Mill draw-bar

[b4dyc]

Hi

I am in the middle of making an imperial draw-bar for my mill and need to thread the end for 3/8 Whitworth for a Morse taper collet. Never had reason to use a Whitworth thread before I need to find out the diameter I need to turn the end of the draw-bar down to.
Had a look through the zuse book and came up with 0.3750 Does that sound right to you (I normally work in Metric you see )

Thanks for any help

Andy

[Tony Wells]

That would be the correct OD. Here is a handy chart:

http://shopswarf.orconhosting.net.nz/bsw.html

[b4dyc]

I will create that tomorrow then!
Thanks for the chart link as well

Andy

[doubleboost]

Hi
Andy Drawbars are normally 3/8 unc (nearly the same as whitworth)
whit is 55 deg unc is 60 deg
John

[b4dyc]

Thanks John,
I was looking at getting the collets from Arc and they say `Drawbar Thread: 3/8" Whitworth` But what I will do is turn the bar and then check the collet thread when its in my mitts.
Best to make sure as even this simple draw-bar has taken a little shop time to make

Andy

[doubleboost]

Andy
Just had a look at mine they are 7/16 unf
So i might have jumped the gun
Like you say best weight until you have them
John

[Mayhem]

Hi Andy - the easy way to get the decimal equivalent of an imperial measurement is the divide the numerator by the denominator.

So 3/8" = 3 divided by 8 = 0.375"

If there is a whole number, you just add that to the decimal.

So, 3 11/16" = 11 divided by 16 = 0.6875". Then we add the 3 = 3.6875"

This holds true for any fraction to decimal conversion. My math teacher will be so proud I remembered something :)

[DaveH]

Andy,

How did you get on with the draw bar you were making?

Got a pic ?

DaveH

[b4dyc]

Hi,
Yeah have progressed a bit further with it, lets see if i can add pictures here
Turned the bar between centres in the trusty Myford


Arrived at the point where i needed the correct size of thread that i asked about


Popped the thread on


Now I try it on the new MT3 collet Success !


All that is needed now is my jig completing so that i can add the squared off end for the spanner to fit

[DaveH]

Andy,

Good looking draw bar, nice job

Always good when things that supposed to screw together actually do!

DaveH