Shielded vs Unshielded and Hypertherm cut guestions????

[cbassjr]

I have a hypertherm power max 85. I have a production run tomorrow for a customer cutting some 1/2" plate. Currently did a test cut and have the machine set up with 65 amp shielded consumables. Did a test cut on some 10 gauge and like the cut. Each part has a 1" hole and wondering what I should have the kerf set to as you can definitely see the kerf on the 10 Guage and am concerned about the holes when I go to 1/2" plate. Also to get a 1" hole pretty exact what should I actually have the hole diameter be in cad as when I mic - ed the holes they were like .945. The first part of the question is when to run unshielded and why?

[muzza]

Only true way to check kerf width is to do a test cut and measure it.

As for circle size, if I want a 1" hole, I draw a 1" hole. The kerf width is accounted for in my Sheetcam settings, when I used PlasmaCam that too had provision to enter kerf offset so I assume other systems would too (not sure what you run). That way your kerf is always offset to the correct side of the cut automatically, saves another chance of a simple mistake by doing it manually.
Murray

[plain ol Bill]

Like Muzza I expect my equipment to cut to dimension. When changing from one type consumable to another the true kerf width can change. Check the Hypertherm consumables cut info for Kerf width for particular nozzles and enter that into your Sheetcam info. Best bet - cut a practice hole in the same thickness material with the same consumables and check it w/ calipers or mike it.

[cbassjr]

Like Muzza I expect my equipment to cut to dimension. When changing from one type consumable to another the true kerf width can change. Check the Hypertherm consumables cut info for Kerf width for particular nozzles and enter that into your Sheetcam info. Best bet - cut a practice hole in the same thickness material with the same consumables and check it w/ calipers or mike it.

All my setting were pre-programmed from arclight. For some reason I can't seem to find them in my hypertherm manual to make sure they are correct. When I did the test cut on the 10 Guage on the 1 inch hole it's exactly 1 inch on the cut side and a 16th less on the kerf side. Since the customer doesn't have a 1 inch drill to take the kerf out and my price doesn't include me putting it on my drill press and finishing the clean up with my 1 inch drill. I'm just concerned when I cut the 1/2 inch that the kerf is no more than 1/16 as I have several other projects for this customer that require holes.

[B Holmes]

I think you mean taper, as the bottom of the hole is smaller than the top. Kerf is the width of the actual cut itself.
Might want to cut a test hole in 1/2" material and just adjust the hole diameter in the drawing as needed. I usually increase hole diameter 1/16" over the desired finished hole size, and have pretty good results.

[beefy]

Like others have said, I'd do some test holes and adjust your kerf width until the hole is the diameter you want it. Of course you have to allow for the taper and measure (usually) at the bottom where the hole diameter will be less. Even if the customer did have the right size drill, there's going to be a hard nitrided surface to deal with. Better to get the diameter right with the cut.

As far as when to use unshielded consumables goes, I believe there main purpose is to get into tight spots that can not be accessed by the extra size of the shielded consumables. What I've mainly heard is always use shielded consumables if you can.

Keith.

[jimcolt]

There are around 25 pages of cut charts (In the Powermax operators manual) for different power levels and material types and thicknesses. Just before these cut charts are the kerf width compensation charts. The numbers in the charts are good starting points...however anything you change (slower cut speed= wider kerf, higher height = wider kerf, worn consumables = wider kerf, etc.) can affect the kerf width.

I recommend using shielded consumables for all cutting. The non shielded consumables will have shorter life and poorer cut quality. They are listed in the manual because there are some 3 dimensional (robotics, pipe cutting, etc.) where they fit into tight spots a little better than shielded parts.

Rule of thumb: Best cut quality is always achieved with the lowest powered process that the cuts charts suggest for the material thickness you need to cut. As an example....you can cut 10 gauge with Finecut consumables, 45 amp shielded, 65 amp shielded, and 85 amp shielded. 85 amps will be the fastest, but will produce a wider kerf and a lot of edge taper. The Fine cuts will be the slowest but with the best accuracy and squarest cut edge.

Jim Colt Hypertherm