Thin Kerf metal saw attachment to Bench Grinder

[BobL]

I know you guys like home shop made gear.

Here is a thin kerf  metal cutting saw attachment for a grinder that I made recently.

The first photo shows the grinder is one of two 1HP 3Phase grinders connected to one VFD with a cross over switch between them.

The grinders were originally 415V 3phase and have been converted to run 240V 3 Phase . One grinder was free and the other cost me $40.

The VFD converts 1P 240 to 3P 240V and provides variable speed so I can run the grinders a bit slower - much less noise, better control traded off for a bit more blade wear.

Apart from the VFD, all parts were either made from scraps or found in my spares box except for the countersunk SS screws which I paid $2.50 for.

The large pulley and belt come from a running machine. I machined up the rest - the bearing housing and wheel collars/flanges have also been fume blued.

Mitre slide is made of scrap ally.

first photo shows how table flips up out of the way for wheel change.

 

[DSW]

While I applaud your skills at fabrication and assembly on this, that wheel scares the life out of me. I've seen too many of those thin zip disks grenade to want to be anywhere near the front of that without wearing armor equivalent to that of a light tank, should that blade come apart for some reason. 

[arftist]

While I applaud your skills at fabrication and assembly on this, that wheel scares the life out of me. I've seen too many of those thin zip disks grenade to want to be anywhere near the front of that without wearing armor equivalent to that of a light tank, should that blade come apart for some reason. 

Presumably you don't use cut of wheels in an angle grinder? It is important to use quality wheels. You fears would be valid if using Harbor Freight wheels. 

[BobL]

Well I also have plenty of experience with these wheel and have used many hundreds of them on an old table saw and in angle grinders. Of the several hundred I would say I have broken at least several dozen and I can reassure you that at low speeds the breakage has always been a non- event.  I Have never seen one shatter at any speed and when they do break they usually break of at the arbor mount but they don't fly off in all directions and just  flop onto the floor. Any pieces of wheels have broken off have very low momentum and a  high surface area so they slow down rapidly in air. The pieces that have hit me (usually I am just wearing a T-Shirt) have never even broken the skin. I do ALWAYS wear a full face shield when using these wheels whether it's on the table saw or using them in an angle grinder.  

[Glenn]

You have developed a nice project.

I would strongly suggest that you place a heavy metal shielding under the table to enclose / contain the disc, belt and sparks. If anything were to happen at least the lower part of the disc should not leave the shielding.

The top part of the table should be adjustable so the disc will be JUST above the metal being cut. This will minimize the exposure of the disc into the metal and above the table. There will be less disc to fly about if anything were to break. 

Run the disc as slow as possible to do the job at hand. Always wear safety glasses, a full face shield, and a heavy leather apron. Any additional body protection will be a plus, so  +++. Each time you start the motor, let it run for a full minute at a speed in excess of what you will use for the work you are doing, in order to test the integrity of the disc and the system.  

PLAN ON AND PREPARE for a full failure, as it WILL happen at some point, usually after everything is working, you feel comfortable, and let your guard down (pun intended)

 

What ever you do, please do it safely.

 

Edited August 2, 2015 by Glenn

[Steve Sells]

I  would insist a guard be installed, both above and below as glenn  pointed out, its an osha nightmare, and the zip disk in a hand grinder do come with a guard,  One cant blame manufacturers if people remove them.

[Charles R. Stevens]

Remember Bob, your skill and experiance may not translate well to the unwashed masses, so the caution and disclamers are not as mich amed at you but at other readers, present and future. I acualy like the concept and the reality. I myself mount worn chopsaw blades to a large, old slow makita bufer/grinder (once the blade will fit in the guard) 

[arftist]

1. The blades are running at less than 1/3 the speed at which they run in a handheld machine.

2. The blades are under significantly less stress than in a handheld grinder (for which they are designed)

3. Setting the blade so it just sticks above the surface increasing the stresses manifoldly, by increasing the surface area of the cut dramatically. This is bad for the blade, the workpiece, the motor and the rest of the works. This is one place where process does not transfer well from wood to metal. 

4. There is nothing new going on here, metalworkers have been running abrasive blades in tablesaws since they were invented. It is automatically guarded better than most handheld setups. 

[Glenn]

I will pass on experience with chop saws applications. The less blade in the work the better. For instance, if you cut angle iron flat side down, the first leg goes fast. The flat really slows things down as you are not going through the thickness but are going through the width of the metal. The same with tubing, when you cut it flat side down you have to go through two widths and two edges. If you turn it on the diamond, you are only going through two edges or thickness of the metal.

