1340GT Metric Thread Pitches

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parshal

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I had the occasion this weekend to cut a .8 metric thread. I found a couple threads here with .pdf and .xls attachments with all the various pitches using change gears. I don't have a computer near my lathe and those docs were too large to print so I 'simplified' them and made the attached. I think it covers all the common metric threads. i realize there are more combinations but this should get me where I need to be for a quick reference.

I need to verify I copied everything over correctly. Did I miss anything?
 

Attachments

  • 1340GT Metric Change Gears.pdf
    6.8 KB · Views: 123
Here's another version I did a couple years ago. I wonder if they agree. LOL
 
When I went through this in 2017, it became clear to a few of us that you can't get to an M4 thread pitch of 0.70 without a 35 tooth gear. I was able to buy that gear from Precision Matthews but I think it was special order from the factory.
 
Thanks David. I'll compare and contrast the two.

PM is sending me the 35 tooth gear. They said they had them available.
 
OK, I went through both our sheets. I like the way yours shows the pitch on each side of the sheet. I added another two columns on mine and added yours as another option. I did find I had an error on pitch 3.

On 3.5 yours shows A4 for the gear box. Both the reference sheets I used show that as A6. You may want to double-check that yours is correct.

I've updated the attachment in the original post to include the most current.

Thanks for sending your sheet along. It shows I wasn't completely off in lala land.

On edit, I found the closest to 5.5 is 5.486. I have no idea if that's too far from 5.5 to be effective, though.
 
I double checked my source info, and for 3.5 pitch, there are two ways to get that pitch - assuming the calculations I'm using are correct (Mark Jacobs did all the initial work on my source data):

35/120 & 127/30 at B1
35/120 & 127/40 at A6

The combination for 3.5 pitch listed on your original post is 35/127 & 120/40 at A6, but according to my calculations that produces a pitch of 3.920. I'll PM you my spreadsheet and have a look.

I don't see a way to get precisely to a 5.5 pitch unless yet another gear is introduced. With the gears we have, the closest I see are 5.526 and 5.486.
 
These should be uploaded to the Downloads reference area so that they would be easily available in the future.
 
middle.road said:
These should be uploaded to the Downloads reference area so that they would be easily available in the future.
Click to expand...
If you know how to do that, then great - be my guest. Here's the latest and corrected version.
 

Attachments

  • PM1340 Thread Gear Chart Rev3 Corrected.pdf
    27.8 KB · Views: 167
Last edited:
After PMs with David I've replaced the attachment my original post with my latest version. I was going to post it in the downloads but I have no idea what category to use.
 
I updated my version as well and deleted the one in dispute. I had the same problem as Brian - there isn't an obvious place in the Downloads area to put this information - nothing related to Precision Matthews equipment is in the Download area.
 
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