a 'nose cone' in red Acetal (a type of plastic) for a forum chum who needed a replacement for a damaged one on a Heathkit probe, but his search proved fruitless. I'd said that if it would help, if he supplied the Acetal and sent me the original, I'd turn him a replacement, as I've now done. It looks a simple little project but there was a bit more to it than meets the eye.

It had to be part turned on the metalworking lathe, then hollowed out internally and shaped externally with woodturning tools. Because Acetal isn't very amenable to being sanded or polished, you have to get the best possible finish 'off the tool'. The thread for the metal tip was obscure. Being American I knew that it wouldn't be metric or British. A chum who runs a light engineering firm ('one man band') discovered that it was in fact 1/4" x 32 TPI 'Model Engineers' Thread', which I'd never heard of, but luckily, he had a tap that size.

I turned a wooden 'gauge' to the internal profile of the old cone to use to judge the internal shape of the new cone as hollowing progressed. It took about 1.5Hrs in short sessions as I couldn't stand too long at the lathe. I enjoyed doing it. It's just one example of many which illustrates how useful a basic lathe can be in the restoration of vintage radios and test gear.

It lifted my spirits to be able to get into my workshop, if only for a short time, having spent rather too long this last few weeks sat with an ice pack on my knee and my feet up, watching banal daytime TV, interspersed with adverts for funeral plans and stair lifts.

(I've waited for confirmation that it comes up to the recipient's expectations before posting this thread!).

Hope it's of interest.
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Old 4th Jul 2018, 12:55 pm   #2
Argus25
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Default Re: 'Red Nose Day' for a Heathkit probe!

Excellent job David (as always).

I really like and admire your work. Patience and attention to detail is your hallmark and your work is not just a little better than the average production, it's a lot better.

You are quite right about a lathe of course, I have found mine invaluable for restorations and project construction over the years. I also use mine for transformer winding, it's hard to imagine doing without one.

Hugo.
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Old 4th Jul 2018, 2:22 pm   #3
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Default Re: 'Red Nose Day' for a Heathkit probe!

I just want to say thank you for taking the time to write this post, adding the pictures and the details that are so interesting in a project like this. I really enjoyed reading it (and also your previous Heathkit posts)!

As I have experience using 3d software, I've come across people who have attempted to 3d-print the nose cone. However, your process certainly seems to have had excellent results! Perhaps it's time I learned to use a lathe...
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Old 4th Jul 2018, 7:16 pm   #4
factory
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Default Re: 'Red Nose Day' for a Heathkit probe!

Quote:
Originally Posted by David G4EBT View Post
The thread for the metal tip was obscure. Being American I knew that it wouldn't be metric or British. A chum who runs a light engineering firm ('one man band') discovered that it was in fact 1/4" x 32 TPI 'Model Engineers' Thread', which I'd never heard of, but luckily, he had a tap that size.
There are also UNEF (extra fine) threads, including 1/4" x 32TPI, the thread angle is slighty different, 60° instead of 55° for ME thread.

David
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Old 4th Jul 2018, 8:09 pm   #5
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Default Re: 'Red Nose Day' for a Heathkit probe!

Well said David, I rather just sit in my workshop and tinker than watch daytime tv.
All the best for your speedy recovery.
Cheers
John
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Old 4th Jul 2018, 8:15 pm   #6
David G4EBT
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Default Re: 'Red Nose Day' for a Heathkit probe!

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Originally Posted by factory View Post
There are also UNEF (extra fine) threads, including 1/4" x 32TPI, the thread angle is slighty different, 60° instead of 55° for ME thread.

David
Thanks for that David - who knows, UNEF might well have been the correct thread, especially if it's favoured by the Americans, but with M.E. being so close, maybe they're near enough to each other to be virtually interchangeable? Until now, I've only been familiar with UNC (coarse) & UNF (fine). I didn't know there was UNEF. Hence, through this little project I'm all the wiser!

Thanks also to Jeremy and Hugo for reading the thread and for their kind comments.
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Old 4th Jul 2018, 8:38 pm   #7
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Default Re: 'Red Nose Day' for a Heathkit probe!

On a plastic widget I doubt it matters much if the thread is a bit loose or a bit tight. The cap doesn't need to be torqued down to the limit for the material/thread.......
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Old 4th Jul 2018, 9:07 pm   #8
factory
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Default Re: 'Red Nose Day' for a Heathkit probe!

I'll be honest I remembered UNEF but had to search for the sizes, as I only keep an edited scan/copy of the UNC/UNF thread chart on the wall in the shed. The chart gets a lot of use, both for repairing vintage US made electronics & miniature O&R engines (very off topic for the forum). I think I will be looking in that book again to do a scan of the UNEF chart as it may be useful.

The UN (Unified National) threads are also known as AN (American National), which is what they are listed under in my old book.

I do agree that the slight difference is unlikely to cause any problems with the new plastic probe nose, also it's possibly easier to find M.E. taps in the UK if they are related to the Model Engineer magazine, although I haven't checked that.

