Cutting a taper

[Dell]

I am trying to make some arbors for my Pultra for diamond grinding wheels and I am having trouble getting the taper correct, I know the included angle is 30 degrees, the overall length of taper is 7.8mm large end 15.2mm small end 11.98 as best as I can measure and I have to convert to ratio for the Rocketronics so I input 7.6 being 1/2 large end ➗ by 15 degrees being 1/2 included angle into calculator like so
7.6 ➗ 15 tan = 28.363 input that into control panel but not getting the correct angle when turning on a bit of scrap aluminium, what am I doing wrong.

[awemawson]

Tool centre height is very critical cutting tapers accurately - needs to be dead nuts on.

[philf]

If you have a taper of length 7.8, Large diameter 15.2 and small diameter 11.98 you don't have a 15 degree half angle! It's more like 12 degrees. (11.605 degrees). For large diameter 15.2, taper length 7.8 and 15 degree angle the small diameter would be 11.02 - nearly a mm difference to what you measured!

According to the manual :-

If you're inputting the Cone Ratio (V). V = L / (D - d); V = 7.8 / 4.18 = 1.866

If you're inputting ZP & XP: ZP – This corresponds to the length of the cone. [= 7.8]; XP – The distance in X by which the cone tapers, i.e. (d1-d2)/2 [= 2.09]

It seems bizarre that you can't enter the angle!

[Dell]

I said as best as I could measure, it’s not very easy with a calliper but I know the included angle is 30 degrees so I will cut another bit of scrap using what you posted.

[philf]

I said as best as I could measure, it’s not very easy with a calliper but I know the included angle is 30 degrees so I will cut another bit of scrap using what you posted.

Dell, Don't use the figure I quoted - I used 7.8 instead of 7.6 - I since deleted that bit. Phil.

[Dell]

I can add the parameters in one of too ways either -Z & -X or as a cone ratio. 

   

[Dell]

Can’t understand why the pictures are so big.

[philf]

I can add the parameters in one of too ways either -Z & -X or as a cone ratio.

Dell,

I may have made a mistake in my previous figures as I drew it out in Autocad at 2:1 and probably forgot to divide measurements by 2.

I believe that, according to the manual, these are the correct numbers:

Entering ZP (length of taper) & XP ((D-d)/2) you should have ZP = 7.800 and XP = 2.090

Entering Cone Ratio (L/(D-d)) L=7.8, D-d = 4.18 therefore Cone Ratio = 1.866

Good luck!

Ideally you'd resize your images to 800 x 600 pixels.

Phil.

[Dell]

Thanks phil
That was a mistake on my part I quickly input the figures to take the picture, the overall length is 7.8 mm.
Thanks for the advice on picture sizing I will look for an app to put on my iPad to resize pictures.
Dell

[Dell]

Okay now I have a perfect taper so I thought I would cut another piece including a bit of shaft ( second picture) but as can be seen before the taper is finished it starts cutting into the shaft , what I did was turn a short 10mm down to simulate the main shank to 9.7mm then proceeded to cut the taper but stopped with 3 cuts left there should be a slight step between shaft and start of taper.
Dell
 

 

[Dell]

Finally figured it out instead of setting both axis to zero I set X axis to .25mm above zero then zero X axis cut taper and it leaves .5mm step.
Dell

[philf]

Dell,

I'm pleased you have sorted it.

I don't have an ELS but the instructions of yours aren't very intuitive.

Phil.

[Dell]

Finally got around to finishing the arbor for mounting diamond discs to the Pultra.
Dell