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all depends on how true your motion is and what kind of plasma source you have, If im right the HPR series from Hypertherm will do that. Im sure Jim colt will chime in on if im right or not.
what kind of machine do you have?
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Is there any way to make a cnc plasma machine that could cut 3/4" holes in 3/8 to 1/2 inch plate with .005 to .010 accuracy?
all depends on how true your motion is and what kind of plasma source you have, If im right the HPR series from Hypertherm will do that. Im sure Jim colt will chime in on if im right or not.
what kind of machine do you have?
We have a thermal dynamics 200 and 150
All we really need is tight tolerance on the hole size.
We commonly do 5/16 holes in 3/8" plate with approx .005" taper (bottom of the hole smaller than the top). 3/4" holes in 3/8" and 1/2" plate can be done very well with the right equipment.
Good hole quality requires:
1. A high definition class plasma system. This is the latest technology that uses oxygen as the plasma gas and air as the shield gas.....these systems produce more energy density in the arc....which means a squarer cut edge.
2. An accurate THC (torch height control) that is designed for use with high definition plasma. Torch heigh accuracy must be controlled to plus or minus 1 volt or .004".
3. CNC control with functionality that will allow for proper timing of the motion as well as the off time of the plasma system.
4. Proper part programming.....torch height disables, arc cutoff time...and overburns when cutting holes are absolutely necessary.
Jim Colt
So with all of that we should be able to cut holes that are 0.750 inch and not 0.760 or 0.740?
Unless you have a LOT of holes to cut (meaning thousands) the cost to move up to HD and all the frills will make you sit down and take a deep breath. Even then I question if you can hold .010 across the diameter (.005 on each side). Maybe if everything is perfect, but depending on your material cost it may be a real disappointment to cut a whole sheet then find some adjustment is off and it's all scrap. I think I would look at maybe a special use CNC drilling machine. If you need conventional shape cutting you could combine a hole saw/drilling head on a table with plasma.
On one job I had where the holes had to be precise I first cut the shapes with the holes undersized and built a gig on a vertical mill to mill out the holes precisely at .750.
TOM CAUDLE
www.CandCNC.com
If the tolerances need to be plus or minus .010....then a drill or a laser will likely be necessary. If you can live with plus or minus .015...then you can do it with a high def plasma on a precision machine in most cases. If you look at capital equipment costs and operating costs over time...the plasma will be the best choice. If capital equipment cost is more important than operating costs...then the drill may be the best choice.
There are a lot of factors that need consideration...capital cost, operating cost, throughput, tolerance, maintenance...etc.
Jim
setup a drill on your table to do spot drilling then you can accurately drill them later. But Ill side with torchhead on this one, you'll be disapointed with an HD plasma if your trying to get things perfect. And overburning the holes with the HPR series of plasma is a major pain in the but Jim! been there done that dealt with the costumers that get very tired of the plasma stoppoing all the time!
Overburn is simply programming holes with a radius that extends past 360 degrees.....and during this overburn, while the motion continues the plasma is extinguished. It is extremely easy to do (if your software allows it!).....and is absolutely necessary if you want excellent hole quality...with any plasma system. We have thousands of end users that are cutting very nice holes using this technique!
Jim
Isnt shopdata one of those programs that is supposed to allow that? It never worked well at any of the customer sites that i was at installing machines. constant arc outs.
It actually is a combination function between the cnc control and the software. The software provids the cut path.....and can design holes with an overburn instead of a lead out. SDS (at least the newer versions) can do that. The cutoff time.....which is a timing or distance function of the cnc that shuts off the plasma before the end of the program...so that the arc extinguishes after crossing the lead in kerf, but before it gets to the end of the motion path....is a combination of machine code (from SDS) and CNC control function.
What cnc control do you have?
Jim
used to work for multicam in canada (western distributor) travelling drove me and my family nuts though so i quit there. But I was always having problems with arc out on holes. Love working on the HPR series though I installed quite a few 130's and 260's all the autogas versions too.
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