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Chestrockwell
07-28-2010, 12:53 AM
Hi all,

I'm putting together parts to retrofit an old Piecemaker 6.5x13' plasma table. It needs a z axis (currently only has a torch lifter) and I'm considering something like the K2 unit.

http://www.k2cnc.com/shop/products.asp?cat=33

I can't see how the floating part moves; anybody have experience with one of these? Is there any slop in the mechanism?

Thanks,


Chester.

DanOSB
07-28-2010, 10:35 AM
there is total of 4 bearings (one for z axis travel that goes up and down... and other is for the home switch (z touch)

hope that concept is clear..

Chestrockwell
07-29-2010, 12:33 AM
Thanks Dan that is a bit more clear.


Does anybody have any feedback on the K2 units? Is there a better z axis out there at a similar price point?

Thanks a bunch.

Chester.

DanOSB
07-29-2010, 04:23 AM
np chester.. I never purchased from them or seen them myself.. I dont know other pre fab z axis for sale too..

multiplex
07-29-2010, 02:50 PM
I bought the 6" version for my table. I have it mounted, but have yet to try it out. For the price, i'm not sure it can be beat.

I like how compact everything is, and how they've worked in the floating aspect

only question i have, which maybe someone can answer? Is there typically a home switch for Z up? The only switch that is on the unit is for the floating head.

during the home process of the table, i'd want the Z to move up first, but how will it know when to stop?

Chestrockwell
07-29-2010, 02:58 PM
Hi Multi,

Thanks for the info. I also wonder about a home switch on the z axis for full up travel.

Any more reviews on the k2 or other z axis'?

Thanks again all.


Chester.

plain ol Bill
07-29-2010, 06:55 PM
Multiplex I don't have a home on my Z axis and don't recall having seen one on any other builds either. The only switch on my Z is for my floating head.

chestrockwell if I needed another Z for another table or to replace the one on my current machine I would buy a K2 - I like the looks of them a LOT.

Boogiemanz1
07-31-2010, 04:15 PM
I think Dnelso's build used a K2 and if I remember there may be a video..............jb

multiplex
07-31-2010, 05:07 PM
you can see the Z axis a little bit in my video - first test runs of my machine. no torch attached yet :(

YouTube- CNC Plasma first test

Torchhead
07-31-2010, 08:27 PM
I bought the 6" version for my table. I have it mounted, but have yet to try it out. For the price, i'm not sure it can be beat.

I like how compact everything is, and how they've worked in the floating aspect

only question i have, which maybe someone can answer? Is there typically a home switch for Z up? The only switch that is on the unit is for the floating head.

during the home process of the table, i'd want the Z to move up first, but how will it know when to stop?


The Touch-off switch on the Z is the Z home. Homing up in the air some distance has no meaning. You use homes on a CNC machine to establish a known position from which to measure your cuts. The Z home is normally at Z zero and Z zero is the top of the material (not some place up in the air). Since that changes (especially in plasma cutting) you have to re-establish Z zero.

I have seen users mount the HOME up on the Z but then you have to either do a bunch of complex math the find the top of the material or reset the Z zero. It won't work with the Floating Torch Holder and the auto touch off for IHS.

Homing is normally used to reference your table. It establishes a Table Zero. Your part may be offset from there but it allows you to always return to the same place. In most cutting operations the Z is measured from the top of the material , either above it (in plasma cutting) or below it (negative numbers) in routing and milling. In routing and milling everything is nice and flat and the material does not flex and warp and change it's height.

I have a custom button that is a REF XY (homes just the X and Y and zeros them). You can jog the Z down close to the material, hit the Z zero and then after the initial move and the first touch-off (IHS) you have a true Z home (0) after the switch offset is applied. If you are using SheetCAM and the proper POST all of that is handled automatically.

The Touch-off move is the homing move and uses homing code to perform. If you try to add another Home switch on the axis it won't work.

Just be mindful if where your Z is and do not do a "Home All" move. A REF ALL is not to be used in plasma cutting! (unless you want to watch your torch slam down and get dragged across the material (or worse the table grid).

TOM caudle
www.CandCNC.com

multiplex
07-31-2010, 10:07 PM
Awesome explanation Tom, and awesome hardware as well. I'm loving the bladerunner so far.

My biggest fear was zeroing the z, and breaking things while the x and y clear. Obviously the method of operation is differnt than my router and something I'll have to get used to.

Torchhead
08-01-2010, 11:09 AM
Awesome explanation Tom, and awesome hardware as well. I'm loving the bladerunner so far.

My biggest fear was zeroing the z, and breaking things while the x and y clear. Obviously the method of operation is differnt than my router and something I'll have to get used to.

The Z is self zeroing as long as it the Z DRO is somewhat close to the actual position. Once you establish a starting Z zero (even if it's just jogging down untilit touches and hitting the Z zero button then jogging it up) then the machine will keep track of where Z is all the time...even after countless UP and DOWN moves. One advantage of having the Control Software (MACH) move the Z even under THC control is it keeps track of where Z is.


