How to make knurling

Ever since the dawn of engineering time (well okay slight exaggeration there) engineers have produced a surface dubbed knurling to enable human hands to get a better grip on slippery metallic surfaces. It's usually produced by using a special cutter that applies pressure onto the metal surface and is moved along and rotated around the circular surface to produce a diamond shaped profile.

What we would need to do first is to create the template for our knurling, let's say for example we know that our object to be knurled is about 90mm long and 60mm in diameter . There are a couple of things we need to prepare for first now. Knurling is "fairly" standard for most human sized objects as the knurl is designed for our skin on our hands to grip well. A typical knurl diamond is approximately 1.5mm long by approx 1mm high.

so knurling is a squashed diamond as opposed to say a equally dimensioned square rotated 45 degrees

In our example there will be 90/1.5 for the length which equals 60 knurls

we then need to work out the diameter which would be PI*D (PI*60mm(diameter)) which equals 188.5

Now we first need to make our diamond. Do this using the disc tool in one view port with sides set to 4 and then size accordingly in the numeric panel like so:

whilst we are here we can take care of the diamond's shape by first creating a bevel with these settings:

then use the value tool to make the new polygon conform to Y=Zero and Z=Zero

your polygon will still be selected so importantly delete it now! Then merge points to eliminate 3 points. You now have the basis for a knurl. Now that we have done this the hard way - here is the easy way to do it ;)

Pick the cone tool and use these settings:

that was a bit easier eh?

Oh and don't forget to DELETE that back facing 4 sided polygon if you use the cone tool!

now we use the clone tool:

Before we do anything else now we have to crucially do a special clone operation to fill in what would otherwise be eventual gaps in our knurling operations and we need to use the clone tool to replicate our row upwards and offset slightly like this:

The next thing we do is to select these polygons at either end of our clone array and merge them:

then select the point right at the end and delete it - this gives us the final result of a flat edge to our end knurls

Remember also that on our other end we have created one extra knurl that we don't need as a result of our offset clone operation - so on the other end first completely delete this knurl:

and then take care of the end as before:

you will find now that if you measure it it will be exactly 90mm long just as we want it to be.

the next step is to use the clone tool again this time for the vertical (or circumferal replications). our circumference measurement was 188.5 and the height of our two rows of knurls is now 1.5mm. However to replicate our knurls properly we need to clone them at a distance of 1mm. Every time we clone our two rows by a 1mm step we create a total extra height of the same amount - 1mm. If we take away 1.5 mm from our circumference we are left with 187mm and that gives us how many times we need to clone our two rows.

and as we can see when the result is measured we have exact dimensions!

we now have Our knurling template - the final step to complete it all is to use the bend tool.

first MERGE all the points -You may need to use a tolerance merge of say about 5-10 microns to make sure you get them all if necessary.

the bend tool is a tricky tool to get right. We have to bear something in mind here - we need to bend this object around a full 360 degrees BUT we need the knurls to meet when we have finished. The way to do this is to select points and bend just them - we need to ensure that our bend operation starts at Y=Zero but that our bottom most points sit at Y= -0.5mm or 500 um.

for example..

Our bend settings need to then be carefully calculated and set up we want our start to be Y=Zero and our end to be Y=188mm

with these set we then bend our object carefully in the top view port by hand. It's a very tricky process (and you can't even use the CTRL key to constrain your cursor movement) but be careful and the end result will be this. No matter how frustrated you get with the bend tool - bear with it.

as you have no doubt observed making knurls is an awkward but ultimately rewarding process. Now that we have the principle of it committed to memory lets take a look a adapting it to a real world example.

we're going to make one of these (minus the thread!). These knobs are roughly 20-25mm in diameter - I'm going to assume a 25mm diameter for the purposes of this tutorial.

First Ii will start with my diamond shape in modeler and make a clone array of 10 of them down the Z axis like so.

same as outlined previously I will then make my second row above that using the methods we have gone through during this tutorial for an end result long these lines:

as before we now have a object comprising of two rows at 1.5 mm in height. Our knurled Knob is assumed to be a diameter of 25mm which gives us a circumference of (PI*25) 78.5mm . 78.5-1.5= 77 and that gives us our clone figure.

As before when we have our template we carefully set it up for the bend process which will give us this result when we are finished.

Now pop to a new layer - put that object into a background layer and create the basis for your Knob using the background as a guide. We are going to be making a Boolean cutting tool so we start off with something along these lines which we create using the pen tool..

then lathe this polygon to get this result:

all the faces should be facing inward - so ensure you FLIP them. Now back to the knurled object and cap off those end pieces in preparation for our Boolean operation like so(hint - use the select loop tool)

finally perform the Boolean operation - when it's complete merge points using a tolerance of say 25-50um and then eliminate single and double sided polygons and admire the end result:

now in retrospect it looks like our knurls were a but too small for this object in that case - use what you have learned to do the same with larger diamonds knurls to start with :)

Here endeth the lesson!

tutorial copyright 2005 - F.Passaro

P.S. I also have several other methods of doing this knurling effect that rely on plug ins like KW Edge Smoother and Vertibevel - maybe in the future I will add to the tutorial


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