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  1. #1
    BobL is offline Member: Blue and white apron brigade
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    Default Thin Kerf cutting wheel attachment for bench grinder

    If you donít want to read the intro just skip ahead to the pics.


    From 2007 until I got my 6 x 4 metal cutting bandsaw in 2011 the main way I cut metal was with a either an angle grinder or a thin kerf cutting wheel in an a small (8Ē blade) woodworking table saw. When I got the bandsaw I thought, well that will be the end of the little table saw, but I still used it quite a bit especially for cutting plate so I then bought a plasma cutter. At that point I really needed to reclaim some very scarce shed real estate so I restored the woodworking table saw and gave it to my son.


    Although Iím happy with what the bandsaw and plasma cutter do, within a couple of weeks I really wish I hadnít given away the table saw that but it was too late to get it back. The things I found it useful for was cutting small things like bolts, or bits of tool steel, and cutting into the ends of bars and rods. My hands arenít steady to begin with but an angle grinder just makes it worse. Plus I really donít like the noise angle grinders make.


    I had in mind purchasing a small/cheap table top table saw and putting a thin kerf cutting wheel in that but recently I looked at moving my multitool finisher onto a variable speed GMF grinder I converted and this got me thinking and this is what I have come up with.


    Standard GMF guard mounting setup normally used to hold the wheel guards.



    Variant on multitool finisher attachment baseplate made out of 5mm plate

    Additional 50 x 6 mm arm - you will see why this rm cannot be combined with the baseplate a bit later on.



    100 mm plastic V-ribbed pulley from an old running machine I picked up at the side of the road..
    There is a homemade 50 mm diameter steel hub with a 6mm keyway between the hub and the plastic pulley.



    Bearing assembly and shaft. Inside the assemble are two 32 x 10 x 12 sealed bearings.
    The allen screws are from an old washing machine I stripped down for parts last year


    Shed made25 mm V-Ribbed Al pulley with 4 mm keyway and end-cap screwed into shaft


    6 rib V-ribbed belt - also from running machine. Now you can see why the arm as to be separate from the main base plate - as this allows for adjusting belt tension.


    On top of all that rides a small table made out of piece of 2 mm thick SS.
    Here it is before the slot for the thin kerf wheel is cut


    The table is hinged at the rear so it can flip up out of the way to get access to the wheel changing hub/nut.
    The U- shaped gizmo at the end with the sprung screw pulls the table firmly down against the main arm


    More to come.





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  2. #2
    BobL is offline Member: Blue and white apron brigade
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    Default Thin Kerf cutting wheel attachment for bench grinder (part 2)

    To cut the slot for the blade in the table top I just attached a fresh wheel and slowly dropped the table onto the wheel so it cut its own slot.
    This effectively gives it a zero width throat which is better than the old table saw which had ~5 mm gap either side of the wheel and I was forever losing bits and pieces down the gap.
    The other advantage over the table saw is the depth of cut has been increased significantly (by some 15 mm) and it is ~5 mm more than for most angle grinders
    The disadvantage over an angle grinder is that the wheel cannot cut at a tangent to the work so the cutting is not as optimised. Nevertheless it does a pretty good job.

    Here it is cutting its own slot.
    You can can see there are countersunk SS screws that hold the top onto the hinged top frame.
    These SS screws are one of three things I spent specific $ for on this project - the other two were some 25 mm steel rod from the steel merchant and I did buy a new cutting wheel.



    Here are another couple of views of the table top folded up out of the way for access to wheel change.




    Now I'm going to play with it for a while before I disassemble it and pretty it up.

