Author Topic: Searching for a 1/8" through-hole collet to repair a Tek sweep knob  (Read 1115 times)

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Offline Vince

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Hi everyone,


When I tightened the nut recessed in the center of the delayed sweep knob on my 2215 Tek scope... it broke ! The threaded part just sheared off. Now I can't use the knob anymore obviously...

Finding a complete knob is hard and expensive. Only one I found so far is 15 bucks from "Sphere", so add expensive shipping + customs to bring it to France/Europe, and I end up with a rather expensive collet...

So plan 'B' is  to buy some generic/non-Tek, new collet type knob, so I can salvage the collet from it and fit to my Tek knob. but even this is not so easy nor as cheap as I would like.

So... I am here asking if someone might know of a place that would sell collets, just the small collet part in itself, not a complete knob.. this way it would be logically dirt cheap, a  few cents each. I could therefore afford to buy lots of different sizes/models, hoping that one might fit the Tek knob.
So far I have been unable to find such a place...

I took measurements from the  broken collet :

- Type : "through-hole", tightened via a nut not a screw.
- Overall length : 8.6mm
- Length of the tapered/conical part : 6mm
- Max/base diameter of the conical part : 5mm
- Shaft diameter/inside diameter of the cone : imperial, 3.2mm or 1/8 "

Measurements from the knob, the cylindrical part where the collet fits : ID 5mm, length : 6.5mm.

Thanks for any address/link if any...  preferably in Europe so I can have affordable shipping and avoid customs. if not well, I will consider US sources as well, as long as it makes economical sense.

This post is my last hope !   ;D


« Last Edit: June 17, 2018, 05:43:38 am by Vince »
 

Offline floobydust

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Tektronix Oscilloscope Repair Part, 214-3159-00, 214315900 Collet maybe is the same part?

Tektronix front panel knobs suffer from dissimilar-metal bonding. The aluminium and (chrome-plated) steel interface corrodes and gets almost welded together.
Everybody breaks the collets or hex set-screws. I don't think WD-40 helps?

edit: WD-40 would surely attack the plastics. Maybe a toothpick and tiny drop only on the threads, to avoid calamity.
« Last Edit: June 20, 2018, 06:39:43 am by floobydust »
 
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Offline Vince

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Hi Floobydust,

Thanks for the link !  From the picture it looks like it won't fit the 2215 knob, so thanks Tek for making a trillion different parts for your sweep knobs... however it's interesting to see that this part bears a Tek part number ! ... because in the service manual, the exploded view does NOT detail the collet. It's only a complete knob assembly, take it or leave it.  So looks like it was enough of a problem that Tek sold these collets separately to service centers, hence gave them a part number of their own...

I guess it's worth e-mailing Qservice and Sphere in case they might have collets for a 2215, but just have not bothered listing it on their website because it's such a small part.

 

Offline Dubbie

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Just buy a lathe.

Free collets!
 

Offline Vince

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Yes sure, why didn't I think of that sooner, thanks, will go get that ! Can't be more than a couple bucks total, right  ? Otherwise it's not viable.

Just gimme a link and I will go buy one.


« Last Edit: June 17, 2018, 06:20:50 pm by Vince »
 

Offline tautech

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Do you have any Mens Shed, Maker groups or Model maker groups handy to you ?
Any old timer engineer or Fitter and Turner could spin one up with little fuss or bother.
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Offline Vince

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Hi Tautech,

I don't know, would have to go search for such people, don't have any address that springs to mind.
The part is quite small, doing an accurate job on something like this requires good eyes and tiny fingers... a tiny miniature lathe maybe.... and a good magnifying glass...

To be honest I am surprised that it's so difficult to sort this collet out, I feel like I am the first one in the world that runs into this problem, when clearly I am probably not ?! ...  :-\

Maybe you are right.. maybe it's so easy and cheap to get one made locally, that there is no" business" selling these little puppies on-line.

If so then surely someone will be able to get some made for me and ship them to me... if I can't find someone locally myself...

It's kinda frustrating to have a non-operable scope just because of such a tiny ridiculous piece of metal...  :(
 

Offline tautech

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Actually they are easily made on a big lathe if you know how.  ;)
ANY half decent engineer could spin that collet up, no sweat!

