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 »

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?
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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 »

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 »

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 »

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 »

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 »

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
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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 »

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

Post by GlennW »

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

Post by rmac »

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 »

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?
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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 »

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

Post by GlennW »

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