    Here are a few specs
    With a 4:1 pulley it's top RPMs @50 Hz is 11400 which is well within the ~12000 RPM limit for the wheel
    At top speed it's fairly humming along but most of the noise appears to be coming from the wheel scraping the slot ion the table - after a while this should open up slightly and quieten down.
    The grinder is of course on a VFD so I can go higher but I will limit this grinder to 50Hz

    When the thin kerf cutting cutting wheel was in the small table saw it was only running at 3000 rpm which was sort of a lot safer, and a LOT quieter, and a lot slower than an angle grinder
    BUT
    it used up more wheel and hence generated a more wheel dust per mm of cut. This is a well known effect and that is why these wheels are run at higher speeds.
    These wheels are cheap so I am not worried about the cost but I would like to make less wheel grit/dust wherever possible.
    However there are an advantages of being occasionally able to run at slower speed and that is one had better control of the cutting.

    Overall I'm pretty happy with how it has turned out - it has taken me ages to do all this but I did not have to make any part more than once (that's rare for me) and all the steel (even the SS) was bought at scrap prices or were laying around in my stash. The pieces of SS were a real find - I have 4 more pieces like the one the table is made of.

    That's about all I can say for now and will have to play around with it and see what it can do at what RPMS etc.
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    Last edited by BobL; 22nd May 2019 at 10:07 AM.

  3. #3
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    I like the concept and ingenuity. I do have a safety concern if the cutting wheel were to break and I have seen it happen. You may get a face full of flying high speed bits.

    Maybe you could add a polycarbonate screen to shield your self that could withstand the impact should a failure occur and deflect any debris?
    Ö..Live a Quiet Life & Work with your Hands

  4. #4
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    Quote Originally Posted by DSEL74 View Post
    I like the concept and ingenuity. I do have a safety concern if the cutting wheel were to break and I have seen it happen. You may get a face full of flying high speed bits.

    Maybe you could add a polycarbonate screen to shield your self that could withstand the impact should a failure occur and deflect any debris?
    What about a safety squint

  5. #5
    BobL is offline Member: Blue and white apron brigade
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    Thanks for all the likes fellas.

    Quote Originally Posted by DSEL74 View Post
    I like the concept and ingenuity. I do have a safety concern if the cutting wheel were to break and I have seen it happen. You may get a face full of flying high speed bits.
    Maybe you could add a polycarbonate screen to shield your self that could withstand the impact should a failure occur and deflect any debris?
    Because this setup enables me to run at higher speed than my previous table saw setup I will look at adding some sort of shield but this may not be as critical as it sounds.
    And I always wear a full PC face shield when grinding or cutting anyway

    Even though they break more often than thicker wheels, thin kerf cutting wheels are much safer. Over the years I reckon I must have gone through a couple of hundred thin kerf wheels on angle grinders and on the small table saw. For a variety of reasons I was never exactly gentle with them and often applied sideways pressure which normally is a no-no. However they never broke directly with sideways pressure although they could have been weakened and broken later.

    I do not recall any of the wheels "shattering" as can happen with thicker wheels. Most of the time they broke they were not installed correctly and broke off in the region around the locking collar collar. At low speed (3000 rpm) table saw all of the breakages were what I would call a non-events as the the broken disc would roll around the arbor a couple of time or flop onto the bench or floor. In the same arrangement, when pieces of the wheel very occasionally broke completely off the wheel, they tended to skid off the table onto the floor. I do not recall being hit once by a flying piece at low speed in the table saw arrangement. Wheels that broke off at the locking collar on an angle grinder were not much different to the table saw arrangement.

    I have been hit in the face shield and lower arms by pieces from a thin kerf wheel breaking at higher speed in an angle grinder and while they sting a bit none of these drew any blood.
    As far as I can tell, the reason for these breakages was unsteadiness of the hands holding the grinder and not being able to clearly see what is going onTypically the grinder hand drives the wheel too fast into the work and that breaks a chip off the wheel. This is much less likely in the table saw setup as the cutting is usually easier to see and the blade and work can be both held very steady and the work fed into the blade very slowly There is also much less noise from the motor so you can hear the cutting noise more easily. The reason the pieces of broke wheel do so little damage is because they have such a high surface area to volume ratio (drag coefficient) that this slows down the pieces very rapidly in air, so within a few 10 of cm they have so little momentum they cannot do any damage except in perhaps the eyes - hence a face guard is essential.