If you can find a hobbyist group local and they have some wise old guys as members, they'll know how frustrating it is to not be able to get a simple part and will most likely gladly help.
Check your local papers and ask around.
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Offline Vince

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Well you know better than I dod for sure.. so I will ask around... sure would be fun to manufacture a part for that scope... what wouldn't people do to restore these old Tek scopes !  ;D  We must be mad...
 

Offline Dubbie

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If you can’t find anyone to make you one, I will make one for you if you send me a proper dimensioned drawing. I can make it from aluminium or brass. Postage will be 10 euros. It might take me a week or three to get around to it.
 

Offline tautech

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If you can’t find anyone to make you one, I will make one for you if you send me a proper dimensioned drawing. I can make it from aluminium or brass. Postage will be 10 euros. It might take me a week or three to get around to it.
Vince probably won't have a thread pitch gauge so the OA dia of the nut could be all you need and then supply one that fits your work.
Nice gesture Dubbie.  :-+
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Offline Dubbie

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I’m hoping someone here might know the pitch. Looks like 1/4” UNC but I have no real clue about these scopes. Could be some weirdo thread for all I know
 

Offline Vince

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Re: Searching for a 1/8" through-hole collet to repair a Tek sweep knob
« Reply #12 on: June 17, 2018, 09:46:45 pm »
Hi dubbie,

Wow, you are my hero, an d a hero in the Euro zone as well, lucky me !  :)

I will try and make as accurate and comprehensive a drawing as I can...
I can also send you the knob and the two bits of the broken collet (and nut) to help you out... since these are of no use to me anyway, as it is...

Indeed I am too equipped for mechanical stuff, other than fixing my car... not the same scale  :(

I don't think we have to worry too much about the thread since we can just make a metric pitch, and I would just go buy a metric nut to go with it ! At least this part should be easy and cheap, I would think...
Problem is that what remains of the thread is soooo short (as you can see on the previous pictures), that it's hard to get a reliable/Accurate measurement.  Normally to measure a thread pitch (since I don't have gauges, I measure 10 "turns" with my calipers, and divide by 10... this is usually accurate enough.
So here I could only measure only one turn, so precision is catastrophic. My best attempt would indicate it's about 0.8mm. Way more than 0.5 and less than 1.0mm, at any rate.

OD of the thread looks to be 4,8mm.... rings a bell, this must 3/16" , since everything in this collet appears to be imperial size...
The flat nut that goes on it, requires a 1/4" socket, at least this bit is for sure..

Will try and do as accurate a drawing as I can, today maybe, and post it here.

If you can give me your address via a private message, I would send you the knob and all the bits and nut from the old collet, in a padded envelope.

No worries about the delay... I have plenty other stuff in the lab (and else where) to keep me busy...

For once I really ought to resume work on the restoration of my old Tektronix 317 scope... it too, requires me to order a bunch of imperial size spanners and wrenches for me to be able to remove all the parts that need to be removed

Aluminium or brass... I think brass is the best. Less prone to cracking than aluminium I think.

I have an old Nixie tube Frequency counter, 10 years older than this Tek scope... all the knobs have brass collets and they didn't break when I took them on and off.. it just inspired more confidence, somehow...

I guess ideally a collet would be "hybrid" : have a brass "cone" to grab the shaft, but a steel thread to that it's strong despite being extremely thin because of it being hollow. Obviously that would be too much trouble/cost, so it gets made from a soft metal all the way... and the user just has to be really, reaaaally careful not to over tighten it... which is sooo easy to do unfortunately ! Maybe these collets should come with a tiny torque wrench like high-end RF connectors do.. so that you don't over tighten them...  ;D
« Last Edit: June 17, 2018, 10:00:18 pm by Vince »
 

Offline Vince

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Re: Searching for a 1/8" through-hole collet to repair a Tek sweep knob
« Reply #13 on: June 18, 2018, 03:32:57 am »
Dubbie... just took some macro shots of the collet, and spent a little time measuring everything. Sorry for the CAD drawing... I hardly master CAD programs as I hardly ever have to use them. So, " Vince CAD (tm) " will have to do !   ;D Hope you can still understand it... I did learn industrial/technical drawing at school... 25 years ago ! Hopefully my drawing makes enough sense... if not, don't hesitate to ask !  The representation of the threaded part I know is not how I am supposed to draw it.. sorry.  Anyway, I carefully drew it to scale (20:1) on 5x5mm paper.

