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Any idea why I am getting angled cuts?

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Greolt
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Any idea why I am getting angled cuts?

Postby Greolt » Fri Aug 04, 2017 3:22 am

Lotos LTP5000 50 amp plasma cutter. Self made CNC table.

I paid $250 for my cheap plasma and can not justify paying ten or more times as much for a Hypertherm. (I don't live in the US, that's how much they cost) It would be nice, but as a hobbyist, it is just not going to happen.

It works really well in all but one respect. I get angled cuts.

Torch is perpendicular to the material. New consumables. AG-60 / SG-55 machine torch. Good air supply.

Cuts in 5mm mild steel are excellent in all other respects. Smooth. Virtually no dross.

Now here is the strange part.

Cutting a 25mm square, two opposite sides of the square are perfect. (A and C)

(B and D) are angled in the same direction. Just as if the torch was on a twenty degree angle. (it is not)

See my rough sketch.

Logic tells me the air stream is not coming out of the torch perpendicular to the nozzle.

Maybe my air pressure is incorrect. Maybe it is just a cheap torch and will never be any good.

Any ideas?

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michmetalman
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Re: Any idea why I am getting angled cuts?

Postby michmetalman » Fri Aug 04, 2017 7:46 am

My guess is cheap torch...you get what you pay for in a plasma cutter.

cstroke
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Re: Any idea why I am getting angled cuts?

Postby cstroke » Fri Aug 04, 2017 8:30 am

check cut direction as well.

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acourtjester
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Re: Any idea why I am getting angled cuts?

Postby acourtjester » Fri Aug 04, 2017 12:09 pm

If you think
Logic tells me the air stream is not coming out of the torch perpendicular to the nozzle.
put some water on the material and see where is moves to when you fire the torch for a second, try with different torch heights.
I should move equally away from the center of the air blast.
You could have a problem with the swirl ring if it has one.
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jimcolt
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Re: Any idea why I am getting angled cuts?

Postby jimcolt » Fri Aug 04, 2017 1:40 pm

There are two basic types of cut edge angularity with Plasma cutting that tell a story:

1. Relatively similar angularity on all four sides of a rectangle. This means that the torch and consumables are likely in good shape. You can minimize the angularity by adjusting your height control lower, however with an air plasma (even a good one) you will not completely eliminate angularity. Here is a picture of a good quality cut on 1/4" (6mm) steel, the cut looks nice and the average angle is just over 2 degrees positive from the expected 90 degree edge.
Powermax45 edge angle 004.jpg
Powermax45 edge angle 003.jpg



2. If the angularity varies as shown in your diagram....with parallel angles on opposite sides, then you either have a torch that has some air flow concentricity issues, a poor designed torch (yours looks like a copy of a 35 plus year old Esab torch design, definitely old technology, but cheap), or you have damaged consumables from piercing too close or with inadequate pierce delay time.

The major brand plasma's (especially Hypertherm) have better torch technology, better consumable design and have many pages of cut specifications that will allow you to pierce materials without damaging the consumables and to cut at the correct height (height control is necessary) and speed every time. It is normal to get well over 1000 starts out of a set of consumables as compared to 100 or so with the low cost imports. There is a difference , and it does cost more to buy better performing systems, however over time they prove to be less expensive (less rework, less scrap, faster cut speeds, etc.). Jim Colt

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WyoGreen
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Re: Any idea why I am getting angled cuts?

Postby WyoGreen » Fri Aug 04, 2017 8:23 pm

You might try rotating your torch 90 degrees and see if the angularity moves to the other 2 sides, which might tell you whether it's the torch or something else.

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Greolt
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Re: Any idea why I am getting angled cuts?

Postby Greolt » Fri Aug 04, 2017 8:55 pm

Steve
Yes I was just thinking that would be a good test to do.
I will get on to it.

Greolt
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Re: Any idea why I am getting angled cuts?

Postby Greolt » Fri Aug 04, 2017 9:58 pm

jimcolt wrote:There is a difference , and it does cost more to buy better performing systems, however over time they prove to be less expensive (less rework, less scrap, faster cut speeds, etc.). Jim Colt


Jim

Thanks for your thoughts. If I was making a living with this plasma table, I would spend $$$s on a top line cutter without hesitation. The harsh fact is, if that was my ONLY option, then I would NOT have a plasma table. Surely I am not the only hobbyist on the forum.

I have made a lot of great things on my table. It really works extremely well for the money spent.

It costs me about a two dollars to replace electrode and nozzle. If that happens more often, then I can deal with that. I am still on my first pack of ten after a year.

So my aim is to see if I can improve my cuts in heavier material, within the budget constraints of a retired hobbyist. :D

Countach
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Re: Any idea why I am getting angled cuts?

Postby Countach » Sat Aug 05, 2017 4:15 am

I had this exact same problem with a Simadre Cut 50dp, fought it for months. I was using cheap eBay consumables switched over to the OEM parts and it was fixed.

Greolt
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Re: Any idea why I am getting angled cuts?

Postby Greolt » Sun Aug 06, 2017 2:22 am

Acourtjester
I could think of no quick way to have the air solenoid turn on without the pilot arc. So did not try your suggestion.

Steve
Turned the torch 90 degrees and the angled cut followed as expected.

So I guess that only leaves the concentricity of the air flow as Jim suggests.

No doubt there is a lot of science around swirl angles, air velocity, nozzle shape and size etc.

It actually improved a bit by increasing the air pressure to about 90 psi. Quite a bit more than the suggested 65 psi.

May try a different torch or maybe even the hand held torch that came with the cutter. See if that makes any difference.

Greolt
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Re: Any idea why I am getting angled cuts?

Postby Greolt » Mon Aug 07, 2017 5:22 am

Put the hand torch on as well as tried a few different air pressures and voltage on the THC.

Was able to get some variation in angularity. Not perfect but better.

So it needs time to go through a comprehensive set of tests at different settings. See how good I can get it.

That would be one great advantage of a Hypertherm or similar. To have those comprehensive cut charts.

Greolt
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Re: Any idea why I am getting angled cuts?

Postby Greolt » Sun Aug 20, 2017 12:12 am

I tried a P-80 panasonic machine torch with the smallest 1.1mm nozzle. (supposedly for 40amp)

That is the only other torch I can find made for pilot arc cutters. Really made no discernible difference.

So I went back to the AG-60 / SG-55 machine torch.

Had to cut a replacement fire grate for a cast iron Chiminea belonging to a friend. Out of 10mm steel.

After trial and error dialling in feed rate, voltage and air pressure, I was blown away with the quality of the cuts.

Angled the same in all directions but only about 2 to 3 degrees. Little bit of dross, but came off very easily.

The cuts look very much like Jim's pics above. So I am a happy plasma user right now.

The lesson for me is that I must spend more time dialling everything in just right for a given material.

Brand X
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Re: Any idea why I am getting angled cuts?

Postby Brand X » Mon Aug 21, 2017 1:09 am

Greolt wrote:I tried a P-80 panasonic machine torch with the smallest 1.1mm nozzle. (supposedly for 40amp)

That is the only other torch I can find made for pilot arc cutters. Really made no discernible difference.
.

Maybe, but there still are other excellent torches.. :lol:

http://www.ebay.com/itm/Thermal-Dynamic ... Swj3ZZizfe


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