    In Physis terms, the KE of a moving object is proportional to velocity squared so a piece of wheel coming off a 12000 rpm wheel has 4 times the velocity and 16 times more KE than the same piece coming off a 3000 RPM. However, the retardation force or air resistance is also proportional to the square of the velocity so fast pieces with high drag coefficients slow down a lot faster than usual.

    Anyway I am happy to experiment a bit and sacrifice some blades to the cause.
    Last edited by BobL; 22nd May 2019 at 10:09 AM.

  6. #6
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    Hi Bob,

    I really like your cutting saw, I think its a brilliant idea.

    You may remember this grinder that I picked up at the scrapyard
    Grinder-62.jpg Grinder-409.jpg
    I stripped it and refurbished it, it had an odd long spindle on one end. I actually found out what the long spindle was for. I originally thought it was for just a polishing mop but couldn't weigh up the threaded extension. It seems that it is intended to drive a flexible cable for a hand held wheel. Anyway I am going to press this end of this grinder into service with a cutting disc along the lines of yours.

    It may take a while whilst I collect some bits and bobs for it, but I will take pictures and I promise to post them.
    Best Regards:
    Baron J.

  7. #7
    BobL is offline Member: Blue and white apron brigade
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    Quote Originally Posted by BaronJ View Post
    Hi Bob,
    I really like your cutting saw, I think its a brilliant idea.
    You may remember this grinder that I picked up at the scrapyard
    I stripped it and refurbished it, it had an odd long spindle on one end. I actually found out what the long spindle was for. I originally thought it was for just a polishing mop but couldn't weigh up the threaded extension. It seems that it is intended to drive a flexible cable for a hand held wheel. Anyway I am going to press this end of this grinder into service with a cutting disc along the lines of yours.

    It may take a while whilst I collect some bits and bobs for it, but I will take pictures and I promise to post them.
    Cheers BJ I look forward to seeing what you come up with.

    I haven't had much time to experiment with the grinder saw but I did manage a quick noise level test today.

    My standard Bosch angle grinders are 95 dB at 1m.
    This bench grinder saw is 80dB at 30 Hz, 82 dB at 40 Hz and 87 at 50Hz.
    That might not seem like a big difference but it is quite significant.
    It cuts surprisingly well even at 30Hz (~7000 rpm)

    There is quite a bit of vibe at 50Hz and have tracked it to the bore of one of the disc collars being a whisker too loose on the shaft - I can actually just see the run out on that collar when it gets going. I'm remaking the collar and hopefully that will reduce the noise a bit as well.
    I have no experience of working at the 12000 rpm range so it's all a big learning curve for me as well.

  8. #8
    BobL is offline Member: Blue and white apron brigade
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    OK I made a new disc collar and checked the noise and vibe.

    The new collar definitely helped and reduced the vibe and the noise by ~5dB and also I noticed the bearing is not as warm is was with the old collar.
    The other thing I have noticed is the vibe is very sensitive to how tight I have the bearing cap bolts, too loose is bad and too tight is also not good - I maybe should take a look at how things are arranged.

    While this is progress I've now found how the vibe gets turned into noise and that is by the table which acts as a bit of a drum.

    With the table off I get between 70 db at 20Hz to 82 db at 50 Hz with a small blip and a dip around 35 and 40Hz
    With the table on its around 5dB higher except for the dip at 40 Hz

    Bear in mid that shed back ground at the time was ~68 dB and the angle grinder is 95 dB.

    I could work a bit more on the mechanism but I might just see if I can dampen the table a bt first.

    Overall I'll be quite happy to run at 40Hz with an occasional stint up to 50 which is the max anyway.


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    Thatbis pretty cool. You obviously have a noise meter and it seems an air flow meter. I imagine yiu have a volt meter. Gonna have to call you meter man

    Dave TTC
    Turning Wood Into Art

  10. #10
    BobL is offline Member: Blue and white apron brigade
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    Quote Originally Posted by DaveTTC View Post
    Thatbis pretty cool. You obviously have a noise meter and it seems an air flow meter. I imagine yiu have a volt meter. Gonna have to call you meter man

    Dave TTC
    Turning Wood Into Art
    Yeah I have a few meters.

