tap drill/bore for 2-1/4"-8 tpi thread

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wally318
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tap drill/bore for 2-1/4"-8 tpi thread

Post by wally318 » Mon Jun 07, 2021 6:14 pm

Hello all.
I need to put a 2-1/4-8 tpi thread into a blank back plate at a 2-1/4" major dia. is it still a .125" thread allowance as on a 1"-8 tpi
or does the thread allowance grow with the diameter?
Or alternatively can anyone give me the bore dia from a 2-1/4-8 chuck back plate or face plate?

Harold_V
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Re: tap drill/bore for 2-1/4"-8 tpi thread

Post by Harold_V » Tue Jun 08, 2021 2:01 am

Minor diameter for a class 2B 2¼"-8 thread is 2.1147"/2.1297".

Happy to help, but you can find this kind of information in Machinery's Handbook. Very useful, especially older editions, those that do not make reference to CNC operations. I regularly use a 15th edition, and was given a much newer one. Each one offers different information.

No, I am not even remotely connected to the publisher of that book, nor do I have stock in the company.

H
Wise people talk because they have something to say. Fools talk because they have to say something.

stephenc
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Re: tap drill/bore for 2-1/4"-8 tpi thread

Post by stephenc » Tue Jun 08, 2021 10:13 am

Ditto on machinery's handbook .
Way back when I first got my lathe I made a collet chuck for it . not having an accurate way to measure the inside threads or the spindle register I made three things that have come in handy once or twice .

First was a ring gauge for the spindle register. Next was a thread gauge for the spindle threads .
And lastly using the first two items I made a copy of the spindle end itself .

A little extra work saved a lot of guessing and finger crossing

wally318
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Re: tap drill/bore for 2-1/4"-8 tpi thread

Post by wally318 » Tue Jun 08, 2021 11:18 pm

Thanks Harold.
I checked google and couldn't readily find a chart with sizes that large.
I guess I've come to depend on google a bit too much.
I have a 17th ed. and just haven't been using it that much lately.
The back plate is for a 6 inch 3 jaw that I'm going to mount to a 5C horz/vertical indexer.
I forgot that there was a thread on nose protector.
I just noticed it the minor dia. is 2.120 vs 2.242 major dia. on the spindle.

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GlennW
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Re: tap drill/bore for 2-1/4"-8 tpi thread

Post by GlennW » Wed Jun 09, 2021 6:45 am

2.250-8.jpg
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rmac
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Re: tap drill/bore for 2-1/4"-8 tpi thread

Post by rmac » Wed Jun 09, 2021 8:04 am

Glenn: Is that thread calculator online somewhere? If so, I bet I'm not the only one who would like to have a link to it.

-- Russell Mac

Harold_V
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Re: tap drill/bore for 2-1/4"-8 tpi thread

Post by Harold_V » Wed Jun 09, 2021 2:58 pm

rmac wrote:
Wed Jun 09, 2021 8:04 am
I bet I'm not the only one who would like to have a link to it.
-- Russell Mac
True, that. It would be exceedingly handy to have a source that combines all the information.

H
Wise people talk because they have something to say. Fools talk because they have to say something.

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GlennW
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Re: tap drill/bore for 2-1/4"-8 tpi thread

Post by GlennW » Thu Jun 10, 2021 6:22 am

A bit pricey for the average home shop type, but if you do a lot of threading using thread wires and of different type threads, it is quite handy.

It also helps eliminate those Dyslexia errors sometimes encountered in calculating this stuff from the info in Machinery's Handbook. :wink:

https://closetolerancesoftware.com/METhreadPal.html
Glenn

Operating machines is perfectly safe......until you forget how dangerous it really is!

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rmac
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Re: tap drill/bore for 2-1/4"-8 tpi thread

Post by rmac » Thu Jun 10, 2021 7:54 am

Thanks, Glenn. I agree that eighty bucks would be a little spendy for occasional use.

I googled a little bit for something similar, web-based, and free. Assuming that it gives correct results, this looks pretty good:

http://theoreticalmachinist.com/Threads ... erial.aspx

There also appears to be a number of other interesting calculators and charts and whatnot on the same site.

-- Russell Mac

Patio
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Re: tap drill/bore for 2-1/4"-8 tpi thread

Post by Patio » Fri Jun 11, 2021 12:07 am

Is the ME thread pal, a downloadable program or cloud ware? Do I need to be connected to the internet to use it, or can I load it on a shop computer?
Live for the moment!
Prepare for tomorrow!
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Harold_V
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Re: tap drill/bore for 2-1/4"-8 tpi thread

Post by Harold_V » Fri Jun 11, 2021 1:57 am

GlennW wrote:
Thu Jun 10, 2021 6:22 am
It also helps eliminate those Dyslexia errors sometimes encountered in calculating this stuff from the info in Machinery's Handbook. :wink:
That is the one negative aspect of the schedules in the handbook. It is VERY easy to grab the wrong information. I avoid that by placing a six inch rule under the line of information that I desire. Than I double check my figures before making chips. Not so important now that I'm just doing home projects, but it sure was when I was making parts for my customers. I have to say, the handbook served me very well for years, along with the multiple H28 handbooks.

H
Wise people talk because they have something to say. Fools talk because they have to say something.

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GlennW
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Re: tap drill/bore for 2-1/4"-8 tpi thread

Post by GlennW » Fri Jun 11, 2021 9:58 am

Harold_V wrote:
Fri Jun 11, 2021 1:57 am
Than I double check my figures before making chips.
I usually went with the two out of three that agreed...
Glenn

Operating machines is perfectly safe......until you forget how dangerous it really is!

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