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Question about turning profiles and G-Code
« on: December 27, 2010, 08:42:47 PM »
Hello everyone!
I am putting together a cnc setup on an old lathe we use to re-profile railway wheels (pictures comming soon).  I am using Panasonic 3P 220V drivers and servos with a parallel breakout and Mach 3.  I was able to wire all of the connectors and setup the servos and Mach 3 without too many problems and I am at the point where I can input single lines of G-code to manually perform cuts.  I am new to mach 3 and CNC machining so please forgive me if this is a stupid question:  Is there a software I can use, where I can input the current profile of the wheel to be turned, then input the the desired final profile to be turned and have a cutting path g-code output generated taking into acount the radius of the insert (its a 1"r round cone shaped insert) and the max cutting depth in order to achieve the final profile?

Thanks!
Frank

Offline Hood

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Re: Question about turning profiles and G-Code
« Reply #1 on: December 27, 2010, 08:51:59 PM »
I have just purchased Dolphin CAD/CAM Turn module and its looking excellent. If you have a dxf of the before and after profiles then you could use them in Dolphin to do as you want. The "after" would be loaded as the main profile and the "before" would be loaded as the stock profile.
I am sure other CAM programmes can do this also but the special offer price Dolphin have on at the moment made it attractive to me, after all I am Scottish ;D

Hood
Re: Question about turning profiles and G-Code
« Reply #2 on: December 27, 2010, 09:58:55 PM »
Thanks!  I'll be sure to check it out!  Now that I know this, then what I need to do is find a way to quickly (video-probe?)  get the profile of the wheel and turn it into dxf spline that I can send to Dolphin.  I am a programmer by trade, I suspect it should be pretty simple to write something up that will do this.  By the way, I just posted some pictures of the lathe as its comming along.

Offline RICH

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Re: Question about turning profiles and G-Code
« Reply #3 on: December 28, 2010, 06:53:38 AM »
You could use LazyTurn to generate the profile code from the dxf profile and it is free. The manual is in Members Docs. Code generated accounts for a button tool.
Doesn't do what Dolphin can do. I would image that the profile should be standard depending on the track it will run on. Would need to ask a friend since their shop manufactures  / rebuilds
custom railcars.
RICH
Re: Question about turning profiles and G-Code
« Reply #4 on: December 28, 2010, 01:29:25 PM »
Thanks Rich, I checked out LazyTurn, but I think that Dolphin has everything we need and isn't outrageous in price.  The finished profile is in fact standard for solid wheels, however it is the uncut profile that changes with each used wheel.  This depending on wear time before removal, train speed, type of terrain, is it a freight car, was it on a 2 or three axle truck on a locomotive, was it flat spotted, etc.  Now, I just need to decide how I can quickly digitize the uncut profile of the used railway wheel and turn it into a spline in a DXF.

Frank
Re: Question about turning profiles and G-Code
« Reply #5 on: December 28, 2010, 01:46:58 PM »
Hi Frank, cool machine !
Just curious, why is it necessary to digitize the existing profile if you are going to restore it to "standard" ?
Is it to minimize the machining time ?
Thanks
oh, I know all about getting over anxious and testing without limits or an estop....arent those screws tough ?
Re: Question about turning profiles and G-Code
« Reply #6 on: December 28, 2010, 03:40:02 PM »
Thanks Overloaded!
I tell you what, after everything I went through to find that large screw used I nearly pooped my britches when I saw how it had bent...just to think about how I was going to explain how I'd screwed it up.  I was floored when it sprung right back to shape like nothing had happened...man they ARE tough!

Decreasing the machining time is definitely a plus, however: One reason to digitize the cut is to limit the passes needed to reach the final shape and preferably be able to perform the cut in a single pass.  The wheel profile is somewhat L shaped with specific radii for the flange cut (keeps the wheel centered on the track).  The flange wears flat on its "in" side, so that the radius becomes flat and the treadwears mostly at the side adjacent to the flange. This means that in order to fit the new profile inside the worn profile you need to be able to fit the new flange radius inside the now narrower flange which causes you to have to cut the tread much deeper than if you were just to straighten out the tread and give it the correct angle.  Normally this is done on a pass-check-pass-check basis with a pantograph or with the eye-crometer-gauge ;D.  Since the inserts wear about the same on a 1 inch cut than on a 2mm cut (provided sufficient coolant) its better to be able to get a single cut...cuz man I'll tell you those inserts get EXPENSIVE at $100 bucks a pop.  

Frank
« Last Edit: December 28, 2010, 03:51:07 PM by zonian1903 »
Re: Question about turning profiles and G-Code
« Reply #7 on: December 28, 2010, 04:14:16 PM »
Great info Frank, sort of what I expected.
I did a bit of welding at our local (small) rail co years ago and witnessed them turning the tires on a locomotive. They used the traction motors and turned them in place. God what a racket, and I think they were cut dry with PCD circular inserts, not sure though. But they did say the tooling was expensive.
It was a neat experience.
Good luck.

Offline Hood

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Re: Question about turning profiles and G-Code
« Reply #8 on: December 28, 2010, 04:56:22 PM »
What I have done before to get a profile of parts on the lathe is mount one of the electronic edge finder type probes in the turret then using the MPG to touch off and note the DRO readings at various points, then its easy to plot the points in CAD and get the shape of the part.

Hood