    Not counting those that measure fundamental quantities like (mass length and time e.g. rulers, verniers, micrometers, digital angle meters, digital scales, stop watches etc, )these are the ones I can remember
    2 air flow meters
    a range of low pressure and high pressure meters
    1 sound pressure level (SPL) meter and 2 SPL apps
    2 induction tachos and one laser tacho
    2 electrical multimeters
    2 current clamp meters
    1 Megger meter
    1 humidity meter
    1 water purity (TDS) meter
    1 pH meter
    4 temperature/thermocouple/meters
    1 Infra red gun/meter
    1 pyrometer
    4 force meters (well Luggage scales)
    1 CO2=/Methane monitor

  11. #11
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    What about a metre ruler
    Ö..Live a Quiet Life & Work with your Hands

  12. #12
    BobL is offline Member: Blue and white apron brigade
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    Quote Originally Posted by DSEL74 View Post
    What about a metre ruler
    That's a fundamental measuring device (length) - I wasn't counting those.

  13. #13
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    Looks good Bob, my first thought was that looks dangerous, but probably no more dangerous than a freehand cut with an angle grinder. I've had thin kerf wheels fall to bits, usually they fray at the edges and go out of round, the first thing you notice is lots of vibration. When you stop and look, half the wheel has disintegrated into little bits.

    The big plus with thin wheels is that they have a lot less mass than the heavier thicker wheels, I know a guy who had a 9" angle grinder wheel explode, he ended up in hospital, never worked again. The thin wheels have much less energy, so potential for damage is less.

    On balance I think that setup would be safer than it looks at first sight. With a bit of care in feeding the stock, and full face shield. ( No safety squint )

  14. #14
    BobL is offline Member: Blue and white apron brigade
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    Quote Originally Posted by RayG View Post
    Looks good Bob, my first thought was that looks dangerous, but probably no more dangerous than a freehand cut with an angle grinder. I've had thin kerf wheels fall to bits, usually they fray at the edges and go out of round, the first thing you notice is lots of vibration. When you stop and look, half the wheel has disintegrated into little bits.
    Yep been there done that a number of times mainly with an angle grinder and a couple of times on my small table saw setup. Given I have used up about 10 times more wheels on the TS it seems to happen much less often probably because the stock feed can be better controlled.

    The big plus with thin wheels is that they have a lot less mass than the heavier thicker wheels, I know a guy who had a 9" angle grinder wheel explode, he ended up in hospital, never worked again. The thin wheels have much less energy, so potential for damage is less.
    It's also the large surface area to volume or mass ratio - this creates a high drag coefficient that slows pieces down so rapidly that they are not going to do much to anything except eyes.

    On balance I think that setup would be safer than it looks at first sight. With a bit of care in feeding the stock, and full face shield. ( No safety squint )
    At low speed I have no qualms about holding a piece of metal just mm from the wheel, at higher speeds I do move the fingers back

    I just used it to cut a 2 mm diam C-Pin into 5 mm lengths. If did that with an angle grinder they'd be different lengths and I'd be still on the floor on hands an knees looking for them.

  15. #15
    BobL is offline Member: Blue and white apron brigade
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    I did a bit more cutting with this gizmo yesterday - it sure is nice to use.

    One problem I did not envisage is heat.
    We all know that the KE is proportional to velocity squared and a lot of this energy goes into heat.

    With the thin kerf cutting wheel on the old table saw (3000 rpm) I could cut a small bolt or piece of steel by holding it close to the cutting edge and sure it got hot but I could cope.
    For larger pieces, which had time to get hotter, of course I could hold the piece further back and there was also the possibility of using the mitre slide.

    Now it turns out I cannot hold something small when cutting at 20Hz (4600 rpm) or more - it just gets too hot so some sort of holding mechanism is going to be needed.
    I was thinking of a mitre slide (which is very useful for cutting angles as well) or even a mini sled?

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