Creo Elements - More gears (yes more) spur gears, helical gears and herringbone gears

So I've done a couple of blog posts now on making gears, first by creating just a section of the gear. then replicating it around an axis
And by creating a big gear with a single tooth. then replicating it around an axis


Now I'll look at a third and final way of creating a spur gear, and show how this is also the way you need to make a helical gear, (with diagonal teeth) and a herringbone gear, (with herringbone -like little arrows teeth)

Even though this tutorial will show now to create all the gear types it's worth looking at the others, mostly because I'm only introducing the tools used once. so the lessons do build on top of each other, also, it's good to know more than one way of getting a part made.




We'll imagine the same scenario as the last post, that we have two axles 50mm apart and want two gears to link them.

The gears mesh together, so again we'll have the raise teeth of the gear protruding the 26mm radius, and the reciprocating grove in the gear at 24mm.

This time draw a circle that's 24mm.
pull the circle into a cylinder 20mm tall.

(you can pull to any height, but with the maths used later I'm using 20mm)

Now create a new work plane on that cylinder, draw guide lines for your tooth profile to be created, again at an angle of 5 degrees.

Once again draw a tooth profile onto the edge of the cylinder, your tooth crown should be 26mm from the centre.
Delete your guidelines that you've drawn and you're left with a single tooth on a cylinder again.

now clearly you can once again pull that tooth to 20mm height and replicate with rotational symetry, (like we did in the last two posts) to make another spur gear.

But this time I'm going to make a helical gear.

Select the helix add tool

Select the axis as the centre of the cylinder part.

Now the pitch and turns are related.

Our part is 20mm high, therefore if we select 20 for the pitch and 1 for the turn, we'll get a single complete turn of the tooth profile all the way around the part.

But we want a tooth that progresses about 5 degrees around the part.

To progress 5 degrees around the part we need 5/360 turns (roughly 0.01)
and to keep the same pitch to turn ration (to make the tooth reach the top of the gear) we need the pitch to change to 20/0.01 = 2000

Now we need to mirror the part to create all the teeth.

since each tooth takes up 5 degrees we'll mirror 72 times, at an angle of 5 degrees.
Giving us a helical gear.

Now imagine that we want a steeper angle on those teeth.
go back to the part where there is just the outline of a single tooth ready to be added as a helix.

now imaging that we want the tooth to extend 20 degrees around the gear.
we need figure our the turns first.

360/20 =~0.04

then we need to figure out the pitch,
20 (gear height) / 0.04 (turns) = 500

Once again, use the rotational mirror tool to make 72 teeth with an angle of 5 degrees about an axis that is the centre of the gear.

HerringBone
Alternatively.
Before mirroring the tooth rotationally, to create a herringbone gear mirror the tooth along the face first.

now you'll have noticed that mirroring creates a lot of individual parts. We're going to apply the rotational symmetry to the herringbone gear that we are creating, so we want to group the parts into a single assembally so that we only need to perform the mirror opperation once.

fter creating the new assembaly (a1) drag the two parts (p1 and p1.1) into the assembly.

Now double click a1 you'll see the edge lines of the whole assembly are highlighted.

And apply the radial mirror tool to extend the gear teeth over the whole gear.

Creo-Elements Tutorial - More gear making

Proof as ever that there is more than one way to skin a cat!

So last week I looked at a way to create a gear on Creo Elements, the approach was to create a segment of gear, that made up a specific fraction of the total gear, then design the teeth profile for a single tooth and then mirror that around a circle to create a whole gear.

Of course you could start with a circle and draw out the gear as a 2d shape and then extrude it all as one part, or you could make a cylinder and then use the pull tool to extrude the teeth in the cylinder.

The method that I looked at last week is good for designing gears, and other parts that have circular symmetry.

But as ever, there is more than one way to skin a cat.

So now I'm going to cover a new way to create spur gears.

This time the scenario that the part will be designed for is as follows.
I have two axles that are 50mm apart.
I need to link these with two gears, the gears should be the same size such that there is no change in speed of torque in the transmission.

Now the first thing to consider is that if these were rollers they'd both be 50mm diameter, touch and transmit force by friction alone, but as these are spur gears they need to have teeth that mesh into each other.


So we start by drawing a circle that's 50mm in diameter. (25mm radius)
then we'll draw another circle inside that with a 24mm radius and finally a circle around the outside with a 26mm radius.

These circles will form and guidelines for the gear teeth, (which will extend out some 1mm over the 25mm radius and nest into pockets 1mm inside of that 25mm radius on it's mating gear.

Now we'll add some guide lines for the amount of space our gear teeth will take.
so drawn a line from the centre of the circle along the 0 degrees line, then another on the 5 degrees line.

Now zoom in on where you will be making that tooth.

draw appropriate guide lines so that you'll have some points that will snap.
(join the points where you lines on 0 and 5 degrees cross the circle, then halve those lines again. this will form five points 0, 25% 50% 75% 100%, at each circle guideline.

Now use either the line tool, or the radius tool to create a tooth profile.

Now delete all your guidelines inside the outer circle, (leave the circle so that you can find the centre for the arc you'll create next.

Now using the three point arc tool, draw an arc from the base point of the gear tooth, in a wide arc.

Now delete your remaining construction lines so you have a 1 tooth gear.

Pull this single tooth gear to a cylinder.

Now use the rotational mirror tool to create a rotational symmetry to fill on the remaining teeth.

Now you have another gear.

Creo-Elements tutorial -Making gears

So I thought it might be time for another kind of lets teach something blog post.

So,

Making gears with Creo Elements

So I'm going to design an actual part (that I will be using in the creation of my own variant of 3d printer, (I have an idea in my head for this at the moment).

