BS250 >> metal cutting

[GrahamRounce]

Hi all - I have a Record Power BS250 which has served me well for wood and aluminium.
I'm now more & more wishing that it would cut mild steel, say up to 6mm thick.

There are plenty of VFD speed controllers for synchronous (= induction?) motors, but they all output 3 phases, I don't know why. Can I just use one of the phases? Would the wattage then be only a third?

Apart from doing rebuilding to allow various belt arrangements, has anyone else managed it successfully somehow else?

Thanks v much,

 

[Fergie 307]

The problem is that a wood saw is just far too fast, you need to aim for a blade speed somewhere in the region of 200 ft/min for steel, so typically around 1/10 of the speed it normally runs at.
I was in a similar position using a Kity with a metal cutting blade. I was able to change pulleys to get it to run at about 1/3 speed, but still much too fast really.
I ended up converting a little Clark CBS 190 by replacing the motor with a 12v 350w one intended for an electric bike. It has a built in 9:1 reduction gearbox, together with a variable speed control. I had to make a new gearbox output shaft to suit, but got the motor from a local guy who repairs electric bikes. The screw on the end of the shaft that holds the sprocket was knackered so scrap as far as he was concerned, and so free!
As I was going to replace the shaft anyway it didn't matter to me. I paid about 15 quid for the saw on e bay. I already had some big mains to 12v DC power supplies so the only other thing I had to buy was the speed controller, which was less than £10.
I put the power supply and electronics in a project box on the back and the speed controller has a pot and LCD, which fits neatly in the space previously occupied by the on off switch.
Very small, and not a great quality machine, but works a treat for cutting the various steel and brass plates I use for repairing clocks. It will happily cut up to about 5-6mm steel and 12mm aluminium using tuffsaw bimetal blades.
So as an "I wonder if" type project I am quite pleased with it, and so is my Kity !
The other issue is that if your machine uses rubber tyres then metal will get embedded in them, and very difficult to get rid of, and may then get into any wood you cut with it subsequently.
My Kity is an old 612 and doesn't have tyres.

 

[ChaiLatte]

Doing it today, one of these might be a good candidate to replace the existing motor:

https://vi.aliexpress.com/item/1005007683855333.html

That is the first one I found; they are available at lower prices and on Amazon.

Maybe have a think about the format in which the steel you wish to cut arrives in your workshop. That will tell you what percentage of required cuts can be made on your existing bandsaw

If the steel is similar to a sheet of plywood, a variable speed jigsaw (run along a straight edge guide) and good blade could be an option.

Another option is to mount the jigsaw upside down, in a table, with a guide for the top of the blade. That allows you to use a fence.

On a vertical bandsaw, cutting a 24" length off a 3m long stick of material will not be easy. For that, an angle grinder and 1mm slitting disk is good (and can be done outside - take the tool to the work).

 

[Sideways]

A vfd will not do this.
If you did buy a single to single phase vfd (there is one, it will cost £ a few hundred) when you dial your machine down to the 1/10 speed that you need from @Fergie 307 and others' experience, your bandsaw motor which only outputs 200W at full power will now only be outputting 20W.
It will barely scatch the metal and stall if you look at it harshly.

A VFD isn't a gearbox.

Portable bandsaw (these are geared for metal cutting), variable speed jigsaw with a metal cutting blade or a special "cold saw" - a circular saw with low speed high torque motor/gearbox.

And remember the feel of a hacksaw blade if you twist it in the cut, these are straight line cutting solutions, not for curves, except maybe the very shallowest.

 

[guineafowl21]

A 3ph VFD on 1ph motor would just trip with a phase loss fault.

You can get VFDs for 1ph, but most 1ph induction motors have a start circuit that is switched out above 70% or so of rated speed. Running them below this will likely burn out the start winding and switch, or blow the cap.

You’re better off with mechanical speed reduction here. Taperlock pulleys are very handy for this.

 

[Fergie 307]

Doing it today, one of these might be a good candidate to replace the existing motor:

https://vi.aliexpress.com/item/1005007683855333.html

That is the first one I found; they are available at lower prices and on Amazon.

Maybe have a think about the format in which the steel you wish to cut arrives in your workshop. That will tell you what percentage of required cuts can be made on your existing bandsaw

If the steel is similar to a sheet of plywood, a variable speed jigsaw (run along a straight edge guide) and good blade could be an option.

Another option is to mount the jigsaw upside down, in a table, with a guide for the top of the blade. That allows you to use a fence.

On a vertical bandsaw, cutting a 24" length off a 3m long stick of material will not be easy. For that, an angle grinder and 1mm slitting disk is good (and can be done outside - take the tool to the work).

The discs sold for stainless steel are very good and last longer than other types.