Help me design - Custom Size threads for anodizing

[JimDawson]

That was my thought. I tend to be a numbers guy, so I was curious how exactly to specify "just a bit loose".

I tend to work to exact measurements in my home shop and I'd like to make all the parts interchangeable if for no other reason than good practice.

That's kind of like ''normal tightness'' I honestly don't know what the numbers might be. In our case, we make a few hundred of the ''nuts'' first (all the same, done on a CNC mill) then test fit the threaded end of the tube on a few random parts. The tubes are also done on a CNC lathe, so once set, they are all the same. It basically should spin on easily with 2 fingers.

Assuming you can make one or the other part all the same, then interchangeability should not be a problem once you get the fit as you want it. If you are doing this on manual equipment, then make all of the rings first. Then you can use the rings to test fit the external threads. Once you find the tightest ring, then use that as your thread gauge. Go for a fit that easily spins onto the external thread, note the numbers on the dials, and make the rest of the parts exactly like the first.

 

[extropic]

That was my thought. I tend to be a numbers guy, so I was curious how exactly to specify "just a bit loose".

I tend to work to exact measurements in my home shop and I'd like to make all the parts interchangeable if for no other reason than good practice.

After thinking more about your original question, I think the answer lies in a science project that involves strict controls on the actual anodizing process used plus accurate measurement of the as machined parts vs the after anodize parts. I think that the threads are not going to respond to etch/anodize exactly the way larger surface area features would. There are some conditions that apply to the 67/33 ratio and I don't know what they are so I don't know if they are precisely applicable to your threads. When faced with the kind of science project I described, I try to reevaluate and consider design alternatives that will avoid the need for the science project. Just to be clear, I appreciate you being a "numbers guy" more than the questions that go on for 1/2 a page of description without providing a single graphic, quantity or unit of measure.

 

[MrWhoopee]

Nobody else suggested the obvious answer:
Ask your anodizer.

 

[mattthemuppet2]

Whatever the anodizing thickness your asking for, add half that to the radius of all of it to the diameter of your part. The oxide layer grows out as much as it grows in.

If you want a specific pitch diameter, turn it to that minus the oxide layer thickness. Then after anodizing you should be at the right PD

 

[tq60]

Here is some CAD of the design.

The blue and black discs are polycarbonate and cut from the table top of the robotic bartender my buddies and I built years ago in college. There are windows through which WS2812B RGB LEDs shine (filled with resin to make them waterproof). The switch detects the presence of a glass to start the LEDs.


View attachment 414202

From the rear (end cap removed) you can the the custom PCB, a small low cost microcontroller to sequence the LEDs, and the switch. The yellow ring is a spacer to allow room for the wiring. The hole through the shell is for a USB cable (power and programming).

View attachment 414203

This section view shows the small lip on the edge of the shell that all the discs stack against. The highlighted blue part is the aluminum shell. The reduced diameter at the bottom is where the thread will be.

View attachment 414204

And the aluminum shell by itself. Not going to be an easy part to turn. Very thin walled. Need to make 8.

View attachment 414205

Looks good but...

It will get wet.

That switch will fail.

If these will be recharged often then some suggestions.

The devices used at restaurants for paging folks stack up and have charging coupling so as stacked on charger they charge.

You could do same or use wireless with a coil of wire, removes pathway for water.

For sensing presence of glass it can get interesting, just guessing but look at current PC mouse.

They have led and sensor in single device.

You could se one of these and figure out how the sensor side works, just look for a change in output.

When you place anything above it activates it.

Wave finger over it would work.

Completely sealed now.

Sent from my SM-G781V using Tapatalk

 

[macardoso]

Looks good but...

It will get wet.

That switch will fail.

If these will be recharged often then some suggestions.

The devices used at restaurants for paging folks stack up and have charging coupling so as stacked on charger they charge.

You could do same or use wireless with a coil of wire, removes pathway for water.

For sensing presence of glass it can get interesting, just guessing but look at current PC mouse.

They have led and sensor in single device.

You could se one of these and figure out how the sensor side works, just look for a change in output.

When you place anything above it activates it.

Wave finger over it would work.

Completely sealed now.

Sent from my SM-G781V using Tapatalk

Totally agreed. These are more nostalgia pieces for myself and my friends who I designed this with 10 years ago. We actually came up with a version 2 that was totally sealed and used a Time Of Flight (TOF) laser sensor to detect the glass.

The original machine was too big and heavy to keep around, so I am cutting it up to make these coasters as gifts.

Also in defense of the original design, the switch is waterproof and completely sealed to the top with epoxy.

 

[Weldingrod1]

Anodizing definitely makes your part grow! I've had O-ring clearances that became interference fits after anodizing both parts. I would do a sketch of the threads, mark the expansion, and work out the change in pitch diameter needed.

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[mmcmdl]

Anodizing is usually half in and half out . .001 would mean the part would grow .0005 per surface . So a diameter , . 001

Three times the thickness on a thread PD after trigging everything out .

 

[tq60]

Look up camera lenses as the filters and other items that screw on at face of camera are similar interface.

Maybe patent drawings or if lucky find some manufacturer prints from obsolete units.

Maybe look at companies that restore or modify equipment?

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[macardoso]

Talked to the anodizer. Growth of pitch diameter is 4x the coating growth (2x the coating thickness only for 50/50 "Hardcoat Type 3"). Coating thickness is ~67/33 for Type II. A 0.001" thickness will grow the part unilaterally in all dimensions by 0.0003". Holes will shrink by 0.0007" and bosses will expand by 0.0007".

Based on this information, my initial calculations will be perfect. I have 8 sets of these to make so this will not be a trivial operation.

I'm going to start with making a pair go-nogo gages for the internal thread. I'll make the NOGO with a undersized major diameter (to make sure the pitch diameter is checked) and a pitch diameter of 3.7794 (3.8156 over 0.0241 wires). The GO gage will be a pitch diameter of 3.7719 (3.8080 over 0.0241 wires).