[Jhenry95]

Brand new to the world of CNC plasma cutting and need some help. I am getting intermitten wavy cuts on a 16 gauge, 4 inch by 4 inch triangular bracket that we are making for a customer. Using a Hypertherm 105 plasma cutter with 45 amp fine cut consumables on an Arclight CNC table. I have layed out a 4x8 sheet of the brackets with sheet cam and running at 250 ipm using Mach3. We will get anywhere from 5 to 10 very good quality cut parts then maybe 2 or 3 with wavy cuts on one of the sides then back to 5 to 10 good ones. I have attached a pic of the issue(notice diagonal cut on top bracket). Any help would be greatly appreciated. Thanks.

[jimcolt]

Rest your hand on the torch while it is cutting a wavy part.....I suspect you will feel oscillation in the drives. From the pictures it looks like it may be more pronounced on the diagonals....which often indicates a drive tuning issue (perhaps the acceleration or gains are adjusted too hot), or it could be a loose component (motor mount, loose belt, loose pinion gear) causing mechanical backlash. While the machine is powered up, but motion stopped....see if you can feel any play or backlash in the torch carriage and either end of the gantry.

Even better, contact Arclight Dynamics...they are the experts on their machine design....and may recognize the issue immediately.

Jim Colt Hypertherm

[Jhenry95]

Jim,
Thanks for the response. I have contacted Arclight and we have tried a few things without any success. I cut out another sheet of a 6x8x10 triangular bracket yesterday and had the same wavy cut issue. I put my hand on the torch and only felt a very slight oscillation in the drives. I also did not feel any backlash in the torch carriage or gantry. While cutting the parts yesterday I did turn off the DTHC for half the sheet and did not have any parts with wavy cuts, as soon as I turned it back on the wavy cuts started again. Is there a way to adjust the DTHC?

[jimcolt]

I am not real familiar with their THC system (I think it is from www.candcnc.com). There are likely z axis speed settings and maybe even acceleration settings that can be slightly slowed or deadened that will likely solve your issue. I would work with ArcLight.....letting them know that the cuts smooth out when the height control is disabled.

Jim Colt

Jim,
Thanks for the response. I have contacted Arclight and we have tried a few things without any success. I cut out another sheet of a 6x8x10 triangular bracket yesterday and had the same wavy cut issue. I put my hand on the torch and only felt a very slight oscillation in the drives. I also did not feel any backlash in the torch carriage or gantry. While cutting the parts yesterday I did turn off the DTHC for half the sheet and did not have any parts with wavy cuts, as soon as I turned it back on the wavy cuts started again. Is there a way to adjust the DTHC?

[Torchhead]

Watch the Z motor shaft or lightly touch the Z axis motor coupler if you can get to it. Does the Z "oscillate " up and down rapidly as it cuts kinda like a sewing machine? There are a couple of settings to combat that on thinner material: 1. turn the Z velocity down by 10 ro 20% and see if it improves. 2. open the Cut profile and find the Span Volts. It is 1/4 volt units (4/4 = 1 volt) raise it to 6/4 or 8/4 and see if the bounce stops. It makes the DTHC less sensitive to voltage change. The THC Rate controls the response speed . If it is the DTHC causing the ripples then one or both of those settings will fix it.

If it is mechanical in the Z motion then you should be able to focus on the tip of the torch and see it moving back and forth slightly or when its not cutting rapid the Z up and down using the Shift-PageUP/DOWN keys. Its not the same as running under THC because there is no acceleration /deceleration curve during THC moves so the motion is more harsh but if is mechanical it has to be in the Z because with the DTHC off the Z does not move.

[Lasersolution]