Messages

2401

General Mach Discussion / Re: using the driver test

« on: September 26, 2012, 06:18:54 AM »

Mach shares time with Windows so the computer can do the necessary pulsing. 25000 is the most stable  because it provides the longest time period for the pulsing. Unless the required pulse rate exceeds what a Kernal speed can provide for, then there is no advantage to using something higher. When running Mach you should not have anything else running since whatever is running would be in competition for computer time. Additonal you want a nice flat straight line in the graph with no big spikes and the reported pulse rate to be very close to the kernel speed.

RICH

2402

General Mach Discussion / Re: Unequal Depth of Cut

« on: September 25, 2012, 05:40:24 PM »

When actually cutting or when checking the table?

You need to have the table parallel to the X & Y axes full travel at all points on the table. So take accurate measurements
with an indicator locked onto the vertical support below point C and do the same for the other side and take a measurement
at each end and in the middle of the table, then mount the indicator in the middle of the brace along C. Resolve the points to a common high or low reference. Can't tell form the photos, but i would first want to know if the brace for the z axis is raising or lowering because of screw deflection.The table ideally should be flat and not bowed or twisted after it was mounted. If you had a nice long straight edge it would make things easier to do.

RICH

2403

General Mach Discussion / Re: losing steps on z-axis (help)

« on: September 25, 2012, 06:43:59 AM »

Sounds like the Z is skipping steps. Experiment some, lower the max X&Y velocity.. Does this happen at a particular part of the code or is it random.
RICH

2404

General Mach Discussion / Re: WORK/ TOOL OFFSETS

« on: September 24, 2012, 07:00:57 PM »

When in the offsets table click the save button.  Save settings, also in general config there are DRO settings  ( lower right of the screen) and you can select if you wnat to be prompted to save the offsets ( doing this from memory so look at the manual ).
Some gcodes will cancell out the offsets and same goes for a initialization  macro, if using one, on startup.

2405

LazyTurn / Re: Multi Sart Acme thread

« on: September 24, 2012, 07:05:53 AM »

Is it possible to do a interior thread in acme?

YES

Is it possible in lazyturn

NO as LT is for doing profiles and dosen't provide code for threading. You need to use the wizard.

Have look at Threading on the Lathe - Mach 3 write up  as  multi start treading is talked about. You really need a good cnc lathe system.
You can use alternate flank cutting to cut acme threads, 5 start ....i would not even attempt it here on the outside yet alone on the inside.

Frankly farm it out unless you have tested and done that kind of work.

FWIW,

RICH

2406

General Mach Discussion / Re: Out of round holes

« on: September 24, 2012, 06:52:25 AM »

I have tried changing motor settings both in the x and y axis, even increasing the steps per inch on the x

Don't do that. Use the calculated values  and just refine them based on actual testing ( should be minor  adjustment).  The backlash can change and even the tested steps per unit may vary over the total travel, but it is due to what the axis components are and as such you have what you have.
Now not to confuse .......changing the actual steps per unit for some operating range to make the circle concentric can be done, but,
it not practical in use and you really need to know exactly why you doing it....but that is for "cutting hairs so to speak" and I am not going to elaborate on it.

RICH

2407

General Mach Discussion / Re: Noob question: Changing cutting start location

« on: September 23, 2012, 08:11:18 AM »

Have a look at using offsets or fixtures in the Mach Manual.
RICH

2408

General Mach Discussion / Re: Trying to understand thread wizard

« on: September 23, 2012, 07:55:46 AM »

Much of the problem seemed to be down to accurately knowing the tool tip radius

Good point John and it makes a big difference. You will never have a zero radius on the end of the tool and if doing fine threads
doesn't take much to trash a thread, heck all threads. The tolerance on small fine threads is very small ie; 0-80 the thread depth is only .011" so if you don't account for it and don't set up properly the thread will be wrong before one even starts cutting it. The problem even becomes worse when the tool is just hand ground and the tool angle is not correct since even if the radius was zero the angle may be incorrect and cuts over or under relative to the pitch line.

