1-1/8x12tpi thread angle

Hi all .

I am about to set up my vertex dividing head with a three jaw chuck 5 inch - (130mm) and do not want to modify the 6 inch (150mm ) back plate as supplied because i want to save it in case i pick up a chuck to suit in the future .

I can get a backplate with the required 1-1/8x12tpi thread that fits a Myford lathe and would like to know the thread angle for this as i will need to machine a stub mandrel to fit so i can machine the register for the chuck .

Am i correct in believing that this thread is 1-1/8x12 unf ?

Ian

Hi there, Ian,

The Myford nose is definitely Whitworth form, i.e. 55 degree angle. It isn't a UNF thread.

Don't get wrongly hung-up about thread tables - threads can be cut with any tpi and any form and any diameter (as long as it's large enough). The thread tables just list threads that have been standardised so that different manufacturers nuts and bolts will be mutually compatible.

Best regards,

Swarf, Mostly!

Hi Ian, just attach the 5" chuck to the 6" backplate., that's what I did!

Tony

Ian B

Just a cautionary word regarding screwed on chucks on a dividing head..

The cutting forces off a regular slot drill / end mill will all to often tend to unscrew the chuck off its dividing head spindle. This is not a climb milling-down cutting issue. Its due to the C/W rotation of the cutter vs the Anti C/W unscrewing of the chuck.

It would be best to leave that 6" flange intact and use the outer edge to mount a safety clamp to the dividing head table and so stop any accidental unscewing as you put a cut on. your favourite casting.

Bob D

Thanks swarf thats what i wanted to know so i can grind up a cutting tool .

I thought it odd for it to be a UNF thread but that was all i could find on the internet that matched the thread pitch .

I will still make mandrel for this because it is a handy thing to have as i can set it up on my lathe to machine other items for the dividing head in the future or it can be used as a master thread gauge to check any female threads i need to make for anything else i wish to screw onto the dividing head .

The dividing head will be used for making gears and to mark out dials etc so the cutting forces will be at 90 degrees to the spindle thread but i may include a locking system just for piece of mind .

I have a rotary table that i use for machining slots , radii etc and the chuck is bolted to a mounting plate so it cannot come loose .

Thanks to all for the replies .

Ian .