Topics

7A13 Knob


Nathan Johnson
 

The main volts/div knob on one of my 7A13s has been destroyed. Sphere and
Qservice don't seem to have it, and none on the 'bay.
Anyone else cross that bridge already?
I was thinking about drawing it up and sending to shapeways for 3D
printing.
Anybody have experience with this? My thought was to draw it minus the
metal
collar, and glue the old collar in place with JB Weld. Any brighter ideas?
Nathan KK4REY

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Tom Gardner
 

On 09/03/16 12:32, Nathan Johnson jdownj@gmail.com [TekScopes] wrote:

The main volts/div knob on one of my 7A13s has been destroyed. Sphere and
Qservice don't seem to have it, and none on the 'bay.
Anyone else cross that bridge already?
I was thinking about drawing it up and sending to shapeways for 3D
printing.
Anybody have experience with this? My thought was to draw it minus the
metal
collar, and glue the old collar in place with JB Weld. Any brighter ideas?
No answers, but if/when I have to do that I'll probably
use OpenSCAD to create the shape. I like the way you
can parameterise designs based around adding/subtracting
simple shapes.

What would you use, and why?


James Brines
 

I have tried this with an epoxy resin and I will say that you most assuredly need the metal inner collar. What is really the hard part is modeling the parts so that there is sufficient space for the collar to fit but not so much that you cant effectively attach them together. I am still trying to find a solution to this myself.


Tom Gardner
 

On 09/03/16 19:28, leetmaster4004@yahoo.com [TekScopes] wrote:

I have tried this with an epoxy resin and I will say that you most assuredly
need the metal inner collar. What is really the hard part is modeling the
parts so that there is sufficient space for the collar to fit but not so much
that you cant effectively attach them together. I am still trying to find a
solution to this myself.
Perhaps if you have a slightly deformable material, e.g.
nylon, then this might help...
1) start with a knob where its internal diameter is the
same as the collar's outer diameter
2) "modulate" that internal diameter with a shallow
(?0.25mm?) sawtooth along the axis of the knob
3) when pushing onto the metal collar, the "proud"
teeth become an interference fit with the collar, and
are pushed outwards into the "negative" half of the
sawtooth
4) if the plastic isn't too thick, then the whole knob might
even expand to accommodate the interference gap.

If I was to try that, I would have a 3D model with
parameters specifying the degree of interference.
Then either submit several separate models for
fabbing, or combine them into a single model joined
by sprues.


James Brines
 

I suspect you could create a replacement of a softer material and simply insert the metal ring but it would have to be hardened after in some way. The amount of torque applied to the metal ring is surprising with the selection knobs and I doubt any soft material would have the ability to handle that torque in its soft state.

I've coincided 3D printing but I suspect it runs into the same issues as simply casting something as I don't know of a way to properly position the metal ring in the print area to a degree precise enough where one could print material directly to it so you would still have to insert the ring just as if you had casted something.


Mike McGinn
 

Hi,

On 03/09/2016 04:37 PM, leetmaster4004@yahoo.com [TekScopes] wrote:


I suspect you could create a replacement of a softer material and simply
insert the metal ring but it would have to be hardened after in some
way. The amount of torque applied to the metal ring is surprising with
the selection knobs and I doubt any soft material would have the ability
to handle that torque in its soft state.

I've coincided 3D printing but I suspect it runs into the same issues as
simply casting something as I don't know of a way to properly position
the metal ring in the print area to a degree precise enough where one
could print material directly to it so you would still have to insert
the ring just as if you had casted something.
I wonder if they originally cooled the metal before inserting it in the
plastic. I know they do this when press fitting some auto engine parts.

Miek

--
Mike McGinn KD2CNU
President, UU Congregation at Rock Tavern
More kidneys than eyes ** Registered Linux User 377849


Nathan Johnson
 

I suspect that the metal ring was inserted while the plastic was still warm, but
that the drilling/tapping of the setscrew may have been done after it was
inserted in the plastic. But I could be really wrong. I'm looking at 3D
printing, as well as CNC machining the entire part out of aluminum.
Nathan KK4REY

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On Thu, Mar 10, 2016 at 00:43, Mike McGinn mikemcginn@mcginnweb.net [TekScopes]
<TekScopes@yahoogroups.com> wrote:
Hi,

On 03/09/2016 04:37 PM, leetmaster4004@yahoo.com [TekScopes] wrote:


I suspect you could create a replacement of a softer material and simply
insert the metal ring but it would have to be hardened after in some
way. The amount of torque applied to the metal ring is surprising with
the selection knobs and I doubt any soft material would have the ability
to handle that torque in its soft state.

