Making a ER11 chuck

[Dell]

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 don’t 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.
Dell
 

 

[BillTodd]

https://www.engineeringtoolbox.com/slope-degrees-gradient-grade-d_1562.html

[BillTodd]

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

[BillTodd]

 :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.

[philf]

Dell,

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.

Phil.

[Dell]

Thanks for the replies I think in cone ratio I can add 5 digits but in Z I can only add 3 or 4 I tried pushing knob and pressing Fn although in other settings I can change more digits but it doesn’t make any  difference in internal cone I will turn another piece of aluminium with the suggested setting in cone ratio see how it turns out.
Dell
I don’t know why there are multiple pictures the same.
I have read the manual many times and keep it by the lathe for future reference but the last time I did any serious math was 60 years ago at school

[djc]

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

Some of these are specified to 3 decimal places.

I have not read the manual, but can you enter the ratio as anything other than 1:something ?

If so, you can achieve any accuracy you want using a continued fraction expansion of the number you need.

See calculator here: https://r-knott.surrey.ac.uk/Fibonacci/cfCALC.html

If you put tan(8*pi/180) into the input, you can find 17/121 through 1387/9869 to 2271/16159 depending on how many digits the input accepts. And not a decimal point in sight.

Also, if that is so, they are doing their users a disservice in the way they quote SK30/40 taper. These have been exactly 24/7 tapers since the day they were born. No matter how many decimal places you use, it will never better the fractional value.

[philf]

Z shouldn't be that important as long as the cone ratio can be set accurately. If you bore the arbor slightly bigger than 7.5mm and/or set Z a little longer it will just cut fresh air at the end of the cut.

[Dell]

Thanks for all the replies and suggestions after making another one out of aluminium I decided to bite the bullet and make the proper one and I must say I am chuffed to bits with the outcome .
djc the math you posted went way over the top of my head.
as can be seen from pictures of the control I input 12.45 in -Z and 1.75 in -X but then I input 3.558 into cone ratio and it didn’t change the other settings so they must have been correct , for the thread M14 X .75 I turned down to 13.98mm and over 10 cuts I input .46 and after the 10 runs I just run the thread at same depth unto nothing was being removed and the nut is a very nice fit , upon checking runout I get  0.003mm so I am happy .
Dell

 

 

 

[philf]

Dell,

An excellent result.

I do think though that the ZP and XP numbers could have been anything (within reason) and wouldn't affect the cone ratio which is what sets the 8 (or 16 degree inclusive) angle. The XP number will just give the large diameter and the ZP how much in Z it will cut the taper.

Phil.