The pulley that I'm going to print now will need to accept T2.5 belt, (5mm thick) and will need to fit over a standard skate bearing (608Z)

So lets have a look at what that actually means.
First we'll have a look at the skate bearing.

These have an outer diameter of 22mm

This means that my pulley wheel must have a hole in it that is 11mm radius.

Next we look at the specification of t2.5 belt.

Basically, any point in the belt to the same point on it's adjacent tooth is 2.5mm.
Each peak is 1mm, each trough is 1mm, there is a slope to the teeth that accounts for the remaining 0.5mm, (a 0.25mm slope)

However, on the pulley I won't put the slope in, I'll leave a sharp angle to allow the belt to bend.

To we're looking at a 1mm crown, and a 1.5mm grove on the t2.5 pulley.
Now we need to figure out the outside diameter of the pulley.

Start by deciding at least how big it must be.

The hole in the middle is 11mm.
We want at least 1mm over the width of this bearing. so we say that the pulley must have a radius of at least a few mm more than this.

Now lets work out the circumference.

14*2 = 32 * pi =88.116
so the outside circumference would be 88.116mm.

I'll round that up to 90mm circumference.
that give me

90/2.5 teeth = 36
each tooth has an angle of 360/36 = 10 degrees

If my circumference is 90, then my radius must be
90/pi / 2 = 14.29mm

I'm going to create a 14.3mm Radius T2.5 pulley wheel, with an 11mm hole in the centre.


So start by drawing a single line that's 14.3mm long on zero degrees.
then a second line 14.3mm long on ten degrees.

Now draw a line 1mm coming into the part, toward the other line.

Then a line that goes towards the centre of the part at a perpendicular angle, that's 0.7mm long (the height of a T2.5 tooth.

finally draw a line directly to the opposite line.

This won't be exactly 1.5mm in length as it's shortened by being closer to the centre of the pulley

now delete the line on zero and redraw to the correct size.

Now you have one thirty sixth of your pulley wheel.

Use the pull tool to make the gear segment 5.5mm tall, (the intended belt width is 5mm, so this adds some space for fit.

You now have a slice of gear.


Next you need to select the structure tab,
pull down the copy part options and select radial copy.

You'll need to copy, 36 times, (there are 36 teeth)
with the axis set at the centre of the pulley
and the angle of each segment is 10 degrees

Press ok and a new gear is produced.

Now delete the work plane.
Now select the circle tool and click on the gear to create a new work plane,

Drag the circle from the centre of the gear to a 15mm radius.

Use the pull tool to make the top of the gear 0.75mm high

repeat on the other side.

Now use the chamfer tool set to 0.5mm to add a slight grove to the pulley wheel edges, this will held reseat the belt if the alignment is slightly out.

now use the circle tool to create a circle with an 11mm radius, and use the pull tool to pull to a depth of -7mm to remove the centre of the pulley wheel.

Now we have a pulley wheel.
It fits over a standard skate bearing.
It has 36 teeth at a T2.5 pitch.

(this will be an idler pulley in the drive system)


This can of course be used to create spur gears as well as pulley wheels, sprockets for use with chain drives, all you need to do is work out the appropriate angle and make your tooth profile fit the job then replicate it.

You can also use this method for making other repeating shapes, for example, spoked wheels, clutch plates, fan assemblies. etc

Creo Elements: Direct Modeling Express

Creo elements is a program that is built on a product that I used a long time ago called pro-engineer, it's a fast and pretty feature rich CAD program, that is used for 3D and 2D computer aided design (CAD for short) -also, it's free!

During the time that I'm waiting for my new printer to arrive I'm going to be re-familiarising myself with using CAD software ready so that I can make things on my printer when it gets here.

I can't see 3D CAD lessons being a regular thing like the electronics and code lessons, because it's just one piece of software. there is only so much that can be shared.

Calibration cube.
One of the first things that should be printed on any 3D printer is an object that you can use to calibrate the printer and settings in the software.

Having your extruder running too fast and squishing out too much plastic will lead to your layers being too fat, and plastic being squashed outwards meaning that your parts appear bigged in out edges and smaller where holes are concerned.

First, open the software, you are presented with a screen that has a blue diamond on it. that's actually a rectangle that's representing your build plane, it's got some perspective about it.

Now since you are going to be building a cube, select the rectangle tool.

Click anywhere on your build platform, and drag out a square, the small numbers that appear at the
edges tell you how big the square is.

when you get to 20 x 20 stop, and click again.

now the square turns black.
 go to the menu bar at the top and select pull

In the options box there is a field called distance, type 20 into this box and press the green tick at the top.

A grey cube now appears.

Click at the dark blue edge of the work-plane so that it is highlighted brown, now press the delete key you're left with a cube in the centre of the screen.

Now you want to turn your cube into a tube.
so click on the rectangle tool again, and the click on the top face of the cube, (anywhere on the top face)

the cube now rotates so that you're looking at the very top, zooms so that the face fills the screen, and generates a new work plane for you on the axis that you want.

move the mouse around, you'll find that as you;re moving around co-ordinates appear that tell you how far from the edge you are, or how far from the middle.

The nozzle on the solidoodle is 0.3mm wide, therefore is we create a wall thickness much more than this, the machine will try to do two passes and make a double thickness wall, but it won't be twice as thick exactly, so we will miss some vital data regarding extrusion width which will be used to help calibrate the flow settings.

click on the box 0.3mm from one corner, and drag a new square to the opposite corner.

Now select the pull tool again.This time, instead of wanting to pull the object up from teh work plane towards you, you want to pull the shape you've drawn down through the object that you've drawn.

In the distance box type -20 to create a tube, or -19 to create an open box that has a bottom face.

I'll cover how to actually use the box to calibrate a printer in a post when I've actually got the printer.