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John Haine22/02/2019 16:33:16
2500 forum posts
132 photos
Posted by Ian Johnson 1 on 22/02/2019 11:46:32:

..... I am hoping this forum can be a good source for CNC knowledge especially as the small cnc support has gone.

I've sussed out photos too! This is my screen:

Just to point out to people that if you are using Mach3 it has an excellent support forum where almost any problem you have will have been solved by someone. It's here.

Ron Laden23/02/2019 11:00:43
1036 forum posts
157 photos

Jason, have you had a chance to investigate the Z function yet, wondered if you had found anything.

JasonB23/02/2019 17:16:39
15325 forum posts
1576 photos

I borrowed a pallet truck so I could move the machine to a better position for fiddling. It certainly looks like the head has been run up past the stops and hit teh top of teh outer casing.

The main issue seems to be that Z does not like to move fast. I this first video I entered -20 into teh Z DRO and you can see me jogging it up 10mm at about 25% speed, I then go to teh screen and click "goto zero" which I assume should take it quickly up teh remaining 10mm or so but I just get a small rotation of teh motor and a sound like it has stalled, DRO read Zero but should have been at about -8.

Second video, I start by jogging at 80% which seems to stall, then change to 25% and it moves OK then back to 75% and it stalls again.
Ian Johnson 123/02/2019 22:19:05
47 forum posts
7 photos

At least it's alive! I haven't looked at my Z axis limit switches but my X and Y axis are installed differently (KX1), mine are in line, those in the video look like they are off set by 90 degrees for some reason.

So it could be worth checking the position and clearance of the switches. Especially if it overshot the Z axis stops.

A friend of mine who installs robots explained how the Hall Effect switches work, It went woooosh right over my mechanically brained head!

Andrew Evans23/02/2019 23:41:31
223 forum posts

Jason, not sure if this is related to your Z axis issue. When mach 3 detects a limit switch is hit it reduces the feedrate as you move back away from the switch. So you hit the limit switch and it stops, you have to hit ''reset" and then move away from the switch, but the initial move is very slow even at Max feed.

You can set soft limits in mach 3 so that even before a limit switch is hit mach3 knows to stop.

Jim Guthrie24/02/2019 00:37:59
87 forum posts
5 photos


If this was the problem machine which might have been messed around with to some extent, then one thing to check would be the taper gib in the head. If the gib has got end play then it can lock the head up when travelling fast in the up direction with the wide end of the taper to the top of the column. That's the way it is in the KX1. That gib is the one thing I curse in the KX1 and it gave me a lot of trouble getting it right when I decided to try and adjust it some years ago. You're fighting the weight of the head, the nod of the head and the gas strut to get it right and I found it very easy to get it wrong, causing the head to be either too loose or too tight. I often wondered why I couldn't have a nice parallel gib strip with multiple adjusting screws. smiley It might also be worth checking if the gas strut is working since that will put an additional load on the head drive if it is not.


JasonB24/02/2019 07:02:58
15325 forum posts
1576 photos

Thanks all, some more things to look at.

X&Y limit switches are micro switches and in line and it also seems possible to jog straight past those too!

The upper Gib adjusting screw was certainly loose so will look closer there. This one just has a coil spring to take the weight not a strut - down the right hand side in the second video.

My other thought was to see if I could set the max feed rate slower for now.

One thing I did notice that I was going to read up on was that the "overide limits" was flashing red and clocking the text box to the left did not change that.


John Haine24/02/2019 09:11:01
2500 forum posts
132 photos

If they're ordinary microswitches you want to be able to jog past them - if for some reason the axis didn't stop they'd get crushed! Assuming the KX3 uses steppers then there is no great issue if an axis drives slowly against an end stop, though you will lose any referencing - the motors just stall, making an alarming noise. Limit switches stop the axis without losing machine datum.

JasonB24/02/2019 10:10:11
15325 forum posts
1576 photos

The way the micro switches are positioned there is no way they can be crushed if things overrun, will take a photo later

Unlike the machine that does get damaged when the Z is driven past the stops, see how the case has bent where the oil union has got squashed


blowlamp24/02/2019 10:40:29
1185 forum posts
82 photos

Are the limit switches properly set up and enabled in Mach3?


