Messages

651

General Mach Discussion / CNC turning of gear cutters

« on: March 17, 2014, 04:14:34 PM »

That would be a good approach too.  Maybe a gearotic version for the lathe could be generated?  Turning the profiles, you can as easily generate a true involute as a circle I guess.  The reasons I didn't do that were, first, the approximation of using a circular profile are probably less than the inevitable tolerances, and second, for the case of a circular profile only, I am pretty sure you can ignore tip radius compensation as the direction of cut is always a tangent to the tip.  Cutting an involute I'd have had to get to grips with cutter compensation on the lathe which I gather doesn't work too well in Mach?

John.


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652

General Mach Discussion / Re: CNC turning of gear cutters

« on: March 17, 2014, 06:25:39 AM »

Yes, there have been at least 3 articles in the UK model engineering press as well as several on the web about using form tools ("buttons") to shape the circular profile.  I haven't seen anything about using CNC but there is little new under the sun!  CNC saves the trouble of making the buttons and a holder, and can make a much wider range of sizes.

John.

653

General Mach Discussion / Re: CNC turning of gear cutters

« on: March 16, 2014, 05:05:48 PM »

Thanks Russ!  Yes, that's exactly right.

There's quite a lot to write up, I want to make sure I understand how I've done this, will be a while before I can post much more.

John.

654

General Mach Discussion / Re: CNC turning of gear cutters

« on: March 16, 2014, 02:54:40 PM »

So, success!  I have developed a method of making form relieved gear cutters similar to the "button method".  The difference is that the circular profile of the tooth, which generates a circular approximation to the involute, is formed by a few lines of G-code which make the lathe tool trace out a circle centred at the appropriate point relative to the cutter blank.  Took a while to figure out the geometry and how to generate the code, but in use it's a lot faster than making buttons and the mount to space them the right distance apart.  When I get time I'll post more details of the method if anyone is interested.

Here are some pictures of the formed blank mounted on a fixture in my collet chuck; the cutter after gashing out the teeth; and the cutter and the fixture, sitting on my big manual mill table.

655

General Mach Discussion / Re: Proper directions of X, Y, an Z axis

« on: March 02, 2014, 05:07:33 PM »

Yes I do have a lathe, but it is a separate machine.  If I were you I would have 2 completely separate profiles, one Machturn for the lathe and the other Machmill.  The axis definitions would be different but you'll have to live with that as the rest of the world uses Z on the vertical axis for milling, including AFAIK CAM progrems to generate milling code.

656

General Mach Discussion / Re: Mach3 PWM issues

« on: February 28, 2014, 12:30:26 PM »

According to the G540 manual, it expects to see 50 Hz on pin 14.  If your PC is outputting 25kHz, then something in the "ports and pins" config may be wrong.  Look at p86 (5-28 on paper) section 5.5.5.2 of the Install/config manual.

657

General Mach Discussion / Re: Proper directions of X, Y, an Z axis

« on: February 28, 2014, 12:21:07 PM »

If you are using Mach, imagine standing in front of your mill looking down at the table.  The table is like a piece of graph paper, positive X to the right and negative to the left, positive Y away from you and negative towards you.  The head goes up and down on the Z axis, positive being up.

If you dial in a positive X movement the table moves to the LEFT, so that the "control point" which is the tip of the tool held in the spindle, moves to the RIGHT relative to the table.  Similarly if you dial in a positive Y movement the table moves towards you.  If you dial in positive Z the head moves up, away from the table.

For all practical purposes, you can set the "zero" of the XY coordinate system at a convenient point on your work, for example at the "bottom left hand corner".  I tend to set the Z zero at the table surface as I have an automatic setting gauge for that; and measure the height of a convenient reference part of the work.  Another way is to set the Z zero at the work surface.  In either case, as the tool moves into the work Z decreases, and if you have set Z at the work surface, it cuts at "negative Z".

In principle you could label the axes differently, but for example the Mach wizards and at least the CAM program I use (G-Simple) use the above definition so you could get in trouble!

 

658

General Mach Discussion / Re: CNC turning of gear cutters

« on: February 11, 2014, 04:56:17 PM »

Fun is the name of the game!

Another question.  In writing the g code for this it will be convenient to operate the lathe in radius mode and zero the X axis off the periphery of the tool blank rather than the rotational axis.  Is there anything I should beware off doing this please?

By the way the code will be generated using an excel spreadsheet.


John.

659

General Mach Discussion / Re: Anyone point to an installation manual for usb to parallel breakout board?

« on: February 11, 2014, 04:43:28 PM »

Bob's point is almost certainly correct.  I have 2 BoBs, the one on the lathe uses USB only to get the 5v supply for the opto isolators from the PC.  That came from a uk source with full instructions and I built it myself from a kit.

On the other one, IIRC, that 5volts is derived locally (at any rate there isn't a USB from the PC).

As John says, post a link to the site where you bought the board.  I think there is only a limited set of BoB designs from china, I can see if it's like the one I have.

660

General Mach Discussion / CNC turning of gear cutters

« on: February 01, 2014, 01:49:12 PM »

Hi all, I've decided it's time I cut some gears and want to make some cutters.  There's a standard method of making cutters where you profile turn arcs of a circle on the edge of a bit of gauge plate, using a form tool which has two hardened circular buttons fixed to a plate with the right spacing and diameter.  Now it seems to me that with a CNC lathe it ought to be possible to form the arcs directly with the right G Code.

So I have found the formulas for the cutter dimensions, but I just thought that I'd ask here if anyone else has done this and has any tips (or even some G code they can share)?

Thanks,  John.