7/8" holes in 3/8" plate

[jcoe1]

I have a buddy at work that wants me cut some wheels centers from 3/8" plate for Rockwell axles.

Over the weekend I attempted to cut some test holes for the wheel stud. The only way I can get an actual hole is leaving the height control in manual mode. With a pierce height of .18 it pierces ok but cutting at that height makes for horrible bevel and and ugly hole. I am cutting counterclockwise also.

Miller 2050 at 55 amp. 10ipm
Red avhc
Zeks refrigerated air dryer
Motorguard filter.

Am I waisting my time and consumables trying to cut a 7/8" hole in 3/8" plate with this equipment? Or can it be done?

[jcoe1]

http://www.plasmaspider.com/viewtopic.php?f=4&t=6278

This thread makes me feel like I'm doing something horribly wrong.

[Shane Warnick]

7/8" holes in 3/8' plate should not be a problem. Make sure your consumables are good, and your air pressure is spot on. If your angularity is that bad you may be higher than you think you are, or a lot lower than you think. I think the pierce height is ok, maybe a little low, but that is about where I cut 3/8" at with 40 amps all the time. It could be you are junking up the nozzle when you pierce, not sure if it would help but maybe if you pierced a few holes then changes to new consumables and went back and cut the holes they may come out with less angularity. Not sure what your pierce delay is but make sure you are all the way through before moving the torch or it will blow molten metal back up into the nozzle. Only other thing I can think of is make sure you are grounded to a clean spot on the plate not just the table.

Shane

[jcoe1]

I'm running torchmate software so my pierce delay is controlled by dwell time which is set to 5.8 sec currently. I have new consumables on they as I destroyed the last of my tips and my electrode finally gave out. I have read in multiple threads that with avhc it should be left in manual mode for small holes but how is anybody getting the correct cut height after a pierce at .18" or more? I have the red display torchmate avhc by the way.

[Gamelord]

I have the same AVHC and cut 3/8" stainless plate with 1/2" holes. It cuts fine for me although I do undersize them by .10 and then drill out afterwords. Double check the direction as you can reverse the CW or CCW direction in the software and although you have it set CCW, it may not be. You may want to try CW direction on a scrap piece as a test, just to see what happens. Also, slow your speed down by 50-60% while cutting your holes. That should really help. I haven't been able to get holes as good as what Jim Colt advertises with his Hypertherm machines, but they have been pretty good.

Hope that helps.

[jimcolt]

These are 1/4" holes in 1/4" plate. Bolt drops through tightly. Getting accurate holes requires:

- A height control freeze. Height control has to pierce at pierce height....and stay at that height until the pierce delay time has timed out (from the Hypertherm cut charts), then index down to cut height and freeze at that height until the hole is done. If the machine goes into arc voltage control....it will dive into the plate and the hole will go out of round.

Some CNC machines will not allow the Arc voltage control unless program speed default setting is met. Torchmate does not have this capability. This function is called AVC disable or height freeze....on Torchmate and other brands you have to put the THC in manual mode.

-Needs to cut the hole at a lower speed....I suggest 60% of book speed on holes under 1" dia.

-A good plasma with the lowest powered consumables installed that will cut the material in question.

Jim Colt

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[jcoe1]

gamelord,

What plasma cutter are you using and what are you doing for your cut height after the pierce?

Jim,

Thanks for your response. You confirmed my idea that there was some functionality that my height control lacked compared to others. I guess I'll try and find a way around it.

[jimcolt]

These particular holes were cut with a Powermax30XP on a Plasmacam machine with advanced height control. Normally I have a Powermax85 on that machine....and cut quality would be essentially the same.

A proper plasma cutting height control:

-Uses ohmic contact to sense the exact location of the material without deflection.
-Retracts to the (operator set) pierce height.
-Pierces, stays in place (no x, y or z movement) until the (operator set) pierce delay timer times out.
-Indexes down to cut height (operator set as a physical cut height, it is based on the system knowing where the surface of the plate is from step 1).
-The software recognizes that the hole diameter is under 1" diameter (operator setup parameter), and freezes the height at that setting for the entire hole.
- Z axis retracts after hole is complete, cycle starts again on the next pierce point.
-If hole is larger than 1" diameter, the arc voltage feedback height is allowed to activate once the x or y speed achieves a certain percentage of the (operator set) programmed speed. The percentage (usually around 80% to 90%) disables (freezes height) when the machine has to slow for intricate areas of the cut that would cause the height control to dive.

Note:....this type of functionality should be on every cnc plasma. If the height freeze functions are not there or are not set correctly....expect collisions and diving or incorrect torch height. Incorrect height will affect hole taper and roundness. Unfortunately...there are height control systems on the market that doi not have this level of performance....and expect shorter consumable life and lesser cut quality.

Jim Colt Hypertherm

gamelord,

What plasma cutter are you using and what are you doing for your cut height after the pierce?

Jim,

Thanks for your response. You confirmed my idea that there was some functionality that my height control lacked compared to others. I guess I'll try and find a way around it.

[tnbndr]

Jim:
To get height control off on holes using Sheetcam is it best to put them on their own layer and use a toolset with DTHC off? Or is there a better way to control this in Sheetcam.?

[jimcolt]

I have never used sheetcam....can't answer that. Maybe someone else can?

Jim

Jim:
To get height control off on holes using Sheetcam is it best to put them on their own layer and use a toolset with DTHC off? Or is there a better way to control this in Sheetcam.?

[I Lean]

Jim:
To get height control off on holes using Sheetcam is it best to put them on their own layer and use a toolset with DTHC off? Or is there a better way to control this in Sheetcam.?

I do essentially this--but I use the M101/M102 commands to turn the THC on/off. (turn off before cutting the holes, turn back on before cutting the rest of the part)

[Brand X]

Jim:
To get height control off on holes using Sheetcam is it best to put them on their own layer and use a toolset with DTHC off? Or is there a better way to control this in Sheetcam.?

Yes,
Sheetcam cutting rules for circles/etc..


https://www.youtube.com/watch?v=hC_TRbmlzpE

[Gamelord]

I am using a Thermal Dynamics cutmaster 101 and I leave my THC on during the cut.