Converting a Clarke mitre/chop saw into a cut off

[Longhorn6120]

You guys seem to know a lot about a lot of stuff so I thought I'd through this out there.

I have a 10" Clarke compound mitre saw which I mostly use for wood, but have also cut the occasional piece of plastic guttering with too. I was wondering about changing the blade out for an abrasive cutting dic so I can use it for metal. The saw runs at 6000rpm which I know is way too fast for a cutting disc, so I wondered about running it through a variac and dropping the voltage to sub-120v to slow it down to around 3000prm.

Does this sound feasible?

 

[CompoSimmonite]

If the saw base etc is made out of aluminium then it will quickly get destroyed by the hot sparks coming off steel. I've got both a compound mitre saw and a TCT chop saw - they do different jobs

 

[frank horton]

as above but rave reviews about Aldi/Lidil metal cutting band saw.....
think it's £125'ish when they have them in...

 

[dobbslc]

The motor can overheat if it's run at a lower speed for too long.

 

[Longhorn6120]

Ok, thanks for the advice all.

 

[Agroshield]

The saw runs at 6000rpm which I know is way too fast for a cutting disc...

Could you expand on the source of this knowledge please.

The biggest standard cutting disk you will fit to it is 9" and these are good to 6600rpm.

Cutting discs are given a maximum safe working speed, which is normally a surface speed of 80 m/s. To achieve this speed, clearly a smaller disk must spin at a fater rpm (that is why your Dremel fair whizzes along at 35,000rpm compared to a 14" Stihl motorbike at 4400rpm).

 

[gaz1]

dont bother for what it costs to change it it would be cheaper to buy an aldi one instead

 

[Longhorn6120]

I got the figure of 6000rpm from the manual that came with the mitre saw. My inference that an abrasion cut off saw saw runs at about half that is based on some internet research. General consensus seems to be if a cutting disc is run too fast it will shatter.

 

[gaz1]

if you try any cut offs via diodes and a variable resister you loose torq

eg; variable light switch

therefore your blade will stop spinning as it stalls out

 

[Morrisman]

I got the figure of 6000rpm from the manual that came with the mitre saw. My inference that an abrasion cut off saw saw runs at about half that is based on some internet research. General consensus seems to be if a cutting disc is run too fast it will shatter.

The max speed will be printed on the disc.

 

[gaz1]

 

[eddie49]

Using a Variac to drop the voltage to a brushed AC powertool motor ( a "universal" motor ) is not the same as using an electronic speed control ( Triac, variable trigger switch or numbered speed dial ) that is built-in to a variable-speed drill, saw, or grinder.
In the latter case, electronics is used to chop off part of the 230v AC sinewave. This is known as "phase control". Speed drops, but torque remains quite high. Lowering the input voltage with a Variac will drop both speed and torque.

You are also going to have issues with the bore size of the saw ( 20mm ? ) vs. the 22mm bore of a 9 inch angle grinder disc.

 

[Agroshield]

I got the figure of 6000rpm from the manual that came with the mitre saw. My inference that an abrasion cut off saw runs at about half that is based on some internet research. General consensus seems to be if a cutting disc is run too fast it will shatter.

A metal-cutting saw using a _toothed_ blade will run at a slower speed than a wood cutting one, as you say, about half. But an abrasive disk needs speed to cut. Your 4 1/2" grinder would not work well on half throttle. If you take the 80m/s surface speed as a guideline, you can work out the max. rpm for any diameter you like.

 

[Munkul]

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a 6600prm limit would suggest that they would run fine in a 6000rpm saw.

whether it's a good idea or not, I'm not sure.

Better than any abrasive saw is a proper steel cutting TCT saw, which runs at much, much slower speeds, and cuts much faster and cleanly. An Evolution 355 saw runs at 1450 rpm.

 

[Longhorn6120]

Thanks everyone for your input. All things considered I agree, it's not a good idea. I'll only need it for small jobs now and again so I think I'd be better off with a mitre stand for my angle grinder.

 

[gaz1]

Thanks everyone for your input. All things considered I agree, it's not a good idea. I'll only need it for small jobs now and again so I think I'd be better off with a mitre stand for my angle grinder.

dont keep hold of your grinder its fast and if it comes loose theres no chance of stopping it until it unplugs itself