Sorry about the crappy colors in the pics as well : I did take the time to adjust the white balance of the camera, colors looked natural/nice in the LCD/ preview screen, was happy... but somehow the pictures that the camera recorded on the SD card, aren't true at all to what I saw in the preview LCD ! I hate cameras... 20 years on, and they are still crappy  :-\
I made a quick attempt at correcting the colour balance on the computer, but I am no expert... Still, I feel it's a bit better, short of being what it ought to be.

Pics don't lie about the manufacturing quality of this collet... it is.... "rough".. to say the least. "Atrocious" dare I say. Still... gets the job done I suppose !

FWIW, I noticed that the collet is actually... magnetic ! So, some ferrous material, no brass nor aluminium.
« Last Edit: June 18, 2018, 04:46:28 am by Vince »
 

Offline MadTux

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Re: Searching for a 1/8" through-hole collet to repair a Tek sweep knob
« Reply #14 on: June 18, 2018, 04:48:56 am »
Thread pitch might also be important. If it's metric, I could do it on my (shitty) lathe. For the slots I would have to buy a saw blade for the mill, though (something in the 10€ range).

Add:
With a bit of luck, I could turn a M5 thread down to 4.8mm and also cut a new steel nut on the rotary table on the mill.
Suitable saw blades:
https://www.ebay.de/itm/HSS-Metallsageblatt-Metallkreissageblatt-Kreissageblatt-Frasmaschine-63x0-8x16/202326253837?hash=item2f1b95a10d:g:dNcAAOSwdnZaHQxd
« Last Edit: June 18, 2018, 04:56:05 am by MadTux »
 

Offline Vince

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Re: Searching for a 1/8" through-hole collet to repair a Tek sweep knob
« Reply #15 on: June 18, 2018, 05:01:30 am »
For thread pitch as I said ealier... can't we just make a metric pitch and then I would just have to go buy a (box full probably) corresponding metric nut to go with it ?

There is not enough (length wise) thread for me to measure it accurately with my calipers. Best I can come up with would be to say it's between  0.5 and 1.0mm, and a bit closer to 1.0 than 0.5. Something like 0.8 or there abouts.... assuming that it's an imperial pitch, and that the nut takes a 1/4" wrench, can't we figure it out using some table of the most commonly used pitches ? I think it's safer to just make a common/wide spread metric pitch that I could easily source nuts for.

Don't go buy tools to do the slots (unless you want to have a go at it "for the fun"...), as it would not be economically viable for me, or barely...

I know crap about machining other than the rudiments of turning and milling I was taught at school when I was 15 or so...

But I guess at the very least one would need a 3.2mm drill bit.. this alone is not really your typical metric size ! :-/   3 or 3,5 is common, but 0.1 steps is not in everyone drawers I guess  :-\
For the outside diameter and tapered part, and threading, I guess a general purpose cutting blade could do it ?
Then a thing blade to cut the slots, as you said...
 

Offline floobydust

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Re: Searching for a 1/8" through-hole collet to repair a Tek sweep knob
« Reply #16 on: June 18, 2018, 05:22:39 am »
210-0583-00 NUT,PLAIN,HEX 0.25-32 Χ 0.312 INCH,BRS ; That would be 1/4" 32 thread per inch, 0.312" thick, brass. Seem reasonable?
 

Offline Vince

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Re: Searching for a 1/8" through-hole collet to repair a Tek sweep knob
« Reply #17 on: June 18, 2018, 05:32:04 am »
Floobydest I don't know how you manage to come up with Tek part numbers that aren't even listed in the service manual parts list, but I love you for that !  :-+

Yes, 32 thread per inch definitely sounds plausible, as this would be about 0.79mm , consistent with the ballpark figure I measured.

As for the 1/4", sounds great too, assuming it refers to the required spanner size... rahter than the diameter of the thread, which is 4.8mm (3/16"), not 1/4".
 

