Messages

11

General Mach Discussion / Lathe Feedrate Problem

« on: March 06, 2013, 02:42:11 PM »

Hi, A couple of months ago my lathe computer died and I replaced it with another with similar specs.

I decided to install Mach3 version 43.066

I noticed that when programming a G95 the feedrate was alot slower if I set F0.15 the feedrate in the dro would be showing F0.09
The machine motion would be moving at F0.09 also.

I have been messing around trying to solve the issue but to no avail. I installed version 43.022 and also 42.040 but still have the same problem.

Things I have discovered,

When running any of my cnc files and G95 is read the feed rate is slower until about 12-15 code lines later the feedrate returns to the correct value commanded.

I can fool the problem by coding a G95 F0.30 if I really want F0.18 and then 12-15 code lines later set the feedrate to F0.18 but this isn't perfect as sometimes I end up with one or two passes moving at F0.30 which really upsets my machine.

This slower feerate problem only seems to be when reading the first commanded feedrate in my cnc files as later in the code the feedrate is changed and the machine moves at the correct commanded feedrate.


Any help would be welcome.

12

General Mach Discussion / Re: Accuracy of Homing Devices? Pro's and Con's of Different Sensors

« on: October 18, 2012, 02:55:37 PM »

Hi Dickybird, I've an Orac and use an opto sensor like the one MC showed one the page before. On the Orac X slide at the rear on the right side there is a hole with grubscrew that had a rod which travelled with the axis and pressed on a switch located just above the stepper motor. I replaced the rod with a flat sided bar with a slot cut in it and replaced the switch with the opto sensor. My X axis rapid is 2000mm/sec and I home the axis at 80% and it is accurate to less that 0.01mm.

John 

13

General Mach Discussion / Re: Steppers making noise but shafts not rotating

« on: August 08, 2012, 12:42:31 PM »

I'm just curious, when its "whiring" have you held the shaft and does it seem to vibrate? possibly a+ and a- are reversed?

John

It does sound like it, I've got the wires the wrong way round before and as Ces explained he gets the stepper jumping around at a low pulse speed- an out of phase situation.

Test for good pulses on all stepper wires.

14

General Mach Discussion / Re: Minor Threading Problem

« on: July 15, 2012, 06:00:18 PM »

Thanks guys for the help and reassurance. I've now added a few buttons on the threading wizard to automatically fill in the X end value for the thread based on the formulas.

ATB

John

15

General Mach Discussion / Re: Minor Threading Problem

« on: July 15, 2012, 01:49:00 PM »

Hi, I did a few internal threads today and found that I needed to adjust the value to pitch * 1.3 to get proper crest form.

The insert tip even with my magnifier looks to have no radius (or perhaps so small I cant see) I also checked to see if it really was a 60 degee tip. I've checked tool offset and backlash, all good.

Still I suppose when it comes down to it, if it works don't worry about it.


John 

16

General Mach Discussion / Re: Minor Threading Problem

« on: July 14, 2012, 03:49:37 PM »

Yay I've got threads. I tried your info on the external thread and got a nice finished thread with a well defined crest.

I then then tried a 0.5mm external and that was good as well.

I then turned to trying an inside thread but still had a good flat on the id so I need to investigate why that happened.

All in all not a bad day.

17

General Mach Discussion / Re: Minor Threading Problem

« on: July 13, 2012, 07:37:51 PM »

Nice threads there, i'd be chuffed at getting those. My insert is just a v pointed tip so when I get to the crested form I can adjust back a bit until i'm happy with them. Most of my threads are going to be quite fine pitch (0.5mm) so my accuracy is needing to be spot on.

John

18

General Mach Discussion / Re: Minor Threading Problem

« on: July 13, 2012, 06:42:32 PM »

Hi Hood, Thanks for that info, I'll give that a try tomorrow, I had a go at doing an external thread as it is easier to check with the thread gauge, same problem so I adjusted the code to cut deeper (start dia - pitch) and although it was deeper there was still a flat on the crests so it looks like your numbers should get me there.

Had loads of fun with it today, no work done but still loads of swarf on the floor.   

19

General Mach Discussion / Minor Threading Problem

« on: July 13, 2012, 11:11:33 AM »

Hi all, I've been recently trying to get to grips with threading on my Denford Orac machine it's not something I've done alot of on the cnc.

The problem I am having is that the thread is not cutting deep enough on an internal thread for the values I am entering into the threading wizard v1.17.

I have adjusted the backlash to zero in software (only 0.035mm in Z and oh my 0.09 in X)

I have adjusted the v point tool offsets (Glanz internal insert tool) so the point just touches the internal bore at 44.67mm

I require a thread pitch of 1.25mm and my math works the depth out using pitch * 0.866025 for crest to crest thread.

So in the wizard X start of 44.67. and the X end value of 45.7525. First pass depth of 0.15 which works out at 20 passes.

The lathe is started and threading commences, all sounds good and small swarfs of aluminium on each pass.

Removed billet and inspect thread, thread is cleanly cut, tracked perfect but the internal crest has a flat of approx 0.5-0.8mm on it.


I've done this thread several times and they all come out the same.

Is my maths wrong or is there something I have overlooked in software settings.

I know I can bodge the figures to "get in right" but I will be doing a large amount of threads at differing diameters so I am trying get the sums right first.

Any advice helpful.

20

Tangent Corner / Re: Strange banding on lathe finished part.

« on: March 09, 2012, 02:01:16 PM »

Hi, I cut some ally bar stock today placed in the chuck and only 50mm protuding, I did a couple of 40mm passes and I can see the same banding although very faint but it's there.

I adjusted the preload on the headstock a couple of years ago because of some chatter I couldnt get rid of, the
motor used to spin up to 2000 rpm but since the extra adjustment I can only get 1800 rpm before the vfd cuts out.

It's something I need to look at again but I'm just thinking I know the headstock is tight.

This brings me to thinking (worrying) and  as Russ mentioned about the ballscrew. But how will that cause a problem?

The carriage runs on a raised V so cannot twist.