Getting started designing a knob

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Steve76063
Posts: 33
Joined: Wed Feb 09, 2022 2:47 pm

Getting started designing a knob

Post by Steve76063 »

I've got a new project for my old (1972) car...printing a new AC knob as the old one is cracked...
I'm looking for suggestions on how best to get started (I'm still relatively new to FreeCAD having designed/printed about 4 projects). The items I' most curious about is :
1. the 'embossed' arrow on the face of the knob
2. the knurled grip around the circumference
3. the 'D' shaped hole in the back

Here's some pictures of the current knob - I'd like to reproduce it as closely as possible.
IMG_2629 (Large).JPG
IMG_2629 (Large).JPG (239.18 KiB) Viewed 2016 times
IMG_2628 (Large).JPG
IMG_2628 (Large).JPG (251.26 KiB) Viewed 2016 times
IMG_2627 (Large).JPG
IMG_2627 (Large).JPG (245.26 KiB) Viewed 2016 times
kisolre
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Re: Getting started designing a knob

Post by kisolre »

Dimension accordingly:
Attachments
Knob_kiss.FCStd
(115.75 KiB) Downloaded 43 times
Workshop_Notes
Posts: 590
Joined: Wed Sep 29, 2021 8:35 am

Re: Getting started designing a knob

Post by Workshop_Notes »

kisolre wrote: Fri May 06, 2022 10:36 pm Dimension accordingly:
Very nice, but it is differs somewhat from the original he wants to reproduce.

And when you are doing a restoration, facsimile is vital, not just something close.

The triangle on the top is just that, a single triangle sticking up not a triangular shaped recess going down.

The knurling is pointy and continuous not rounded and intermittant.
Workshop_Notes
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Joined: Wed Sep 29, 2021 8:35 am

Re: Getting started designing a knob

Post by Workshop_Notes »

Steve76063 wrote: Fri May 06, 2022 10:04 pm 1. the 'embossed' arrow on the face of the knob
2. the knurled grip around the circumference
3. the 'D' shaped hole in the back
I would start in PartDesign, sketching on the X-Y plane. Numbers below correspond with your own

1. Draw a single triangle on the X-Y plane, the correct size and distance from the origin. Change its attachment to the height of the knob and then pad it upwards.

3. Draw a circle centred on the origin. Constrain its diameter to the correct measurement. Draw a straight line parallel to one axis (horizontal or vertical constraint, offset distance to suit the 'stem' of the 'D'. Trim the line both ends using the circle. Once the main body of the knob is made, use this sketch to form a pocket the correct depth. This is the same as is done in the example file above.

2. You will have to count the number of points on the knurling and guess the angle (maybe 60 degrees). You can measure the OD of the knurl points. Use a calculator and geometry to work out the ID of the knurl inner points. Draw a polygon with twice the number of sides as the number of points, to suit the OD measurement. Draw another polygon, same number of sides but to suit ID measurement. Join alternate points on ID and OD polygon with a polyline.

One thing you might have to look at is the relative position of the 'D' and the arrow on the top (the clocking relationship between the two). You can import the 'D' sketch geometry into the arrow sketch and then change it to construction lines to help with this.
kisolre
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Re: Getting started designing a knob

Post by kisolre »

Workshop_Notes wrote: Sat May 07, 2022 6:12 am The triangle on the top is just that,
It looks like a colored recess to me from that picture. Any way it can easily be replaced with a Pad at the same place in the tree.
Workshop_Notes wrote: Sat May 07, 2022 6:12 am The knurling is pointy
And this again is just as easy as replacing the Pad with corresponding pocket and fixing the polar pattern to use that.
For orientation of the arrow just rotate its sketch around sketches Z axis the needed value.
The general design and steps are basically the same.
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Shalmeneser
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Location: Fr

Re: Getting started designing a knob

Post by Shalmeneser »

The Kisolre file is perfect for understanding the different steps.

You can use Image_Workbench. With good pictures (perpendicular to the object), you can rescale it to match the original dimensions and use it to copy dimensions. https://youtu.be/PMUxmlnYv1M?t=234
domad
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Re: Getting started designing a knob

Post by domad »

Steve76063 wrote: Fri May 06, 2022 10:04 pm .....
Hi Steve76063, greetings to the Community!

Given that we intend to give an idea of how to do it, attached an example of the many modeling possibilities or workflows offered by FreeCad.
The "Draft" and "Part" workbenches were used.
Since it was not possible to attach the complete file created with "Part Design", we attach the file containing the sketches (with the progressive steps indicated) that can be used as a "guide" for modeling.
The sketch used for knurling should be repositioned using as a reference a "shape binder" obtained from the edge of the revolution of sketch002.
Not being in possession of the real dimensions, obviously it will be necessary to redefine all the sketches indicating the right dimensions detectable by the physical model.
Obviously, everything can be improved and / or optimized.
Correction: step 3 (sketch004) is a "Pad" not a "Pocket", I apologize for the mistake.
Attachments
knob_sketch.FCStd
(12.37 KiB) Downloaded 27 times
knob_Part.FCStd
(610.97 KiB) Downloaded 22 times
knob_Part.png
knob_Part.png (239.54 KiB) Viewed 1775 times
knob_Sketc.png
knob_Sketc.png (85.11 KiB) Viewed 1775 times
Steve76063
Posts: 33
Joined: Wed Feb 09, 2022 2:47 pm

Re: Getting started designing a knob

Post by Steve76063 »

You guys are AMAZING :)

You've given me wonderful ideas to get my know printed, and I thank each and every one of you.
Steve76063
Posts: 33
Joined: Wed Feb 09, 2022 2:47 pm

Re: Getting started designing a knob

Post by Steve76063 »

kisolre wrote: Fri May 06, 2022 10:36 pm Dimension accordingly:
Thanks kisolre :) I took you model and modified it (dimensioned to match, and change the cylindrical bumps around the top to small triangular pockkets)...Here's a photo of my old knob and my new one :) Not perfect, but good enough for me.
IMG_2661.2.jpg
IMG_2661.2.jpg (689.12 KiB) Viewed 1167 times
kisolre
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Re: Getting started designing a knob

Post by kisolre »

@Steve76063 Glad I could help. I hope you learned something from that file :)
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