Offline floobydust

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Re: Searching for a 1/8" through-hole collet to repair a Tek sweep knob
« Reply #18 on: June 18, 2018, 05:48:39 am »
I was looking at the 2235 service manual May 1983, can't remember where I got it from, possibly ElectroTanya.

I look at service manuals within the product line, to find the newer versions.
The mid or high end models can have more info, and companies use the same parts within a lineup.
 

Offline Vince

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Re: Searching for a 1/8" through-hole collet to repair a Tek sweep knob
« Reply #19 on: June 18, 2018, 06:09:36 am »
Quite clever indeed... will try to remember it next time  ;D

Yeah the 2235 is essentially the same as the 2215, just faster.

Just downloaded the service manual for it... indeed this manual does detail the nut, unliek the 2215 manual, go figure.

They still don't detail the collet though, so it must be part of the knob assembly... which ought to be the same... but just because I am paranoid, I checked the part numbers and... they do NOT match ?!  :o

They are real close... only the very last digit differs :  2215 knob P/N is 366-1840-00  and the 2235 knob has -02 at the end.
IIRC when only the last 2 digits differ, it's only a minor change, and the parts are still interchangeable/compatible ?

The descriptions are identical any way.

So yeah, it's not too much of a gamble to assume that the nut/pitch indicated for the 2235 is the same as that used in the 2215...so let's go for that ! ;D

 

Offline tautech

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Re: Searching for a 1/8" through-hole collet to repair a Tek sweep knob
« Reply #20 on: June 18, 2018, 06:43:43 am »
Vince.
How thick is the nut, it looks like what's known in the trade as a half-nut, that is; ~ half the thickness of normal.
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Offline Dubbie

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Re: Searching for a 1/8" through-hole collet to repair a Tek sweep knob
« Reply #21 on: June 18, 2018, 06:53:20 am »
I'm not sure about that nut...

1/4" 32 tpi doesn't sound right for this collet. Nobody lists nuts by their spanner size, it's always the thread nominal diam.

Also because I live in a civilized country, I don't do much imperial work, so don't really have the tools.
Doing an M5 thread would suit me just fine. It should be easy for you to find nuts for also.

Thanks for the drawing. No need for a computer, it is perfect.
 

Offline Vince

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Re: Searching for a 1/8" through-hole collet to repair a Tek sweep knob
« Reply #22 on: June 18, 2018, 06:55:01 am »
Yes the nut is very thin as you saw in the pictures. I just measured it : 2.3mm thick.

"Half nut" .. alright I learned a new term today  :)
 

Offline Vince

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Re: Searching for a 1/8" through-hole collet to repair a Tek sweep knob
« Reply #23 on: June 18, 2018, 07:02:34 am »
I'm not sure about that nut...

1/4" 32 tpi doesn't sound right for this collet. Nobody lists nuts by their spanner size, it's always the thread nominal diam.

Also because I live in a civilized country, I don't do much imperial work, so don't really have the tools.
Doing an M5 thread would suit me just fine. It should be easy for you to find nuts for also.

Thanks for the drawing. No need for a computer, it is perfect.

OK for M5 but remind me : what size spanner will I need for the nut ? I could just about fit the 1/4" (6.35mm) wrench inside the knob. I tried my metric 7mm wrench and it did not fit... might fit if I grind it down a bit, though. No way I am going to grind my Facom tools though, but I could just get a cheap ass wrench and grind that down...  However if an M5 thread requires an 8mm nut, I think it will be way too big, no way I could get the wrench in there to tighten it, there would not be enough space left around the nut, assuming it could get into the knob recess at all...

I think there really isn't that much head room in this knob design ! Either 1/4", or 7mm, but not more...  :-\

Do you have a 3.2mm  drill bit to bore the inside of the collet all the way through ?
 

Offline tautech

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Re: Searching for a 1/8" through-hole collet to repair a Tek sweep knob
« Reply #24 on: June 18, 2018, 07:05:07 am »
According to my thread chart 32tpi on 3/16" shaft is UNF #10.

Below 1/4" UNF the sizes are numbered, 12, 10,8 6, 5............
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