JasonB24/02/2019 13:07:58
15325 forum posts
1576 photos

That's what I need to read up on.

JasonB27/02/2019 16:15:31
15325 forum posts
1576 photos

I have slowed the Z axis motor down which seems to allow it to move without complaint. Ian @ ARC sent through my licence file earlier today so I could run a longer set of code to see what came out.

Not the ideal cutter and the work was a bit thicker towards the bottom hence the scuff mark on the circle but for a first go I'm quite chuffed.

sieg logo.jpg

Thanks again to Ketan and the guys at ARC.

Ian Johnson 127/02/2019 17:03:19
47 forum posts
7 photos

Yay! making progress now Jason. I think every Sieg CNC owner has one of those!

sieg logo.jpg

mike T27/02/2019 17:22:54
166 forum posts
1 photos

Hello Jason

There is this strange desire, especially from newcomers, for all rapid moves to travel at the speed of light.

After 20 or more years using CNC for model engineering, I find that setting the maximum traverse speed to about 20 inches per minute ( 500 mm per minute) is more than adequate. The moves are well within my reaction time and they do not beat up the hardware needlessly.

Moderate traverse speeds and reduced axis accelerations are the best way to avoid lost steps and erratic stepper motor behaviour. The Sieg headstock looks to be a massive lump of iron to try to accelerate rapidly. So slowing down the Z axis rapid moves is a very logical solution.


Edited By mike T on 27/02/2019 17:26:00

JasonB27/02/2019 18:17:32
15325 forum posts
1576 photos

500mm was what I brought it down to (from 1000) and also halved the acceleration.

blowlamp27/02/2019 18:57:05
1185 forum posts
82 photos
Posted by JasonB on 27/02/2019 18:17:32:

500mm was what I brought it down to (from 1000) and also halved the acceleration.

Beware of setting acceleration too low or you'll find the machine won't reach its set feedrate, particularly if the gcode has lots of consecutive short lines.

Just ask if you want something CAM'd to get you going.


Phil super727/02/2019 19:22:47
7 forum posts

A word of caution about changing motor speeds and acceleration , be careful as not getting these set proportionally can effect your tool path.I had a problem cutting a rectangle with square corners, I kept getting rounded corners(radius). drove me nuts endless checking of software. Eventually found it was my speed and exceleration was causing the problem too slow acceleration, mach3 has decelerate and accelerate when changing direction hence round corners. Hope this is of some help to anyone

JasonB27/02/2019 19:53:36
15325 forum posts
1576 photos

Thanks for the offer Martin but I have already been cutting something that Vectris through out, think of a loco Nameplate but with my initials on it.

This has shown up that there are still issues with the Z-axis one of which is that the tool is loosing height part way through the program so the early part is being cut to full depth but by the end it is above the work. At the end of the program the tool stops about 2mm higher than when it started but Mach3 DRO says it is in the same position..

I have run the program several times with a DTI on the top of the head and you can see it ramp down to the same position then all of a sudden it does not ramp back down as much, last time I acuually heard a slight change to the motor tone.

I have found something that may have been loosened in the previous crash so will run it again in the morning to see if there is any improvement. I have also put some better marks on the motor, coupling and screw to check there is no slipping in that area.


Andrew Johnston27/02/2019 21:10:34
4630 forum posts
522 photos
Posted by mike T on 27/02/2019 17:22:54:

After 20 or more years using CNC for model engineering, I find that setting the maximum traverse speed to about 20 inches per minute ( 500 mm per minute) is more than adequate.

Interesting; in soft materials (brass and aluminium) I often cut at nearly twice that (900mm/min) on my hobby CNC mill. For steel I usually cut at around 300-400mm/min. The rapids on my mill are 65ipm (1650mm/min) and that's what I always use for G00. In around 1000 hours of running I've never knowing lost steps or had a problem with the stepper motors.

But then again I am known to be impatient. embarrassed


Emgee27/02/2019 22:36:34
1088 forum posts
199 photos

Jason, without encoders on the steppers position is not indicated to Mach, the program calculates displayed position on data sent which may not have functioned, hence the incorrectly displayed position.

If you mount a dial indicator acting on the Z axis you may be able to spot when the axis malfunctions.


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