# 1340GT Metric Thread Pitches



## parshal (Jan 13, 2020)

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?


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## davidpbest (Jan 13, 2020)

Here's another version I did a couple years ago.   I wonder if they agree.   LOL


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## davidpbest (Jan 13, 2020)

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.


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## parshal (Jan 13, 2020)

Thanks David.  I'll compare and contrast the two.

PM is sending me the 35 tooth gear.  They said they had them available.


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## parshal (Jan 13, 2020)

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.


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## davidpbest (Jan 14, 2020)

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.


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## middle.road (Jan 14, 2020)

These should be uploaded to the *Downloads *reference area so that they would be easily available in the future.


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## davidpbest (Jan 14, 2020)

middle.road said:


> These should be uploaded to the *Downloads *reference area so that they would be easily available in the future.


If you know how to do that, then great - be my guest.   Here's the latest and corrected version.


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## parshal (Jan 14, 2020)

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.


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## davidpbest (Jan 14, 2020)

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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## middle.road (Jan 14, 2020)

I would put them under the category 'calculators or metalworking'
Even though you guys did them up for a PM1340 there's info in them I for instance can use on my 1440G clone.









						Calculators For Metalworking
					

Computer calculator programs.




					www.hobby-machinist.com


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## davidpbest (Jan 14, 2020)

middle.road said:


> I would put them under the category 'calculators or metalworking'
> Even though you guys did them up for a PM1340 there's info in them I for instance can use on my 1440G clone.
> 
> 
> ...


You have my permission to put it there.


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## Larry42 (Jan 14, 2020)

David, "and I'm single." No wonder you have a nice set of equipment! My wife has never complained about what I spend on equipment. On time she did give me one of those "looks" when I told her I had just spent $85K on a used router. 
5.486 seems close enough for most threading.


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## middle.road (Jan 14, 2020)

-=- Done...


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## Larry42 (Jan 14, 2020)

I tried to view Calculators for metalworking but got this message "You do not have permission to view this page"
Why?


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## middle.road (Jan 14, 2020)

Larry42 said:


> I tried to view Calculators for metalworking but got this message "You do not have permission to view this page"
> Why?


Sorry about that.
you need to be a donating member to be able to download resources.







Latest info on membership can be found here:








						Updated Membership Levels, Permissions and Site Features
					

As of today, January 11th, we have made some updates and changes to the Hobby Machinist membership levels, permissions and upgraded some features. There are lots of changes to the site so please read carefully. I will schedule an online chat session for later tonight so people have a chance for...




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## davidpbest (Jan 15, 2020)

I dunno if 5.486 pitch is close enough.   Here's the comparison of a 5.5mm pitch nut (hashed) with a 5.486 pitch shaft inside it - for 10 thread lengths.






Tighter fit than any wife I've known.   LOL


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## parshal (Jan 15, 2020)

I wonder what change gear would be needed to actually get a 5.5.


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## mksj (Jan 15, 2020)

You would need a 44 to 127 on the headstock pair and 120 to 32 on the gearbox pair.I do quite a bit of metric threading but rarely do a pitch more than 2.0. If you review the attached chart, I still recommend feeding the headstock output to the 127 tooth gear and the gearbox to the 120 tooth transposing gear. The only time one would need to feed to the 120 gear and output to the 127 tooth gear would be for a metric 0.700 pitch.


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## parshal (Jan 15, 2020)

Thanks Mark.  It looks like .35 and .45 are also only available with 120 on the top.


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