If you follow some simple rules you will never have to worry about damaging your torch.

1. Never do any Reference (Home) without material on the table (or the grid covered with a flat sheet of something).
2. On the first Ref of the day (when you first turn on the machine) Ref each axis separately so you have total control of the moves. Manually Zero each axis after it homes. If you park the gantry at a known spot (0,0 or some distance from it) and manually enter the spot in the XY DRO's THEN do a REF to get dead on; it's a 2 minute drill.
3. Have your torch move up to a higher spot at the end of a job (you can define a XYZ Ending location in the POST) or use a higher Rapid Clearance value in SheetCAM. To save time I usually run at 1/2" rapid clearance but that can leave you open for crashes from tip-ups. It depends if you are going to monitor the cutting (and have your handy magnet close by) if you want to walk away. I would use higher clearances for un-attended cutting.
4. In 7 years of cutting I have had a few head crashes but have never damaged my torch. The floating torch holder can be your friend as it will save the torch as long as it can ride up over the obstruction.
5. You can set the Z home as a limit in MACH. That makes it so if the switch is tripped on anything but a REF (home) move it shuts off motion (E-stop). Just make the Z++ the same pin number as the Z home and you are good to go. The down side is that, depending on the way Z is setup, the homing move may not back off the Z home switch far enough to disengage. If that happens the system will instantly shut down (sees a limit as soon as the homing move is over) and you will have to manually back off the switch. A ramp approach to the switch that has to be at the peak before it triggers will make it easier so the back off distance disengages the switch. That distance is NOT programmable in MACH so you have to try and deal with it mechanically. The other way is to have another switch above the Z home (if you have a design that allows travel past the home switch) and set THAT up as a limit. If you are really paranoid you can mount another limit at the top of Z to prevent moving it too far up.
6. If you have to create a checklist of things on your table (like every good pilot uses no matter how long they have been flying) and hang it at the monitor. Startup and shutdown checklists.
7. Program and use the Load Material option we have in the MACH setup and screens. You can preset a location in XY and Z that you can hit the Load Material button and the gantry and torch will move out of harms way, so busting your torch loading a big sheet of material won't happen.

Cutting with plasma is a different critter than routing. Things happen a lot faster and at there is less reaction time. Keep your head in the game to prevent costly mistakes!

TOM caudle
www.CandCNC.com

multiplex
08-03-2010, 03:25 PM
again, thanks for the wealth of info. should save alot of messing around once i get the torch wired up.

quick question while i have you here :)

would THC be able to handle something like this? or what is the best way to handle it

specifically speaking of the dip towards the right of the panel. it goes down about 1/2"

http://voytilla.com/gallery/albums/userpics/10003/normal_photo%2810%29.JPG

Torchhead
08-03-2010, 05:21 PM
again, thanks for the wealth of info. should save alot of messing around once i get the torch wired up.

quick question while i have you here :)

would THC be able to handle something like this? or what is the best way to handle it

specifically speaking of the dip towards the right of the panel. it goes down about 1/2"



It looks like it's about a 45 deg slop. The ability of the THC to follow the cut will depend on a couple of things:

1.)The speed of the Z axis. To cut a 45 deg slope at constant height you need the same speed on Z as you are running X&Y. Lets say you are cutting at 150 IPM on XY. Z needs to be able to do at least 150 IPM. Because the Z axis does not use Acceleration/Deacceleration numbers while under THC control it "cheats" and lowers the velocity to prevent not overrunning the motors. Typically that percentage is about 30% (the Z runs at 30% of the Max Z velocity while cutting with THC). So using those numbers your max Z velocity setting in motor tuning, would need to be about 450 IPM. If your leadscrew is too fine you can't spin it fast enough with a stepper (max of about 800 RPM) to hit that upper speed.

2.)The feedrate of the cut (XY). You can use a really small orifice tip and cut at lower current and that will let you drop your feedrate and still get a good cut. Don't just crank the current setting down with a big tip. It will mess with the gap volts and the THC will either cut too high or pound down on the metal. It will also give you less than optimum cut.

Keep in mind that the plasma likes to cut at 90 deg to the material. As the angle changes so will the cut characteristics. If you do a lot of that cut you can probably workout the settings as it cuts the slope and change the preset on the fly as you cut. With the DTHC it's possible we could use a macro (embedded in the g-code at specific points) to automatically adjust the cut parameters (preset volts and even Span Gap volts and Tip Saver actions). Contact me if you need help with that.

TOM caudle
www.CandCNC.com

bandsaw.king
08-04-2010, 12:02 PM
I just received my K2 but have not mounted it yet. (too many summer projects). What I can tell you is that the service was great, the unit seems solid and the price was right.

multiplex
08-04-2010, 09:27 PM
so far the only downside i've seen is the screw pitch is very low, 1 start maybe? i need to check into it.

reason this is a problem for me is the G251 Gecko cards are locked in at 10x microstepping, so it takes way too many steps to move an inch. I may need to swap this screw out, not sure yet