David
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Old 4th Jul 2018, 9:54 pm   #9
David G4EBT
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Default Re: 'Red Nose Day' for a Heathkit probe!

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Originally Posted by Herald1360 View Post
On a plastic widget I doubt it matters much if the thread is a bit loose or a bit tight. The cap doesn't need to be torqued down to the limit for the material/thread.......
It actually seemed spot on Chris, and just like the original one - neither loose nor tight.
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Old 5th Jul 2018, 4:34 am   #10
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Default Re: 'Red Nose Day' for a Heathkit probe!

Quote:
Originally Posted by jeremy_pdx View Post
As I have experience using 3d software, I've come across people who have attempted to 3d-print the nose cone. However, your process certainly seems to have had excellent results! Perhaps it's time I learned to use a lathe...
You have raised an interesting question. David's machining work reminded me of these replacement feet, this ebay reference is just for the images to show what I'm talking about:

https://www.ebay.com/itm/Tektronix-4...IAAOSwLVZVs~DX


They are lathe machined replacement feet for the 465-75 scope series. They are also of a harder type of plastic to that commonly used on 3D printers. There are some 3D printed replica 465 feet too.

But its fair to say, I think, that machined items beat 3D printed ones for surface finish and often durability too. I think David's example also demonstrates this point well. But it is also an art to learn machining different materials and its more time consuming than whipping something up with the 3D printer. The investment in hardware is similar though comparing a small lathe to a low range 3D printer.
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Old 5th Jul 2018, 8:48 am   #11
David G4EBT
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Default Re: 'Red Nose Day' for a Heathkit probe!

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Originally Posted by Argus25 View Post
You have raised an interesting question. David's machining work reminded me of these replacement feet, this ebay reference is just for the images to show what I'm talking about:

https://www.ebay.com/itm/Tektronix-4...IAAOSwLVZVs~DX


They are lathe machined replacement feet for the 465-75 scope series. They are also of a harder type of plastic to that commonly used on 3D printers. There are some 3D printed replica 465 feet too.

But its fair to say, I think, that machined items beat 3D printed ones for surface finish and often durability too. I think David's example also demonstrates this point well. But it is also an art to learn machining different materials and its more time consuming than whipping something up with the 3D printer. The investment in hardware is similar though comparing a small lathe to a low range 3D printer.
Those are almost certainly turned from Acetal, Delrin or something very similar. It isn't cheap - in the UK enough material to turn four of those feet would cost around £10.00. There's quite a lot of turning involved and whilst a CNC lathe would turn them quite quickly, to turn them manually would involve quite a lot of stopping and starting of the lathe to take measurements. (It's one thing making four items that are 'similar' to each other - it's quite another matter to make four that are identical). He must enjoy turning them, because the price doesn't reflect the time involved.

As to 3-D printers, I've seen really expensive ones in use at the Science Museum in London, and whilst they can create fantastic shapes, they all seem to have 'striations' on the surface rather than a smooth glossy finish. Great for functional parts where the finish isn't important, but not so great where the cosmetic aspect is a key requirement. That said, these remarks are based on limited experience.

Given how long 3-D printers have been around, and how the prices have fallen, they seem to have been slow to take off. Maybe in part, that's due to the software aspects in programming the printer to do as we wish it to. That would certainly be my downfall!
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Old 5th Jul 2018, 9:20 am   #12
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Default Re: 'Red Nose Day' for a Heathkit probe!

A great job David. I wish I had the space and knowledge to have a lathe. I have a 3D printer but although printing screw threads is possible, it is beyond my ability to draw in the cad software which is the tricky part. Depending on the material used you can achieve very good quality prints. Acetone vapour will allow you to achieve a shiny surface post printing which gets rid of the ridges. I tend to use abs mainly which can be sanded back with wet and dry paper then polished to a high shine with plastic polish.

I always enjoy reading your posts and I hope you are fully mended soon. Keep up the great work.

Regards

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Old 5th Jul 2018, 10:06 am   #13
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Default Re: 'Red Nose Day' for a Heathkit probe!

I'm another member who finds a small lathe very useful for vintage radio, etc, repairs. When my late father retired, he offered to buy me a cheap car. I chose a lathe instead (and I still can't drive...). I think I made the right choice.

A lathe makes some repairs very easy, how ever little experience you have with one. The only downside is the price and having somewhere to put it.

As for the difference between ME and UNEF threads, I don't think the thread angle/profile will make any difference on something like this. Another (off-topic) example, the camera tripod thread is desribed as 1/4" BSW (or 3/8" BSW for larger cameras) in the UK and 1/4"-20 UNC (or 3/8"-16 UNC) in the States. They have the same pitches (20 tpi and 16 tpi respectively), just different thread angles. But I've never had a problem putting any camera onto any tripod.

I have a (probably unfounded) concern about 3D printing. And it's that the final object is made from plastic filament that is melted and fused together. I wonder how strong it is, whether it might come apart again. At least with turning/milling you start with a solid block of material.
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