Here we go again . . . MK4

[routercnc]

Did you by any chance stop it in a canned cycle I have a feeling that it happened to me once.

I don't think so - I'll check the g-code when I get home as I wrote down the line number I stopped it on. I seem to remember lots of X and Y positional commands so probably not in canned cycle? It was cutting out the outline profile to a part which was almost a rectangle.

The last feedhold problem was done on a pass which had tabs on it, but it was about 50mm away from having gone up, across, and down to create the tab and was going in a straight line to the corner. I was about 20mm from the corner going X- when I pressed feedhold. Upon starting it went Y+ as if it thought it had reached the corner.

Next time I'm in the workshop I'll do some air cuts on the same file to see if I pressed the feedhold twice or something . . .

[routercnc]

OK, looking at the gcode where I had the 2 crashes (when 'starting' after a 'feedhold') and I can see there are several straight line moves (must be geometry nodes all along in a straight line from when I was creating and changing the CAD), followed by a G2 radius arc in both cases.

#1
I've read about problems with feedhold in arcs so always feedhold on a straight edge. But I was definitely on the straight bit about half way along the top edge when I pressed feedhold. About line 930. It was some way off getting to the G2 ARC at the corner. When I hit start the machine went up in +Y and snapped the tool clean off.

I've loaded the file onto my house PC (hence the DROs are all zero!) Here is the first one:


#2
This time, on the same part, I was cutting along a straight edge at the bottom, -X direction, when I hit feedhold. It had just done line 1060. This time cycle start moved the machine in +Y. I hit e-stop straight away this time and recovered it. However, there was a gouge in the work piece (!). It's cosmetic but annoying none-the-less.

Looking at the gcode shows another set of linear moves, followed by a G2 arc radius at the corner:


I'll go back to the CAD and see if there are repeat nodes in the geometry as a start, but I'm confused by this as I've used feedhold for years and not had this problem. Now twice on the same part!

I went to Mach3 website in case there was a later version - but it's still R3.0.43.066 I which is what I am running now.


EDIT:
OK, the reason for the repeat straight moves is that there are tabs on those sides. Vectric obviously adds those moves in on every pass, but only adds the Z up and over move when the required depth is met. However, I was nowhere near the depth to create the tabs (they are only 2mm high) so that might be a coincidence. So, still confused about what is going on . . .



EDIT2 / side note:
I've had to do a few 'run from here' operations after hitting the e-stop recently. It is probably out of position as it could be mid-step so I've found you need to:
1. Raise the tool right out of the workpiece
2. Re-home the machine
3. Press 'run from here' on the line you e-stopped on
4. It will show you the required resume coordinates in a window. Before accepting these you should jog or MDI to the X and Y positions it shows. If you do not it will try to move straight to that location which could be through a clamp or the workpiece etc. if you are low. This has caught me out a couple of times!
5. Press OK and it will rapid down in Z to the position it got to when the e-stop was pressed
6. Start the spindle (or there is a check box if you use spindle control from Mach)
7. Hit cycle start

[routercnc]

Some pictures of the matching 2nd upper end part - cleaned, drilled tapped and finished:


Then onto the next set of parts. Bed cleaned down and a new 10mm plate ready to cut out 4off bracket plates:


Small pockets cut and holes spotted in all 4 parts:


First one cut out:


Last one cut out:


Opening up the light cnc spots with the same 6mm spot drill:


First pair of them cleaned up, drilled out, counterbored:

The counterbore in each part was a bit nerve racking as it is to take an M8 cap head slightly under flush. This means a depth of 8.1mm in a 10mm part, which leaves just 1.9mm left. Although I had my DRO set on the drill press you still drill them blind and need to trust in the gauge not to go all the way through! I guess I could have used the depth stop nuts as a backup.

Second pair straight off the machine ready for drilling:

[routercnc]

Finished the 2nd pair off, cleaned up, holes drilled etc.


