I need to model a 50mm X 1.10 pitch internal thread

[fishtruk]

I don't see this available in the various dropdowns. It's a one off (camera adapter for my telescope thread).

I'm assuming I have to get the calculator and crunch the numbers.

If there is an easier way that would help a lot.

Thanks!

[fishtruk]

OK, so I crunched the numbers and did a ramp in 2D contour. Problem is the ramp angle kept being 20% too shallow. I did and redid the numbers. No luck.

I used Simulate and observed the actual Z depth in 1 revolution and increased the ramp angle according to the ratio of intended to observed Z per revolution and I can make this part now.

I have no idea why that ramp angle discrepancy exists.

[HughesTooling · Accepted solution]

Why not use Thread, it has a pitch setting.

Mark

[fishtruk]

Thanks Mark, I looked at it. The feature should be sized to the major diameter it looks like in model I suppose.

In 2D contour with Ramp adjusted to the angle is what I used. It was odd. It accepted a ramp angle with 4 digits after the point without issue, but the resulting ramp angle was not what I entered. As I said, I used Simulate and noted the actual Z depth per revolution, then corrected the Ramp angle accordingly.

I know my trig. This I don't understand, unless the nightshift put a Pentium I in my machine 😉

Looks like a bug to me.

[HughesTooling]

Where's the ramp angle calculated, probably centre of the cutter not the contact point or did you take that into account?

Mark

[fishtruk]

Thanks Mark,

Here's the file. The 2nd op is the threading. The thread is actually 2-24, not metric as I first thought.

The Ramp angle there works. The computed angle should be .3827 degrees. For a 24 tpi pitch Simulate should show -.041666 in Z per revolution, it didn't so I corrected it proportionally, tried Simulate again and it was correct, so I cut it. I took it nervously home to see if it fit, and it did. Luck!  I'd have to remake it if it was too tight because I didn't put any registration mark on it to align for a recut of the threads.

[fishtruk]

To clarify, I lied to Fusion. It wouldn't accept a threading tool for a Contour so I said it was an end mill with the diameter of my threading tool.

[HughesTooling]

Just remembered there's an easy way to do this, set the maximum ramp step to the pitch and the angle can be anything as long as it bigger than the helix angle.

Mark

[fishtruk]

I don't understand, I set the maximum ramp stepdown to 1 inch knowing my thread is only .3 inches so the ramp would be continuous, making the thread.

[HughesTooling]

Have you tried with the settings above? The max ramp step is the max depth of cut and the angle is adjusted to match, so all you need to do is enter the pitch as the max ramp step.

Mark

[fishtruk]

I see my error now. I'll give your idea a try. The part is done and accepted by the customer (me), so I'll have to make another blank for that.

[HughesTooling · Accepted solution]

Didn't have Fusion running earlier but I've attached the file. The max ramp step is quite useful, if you have a long ramp and set the angle to 2° you could end up taking a very deep cut, so you can set it to say 5mm and the ramp is adjusted so you never take more than 5mm.

Also did some checking and you had your trig wrong. Here you can see the helix angle for the od of the thread is 0.3799 and the helix angle for the centre of the cutter is 0.46334879. Not sure how you checked the toolpath but I used the simulation with points enabled and measured between points,

Mark

[fishtruk]

my bad. shame on me!