Full profile inserts like Hood mentioned are great in that the thread is being chased, but, you also need  a lathe capable of using them and
they are not cheap.

RICH

2409

General Mach Discussion / Re: Trying to understand thread wizard

« on: September 22, 2012, 10:39:41 PM »

Phil,
Have a read of Threading on The Lathe - Mach3 as it covers threading from beginning to end and then some.
I used backlash on the lathe when threading. Yes you can use it but it needs to be setup correctly, but even then, threading in terms
of meeting some tolerance will be challenging.
Threading will only be as good as your system, so you need constant spindle rpm, thread lead and and depth of thread will only be as good what is mechanicaly driving the axis.

On the rpm question....suggest,when in the wizard click the Calculation button as that will tell you what your axis velocity and acceleration is and warn you if you are exceeding them. 200 is ok , but, depends on the tpi you will cut, and when fooling around with threading on my little lathe at 120 ipm seemed like driving a car at 150 mph both of which is just too fast for me!

RICH

2410

General Mach Discussion / Re: Thread cutting on the lathe...What am I doing wrong?

« on: September 22, 2012, 10:04:54 PM »

Doug,
I have a Sherline lathe, so don't think I am bashing the product, don't use it much anymore though. Also just spent some time helping someone who was having some problems threading with his just last week. He cut 3/8-18 in 6061 AL.

So first i will make comments from experience with it.
The motor is wimpy even if you have the newer one on your lathe. You must have everything going for you, and by that I am mean razor sharp thread tool, properly set tool, all the gibs adjusted to remove play, preferably a backlash attachment mounted and adjusted, minimized overhang of the thread tool, and using the wizard to your advantage, the stock prepared by machining it to proper size ( concentric and not having say .003 runout.

24 tpi and below is reasonable to do, 18 can be iffy, 16 probably not ( but can be done if somewhat tricky about it, but the quality may be poor), forget about doing muti-start threads.

What is probably happening. The first few threads are ok and you are not getting much rpm change, but the rpm change will get progressively
worse as you cut deeper. Mach is constantly trying to provide for the rpm slowdown, but, it can only do so much. At one time one could actualy have the spindle almost stop and the thread cycle would try to fix things and the resulting thread was ,well lets say the the nut went on. The thread cycle was changed and slowdown of say  25% may mean a ruined / trashed thread. We did the 3/8-18 at 200 rpm, rpm change was around  30% max decrease for example.  Thread didn't look bad but it was just a case of a poor quality thread. Yeah the nut when on!

Now besides the above, the axis just dosen't move as accurately as it should, so if you are off on a cut by say .002", that could be enough to cause an additional slow down of the spindle.

Rather than rambling I will say watch, know and learn what is happening very carefully monitoring the threading cycle and learn from it.
Also have a read of Threading on the Lathe-Mach 3Turn.

------------------------------------------------------------------------------
Here is what you can do that will help:
1. Don't use radial cutting and instead do flank cutting. use 15 degree instead of 30 degree in the settings.
2. Make sure you allow 3-5 min pitches before threading starts
3. Use finer cuts depths, maybe .004 to .007 for the first cut and then limit to .003 or .004 there after.
    You can do even finer ....but depends on axis positioning accuracy
3. You can try alternate flank cutting but don't think the your Sherline is accurate enough, but it may avoid a plunge on some cuts.
4. Experiment with the material, brass will work harden for example.
5. I can say adjust the gibs to be on the tight side and well lubricated, but not kowing what size motors you have ...that could
    cause skipping
6. If you have backlash you will never do accurate threading, backlash compensation can help but is not the answer, due to improper
    tool location you will / may cut deeper than wanted and thus have reduced rpm during the cycle.

So don't get frustrated, you can do some nice work on the Sherline, but know it's capabilites  and that only comes from
having fun playing with it.

Have fun,
RICH