Messages

121

General Mach Discussion / Re: Bridgeport Knee Mill Conversion?

« on: December 30, 2017, 12:41:19 PM »

If you want to use the knee for tool length compensation the tool length would simply need to be passed to the knee axis to move it up or down by that amount BEFORE a tool is actually changed so you have room for it at your normal tool change Z height. Then the program sees all tools as the same length.

122

G-Code, CAD, and CAM discussions / Re: Need help with this drawing for G Code

« on: December 30, 2017, 12:35:38 PM »

This is clearing a classroom exercise not a real part, so I’d say cam is out. I think you will find that programming without G41 and adding it after the tool path is proven will make it easier for you.  If Mach 3 is not in exact stop mode it will try to go around the P8 corner at speed and likely would round it off. The other inside corners are sharp enough to force an almost complete stop. Enable full stop mode and all the corners will be as expected.

123

General Mach Discussion / Re: Bridgeport Knee Mill Conversion?

« on: December 27, 2017, 05:16:55 PM »

Issue 1 poor z axis travel.  Yep that is the one that makes a knee mill conversion really really suck.  Lots of time and money spent getting short drills, short holders, cranking the knee up and down. Used one for 4 years,  this time bought a bed mill.  For home my homebuilt mini mill has an 18” Z!

124

FAQs / Re: Yet another newbie needing any help possible

« on: December 27, 2017, 05:03:31 PM »

Russel,
The post would be for Mach 3 and then may have some tweaks specific to the machine. Sheetcam produces a gcode file with one of several possible extensions like .nc. Gcode files are simple text files you can open in any text editor.

The Mach 3 manual is really quite good and you need to spend some time reading so you at least have some idea of the lingo associated with CNC.  Saying “the thingy on the left” just frustrates everyone.

Mach 3 is a G-code interpreter that outputs motion commands in several possible ways. The basic method is step and direction commands from a PC parallel port. If the connection to the machine is not by parallel port then the machine must have a motion control card installed which then does the step and direction stuff. It would be connected by USB or Ethernet.  Find out what you have so we can help.

125

General Mach Discussion / Re: How to slow down on rounded corners?

« on: December 24, 2017, 11:50:50 AM »

I don't think a lot of people understand how little rigidity many machines have.  There can be looseness in the linear bearings, looseness in ball screw nuts and end bearings, looseness and stretch in timing belts, flex in the machine frame, flex in the moving cross members, looseness in the spindle bearings, flex in the spindle, flex in the toolholder, and flex in the too itself.  This explains why industrial machines weigh thousands of pounds.

An interesting experiment that may help many of you get better results.  Place a dial indicator on the table and against the tool in the spindle.  Press on the tool with you finger and see how far the indicator moves.  If you take the torque rating of your spindle motor and convert it to force at the radius of the tool you want to use you can then push on the tool with that amount of force to see how much deflection would occur at maximum load.  Moving the dial indicator up onto the spindle will remove tool deflection from the measurement.  Moving it onto the spindle housing removes the spindle deflection. Moving it on to each axis shows the axis motion.

The axis themselves may see much larger forces as they accelerate and decelerate in each direction. You can estimate that force from the motor torque rating and the gear ratio applied to drive the axis.  Pressing against the axis with that amount of force will show how much deflection there can be in a rapid turn around a corner.  If you move the dial indicator to show deflection in one part to another you may find there is a real weak link worth fixing.

Years ago I built pneumatically actuated bagging machines and a thermal printer mounted on the machine printed very poorly due to vibration.  Everyone suggested changes to fix the problem.  Using the dial indicator as above I isolated the bulk of the problem to one frame member no one suspected.  Beefing that up solved the problem very simply.

126

General Mach Discussion / Re: How to slow down on rounded corners?

« on: December 24, 2017, 11:28:42 AM »

I would try Exact Stop just to see what difference it makes.  In exact stop the machine will come to a complete stop before rounding the corner. So it will be starting from zero speed and accelerating through the corner, effectively slowing it way down on the corner only.  This doesn't work well on tool paths that have lots of little segments to a curve, but may work well here.

127

Mach4 General Discussion / Re: Axis directions

« on: December 21, 2017, 08:45:36 PM »

You had it right for X and Y  the first time and Z is positive up always.

128

Mach4 General Discussion / Re: Manual Tool Height Z Measurements

« on: December 15, 2017, 05:00:08 PM »

The positive Z tool length for a tool longer than the one you used to set zero is correct.  You are confusing Z height with Tool Height which is properly called tool length.  Here is what happens when the tool length gets called.  If the tool was shorter than the reference tool and the Z axis was at 2" above the part it would move down until the shorter tool is 2" above the part before a cutting move.  Call a different tool with a positive length when the Z axis is at 2" then the Z axis will move upwards until the tool is 2" above the part before a cutting move.  This causes more confusion than almost anything else about CNC! 

I once worked at a shop where I replaced another guy and he had a huge valve forging in the machine.  There was a nice smooth slot cut in the top of the forging about 1/4" deep and 1" wide. I asked another machinist what that slot was for.  He said "He always does that. That is Z zero where he sets off all his tools!  OMG!!!  He clearly had no understanding of tool length offsets. So don't be discouraged, this guy had run the machine for 7 years.

129

G-Code, CAD, and CAM discussions / Re: CAM ( or CAD/CAM) software for horizontal drilling in MACH3

« on: December 08, 2017, 06:20:33 PM »

Krep,
Just to let you know. I tried a custom drill routine in CamBam to put out G-code for horizontal motion.  The G-code it puts out appears to do what you want.  I used incremental mode G91 in the custom code and canceled it on exit.  So you send your drill to the location  of each hole using a point list and at each location it strokes the drill one time.

130

G-Code, CAD, and CAM discussions / Re: CAM ( or CAD/CAM) software for horizontal drilling in MACH3

« on: December 07, 2017, 04:58:27 PM »

Krep,
If you need help with CamBam you will find the user forum extremely helpful.  I would be happy to help as well.