[HELP] First thread turning.

[marfaguy]

First off I want to thank all the members here. You guys have been great in offering help and suggestions. Hopefully someday I can do the same.

So my next challenge/adventure is going to be threading. I've got a chunk of 1.25" cold rolled about 2.25" or so I want partially turn down then thread for 3/8-16 UNC thread. I assume (and think I've confirmed) that this means I want to turn down the threaded part to Major Dia 3/8" (maybe make that .3745?) and make the threading exit diameter .2983". Does that sound right? I'm going to assume for the moment that I've got that part at least workable but if I'm way off please let me know.

Here's the part where I'm a bit more shaky. Setting the dials and choosing the right change gears for tpi.
The owners manual for my lathe is here,
http://cdn0.grizzly.com/manuals/g9972z_m.pdf the relevant part, I think is page 35.
I set the left dial to I and the right dial to A and in the change gear "a" position I use the 35 change gear AND in the 'b" position I use change gear 70. This should give me a 16 TPI, correct?

[EdK]

That sounds correct except for the "the threading exit diameter .2983" which is .3125 (the minor diameter for that thread size) but I don't think that will matter much if you're just looking for clearance where the thread ends. You might want to practice on some thick walled conduit you can get cheap at any home center. Look for the grey colored PVC conduit. It's cheap and you won't likely damage your lathe or yourself while you practice.

Good luck.

Ed

[marfaguy]

Thanks Ed.
Can you tell me which reference you're using? I'm going off of this one,
http://www.carbidedepot.com/formulas-tap-standard.htm .
I'm only seeing .3125" as major diameter for 5/16" which makes sense since .3125"=5/16"
What am I reading/comprehending wrong in this chart?

[EdK]

Your first post says you're wanting to turn for a 3/8-16 thread, not a 5/16" thread. For a 3/8-16 thread the minor diameter is 5/16" (.3125). What thread are you wanting to turn? A 3/8" or 5/16"?

Ed

[TomG]

Ed,

5/16" is the minor diameter of a 3/8-16 internal thread (tap drill size). The minor diameter of a 3/8-16 external thread must be slightly smaller for clearance, hence the .2983 dimension.

Marfaguy, your gear selection and settings sound correct for a 16 pitch thread, but you should always take a scratch cut and verify the pitch before cutting the thread. You may also want to invest in a copy of the Machinery's Handbook (any edition). That is the machinists bible and will include pretty much any information you'll ever need.

Tom

[EdK]

Ah, OK, got it Tom. Thanks for clearing that up.

Ed

(07-13-2013, 10:06 PM)TomG Wrote: Ed,

5/16" is the minor diameter of a 3/8-16 internal thread (tap drill size). The minor diameter of a 3/8-16 external thread must be slightly smaller for clearance, hence the .2983 dimension.

Marfaguy, your gear selection and settings sound correct for a 16 pitch thread, but you should always take a scratch cut and verify the pitch before cutting the thread. You may also want to invest in a copy of the Machinery's Handbook (any edition). That is the machinists bible and will include pretty much any information you'll ever need.

Tom

[Mayhem]

(07-13-2013, 10:06 PM)TomG Wrote: ...You may also want to invest in a copy of the Machinery's Handbook (any edition). That is the machinists bible and will include pretty much any information you'll ever need...

Plenty of these on eBay and you are looking for the actual "Machinery's Handbook", not the "Machinery's Handbook Guide". HERE is one that ends today, has no (visible) bidders and the starting bid is $20.00.

If you are patient you can get them cheaper and don't be afraid to buy one that is 50 or 60 years old, Such as THIS ONE

[marfaguy]

Thanks guys. Sorry for the confusion Ed.

[ieezitin]

Marf.

Single point threading is extremely easy and nothing to worry about. I would take the suggestion earlier mentioned regarding practicing on some PVC pipe it works like a charm.

one of the best tutorials on the web for single point threading has beed done by Tubial Cane Here is the link

http://www.youtube.com/watch?v=9y0MmvscBzg

A little advice, your going to get a little flustered achieving the minor diameter at first, its very hard to measure if you have not done it before, the offset compound will get you there if everything works well, dont forget if you get close you could always finish it off with a die there is no shame in that.


Enjoy your threading,, let us know how you get on.

[wrustle]

As everyone has mentioned.......PRACTICE!


Your hand to eye coordination must be pretty good too......especially threading up to a shoulder!


The Machinery Handbook "can" be a useful item to have around, however......I have one sitting on desk that I seriously doubt I have opened in ten years. FAR from knowing it all.......it's just MUCH easier and MUCH quicker to get a response in simple laymans terms on the internet, and often times several different approaches with tips and tricks for achieving what you need to know or do.

When you do find what you're looking for on the net, (which often times is a page of charts or formulas for what you need) simply bookmark it and it will always be there just a simple click away from providing you the info you need.

Here's an example of some I use that you may find of interest:

Form Tap Chart: http://www.championscrew.com/form_tap_drill.htm

Thread Chart: http://www.shender4.com/thread_chart.htm

Trig Calculator for right angles: http://www.carbidedepot.com/formulas-trigright.asp

Milling Formulas: http://www.carbidedepot.com/formulas-milling.htm


More Charts than you can shake a stick at! :

http://www.carbidedepot.com/resources.htm


Best Regards,
Russ