Cutting a 1 1/2 Inch 8 TPI - UN thread

[19brendan81]

Hi All,

The spindle for my lathe (according to the manual) is a 1 1/2 Inch 8 TPI - UN thread. Is this the same as a 1 1/2 Inch British Standard Fine thread pitch? I have the thread data for BSF in front of me but am unsure about the "- UN" part that is mentioned.

Cheers,

Brendan

[Vernonv]

I reckon it's a 1 1/2 x 8 unified thread - see here http://www.truthread.com/docs/unifie...0dimension.pdf

[Col2310]

Hello Brendan,
My 9" Craftsman manual states11/2" x 8 TPI USS .
Is this equivalent to a UNC?

Col2310

[JTonks]

Hi Brendan

UN threads have a 60 deg included angle, BSF (and BSW for that matter ) have a 55 deg included angle.

1 1/2" BSF is 8 TPI like the thread you are concerned with so the thread data will be somewhat different. Google UN threads and you should find the thread data you are looking for.


Regards, John

[pipeclay]

Easiest answer to your question is NO.

[bollie7]

UN stands for Unified National thread

UNC = Unified National Course
UNF = Unified National Fine
are classed as "Series with Graded Pitches" (Machinerys handbook, 27th ed page 1735)

Your size is not a std UNC or UNF size.
1 1/2" UNC is 6 TPI (Threads Per Inch)
1 1/2 UNF is 12 TPI.

Yours is a 11/2" x 8-UN [8TPI] "Series with Uniform (Constant) Pitches"

If you are thinking of making a backing plate or faceplate to screw onto your spindle, you will be going to get a tap that size (at an affordable price) if thats what you are thinking. You will have to screwcut the thread, ( which you should do anyway for this application).

hope this helps
bollie7

[19brendan81]

Thanks guys, lucky I asked before forging ahead.

I am planning on making a spindle mounted collet holder for my ER40 collets. I am looking forwards to cutting the thread on my lathe, knowing in advance that its going to be difficult.

[bollie7]

I am looking forwards to cutting the thread on my lathe, knowing in advance that its going to be difficult.

Don't think that way. Do a bit or research re working out the thread depth etc, set the machine up right and you should have no problems. Machine the thread first so in the event that you do stuff it up you haven't wasted time machining the rest of the nut. Once you get to where you think is the correct depth, leave the job in the chuck and unscrew the whole lot to trial fit on the spindle. Take your time and think through each step. Use HSS tool so you can run the machine slow. Easy peazy.
Just had a look in the machinerys. 11/2" - 8UN the nut has a minor dia of between 1.365" - 1.390"
Depth on internal thread is .0676" (depth is 0.54127" X .125" [pitch] ) Take note of the decimal point.
But please, do your own research, it will be good practice for you.

bollie7

[19brendan81]

Hi Bollie,

Im definately going to machine the thread first. This is sound advice, and was the way I have been planning on tackling it. I would be filthy if I made the rest of the chuck then rooted the thread cutting part. Plus this way, I will be assured that the recess I cut for the collet will be concentric to the spindle.

Brendan

[Chief Tiff]

Does your lathe not have a Morse taper, because you can purchase ER collet holders with MT shanks.

[Big Shed]

Does your lathe not have a Morse taper, because you can purchase ER collet holders with MT shanks.

I have one those for each of my 2 lathes, but they have a serious drawback, they will not allow the material to pass through thereby defeating some of the usefulness of the collet system.

I now have a backplate mounted collet chuck which allows me pass through material up to the maximum size of the collets, much more useful.

[19brendan81]

Yep - what Big Shed said.