Chop saw lessons learned

I posted recently about setting up a garden shed as a mini-workshop for metalwork:

"Setting up a home metal workshop"
https://bkhome.org/news/202511/setting-up-a-home-metal-workshop.html

It shows a cutoff saw, also known as a "chop saw", with fibre abrasive disc. This is relatively cheap, it cost me AU$169 several months ago. When using it, there is a huge plume of sparks, and the cutoff piece is very hot, too hot to touch. In fact, the abrasive cutting does seem to melt the metal slightly, and there is a huge burr that has to be filed off afterward.

As mentioned in the above link, discovered that carbide discs make a clean cut, negligible burr, and the cutoff piece is cool, can be immediately picked up. This looks real good, so I ordered one of those discs from AliExpress. After it arrived though, I realised something; it is rated for a maximum rotation speed of 1,000rpm, whereas my cutoff saw rotates at 4,400rpm.

Hmmm, did some research and found that special chop saws are required, that rotate at 1,000 - 1,200 rpm. Bunnings here in Australia, only have one of those, asking price AU$1,299. Hmmm again.

Then I found a YouTube video, a guy used a fan speed controller to reduce the voltage into the cutoff saw, and he was able to convert an old cutoff saw to use a carbide disc:

https://www.youtube.com/watch?v=T6U1vRG9RJ8

That looks good, so I bought one of those speed controllers from eBay. They are fairly cheap, about AU$30.

Connected it to the cutoff saw, with great anticipation. However, when the voltage was wound down to about 185V, the cutoff saw motor became very jerky, then just stopped. Hmmm, did some more research and found that some motors don't like that kind of "chopped" voltage input.

We have 240V 50Hz AC here, and it is a sine wave. The speed controller doesn't actually reduce the amplitude of the sine wave, it chops it, using PWM (Pulse Width Modulation). I found another reference, the guy said you need to use a variac. I know about variacs from my student days; it is a variable transformer, and will put out a nice sine wave that can be wound down as much as required.

Looking on AliExpress and eBay, found them with required power capability, but very expensive. No, don't want to go down that path, buying something that may or may not work.

So, give up? Watched more videos, that convinced; the difference is like night-and-day, for example:

https://www.youtube.com/watch?v=ztbiGz9_Fok

After some searching, found a chop saw with carbide blade, and this is a proper cutoff saw that rotates at 1,200rpm, so specifically designed for carbide discs. Asking price AU$406, including disc and postage:

https://www.vevor.com.au/chop-saw-c_12099/vevor-chop-saw-14in-mitering-chop-saw-for-cutting-metal-dry-cut-saw-45-angle-p_010263574911

Good reviews, so decided to go for it. An indulgence probably, but anyway. After ordering it, next day looked at the website and price had jumped to AU$486; I got it on the last day of a sale price.

It arrived and I've been using it. Absolutely fantastic. Beautiful clean cuts, negligible burrs, and the cut-off piece is cool, can be picked up immediately. A bit of a saga, but got a successful end result, and, for me anyway, definitely worth the money.   

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