I've coincided 3D printing but I suspect it runs into the same issues as
simply casting something as I don't know of a way to properly position
the metal ring in the print area to a degree precise enough where one
could print material directly to it so you would still have to insert
the ring just as if you had casted something.
I wonder if they originally cooled the metal before inserting it in the
plastic. I know they do this when press fitting some auto engine parts.

Miek

--
Mike McGinn KD2CNU
President, UU Congregation at Rock Tavern
More kidneys than eyes ** Registered Linux User 377849




[Non-text portions of this message have been removed]


Brian Bloom
 

What are the chances of heating up the metal insert with a propane torch on a metal rod and pressing it into the fabricated or 3d printed knob?

Granted it may make the set screws a bit tight due to expansion, but if you were to put heat proof grease on the threads first, then stick the knob in the fridge or freezer for a while... I have no idea if that would work - just a thought.


Brian Bloom
 

Should have proof-read that....

What I mean is to lock the insert on a steel rod, then heat it up with a propane or Mapp gas torch. (solder torch used for copper plumbing)


Nathan Johnson
 

That would almost surely work with a cast/molded part... The million $ question
is how various 3D printed materials would behave in that application.
I drew something up quick n dirty in OpenSCAD and I'm going to send it out to
try Shapeways and maybe another service. I'm sending a good original to a guy
who does CNC work. My impression is that not many knobs were made as spares, and
that most knobs for sale come at the expense of a complete plugin. Combining the
fact that this knob is unique to the 7A13(Not quite, I think it's used on the
calibrator controls on the 7904 non-A), the fact that the 7A13 is slightly rare,
and slightly more expensive contributes to why there aren't many around.
Nathan KK4REY

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On Thu, Mar 10, 2016 at 01:57, analogaddict013@yahoo.com [TekScopes]
<TekScopes@yahoogroups.com> wrote:
Should have proof-read that....

What I mean is to lock the insert on a steel rod, then heat it up with a propane
or Mapp gas torch. (solder torch used for copper plumbing)

[Non-text portions of this message have been removed]





[Non-text portions of this message have been removed]


Brian Bloom
 


Nathan Johnson
 

That sure looks like it. How did you find it? Searched "Tektronix knob" and
waded through all the results? Thanks!
Nathan KK4REY

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On Fri, Mar 11, 2016 at 05:11, analogaddict013@yahoo.com [TekScopes]
<TekScopes@yahoogroups.com> wrote:
Does this happen to be the knobby you seek?


http://www.ebay.com/itm/Tektronix-Knob-Gray-New-inch-diameter-366-XXXX-selector-flute-/281723250176?hash=item419803a600:g:xcsAAOSw~ZdVfje5
http://www.ebay.com/itm/Tektronix-Knob-Gray-New-inch-diameter-366-XXXX-selector-flute-/281723250176?hash=item419803a600:g:xcsAAOSw~ZdVfje5







[Non-text portions of this message have been removed]


stefan_trethan
 

It'll work fine with the thermoplastic 3D printing material.
I have inserted nuts before to get a stronger thread, just used a
soldering iron to heat them up.

With something large and thin like a knob, I would recommend to have
cold water nearby so you can set the plastic as soon as the insert is
in place. Otherwise the stored heat will transfer from the metal into
the plastic and possibly deform it on the outside.

I don't see why you couldn't make it a slip fit and epoxy it in.

ST

On Thu, Mar 10, 2016 at 12:11 AM, Nathan Johnson jdownj@gmail.com
[TekScopes] <TekScopes@yahoogroups.com> wrote:
That would almost surely work with a cast/molded part... The million $ question
is how various 3D printed materials would behave in that application.
I drew something up quick n dirty in OpenSCAD and I'm going to send it out to
try Shapeways and maybe another service. I'm sending a good original to a guy
who does CNC work. My impression is that not many knobs were made as spares, and
that most knobs for sale come at the expense of a complete plugin. Combining the
fact that this knob is unique to the 7A13(Not quite, I think it's used on the
calibrator controls on the 7904 non-A), the fact that the 7A13 is slightly rare,
and slightly more expensive contributes to why there aren't many around.
Nathan KK4REY


Brian Bloom
 

:
That sure looks like it. How did you find it? Searched "Tektronix knob" and
waded through all the results? Thanks!
Nathan KK4REY

.........
I'm actually that guy that stalks the Tektronix listings religiously. It came up in the "ending soonest" category. I hope it's the one you're looking for!


