Thread issue

[mckeehan86live]

Hello everyone. I am pretty stuck on this model of mine and could use some guidance please. I have a hole in my model that is 86mm in diameter. I need to model threads into it but can't seem to/lack the knowledge of how to model in the ones I need. I usually have no issues modeling threads but this one stumps me. Like I said, I have a 86mm hole, the part that needs to screw into it my my craftsman pitch gauge tells me 11tpi. I cannot seem to find either a conversion or the right type of thread to make this work. Any info is appreciated! Thank you.

  

Attached are screenshots of my model and the filter that I need to fit it.

[jhackney1972]

Please attach your model and make sure it is clear where the thread goes and what the thread should be.  If you do not know how to attach your Fusion 360 model follow these easy steps. Open the model in Fusion 360, select the File menu, then Export and save as a F3D or F3Z file to your hard drive. Then use the Attachments section, of a forum post, to attach it.

[mckeehan86live]

Thank you. I have no idea how I missed that part. The highlighted hole on the bottom is where my threads need to be.

[MRWakefield]

I'm guessing you have one of the filters in your possession (hence the 11TPI) so can you measure the diameter of the thread?

[TheCADWhisperer]

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@mckeehan86live wrote:

my craftsman pitch gauge tells me 11tpi.

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Do you have a metric pitch gauge too?

The only inch pitch close to that in 3.75-3.875 inch diameter is 10 or 12 TPI.

What is this diameter (in inch or metric (I can convert))?

Also - a link to a site of the manufacture/model or sale of the filter might help.

[mckeehan86live]

Thanks for the reply. It is 86mm.

[mckeehan86live]

Hi, thanks for replying. I don't have a metric gauge but it is 86mm.

[MRWakefield]

The nearest standard thread I can find around that size and TPI is G3 (3" BSP) but it could well be a special or a standard that I haven't found yet. The G3 thread has a major diameter of 87.88mm so is nearly 2mm larger than you've measured. How confident are you with your 86mm? Could it be nearer 88?

[mckeehan86live]

I just took it to home depot and it only fits in a 3" electrical conduit.

[MRWakefield]

Ok, that could be useful information. I've done a quick search and 3" BSP seems to be quite common on plastic pipes here in the UK, I don't know whether that's the same in the USA. I've got to go out so don't have the time right now to investigate further. If you haven't found a solution by the time I'm back I'll look into it further then.

[mckeehan86live]

Thank you. It seems Fusion only goes up to 2"bsp. However, it looks like it converts to 87.88 iso metric threading. I'll try that. I truly appreciate your help!

[MRWakefield · Accepted solution]

Ah yes, you're right! The ISO Pipe Threads in F360 cover a larger range so that definitely looks like it's worth a try.

[MRWakefield]

I just thought I'd give you a bit of a heads-up in case you're going to 3D print your mating part. Please ignore me if you're aware of any of this.

When 3D printing threads you usually need to adjust the diameter(s) of the thread to compensate for the inherent inaccuracies of the process. The most common trick is to offset the major, minor and one of the flanks by a certain amount. This works just fine for a 60° trapezoidal thread but because the BSP thread is Whitworth form (55° with radiused crest and root) this trick doesn't work. What you'll need to do is adjust the actual figures in the XML thread file. However, rather than edit the Fusion 360 thread file you'd be better off creating a custom file to suit your printer. If you need any help with that just shout!

[RufusToad]

Hi I do not want to highjack here but you stated,

What you'll need to do is adjust the actual figures in the XML thread file. However, rather than edit the Fusion 360 thread file you'd be better off creating a custom file to suit your printer. If you need any help with that just shout!

I am wondering if you have a link or know how I might get help getting into this XML file and creating a new one? This seems a bit cumbersome.

[jhackney1972]

In this Forum post, in @MRWakefield signature you will find the link to his custom thread creation utility.  Could this be what you are looking for?

[RufusToad]

Hi John,

I think that might be it. I am sorry I am not real computer savvy at this stuff. I was originally looking for the actual 360 Thread files but I think this app gets those for you. 

I just downloaded his Thread Utility and will try to do a bit more research as I believe this writes the script as well as syncs it? I will try to understand it more tomorrow. Thanks for your help!!

[MRWakefield]

Thanks @jhackney1972 for guiding @RufusToad to my application.

The application should be pretty easy to work out but there is a rough guide document which should get you going. If you have any problems after reading the thread and the rough guide just ask.

[HughesTooling]

Another option for BSP threads is to use a non uniform scale to increase the diameter without affecting the pitch. If you are doing a lot of BSP threads then creating a XML file will probably be a good idea but if you only need it occasionally scaling might be quicker.

So first create a ring the correct length but with a smaller OD than your part will end up with and add the modeled thread. Because the scale will depend on the diameter you need to to work out what will give the correct offset. So in the attached file with a 3/4 BSP thread the core diameter is 24.338mm so to add 0.1mm offset per side set the scale to 24.538 / 24.338.

Edit got the scale wrong so updated file to 24.538 / 24.338

Then create the rest of the part and consume the threaded ring. Note to add a chamfer to BSP threads you'll need to use a revolve cut.

Mark