These are the corner pieces on the gantry-


Not that exciting so I thought I'd also post another way I just tried out of tapping the threads in those parts (well starting them at least) which is much quicker. I started with one of these tapping chucks from RDG tools - designed to either replace the drill press chuck or for use in the tailstock of a lathe. It has a tommy bar and the chuck is free to rotate and slide inside the morse taper housing:


Link below (they are also on e-bay)
http://www.rdgtools.co.uk/acatalog/2...ent-88025.html

Although you are supposed to tap out the existing chuck and replace it with this one I didn't want to keep swapping them over. I'd looked these over at a show so knew that the MT3 taper comes off the chuck leaving a 12mm straight rod - perfect :


Because the 12mm rod was greased I put it inside a plastic bag (to stop the grease going onto the chuck jaws) and then put in lightly in the chuck - just enough to hold it but still allow it to rotate and slide up and down:


Here it is well into tapping the M5 thread:

This takes seconds to do and you can feel the bite / back off and reduce the risk of breaking the tap.

Note that the drill press is NOT powered - I'm using the tommy bar to rotate it manually.

This worked really well, was very quick, and created threads which were perpendicular to the face. I finished them off by putting the parts in a vice and using a cordless drill.

I think the plastic will not last long, it started has started to tear already, so one option is to make a metal adapter tube which is clamped in the drill press chuck at the top, and contains a long bored out 12.05mm dia or so hole in the bottom to hold the greased rod on the end of the tapping chuck. If the bore is a good fit and there is grease in there it should stop the chuck falling out when you raise the drill press.

To have something set up permanently I might even modify a cheap drill press/stand (the ones where you put a mains drill in) to house a long rod attached to the drill chuck - a bit like the Arc Euro ones but their's only goes to about 6mm or so tap size whereas this goes to 13mm.

[Neale]

I cheated a couple of days ago when I needed to tap some M8 holes in a slab of Ecocast I had just drilled. I held the M8 spiral-point tap directly in the drill chuck, and took off the drive belt on the mill (Warco VMC with multi-speed belt drive so easy to do). I could then turn the drive pulley by hand. Light down pressure on downfeed handle, and this was enough to get a good thread started, finished by hand later. For small taps, I have lightly guided them in the chuck jaws and tightened a tap wrench on to the shank (not square) of the tap to turn them. Especially with these easily-driven spiral-point taps, this works ok to get a thread started. But I'll have to have a look at the RDG tap holder the next time I see them at an exhibition - thanks.

[routercnc]

Hi Neale,

Yes, done something similar to that by slackening the motor / belt tension levers on the drill press. But even with the belt slack there is still quite alot of friction and it still tries to turn the motor.

To remove the belt on my Warco pillar drill completely takes a bit of time and involves a ladder, a screwdriver to open the lid, and releasing the motor bolts and is not very efficient. It's not much fun for long due to the effort of turning the chuck & motor.

The method above is quick to set up (just a quick adjustment on the chuck jaws) and is then very easy to turn.

One thing I will note is that the tap slipped occasionally, even though I tightened it as much as I could. I don't know if they do a keyed chuck version but that might be better. Maybe a bit of degrease on the inside of the chuck jaws would help. Next time I'll also try a tap handle on the round part of the tap shank as you did.

[routercnc]

Bit more progress. One of the gantry end plates was cut out over the weekend:


Tonight I drilled and tapped all the various holes. Couldn't resist a trial fit of a couple of the previous parts:
OUTER VIEW

(Note the tabs on each end still need facing off. I'll wait for the other one to be machined then do them in the same session.)

INNER VIEW


With the side plates offered up:






Another reminder of what the end sections should look like . ..



I used the tapping chuck again which made light work of the threads. Also discovered I was holding the tap wrong. I had been putting the tap right into the chuck and it gripped on the round shank - liable to slip. Looking at the 3 jaws of the chuck I noticed that it has ridges in the centre of each jaw. If you put the square part of the tap into the chuck these grip the 4 sides nicely, with 2 jaws on the flats and 1 jaw (with the ridge) on one of the chamfers of the square. Hard to describe but just put the square shank of the tap into the 3 jaw chuck and it will not rotate.