 

The first thing I would try is knurling the outside of the metal
insert and using epoxy or hobby grade cyanoacrylate glue to set it
within the plastic. Ideally the fit should be an interference fit to
provide for proper centering.

I am tempted to start an index of which plug-ins use which knobs.

On Fri, 11 Mar 2016 07:24:21 +0100, you wrote:

It'll work fine with the thermoplastic 3D printing material.
I have inserted nuts before to get a stronger thread, just used a
soldering iron to heat them up.

With something large and thin like a knob, I would recommend to have
cold water nearby so you can set the plastic as soon as the insert is
in place. Otherwise the stored heat will transfer from the metal into
the plastic and possibly deform it on the outside.

I don't see why you couldn't make it a slip fit and epoxy it in.

ST


Malcolm Hunter
 

On 11 March 2016 at 06:29, analogaddict013@yahoo.com [TekScopes] <
TekScopes@yahoogroups.com> wrote:

That sure looks like it. How did you find it? Searched "Tektronix knob"
and
waded through all the results? Thanks!
Nathan KK4REY

.........
I'm actually that guy that stalks the Tektronix listings religiously. It
came up in the "ending soonest" category. I hope it's the one you're
looking for!
‚ÄčThat's how I found a cheap 465 front cover - they only specified
"Tektronix cover" and gave its dimensions.

Malcolm ‚Äč


[Non-text portions of this message have been removed]


 

Does this happen to be the knobby you seek?
Unfortunately, it isn't.

The correct knob does not have the black insert at the front. Instead, there's empty space in that area to allow the pull-out variable attenuation button with its white ring to "sink in" at least 5 mm, probably more like 7-8 mm.

The knob on Ebay looks like what's used on e.g. the 1481 Waveform Monitor's front, at the right side.

Raymond


Brian Bloom
 

Does this happen to be the knobby you seek?
>>
>Unfortunately, it isn't.

>The correct knob does not have the black insert at the front. Instead, there's empty space in that area to >allow the pull-out variable attenuation button with its white ring to "sink in" at least 5 mm, probably more like >7-8 mm.

>The knob on Ebay looks like what's used on e.g. the 1481 Waveform Monitor's front, at the right side.

>Raymond

Well that's a bummer.

I wonder if it's just a variation of the same knob, or if there is some other difference such as the shaft diameter..
If the only difference is the black plastic insert... well..
If I was the person needing that knob, I would buy this one and cut the black insert out.
The only problem is that I would have to physically have the knob in order to make sure that it'll fit the 7A13 in the first place.

Maybe the seller wouldn't mind breaking out a caliper and taking some measurements, though...?

*Actually, this knob appears to be the very same knob that is used on the 454 for V/div control. If it is, I have ones on my 454A that I could measure so we'll know if it's the same apart from the insert*


Making ones own replacement knobs may well end up being a very useful project for many people, though. Tek replacement knobs are bound to disappear at some point.

A database of replacement knobs would be useful... then part B of that database project could be adding 3D scans of good knobs so people can print off or machine replacements.

-Brian


 

The problem with the "replacement" knob on the 'bay is that the Al insert is more in front (from the faceplate) than with the original. The hex fastening screw is as well. I'm not at all convinced that it (the inner knob) would fit, even after removing the plastic black insert. I have both one of those knobs (I think). I'll be in my lab again early next week and can try if it fits my 7A13.


Raymond


Nathan Johnson
 

I'm going to buy the used knob from the member who offered it above, and then
try to make several Tek knobs.
A coworker with a lathe is making metal inserts, and with some decent CAD, I'll
probably send the files to Shapeways. Probably won't be anything like perfect
looking, but functional.
Nathan KK4REY

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On Sat, Mar 12, 2016 at 15:29, hewpatek@gmail.com [TekScopes]
<TekScopes@yahoogroups.com> wrote:
The problem with the "replacement" knob on the 'bay is that the Al insert is
more in front (from the faceplate) than with the original. The hex fastening
screw is as well. I'm not at all convinced that it (the inner knob) would fit,
even after removing the plastic black insert. I have both one of those knobs (I
think). I'll be in my lab again early next week and can try if it fits my 7A13.


Raymond

[Non-text portions of this message have been removed]