Chop saw

Sheet Metal Fabrication techniques, questions and help. "Tricks of the Trade"

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Jorg50
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Re: Chop saw

Post by Jorg50 »

liveaboard wrote: Thu May 28, 2020 5:47 am Check the motor brushes; if they're worn out the motor speed could be dropping. That would cause your problem.
If the speed is right, then it has to be the disk that's wrong.

I have a carbide tooth one for 20 years; it works ok but the blades are expensive, and wear out quick if heavy things or hard things are cut.
When I cut angles, I add a clamp or big vicegrip to hold the stock to the fence. That works well.
I spray cutting fluid at it when I cut anything even a little bit heavy, that really helps.
Thanks for your advice. The speed is right. I am going to try to find the aluminum oxide disc that Harold recommended. Yes. the carbide teeth disc's are expensive but they give a better cut without heat and dust. I can not find one for my chop saw with that rpm. The cutting fluid that you use is the that you mix with water? You are right when cutting angles it is always better to put a clamp or vicegrip.
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liveaboard
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Re: Chop saw

Post by liveaboard »

Yes, milky oil/water mix, I use a squirt bottle for the saw, drill press, and sometimes the lathe.

Harold is usually right.
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GlennW
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Re: Chop saw

Post by GlennW »

liveaboard wrote: Thu May 28, 2020 9:02 amHarold is usually right.
Often more than usually!
Glenn

Operating machines is perfectly safe......until you forget how dangerous it really is!
Jorg50
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Re: Chop saw

Post by Jorg50 »

GlennW wrote: Thu May 28, 2020 2:32 pm
liveaboard wrote: Thu May 28, 2020 9:02 amHarold is usually right.
Often more than usually!
I have to agree with what you said!
The grinding that were used to cut steel really do not know if they were aluminum oxide but they did glazed a lot and when you are in the middle of a job it is frustrating and the use of the stainless disc did cut better. Harold has written great information in great detail, the soft jaws, the grinding with stones. He should write a book in my opinion :).
Jorg50
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Re: Chop saw

Post by Jorg50 »

With a angle grinder the discs never glaze. I think probably is because (spm) surface speed per minute of the disc.
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liveaboard
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Re: Chop saw

Post by liveaboard »

That's where we started out; the speed / material / disk don't match.
Does it slow down much when you lean on it?
Jorg50
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Re: Chop saw

Post by Jorg50 »

It doesn't slow that much and the metal glows red and glazes and does not cut anymore and that is with the Makita grinding disc for iron and steel. Probably the best idea would be to slow down the RPM with a VDF and use a carbide disc, the problem with this solution is the price for the VFD. If I can ask what part of Portugal do you live?
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liveaboard
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Re: Chop saw

Post by liveaboard »

So the disk is rubbing and not cutting the stock; in that case, I'd say you're back to what Harold said, you have the wrong disk.
Is the motor a heavy synchronous one, or a light weight type with brushes?
I'm pretty sure that a VFD won't slow a brushed motor.

You have an angle grinder to compare it to;do you think it turns slower?
You can get an optical tachometer from ebay for around 10 euros / dollars. I have one, does this sort of thing ok.

I'm near Aljezur.
Jorg50
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Re: Chop saw

Post by Jorg50 »

This is right for the material that I am cutting which is iron, it has on the grinding disc for steel the dimension of the grinding disc 355x3x25.4 millimeters, 3860 RPM, 72m/s. The Dewalt for stell same dimensions, 4300 RPM, 80 m/s. Rapolex also same dimensions 3500 RPM max 100m/s. Dronco 350x2.8x25.4 mm, 4400 RPM, 80 m/s. The chopsaw RPM 3800. My angle grinder, the disc brand Tyrol it, 6650RPM, 80m/s dimensions 230x2x22.23. Yes, the motor from the chop saw has brushes it is a universal motor, it was my mistake it is not a VFD, it is a Kemo Drive with a rehostat. I really do not what these grinding discs are made of for certain it is for cutting iron or steel. I gone keep looking for the aluminum oxide that Harold recommended.
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Harold_V
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Re: Chop saw

Post by Harold_V »

It is important that you understand that iron and steel are not one and the same thing, and each requires a different medium. Here's why. At high temperatures, silicon carbide dissolves in to steel (which has a high affinity for carbon). The necessary temperature is achieved with a grinding wheel or blade when operated at high surface speeds, such as those achieved with chop saws. Interestingly, aluminum oxide does not dissolve in steel, so it performs much better, for a longer period of time in spite of not being as hard. That's true for steel, but not true for cast iron.

The problem comes from the silicon carbide dulling almost instantly when it comes in contact with steel. As it dulls, one bears down all the harder, which increases temperature, which accelerates dissolution. The blade becomes totally dull and refuses to cut.

While I am unable to explain why, it is commonly held that for grinding cast iron, silicon carbide outperforms aluminum oxide. While it, too, requires considerable force to maintain the cut, it should break down fast enough to continually expose fresh grain, so it continues to cut.

Why cast iron does not dissolve the silicon carbide I do not know, but I strongly suspect it's because there's an ample supply of free carbon in the iron, thus it doesn't absorb any.

If they do not specify the material from which a blade is made, just make sure it is suited for cutting stone and concrete. That's a sure sign the blade is not made of aluminum oxide.

H
Wise people talk because they have something to say. Fools talk because they have to say something.
Jorg50
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Re: Chop saw

Post by Jorg50 »

Harold, thank you for taking the time to assist me with this issue and explaining in detail as always. I have bought several brands of griding discs for steel for this chop saw with no sucess as you can see in my post up above. My surprise is that when the chop saw does not cut because the metal got glazed I get my angle grinder and finish the cut with a disc of the same brand. The RPM is different for the machines but the SPM in this case 80 m/s is the same, since the angle disc has a smaller diameter the RPM has to be different from the chop saw which has a lower RPM and a bigger diameter griding disc. With this chop saw the more pressure you put on the grinding disc the worst the cut will be regarding to 90 degrees or 45 degrees which ever you are cutting it is with the 45 degrees. I went to the store which sold me the chop saw for them to get an aluminum oxide disc because the one that came with the machine does not cut and glazes. What I cut the most is iron.
Jorg50
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Re: Chop saw

Post by Jorg50 »

Harold, I am having difficulty in getting the grinding disc that you have recommended "aluminum oxide" none of the manuals specify what they are made. Do you know if there is a reference or code with numbers or letters to identify this disc?
Thanks in advance for all of your help!
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