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Making a ER11 chuck

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Hi all
I need to make a ER11 collet chuck for my Pultra using my Myford equipped with Rocketronics I decided to make it out of aluminium first so I donít mess up the arbor but I am a bit stuck , the taper angle is 8 degrees and I need to put 12.452mm in -Z but there not enough digits so I can only input 12.4 or 12.5 but there is an option to input cone ratio but even after a google search I am none the wiser as to how to convert to cone ratio not even sure if it will help the parameters are large end 11mm small end 7.5mm with an overall length of 12.452mm giving 8degrees 16degree included  angle so if anyone on here knows how to convert to cone ratio it would be much appreciated.


You just need to convert the dimensions you have to whole numbers in Z or X

Slope is (11.0 - 7.5)/2  =1.75  in 12.452 or 1 in 12.452/1.75= 1in 7.11542857143

Edit (major brain fart later) unless it requires the inverse (taper): offset distance per unit length

1,75 /12.452 = 0.14053967234 in 1

 :headbang:Reading the manual it is as clear as mud.

However it is clear they require the included angle so 1.75 x 2

12.452/3.5 = 3.55771428571

So cone ratio is smaller compared to their examples.


From the manual (p52/53):

"Input of values:
Values such as F, ZP and XP are entered using the rotary knob. The cursor (>>) on the left of the display indicates which value can currently be changed. Use the up and down keys to move the cursor to the value to be changed. Then turn the knob to change the value.

The button also has a push-button function: to fine-tune the increment of the changes, you can also press the push-button down before turning, it also has a push-button function. For furtherrefinement, press the FN key and then rotate. So you can enter in steps of 1.0, 0.1, 0.01 and in some places also 0.001. The step sizes are adjusted according to what is to be entered."

Does this work when setting the cone ratio?

The Cone Ratio is described in the Appendix of the manual (p 104) and gives some examples of common tapers:

"You can read off common cone conditions from table books, usual are e.g.
MK1 1:19,047
MK2 1:20,020
MK3 1:19,922
SK30/40 1:3,429
HSK 1:9,98
Hydraulic fittings 1:16"

Some of these are specified to 3 decimal places.

The cone ratio for your ELS is defined as V=L/(D-d) or, in your case V= 12.452/(11-7.5) Which equates to 3.557714.

If you can input to 3 decimal points put in 3.558

Hope this helps.



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