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Replacement Knobs, Feet and Fittings for Test Equipment

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As part of a mod to replace the factory original high flow high noise fan on a HP 54600 series oscilloscope, I made some clip-on front feet risers to provide more space, and more air flow for the very low noise, lower flow Noctua fan I fitted.
I designed and 3D printed two spacer feet that simply slide over the factory molded front feet and lock in place.  The feet lift the scope a few millimeters to increase the space for exhaust cooling air to escape.  The only exit for cooling air is a grill in the base of the enclosure. 

Others have done the Noctua fan mod without raising the oscilloscope, so the feet mod is definitely optional with questionable and unmeasured benefit.  I could have done a before and after measurement of fan current to detect a change in air flow, but I didn't.

As always, I try and make my mods look like they are factory made. The new feet are close to the factory colour so it is not obvious the feet are fitted.  No screws, no holes, no modifications to the enclosure and all completely reversible.  The feet just slide on and lock into place.    They will not slide off with just lateral force (ie. normal use).

I included a shallow relief in the foot for gluing on a piece of rubber roofing material.    The rubber will provide some extra grip and reduce noise transmission by at least a few femtodecibles.

Just in case someone wants to do the same mod, I have also attached the 3D file of the design.    I printed with PETG. 

On a scale from brilliant to useless, this mod definitely leans to the useless side, but I got to design and make something.  Fitting the Noctua fan was definitely a good thing to do.  The fan is barely audible.

Anyone know how to get a 3D model for one of these?

I am sure you have tried a search of the internet for the .stl or .step or .iges file format using the Manufacturer and Model number of the instrument this came from.  This works if either the manufacturer has released their design files to the internet, or if someone else needed the part, modeled it and donated the result.  My personal success rate in these searches is low, but it works often enough to be worth the attempt.

You have several options if that fails.  Find a local engineering firm and contract them to make the model (expensive and slow).  Or find a nearby student or hobby person willing to to do it for free (maybe at a maker space or local electronics club meeting).  Or get micrometer and calipers and make detail measurements of the part and post it them here with a plea for someone to turn them into a model.  Identifying what this came from may help in getting interest in doing this.  Or purchase/rent/borrow one of the 3D scanners, generate a point cloud of the part and use associated software to turn it into a model.  I don't think this approach would be very successful on this part because of the small size and potentially the need to duplicate internal geometry on the base of the part.

Or you can get one of the free modeling programs, and learn to do it yourself.  Fusion 360, FreeCad, Blender and others are among the most popular programs.  Learning FreeCAD  and doing this on my first knob, an item not too dissimilar to your part only took a few days.  This approach is beneficial in implementing the corrective iterations that are almost always needed in this type of project.  It is almost impossible to get the measurements for some of the critical dimensions so a bit of cut and try is often needed.

Thanks. Yes, I've searched the net and Thingiverse. It would seem I've found a forumite willing to lend a hand ;-)

All my attempts to get into something like FreeCad have failed. At some point I realise I'll never "really" be good at it and I don't need another skill that I "kinda" can do ;-)


--- Quote from: Ice-Tea on October 04, 2023, 08:37:14 am ---Thanks. Yes, I've searched the net and Thingiverse. It would seem I've found a forumite willing to lend a hand ;-)

All my attempts to get into something like FreeCad have failed. At some point I realise I'll never "really" be good at it and I don't need another skill that I "kinda" can do ;-)

--- End quote ---

I would encourage you to give another try to FreeCad.  I won't pretend that I am doing modeling right. My sons, who both do mechanical modeling professionally sneer at my efforts, but doing simple things comes fairly easy.  And even "kinda" doing like I do has proved extremely useful.  Having a specific project aids me tremendously in learning, you may find it the same.  When I run into a block trying to accomplish something I look for an Online tutorial and it is usually cleared up quickly.

Basically your knob appears to be a truncated cone with a hollow square rod for attachment to whatever it is going on to.  Using the Parts Workbench these are canned shapes.

A big aid can be if you can figure out the manufacturer of the switch or pot this knob attaches to (or a similar product).  These 3D files are much more readily obtainable, and can be subtracted from a simple knob model to get the attachment right.

Why don't you post some key measurements of your knob (diameter at top and bottom) and measurements of the base.  I (or somebody more competent) might get motivated to do at least a rough model to get you started.

As another path, you might search this forum and eBay for the instrument that this knob comes from.  On eBay you might find a non-working one sold for parts that meets your budget, while on the forums you might find someone who has a parts donor.

Finally, if your need is only for functionality and you don't care about appearance you can take some scrap plastic and with a drill, some jewelers files and an exacto knife carve something that does the job.  I have done this on a couple of occasions. 


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