This became a real lesson when I tried cutting 1-1/4 inch solid bar stock. A straight cut was good for about 1/4 to 1/3 the thickness then slowed as the width of the metal being cut increased. As the cut continued the motor started to strain. If the stock was rotated to keep only a small amount of the cutting disc in the metal, everything worked much better than a single deep cut.

Another advantage of a small amount of the cutting disc in the metal, if the work gets out of align with the disc, there is much less leverage against the disc.

As Charles said, it is not just you we are talking to here, but also those who read this in the future. This includes anyone who may come into your shop and flip the switch without knowing the dangers involved. Yes, although unlikely in a personal shop, it can happen. Please, be safe.

 

[BobL]

Artist has pretty well nailed it, especially his point number 3 about It is much better all round to more blade exposed not less. 

I agree that newbies have to be looked after so for anyone contemplating this idea I would not recommend doing this with any wheel other than a thin (1mm) kerf wheel which is capable of handling these higher revs and if it does shatter represents a much lower risk than thicker wheels.

Perhaps a bit of background, I have a variety of metal cutting gear, e.g. plasma cutter, a bandsaw, angle grinders and a 12" chop saw and have used all of these extensively and are used to cut larger pieces.  This saw is only used to cut small pieces of tool and other steel that are difficult to cut with these other machines.

One incentive for doing this is that  I have hearing damage and even though I have several good pairs of ear muffs I dislike noise so the angle grinders and chop saw rarely get usedl. I measured the sound pressure levels of my saw compared to the angle grinder. At 4000 rpm my saw is is 25 dB less and at 9000 it is is 15dB less than the angle grinder. This may not seem like much but it is significant.

Comparisons between these thin (1mm) kerf wheels and any thicker wheels are limited. A better comparison is with the 30,000 rpm cutting wheels used on Drenels with no guards. I don't know about others but I struggle to use these wheels on a Dremel without them breaking. Do parts of the wheels fly off in all directions across a workshop ? No - why? read on, Do I use appropriate safety gear when using these - yes of course a full shield - that is all that is needed. There is no need for a leather apron or other protection when using these wheels.

As I said before  I have been hit a number of times on the hand and forearm by piece off these thin wheels and it is about the same as being hit by wood chips from a fast revving chainsaw. If you leave skin exposed to a continuous stream of chainsaw chips it will eventually draw blood but there is no stream of pieces coming of any broken wheels. The reason they don't do much damage to skin is they have a high surface area to mass ratio so their coefficient of air resistance is very high. as they leave the  wheel they immediately tumble  and turn and slow down rapidly. Do I use appropriate safety gear when using a chainsaw -  of course I do, full chaps, full face shield and ear muffs - people that know me think I am a safety sissy. Do I recommend appropriate safety gear when using this saw - yep a full shield - that is all that is needed.

The downside of the slower speed is there is more wheel grit and dust generated which represents some sort of health risk but I have good ventilation and dust extraction.

To demonstrate good safety practice I have made a guard for the top of the saw and am in the process of making one for the underneath - however that is mainly to collect the grit and metal dust.

The transparent shield is polycarbonate so even though it is thin it it very tough.

Edited August 4, 2015 by BobL

[ianinsa]

That looks like a very useful tool, looks like you've got a well stocked shop too! 

[Glenn]

Thank you for the explanation. It goes a long way in clearing things up.

[Kozzy]

Taking this on a bit of a side trip....go to Mcmaster.com and search on "slitting cutters".  These are essentially thin kerf saw blades/cold saw blades that can be had in diameters similar to the abrasive wheel that's on the current iteration of your machine.  You'd need an arbor adapter (probably) as most use a 1" bore.

What you've done is create a typeset-saw.  These were very small table saws from the old days which were designed mainly to cut up bits of typeset for fitting into larger advertising blocks.  If you can ever find a real one, snap it up at any cost--super accurate and well made.

Although type material was generally soft metals, they will work like a super accurate (and stable) miniature cold saw on many harder metals.  Nice tool to have around if you work with small stuff like dies.

Since the VFD is already on the machine so you can dial in any speed, the only thing in question seems to be rigidity.  You're 80% to a cold saw/typeset saw so it might be worth the fiddle to test a slitting cutter.  

Here's a commercial typeset saw: