.25 6061 Diamond Plate cut issues

[Largemouthlou]

1250 HT
40 amp nozel
55 ipm
156 V
2 seperate issues

49 ipm is what the book suggests for the .25, I will slow my speed down the next time I cut but was wondering if the speed is the problem here?
On the cuts you can see where the cut bumps out at the diamond.

I have the same issue with .125 diamond plate as well and it will leave a little dross by each diamond or on the one edge which is a bear to try and clean if the customer wants polished diamond plate for the sign.. If I cut the .125 with a fine cut tip at a slower speed then I don't have the issue..

I'm assuming the answer is to slow down a little but want to be sure there are no other issues here..

Thanks gang

[REDSTRIPE]

I would say slow down your cut or increase your amp. what's happing is the steel is thicker @ each diamond so it will effect cut quality. you need to try some practice cuts and find a happy medium for you machine.

[Marty]

just curious.....do you use/have a torch heigth control system?
I will be needing to cut some diamond plate so I want to see how this plays out
thanks

[jimcolt]

The little dross beads where the bumps are are pretty much unavoidable. If you have a height control that cannot rise over the bumps, cut it from the bottom (dross beads will still be present due to the thicker sections at the bumps). If you have a better height control...put the bumps up and you will see the heigh rise over each bump....beads will still be there. They will wipe right of, and are caused because of the transition between the thicker and thinner sections. It maybe could be minimized at slaoer speeds...it is worth a try.

Jim Colt

I would say slow down your cut or increase your amp. what's happing is the steel is thicker @ each diamond so it will effect cut quality. you need to try some practice cuts and find a happy medium for you machine.

[REDSTRIPE]

I have hieght control and it helps but it's not perfect. I still say try some practice cuts. Every machine set up is a little different. I keep a log on material cut and settings used. It's helpful for reference. Getting to know your machine and how it runs is part of the fun of plasma cutting.

[Diverdude]

I have a small file with a straight line, a zig zag and a circle I use to do test cuts with and fine tune my settings. I will even build special tools in sheetcam for things like diamond plate seperate from the same size smooth plate to cut the diamonds smoother.

[hooked]

Lou, the .25 diamond plate is it true bright? which is softer more like 5052 alum or is it diamond plate like one would use for doors on drains and sump pumps, which is normally 6061 t-6 and ive always had to slow down to get a nicer cut! and Jim's right the little dros beeds never go away! kyle

[Largemouthlou]

Thanks gang.. I keep forgetting to put in my machine set up when I post..

Yes I have an older CandCNC Dragon cut with DTHC, and it works pretty dang good but I'm always still a little nervous cutting diamond plate.. This is 6061 mill finish.
I do know I'm cutting a little high at the moment, but not wanting to totally trust the THC yet I guess and mess up a expensive cut..
My .25 flat plates cut with the same cut profile as the diamond plate, guess that is where learning the machine a little more will pan out.. Heck I have yet to cut a lick of steel and only a few pces of stainless so yes, I have a lot to learn

I will have to play with the cutting of diamond plate even more as time allows, I was a little more concerned with the side of the cut where the cut bumps out just a touch at the thicker part of the diamond..

Good to know I'm not far off with the dross at the diamonds.. Like I mentioned earlier on .125 polished 5052 that I use for lettered panels the fine cut seem to work better and leaves virtually no dross at the bumps which is important for a finish product... Maybe I just have the fine cut dialed in a little better..

[beefy]

If you can't get a fast enough THC Rate before losing steps, change out your motor for a higher torque one. Nema 23 motors can be had up to 620 oz/in.

The Candcnc THC is good but the mechanics have a part to play too. You could set your THC Rate to a much higher % but a tiny motor lifting a heavy z axis will lose steps. People who want very fast THC have used servos on their z axis.

Keith.

[Largemouthlou]

Thanks Keith.. I have the 620 oz motors now with a light weight gantry from Precision plasma. (some of his first to come out)
I also have his gear reduction boxes on all 3 axis.. The thc set in mach is either 25 or 28% now and it seems to have worked the best..

The one problem I have now is I need to fix the knuckle that connects the motor to the screw rod on the Z.. For some reason when I assembled I left the collar on the motor shaft to high and it is barely making contact with the other half on the screw rod so there is a touch of play (backlash) when the Z is first told to go in ither direction.. Unfortunatly the set screw stripped out when I tried to lossen it for adjustment, so untill I get time to drill it out and retap the collar for a new set screw I will have to deal with the cuts..

Thank you for your time in the last post and I do also visit the yahoo group from time to time, still learning here

[vmax549]

With the Z and THC it is not always about a stronger motor. Even a stronger motor will loose steps IF you run it too fast and it runs out of torque. It is MORE about proper gearing of the torch to motor ratio.

A stepper has a useable torque range as far as RPM. Get above it and you can loose steps .

Ideally you want to gear it to move the torch head 1 inch per rev of the motor. YES that seems backwards but it is NOT.

At that range the motor is normally in the middle of its useable torque range RPM wise.

A slow reacting Z can make cutting HARD to tune for a quality cut as the torch correction constantly LAGS too far behind the cut.

Just a thought, (;-) TP

[beefy]

Hey TP, how you going. I haven't had much action on the zone lately but I'm here quite a bit.

TP by the way has helped me out with quite a few things on another forum. He's been a significant part of my learning curve (thanks again TP).

TP it never occured to mention about the ratio of stepper turn to linear movement, thanks for bringing that up. Guess I'm just assuming the z axis is made as per Candcnc recommendations. However I think that 1" linear travel to 1 stepper revolution does not apply to the Candcnc Z-axis. Tom gives an ideal thread pitch for a stepper driven z axis which I think gives 1" of z travel for FIVE turns of the stepper, and for servos I think it is 10 turns to 1" inch travel.

I'm guessing this is because there's no acceleration / deceleration in THC moves and so the gearing must be a lot lower. The main axis have acceleration / deceleration to help and then the 1" to 1 stepper revolution is ideal. But maybe that's a terrible shock load to THC moves which can't build up the speed or slow down to a stop, it's either instant on or instant off at the speed the THC Rate setting gives.

Keith.

[vmax549]

HIYA Keith, As a rule I always gear the Z op that I can actually get Z occilation where the THC cannot keep up with the Z. Then back down the THC% untill the occilations stop. THAT would be the optimum and fastest possible Z speed.

Also most run a 23 series stepper on Plasma Z I run a 34 series.

The faster the Z can move means smoother cutting.


(;-) TP

[beefy]

Good info TP.

I've actually had my Z become a jack hammer before and turning down the THC Rate is what stopped it. However my gantry and drive system lacks rigidity and so it probably compounded the problem. Wow, that never actually occured to me until now. Not only will my lack of rigidity affect the cut edge (as it does), it will also make my z more susceptible to jack hammering above a certain THC rate setting.

So the breaking point of the THC speed could be when this jack hammering starts. Increasing the span setting would reduce this tendancy but of course gives a less "tight" control of arc volts (= cut height).

The way I'm working it out in my head now, is if you have a high torque z motor then the point at which oscillating starts will be your max. THC Rate, whereas with a low torque z motor the point at which you start losing steps will be your max. THC Rate.

I'm still learning from you TP.

Cheers,

Keith.

[vmax549]

HIYA Keith, YOU have it correct. With a small motor MOST try the "speed it up with lower gearing first", which is normally backwards to where you need to be. Steppers have a torque Band (rpm range that they work best in) you have to stay in it to work correctly and not loose steps.

(;-) TP