Cutting down a back blade - good idea?

[texasranger556]

Job done! Took longer than I thought only because my welder, plasma cutter, and air compressor are all sharing one 220v outlet. What a pain! I really need to put in a sub panel and bring more juice to my shop.

Plasma easily cut the 1/4in but struggled with the 1/2in. Got some ideas why but think I will start a new thread in the welding forum because I don't think it is a simple solution due to the tapered thickness of the cutting edge.

What plasma cutter do you have? You can just max it out and go slow to go slightly over the rated thickness...assuming it is a hypertherm. Mine is rated for 1/2 but it will cut 5/8 fairly cleanly if you're patient.

 

[dragoneggs]

I have the Hypertherm 45xp and turned up to the max. Several potential issues. First I am running a 100ft extension cord from a dryer outlet so maybe that doesn't help. But I didn't trip a breaker. I was going very slow and it started cutting fine at the ends (1/4in thick) but when I approached the thickest (1/2in) it didn't want to cut it. Lots of rust and paint... does that matter? Tons of dross that I had to grind off.

I was thinking maybe the 45xp auto adjusts for thickness when it starts and if the material thickness changes during the cut, maybe it can't adjust on the fly? I was drag cutting and it was hard to pull smoothly on the rougher and sloped surface. Until now I have only cut thin clean material that is flat and horizontal. Lot's to learn.

 

[BukitCase]

Dragon, your PM45XP should have less problem with that thickness than my older PM45, and mine will cut up to 1" material - it's REALLY slow at that thickness tho, rated speed is 4"/minute with 1" material -

Also, those bolts look like standard plow bolts, they have a square shoulder between the head and the threaded part - if you got a nut a bit loose, it's possible you pushed the head out just far enough for the shoulder to MISS its square hole - whatever, when you put the cutting edge (most of it) back, I'd recommend making sure the square holes are good (might be able to mig 'em a bit tighter if not) and find a REAL fastener place that has new plow bolts... Steve

 

[dragoneggs]

Steve, the bolt holes were rounded enough that they spun. I did put them back in and they cinched up fine so I guess I'm good to go. I probably should have cleaned it all up and painted before reassembling but it just a dang blade that gonna get tortured some more. Maybe I will take it apart and paint it Kubota orange and the cutting blade black just to give it some love.

Something isn't right with my cut though. Maybe the cutting blade is hardened steel and harder to cut??? I am confused. I have some 1/2in mild steel plate scrap that I might try and see if the results are different.

 

[texasranger556]

I have the Hypertherm 45xp and turned up to the max. Several potential issues. First I am running a 100ft extension cord from a dryer outlet so maybe that doesn't help. But I didn't trip a breaker. I was going very slow and it started cutting fine at the ends (1/4in thick) but when I approached the thickest (1/2in) it didn't want to cut it. Lots of rust and paint... does that matter? Tons of dross that I had to grind off.

I was thinking maybe the 45xp auto adjusts for thickness when it starts and if the material thickness changes during the cut, maybe it can't adjust on the fly? I was drag cutting and it was hard to pull smoothly on the rougher and sloped surface. Until now I have only cut thin clean material that is flat and horizontal. Lot's to learn.

Ok, same machine as mine but newer. Hardness shouldn't matter, I've cut through sockets and spring steel just the same as mild steel. I will say that when I cut my scraper blade it was the first thing I cut with my plasma cutter and I knew the bolts would spin like yours so I just left an extra 1/8" and burned though both layers then cleaned it up with a flap wheel. Since then I've cut the scrap cutting edge for another project and had no issues.

Practice again on the scrap piece you just cut off. I suspect it is just a case of your tip sticking to the metal and then "jumping" as you drag. If you jump or go too fast you'll see the sparks shoot back up at you for a split second rather than a nice consistent shower down through. On really scabby steel I will run the grinder down where I want to cut to smooth it out which helps you drag cut smoothly.

How heavy is your extension cord? If it is only #10 wire then you could be dropping too much voltage at 100'. My extension is #6 wire and about 20' long from a 100 amp sub panel in my garage.

 

[ovrszd]

A Plasma Cutter doesn't like dirty metal. Mostly for the reason Ranger mentioned above. Hard to be steady with tip movement when it's catching on every rough spot it comes to. I flapper wheel everything first to get a smooth "slide" of the tip.

I was pretty sure you were going to end up taking the cutter edge off. I like my Plasma Cutter a LOT. One of my most valued tools in my shop. I NEVER try to cut two layers at once. All you are doing is ruining expendables.

As to your electrical limitation. I have my Welder and Plasma Cutter mounted on a cart. The cart has three 220V plugins. One long cord that I plug into an outlet. The two machines are plugged into the cart terminals. So I can switch from one tool to the next without any change of cords.

Glad you got your project done. Hope the blade works as you expect.

 

[dragoneggs]

Thanks guys... yeah it was difficult to smoothly drag on the blade. I will clean next time. I do think I have too much voltage drop and that is main culprit along with my unsteadiness at very low drag. Think I will go out and measure my voltage without load but I assume it is really the voltage under load that matters and not sure how to check that.

 

[texasranger556]

100' of #10 copper at 240v AC is estimated to drop 6 volts when pulling 30 amps. Add in whatever is between your dryer plug and the panel and you're probably closer to 8 or 9 volt drop from the panel. While that is more than the recommended 3% voltage drop, I'd be surprised if it is causing problems for an inverter based cutter.

