Mistery spindal thread - Help to ID

[Majorstrain]

Hi all,
I'm making an ER32 collet chuck like Arnold http://www.homemodelenginemachinist.com/index.php?topic=5843.0 for my lathe, but am not certain as to the correct nominal spindle thread size.

The major diameter on the spindle is 1.910" and the minor diameters on the three chuck back plates are 1.791" , 1.790" , and 1.797"
The pitch is 8TPI.

The closest match I found in the books was a 1 15/16" - 8 UN - Ext Major D 1.9375", Int Minor D 1.802"
Does that sound right, is it a common thread on a 12x lathe spindle?

The Name plate says it's a RATRA lathe but the manual says it's a SHUN SHIN SSB-10BS lathe. Date of manufacture is 1984.

Cheers,
Phil

 

[arnoldb]

Phil, welcome to the club

When I saw Shun Shin = Far Eastern, my immediate thoughts were for a metric spindle for your machine....
But your measurements converted to metric does not make much sense either - it ends up 48.5 mm - which could be 49 mm - which would not make sense; it will either be 48 mm or 50mm for metric, with a 3 mm pitch being closely equivalent to 8 tpi

How did you arrive at the 8 tpi for the threads? - Did you measure them using a thread guage ? - also, the thread angle is important; is it 60 degrees or 55 degrees?

It is also likely that the manufacturers used a non-standard size/pitch combination; nothing is impossible ;D

Otherwise you could "wing" it - the "tightest" thread you have on a backplate is 1.790 - so you could use that for Internal Thread ID. Then cut the thread so that the internal thread OD is _just_ bigger than 1.910"...

The reason why I started off with the spindle nose replica and made sure it can screw properly into my other chucks was to be able to test the tread of the collet chuck as I was turning it. There is one flaw with this however... You cannot test the thread full depth without turning the register first, and you cannot turn the register first and test it's accuracy with the spindle replica. A very good and respected mate sent me a picture of a much better guage. - it has a thinnish central stem, with the spindle thread guage on one side, and a plug guage for the register on the other. (One could make 2 separate guages for that matter)

I'll be continuing with my build this weekend, as I finally received the collets this morning ;D

Regards, Arnold

 

[Jasonb]

It could be 49mm as some of the smaller FE lathes use a 39mm thread.

Jason

 

[Majorstrain]

Morning Arnold and Jason,
Thanks for your replies.

I checked for metric pitch with the gauges with no success, I'll check the books and see if 49mm matches there tho.

Some good points there Arnold.
To fill in the gaps, the thread is 60° (checked with a triangle cutter insert) and I measured the pitch with a thread gauge and it was a good match for 8 TPI.
I'll be starting on the nose replica this afternoon and as you suggest, I'll wing it.

Look forward to see the rest of your build Arnold.
Thanks again guys.

Phil

 

[steamer]

Majorstrain,

I'll second making a "spindle nose" too. Best way to do odd threads.

Take your time with it.

Dave

 

[Tin Falcon]

Phil:
In my experience it seems like thread dimensions as measured are often a bit different that the published numbers the. info you give does make sense.
If you are using a caliper that may count for some error . But a caliper should still get you within 2-3 thousands . like the other guys have said I would go the replica spindle nose route. The actual numbers are not that important the important thing is a nice precision fit of your chuck to the spindle nose. take your time make careful measurements and debur maybe even take the last few tenths with silica carbide paper and oil. This can be a valuable tool for later work.
Tin

 

[arnoldb]

Just to show what I meant in my earlier post about the gauge.
I was very graciously permission to add it, as it may be useful to others. (Thanks Mate!)

The one side is the spindle thread, and the other the register.

Regards, Arnold

 

[mklotz]

When I made a copy of my spindle thread (used to make my 5C collet chuck), I made an extra before I broke down the setup. This was bolted to a plate that can, in turn, be bolted to my rotary table, thus allowing me to mount chucks to that device.

Although this works fine, I've only used it once or twice. I find it far easier to mount work directly to the RT without the chuck - also saves headroom on my round column mill.

Nevertheless, it's something that folks who may be undertaking this want to consider.

 

[idahoan]

Hi Phil

I went through this vary thing quite a few years ago. I had a Darsin 10 X 24 belt drive lathe from China. It was very similar to the Jet models of the same vintage. I needed to make a backplate for a new chuck and it was an oddball like yours. I sold the lathe but kept the chuck and back plate because it is a nice Yuasa (sp) 3 jaw with 2 piece jaws.

I just pulled it out of the drawer and measured the register ID. it measures 1.970 which is just a little over 50mm. Mine is also 8tpi. I don't think you will ever find any thing in a catalog that will fit your spindle nose; you will probably just have to wing it and machine it to fit.

Good Luck,
Dave

 

[Majorstrain]

Hi Guys,
Thanks for the advice.

I'm just doing the thread on the spindle nose now. Having lots of fun single point threading mild steel with a 1/4" HSS tool. :wall:
Even using the 29.5° method, 8TPI puts a lot of load on the cutting edge near full depth. It's the largest thread I've done to date, not that I've done many.

Cheers
Phil

 

[Blogwitch]

You will find that yours isn't a mystery thread at all.

People are under the misapprehension that a 2" x 8tpi will measure 2" diameter.

The stated OD is only a guideline, and can be almost any size lower than it. If you start with that figure for your blank, you will be guaranteed that you can get your external thread out of it.

I have just measured up a perfect fit Myford nose, and that is classed as a 1 1/8" (1.125") diameter thread. The actual measurement of that and two others that I tried was 1.110" (give or take a thou or two because of caliper use). Even the new taps I have bought measure the same OD of 1.110".

The only way to make anything to fit an original nose or nose fitting, is make it to fit, not make it to expected or stated dimensions. That goes both ways, whether internal or external screwcutting.

Your most important part is the back register and rear butting face. If they are not within very close tolerances, you are onto a loser straight from the outset, no matter how close and good your threading is.

Blogs

 

[Majorstrain]

Finally,
The spindle nose is done. woohoo1

Thats interesting info on the threads Blogs, I did go the way of making it to the measurements I had taken off the spindle. The register was machined to within a few thou and then oil sanded down to a snug fit with 320 wet and dry.

I'm happy with the result.

Cheers
Phil

 

[Tin Falcon]

good job MS another happy customer. mark it up as a tool with the lathes serial number .
Tin

 

[arnoldb]

That is a very good looking job Phil Thm:

Now just don't copy me too closely :big:

Kind regards, Arnold