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Making a ER11 chuck

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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:

--- Quote from: philf on October 05, 2023, 02:03:54 PM ---
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.


--- End quote ---

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.

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