Cutting down a back blade - good idea?

[BukitCase]

Dragon, good luck on your first "real" cuts; the only thing I might like better about MY PM45 is if they'd come out with the XP version BEFORE I bought Still, it hasn't let me down YET, heaviest thing I've cut so far is 3/4 plate...

You may have already come up with a plan for your curved cuts, but if not here's what I do - use a straight strip of 1/4" plywood or masonite for a guide, typically 2" wide and just a bit longer than the cut - use maybe 4 large flat washers for spacers between the guide and the blade - you'll need to measure from the FAR side of the tip orifice to the part of the torch you'll use against the guide so you'll know where to place the guide -

Then clamp one end of the guide to the blade with a washer UNDER the guide (recessed enough NOT to "bump" the torch) - then more washers under the guide maybe every 4-5" as you pull on the other end of the guide, keeping enough tension on the guide so they don't fall out (convex side of the blade UP will make this easier, WITHOUT the torch lead dictating what angle your torch is at) - clamp the other end while pulling as much tension on it as you can -

IF you do this right, your guide probably won't even be singed (especially with the washers under so there's less heat transfer to the guide) - check your manual's cut speed chart and do a couple "dry runs" - you want your travel speed just a LITTLE bit slower than the chart for minimum HAZ (so you don't hafta make ANOTHER guide

Another thing I sometimes do - convert cut speed # to inches per SECOND, then mark the guide in SECONDS (60 ipm = 1" per SECOND) that way, in the DRY run I can practice counting (one thousand one, etc) - the torch should pass a marker every second, or you're going too fast or too slow - I know, sounds **** but it works...

Cutting edge - if its holes are equidistant, I would REMOVE it for TWO reasons - the obvious: it'll just be in the way of a clean cut, and (2) usually ONE 12" piece of cutting edge might be a more useful "resource" for another project than TWO 6" pieces...

Or, you could just FREEHAND it, and call those wavy edges an ARTISTIC FEATURE .. Steve

 

[ovrszd]

You'll want a guide. The above described homemade guide will work fine.

I just use sunglasses.

Plasma Cutters are picky.

They don't like very rusty metal. Knock off the big chunks with a flapper wheel or grinder.

They absolutely don't like to be struck on solid metal. Pull the trigger with the tip off the edge, then progress into the metal. Fastest way to ruin a tip is causing the heat to reflect back into the tip.

They don't like to cut thru more than one layer of metal. You'll likely ruin the tip if you try to cut thru the moldboard and cutting edge with them bolted together. At a minimum you'll make a terribly nasty looking cut.

Remove the cutter, make a good guide, use patience. Not sure what Cutter you have so can't suggest an appropriate speed. I watch the existing material and can tell if I'm going too fast. Don't think it's possible to go too slow.

You got this, go for it.

P.S. Definitely need video of chopping up the hot tub with a chainsaw!!!!

 

[BukitCase]

"Don't think it's possible to go too slow."

Too slow for me, and I end up with a LOT more slag around the cut - but I use one of these

Air Impact Hammer Kit

with the flat chisel, heavy gloves on, hold the flat side of the chisel against the cut edge and "tease" the trigger (easier to control) - run it along the edge and any slag that sticks up will be gone. If I want the edge itself smoother, a flap disk works pretty good.... Steve

 

[ovrszd]

"Don't think it's possible to go too slow."

Too slow for me, and I end up with a LOT more slag around the cut - but I use one of these

Air Impact Hammer Kit

with the flat chisel, heavy gloves on, hold the flat side of the chisel against the cut edge and "tease" the trigger (easier to control) - run it along the edge and any slag that sticks up will be gone. If I want the edge itself smoother, a flap disk works pretty good.... Steve

Yep, if speed is appropriate slag will be minimal and easy to remove.

I figured for his first time he'd be wiser to know when he's going too fast than too slow.

 

[dragoneggs]

Thank you Steve and Richard for the tips and confidence. I like the template idea. I will see just how easy it is to remove the mold board. That might be too big a chore. I'm indeed the **** type so I do appreciate your suggestions. But since this is just something to drag in the dirt and rocks... I suppose an imperfect edge or two and the fact that it won't be staring me in the face, it shouldn't haunt me later.

Hot tub update: Ripped off the side boards and severed many of the air and water lines with my sawzall and uncovered lots of critter poop and quite the ammonia smell! Now wife has instructed me to wear full respirator with P100 filters. Luckily I have one. She also wants me to sterilize the area with beach/water solution before I start the major portion of the slaughter. I might pass on that part. I don't feel like making diarrhea! :laughing:

 

[Oldoak]

That's what I'm thinking but always nice to get a bunch of second opinions! This is moving up on my to-do list now that I can make relatively quick work of it. This will be fun! First I need to chop up my 20 year old Coleman hot tub. Thinking a chainsaw for that! Probably ought to do a video of the potential debacle.

Wow! I'm glad you explained what you were planning to do with the chain saw. Thought for a second, you were going to cut the back blade with it.

U-tube title, "Don't Attempt This".

 

[dragoneggs]

Well my small chainsaw threw the chain. Did not like the fiberglass. My big saw chain dull so I gave that up after a few vertical slices. The hero was my 20v Dewalt recip saw! Here is the progress so far... taking a breather. Nasty cutting.

 

[Thomas]

Good guide plasma cutter hand ginder your all set...save the cut piece never know when they will come in handy.

 

[ovrszd]

Well my small chainsaw threw the chain. Did not like the fiberglass. My big saw chain dull so I gave that up after a few vertical slices. The hero was my 20v Dewalt recip saw! Here is the progress so far... taking a breather. Nasty cutting.

View attachment 503440

With a view like that I'd struggle to stay productive!!!!!! :thumbsup:

You'll probably want a shower after this.

 

[BukitCase]

"You'll probably want a shower after this."

Richard, he lives in western Washington; if he stands there another 5 minutes he'll GET a shower :laughing: ...Steve