You're correct that measuring open circuit voltage isn't going to tell you much.

Also check your nozzle. I burnt my first one up pretty fast before I added a filter dryer to my air compressor.

 

[BukitCase]

"I assume it is really the voltage under load that matters and not sure how to check that."

Best way is to already have that multi-outlet setup you're talking about (and I already have) - then you can have a helper run (watch) the volt meter (as close to the machine as possible, NOT at the dryer outlet - you can check non-loaded voltage first, then have the helper watch the meter while you do a cut. Hint - first make sure the meter is NOT on "auto-range", usually they have a Range button you push ONCE to lock that range with a stable input, then successive pushes increment/decrement the range.

Without a multi-outlet box, you MIGHT be able to pull the PM45's plug out just far enough to get the meter leads to touch both hot pins, but this is not for the faint-of-heart or shaky-of-hand, or a wife that's not used to being a helper -

If I were you (as in, haven't built that multi-outlet box yet) I would do that first - I'd use heavy enough wire (#6 on mine), and use a nema 6-50 plug and sockets - then you could just plug THAT into your extension cord, plasma into one of the females and test leads into another (you'd still need a "watcher", and still defeat auto-range) -

You may wanna make your multi-plug just long enough to reach your intended NEW weld plug from wherever your welders will be, and make another extension for use when you need extra reach - I have a 6-50 extension that's 85 feet long with 2 females, another that's 25 feet with 3 females, and one more that's 10 feet with 3 females (did I mention I like OPTIONS??!? )

I mount 1 6-50 female per 4-plex deep box, and for multiples I'll knock out TWO plugs between 2 boxes and tie them together with 2 chase nipples - this keeps them from wanting to rotate on a single chase nipple - Also, with that heavy a wires it lets you run the "daisy-chain" thru BOTH nipples, typically 2 hots thru one nipple and ground/neutral thru the other.

For running over rough surfaces, and for circle cuts - I use one of these

Plasma Cutting Guide | Flange Wizard

check out the whole page, they also have a bevel guide that works with it. 2 wheels with straight cuts, set just enough tip height to clear the "crusties" - for circles a single wheel works well, check the page for more... Steve

 

[Code54]

If you have not tried it, look at metal cutting circular saws. For straight cuts I use it over my plasma every time. Was cutting 6" wide 1/4" C channel the other day in about 15-20 seconds a cut. Nice clean perfect cut every time. I have the Harbor Freight saw (think it was $69) but don't think they sell it any longer. More than worth the price! Even cut some 1" solid steel rod without any issues and ready to weld soon as the cut is done!

 

[dragoneggs]

If you have not tried it, look at metal cutting circular saws. For straight cuts I use it over my plasma every time. Was cutting 6" wide 1/4" C channel the other day in about 15-20 seconds a cut. Nice clean perfect cut every time. I have the Harbor Freight saw (think it was $69) but don't think they sell it any longer. More than worth the price! Even cut some 1" solid steel rod without any issues and ready to weld soon as the cut is done!

I have been considering a dry cut saw. Been looking at a few namely Makita and Evolution. Like the miter cut ability. What I liked about the plasma is I never had to unload the back blade from my FEL bucket... made a great saw horse and I could raise it to the height I wanted.

 

[texasranger556]

I've got the Evolution saw. Works amazing for angle iron, box tube, pipe and even pieces of I-beam. Seems plenty powerful, although I have managed to chip enough of the teeth to warrant replacing the blade. $50 for a new blade hurts a bit.

The table is not as sturdy as it could be, and the clamp doesn't have a quick release, but for the ~$225 I paid several years ago I have no regrets.

 

[dragoneggs]

Just thought I would add... after reading the manual again tonight. The new 45XP standard tip is a specially designed drag cutting tip and the manual recommends drag cutting. Even with my sophomoric plasma cutting efforts to date my tip still looks good. I have really appreciated all the comments on this thread. From now on...

1. Clean the cutting surface.
2. Go slow and follow the cut speeds for different thicknesses
3. And most important... get more power to my shop!

I also learned how the lack of C25 gas affects MIG welding. First time I used my MIG outside to tack weld the plow bolts and it wasn't windy but I thought that was the reason for the sizzling ugly tacks. But in haste, I never turned the gas on because I was so focused on getting the dang nuts off. :duh:

 

[ovrszd]

Oh man,,, I've done that soooooo many times.......

 

[shaeff]

Oh man,,, I've done that soooooo many times.......

Me too! Always in haste, need to get this job done NOW!

"Why do my welds SUCK!?"

...
...

"D'oh!!!"

 

[ovrszd]

Me too! Always in haste, need to get this job done NOW!

"Why do my welds SUCK!?"

...
...

"D'oh!!!"

And it's ALWAYS where the weld is most seen......

 

[shaeff]

And it's ALWAYS where the weld is most seen......

Haha! I'm glad it's not just me!

 

[dragoneggs]

Someone suggested saving my scrap for something else and of course I save all my trimmings. But tonight the brain wires touched briefly and I think I will attempt to make a 4 1/2in wide trencher. Actually I can make two! Thinking one could be a very useful BH mounted version, and the other... if it doesn't end up as a sad first prototype... maybe it could become a FEL bucket mounted trencher/shovel?

 

[ovrszd]

I can hear the brain churning from here!!!