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PS4steam
06-15-2010, 01:06 AM
Hi

I have looked through my stuff for this info and seem to have lost it. I need to make a backplate for my Myford as well as a special myford spindle nose adaptor for another lathe.

I know the thread is 1 1/8 x 12 , 55 degree Whit. what I do not know is the bore for the backplate ie the internal minor diameter. I could just measure a few of the plates I have and average them but it would be good to have the number.

Also I need the external minor diameter for the spindle nose I need to make. Again I can measure the spindle but the real number would be a help

Thanks

bob

ammcoman2
06-15-2010, 09:34 AM
I think it is 1.018".

Not sure what you mean by the "external minor diameter" though.

Geoff

legendboy
06-15-2010, 02:52 PM
will be in machinery handbook, somewhere around page 1217 i think?

if i have time i will measure it for you, i have one sitting in the garage

Rich Carlstedt
06-15-2010, 03:49 PM
Bob Excuse me for the long post, but I hope to educate others about how to get where you want to go..

1.125 -12 BSW

Pitch =.08333
Depth of thread (H) =.0534"
Major Diam =1.125 ( theoretical )
Minor Diam= 1.0182 ( theoretical )

For boring:
Since British threads such as these are supposed to have radiused crests, they are tough to single point. The crest radius is .0114".
I prefer just using a flat . It works
The distance from the 55 degree flat to the point when looking at a crossection of the thread is H/6, so you have .0089 " ( now this is on one side of the thread only @)
That means the 'tap drill size" for internal threads is your minor diameter plus two H/6's
so you now have 1.0182 + 2(.0089)=1.036", and you would thread outward until you hit the 1.125" Major Diameter

For turning"
Here your major diameter becomes 1.125 less two of the H/6 dims
So you have 1.125-.0178= 1.1072 " OD
Turn the Spindle blank to this size.
You would sharp point the 55 degree tool to a depth of .0534" from the Original OD (1.125) but since that is now reduced, by .0089 (per side !), we
revise our threading depth to .0445" for your OD Thread depth.

Now realise all the above is without tolerances.
I can't figure out British tolerences so you will have to fly by your pants on that. I would suggest you start by putting three wires on the Myford spindle and measuring them with a 1-2" mike. Your answer is irrelivant.. just write it down and when you turn the spindle standard OD, use the same method to match the Myford ...this is when you are cutting the .0445" thread depth.
Matching the Myford will give you a good start.
Just remember you want the "fit' on the loose side with the plate !
Don't be afraid to take a little more--it will NOT hurt you---less may cause the chuck to seize on the spindle !
Turn the Spindle spud first ! then you can use it to check your bore threads (later)
Remember the most critical part, and that is Always turn the treads and the "Face*" at the same setup....never , never do it in seperate setups.
Your chuck is held in perfect position by the helical threads and the rear face of the spindle. they are perpendicular, because you did them at the very same time. Important !


Rich

*PS this is the face on the back of the mounting plate, and the face on the large shoulder (chuck stop) on the spindle spud

Reference Pg 1370
Whitworth Threads
Machinery's Handbook 20 edition

PS4steam
07-25-2010, 09:04 PM
All

I wanted to let all that helped out know how the thread cutting came out. Pictures in the photo section.

Now this is a little long but it might help someone in the future. First it turned out I found some 5” back plates that I had ordered in 1986, as I recently moved my shop they were not where they belonged, so no internal threading.

Thanks to Rich Carlstedt’s and Alan Moores’s info and digging out my 14th edition of the handbook I found all the technical info on Whitworth Threads. Their calculations were right on relative to the specifications which interestingly varied all over the place. However read on to see what Myford actually did.

Let me tell you what I found when I carefully measured my spindle nose, the tailstock adaptor nose, and the dividing head nose.

The OD of the spindles across the top of the threads ranged from 1.1212 to 1.1237. According to the handbook the OD should have been reduced by a value called h/6 which Rich had at .0089 (handbook 20th), Alan at .004 and my 14th edition has the h/6 as .01334 assuming the number means radius. Rich’s number produces a 1.1072 diameter, Alan’s a 1.117 diameter, my number if you assume it is a radius produces a 1.098 (if a diameter 1.1116) when rounding the tops of the threads. Notice big difference in handbook values themselves and actual Myford spindles.

I checked the depth of the thread on the tailstock nose that had centers so I could set it up in the lathe. As best I could measure by lining up the 55 degree cutter and using my DRO to give distance from top to bottom it was .054 which is in line with the Handbook if you start with a 1.125 OD and ignore the rounding of the threads.

Conclusion: Myford nose is 55 degree thread with modified OD; basically it’s a Whitworth ignoring the rounding.

Just for completeness the length of the threads ranged from .54 to .56. The register diameter ranged from 1.249 to 1.250 and its length .43 to .44 to the register face.

I of course decided to match as close as possible the actual Myford spindle.

I made a test spindle using 1018 which I was just going to pitch but it came out so well I finished it by boring a recess for 3/8 cap screw. I now have a spindle nose I can set up on the mill table, rotary table, and my little Sherline CNC rotary table. The sleeve on the right of the picture is for the Sherline. This was a nice bonus.

I made the actual spindle on an unmachined 6 inch cast iron back plate. Turned up the large side to fit a L00 back plate and bolted in on, then turned the spud side to the spindle. Other than the cast iron was of dubious origins and did not finish up real nice, the whole exercise came out great. I used my Myford chucks, back plates and face plates for final fitting as I turned the threads. I have a Grip Thru chuck and set up a test bar in it on the Myford to turn about 5 tenths TIR. When mounted on the Clausing L00 it actually turned with almost no needle deviation. I also bored a .54 hole through the spindle. So a success was declared.

My threads were 1.1205 to 1.1225 and the depth on both is .053.

My goal was to be able to use my smaller Myford chucks on my Clausing 5900. Now time will tell if the exercise pays off. Certainly the extra spindle nose for the mill will be useful.

Thanks to all who provided the information. On the Myford Yahoo site I posted pictures, go to this link (you need a yahoo login and to be a member) and then to pictures, it is under Bobs Myford.

http://groups.yahoo.com/group/myfordlathes/messages


Bob

snookered1ca
07-26-2010, 01:24 AM
If you happen to be looking for other spindles to make for a Myford get the Workshop Practice Series # 27 " Spindles" the author focuses directly on spindles for the Myford Super 7B.

Blackadder
07-26-2010, 08:55 AM
to throw a spanner in the works


current Myford spindle noses are very different
Big Bore Spindles - threaded M42.5 x 2mm pitch and have a 25 mm bore and a chuck retention grove because of the 3000 rpm speeds


Stuart