ORAC taper turning

[Steam-Chris]

Hi all, new to this forum and CNC. Have recently purchased a 1983 ORAC, not working when i first tried to power it up but have since fixed the power supply probs, i have familierised myself with the programming and got my head round the loss of "0" position when powering up, easy just set the tool offsets each time.
What i need, is to understand the interpolation when taper turning, through trial and error i have found the max taper is .0125" over 1 inch at a feed rate of 15, i have the manual but no mention of intrepulation between axis, either for taper or radius, i take it the feed rate is a factor as too slow a feed would cause steps in the finish
Can any body help.
I see that most here rework thier machines with electronics to work under Mach3, anyone tried taper turning with Mach3, can i get it to do 50 thou over 8 inches ?

Thanks all

Chris

[rasp]

you can do any taper you like

if you start at 1.000" diameter and want to put a taper of .050" over 8" then the code looks something like this :-

G00 Z0.1
X1.
G01 Z0 F.01
X1.05 Z-8. F.005 (form taper)
G00 X2. Z.1

Graham

[Andycnc]

I see in the specs that taper interpolation is 20:1. I've no idea what that means though!

But,
(i'm converting your numbers roughtly to metric)
with a resolution of .01mm, and a taper of 1.25mm

you'll be able to resolve 1.25/.01 discreet positions (=125)
therefore over a length of 200mm you'll be stepping (.01mm steps!) every .625mm.
You'll never get a true 'smooth' taper (with stepper motors).

With mach3 and some updtated microstepping drives you'd be able to resolve finer steps.

Make sense? Happy to be corrected if I'm going mad!

[Denford Admin]

Andycnc is right - the taper will never be smooth with a regular stepper.
The step resolution plays a major part in how good the result would be.
Depending on the stepper pulley ratios, a regular stepper drive outputs 200 or 400 steps per revolution.
Generally our machines worked out at between 100 and 200 steps per mm which gives a movement resolution of 1mm/200 = 5 to 10 microns.
ie, your machine will "jump" 5 microns every so often when taper turning.

If you went the Mach route and fitted micro-stepping drives, you can increase that resolution by 10 (or more) to get 0.5 microns. So in the example, you'd get 1,250 steps over the taper rather than 125 which would make a lot of difference.

Hope that makes sense !

[Steam-Chris]

Thanks for all your input, i understand that a taper machined on a stepper driven machine will never be the perfect finish.
Entering the code, not a problem but while trying to run the job i found that if the feed rate was not high enough the machine would seperate the x and y, first traveling along the y axis to the finish point and then in to the x axis finish point.
To overcome this the feed rate had to be increased, i ended up with a feed rate of 35 (i take it that is "inches per minute") to obtain the desired 50 thou taper, that left the job looking like a tapered thread, so some reprogramming of the VFD took place, spindle speed increased to 3400 rpm, minnium depth cut as all the torque had dissapered, hey presto a good job.
A steep learning curve !

once again thanks to all, Chris

[cncbasher]

Don't forget steppers loose torque the faster they run .
so it falls off dramaticly once it reaches it's spec'd limits

if you need torque slow the axis down etc

[Steam-Chris]

Yes, lots of vairables but have to run at fast speed to get the taper as x axis will not step at slow speed over length. has anybody got the original spec for operation ?