Extrude form at an angle?

[David George 1Participant @davidgeorge1]

Alibre Atom drawing program.  I am trying to draw a gear 16 tooth on a 3/4″ blank diamiter. I have drawn the blank and the tooth profile and can extrude the profile which is repeated 16 times to make the gear. The problem I have is that I need to extrude the profile at 4 degrees as the gear has to match the angle of the thread on a leadscrew. I can’t see how to extrude the tooth shape, tried creating a plane at 4 degrees or is there another way of drawing a gear with the profile at an angle.

David

[David JuppParticipant @davidjupp51506]

You need to use helical boss to apply a twist whilst extruding the profile. There is also a utilities add-in available which will generate gears in Atom3D, I’ll check in the morning if it includes helical gears.

Another option is to sketch a second (rotated) profile and loft between sketches.

I also recall an example from the Alibre user forum that uses just the inbuilt equation editor to build gears.

[JasonBModerator @jasonb]

As David says draw one tooth and use a helical cut. Depending on how accurate you want to draw it the sketch should be on a plane that is angled 90deg to the Helix angle otherwise you won’t get a true shape.

The script in Alibre only does spur gears, F360 has “FM Gear” which will do helical. From the one below you can see that the profile along the edge of the gear is very different to the involute and that is why the sketch should be at an angle. This one was to be 3D printed as a pattern so needed to be accurate.

[JasonBModerator @jasonb]

One half way option is to use Alibre’s gear script to get the profile, modify it slightly and then use as the sketch to apply the helical cut to, comes out like this, as 4deg there won’t be much change in the profile so it may do if it is just a gear for a thread indicator. ( not the exact pitch on my example you will need to work that out.)

[David JuppParticipant @davidjupp51506]

Alibre Script is not available in Atom3D – so that one isn’t an option.

This utility does create helical gears and can be used with Atom3D

https://www.alibre.com/forum/index.php?resources/utilities-for-alibre.125/

 

This set of part templates work entirely within Alibre, and should be OK in Atom3D – edit the values in the Equation Editor to modify the gear to your purpose.

https://www.alibre.com/forum/index.php?threads/gear-templates.23316/post-155801

These are the work of others, I claim no credit for them.

[NealebParticipant @nealeb]

I have done exactly the same thing to generate 3D models for printing alternative ratio leadscrew indicator gears for a metric leadscrew. I actually used F360 starting with a gear profile sketch and then doing a helical extrude to produce the gear. I realise that that might not apply to Alibre but I wanted to assure the OP that despite theoretical tooth form errors, in this low-load, low-speed application it makes no difference – my printed helical gears work very nicely.

[JasonB]

On JasonB Said:

From the one below you can see that the profile along the edge of the gear is very different to the involute and that is why the sketch should be at an angle.

The profile is still an involute function, just projected on a plane that is perpendicular to the axis of the gear.

This has been an interesting thread. I have been somewhat out of date with the functionality of the helical extrude function in Alibre. It now seems that it will be fairly easy to generate an accurate 3D helical gear model so I can try machining one on the 4-axis CNC mill rather than old school on the manual mills.

Andrew

[JasonBModerator @jasonb]

This is how I did that example in my earlier post.

Used teh gear Script in Alibre Pro to generate the gear which is does by extruding this profile.

I then copied and modified that by trimming off the crests and joining the valleys. I tried it with just one tooth but it did not like that so did the lot.

Finally did the helical cut with that profile. Ideally the profile should be pasted onto an angled plane and then you will get the true shape, more important if you have say a 90deg pair with both PCDs the same.

It’s certainly one of the things it would be nice to have the 4th axis for as there are a few engines I’d like to make that have helical timing gears, luckily I was given a pair for the engine I’m working on at the moment which I believe were one of several sets done as a special order by HPC 20 odd years ago.

[JasonB]

On JasonB Said:

 

Ideally the profile should be pasted onto an angled plane…

Helical gears have the concept of normal pitch and transverse pitch  (and normal/transverse PA). Which one is correct depends on how you sweep the profile along the helix.

If you keep the profile square to the axis of the gear, I think you can use the normal pitch to generate the profile. If you map the profile normal to the helix, you need to use the transverse numbers (though it is possible I have that back to front).

All the helical gear texts deal with this: when you reach the part when you are dividing by the cubed cosine of the helix angle, you are in the right place.

The script that generates the profile in the screenshot above is not too sophisticated as it has sharp corners in the tooth roots. That is easier to compute but not good engineering.

[DC31k]

On DC31k Said:

…though it is possible I have that back to front…

Correct, it’s the other way round.

I didn’t know there was a gear script in Alibre. I am using Alibre Expert so will have to look for it.

Andrew

[David JuppParticipant @davidjupp51506]

The gear script provided with Alibre Design is less flexible than it might be.  The inputs aren’t those you might want – I have some modified versions which accept different input combinations.

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