Page 2 of 4 FirstFirst 1234 LastLast
Results 16 to 30 of 50
  1. #16
    Join Date
    Sep 2012
    Location
    York, North Yorkshire UK
    Posts
    6,444

    Default

    Hi Bob,

    Couple of questions. What is the disc diameter that you used ? I have some 115 mm X 1 mm ones and they seem a bit small. Are 6002 bearings ok for this application. My grinder motor runs at 2850 rpm and I was thinking 2:1 step up in speed using a flat rubber stretch belt from a vacuum cleaner for the drive. It would avoid the need to adjust belt tension.

    Thanks
    Best Regards:
    Baron J.

  2. #17
    Join Date
    Aug 2010
    Location
    Horsham Victoria
    Posts
    113

    Default

    My thought would be to go the 125mm. Same size centre but extra cut depth and blade should last a bit longer

    Dave TTC
    Turning Wood Into Art

  3. #18
    Join Date
    Oct 2011
    Location
    Norwood-ish, Adelaide
    Age
    59
    Posts
    6,542

    Default

    Quote Originally Posted by DaveTTC View Post
    ... but extra cut depth and ...
    Think about that for a bit though - if you use a 125 diameter wheel you may get a 40mm DOC. Are you really going to try cutting something 40mm thick in one pass like a circular saw does? Even cutting something like 10mm strip with a thin kerf disc, the cut is better made with several shallow passes rather than one deep cut.

    Michael

  4. #19
    Join Date
    Aug 2010
    Location
    Horsham Victoria
    Posts
    113

    Default

    Should have clarified better. More depth of blade thus longer life. I use an angle grinder a reasonable amount and find a 125 far superior in most applications to a 100.

    In both instances mostly what i cut other than bolts is 0.42.

    I cant imagine using a grinder to cut 40mm steel but i guess some may have tried

    Dave TTC
    Turning Wood Into Art

  5. #20
    BobL is offline Member: Blue and white apron brigade
    Join Date
    Feb 2006
    Location
    Perth
    Posts
    7,183

    Default

    Quote Originally Posted by Michael G View Post
    Think about that for a bit though - if you use a 125 diameter wheel you may get a 40mm DOC. Are you really going to try cutting something 40mm thick in one pass like a circular saw does?
    True, but one issue with a any circular wheel type cutting is cutting angle relative to the radius of the blade.
    The ideal angle is 90º which creates as short a cut as possible, but in a table saw arrangement there is no way to get 90º because the arbor and table conspire get in the way so this is where a bigger wheel helps.
    It doesn't look like there is much difference between the 115 and 125 but its makes a difference in the cut.




    Even cutting something like 10mm strip with a thin kerf disc, the cut is better made with several shallow passes rather than one deep cut.
    If that is done on a table saw arrangement the cut cannot be seen and the cut is being made at max length for max load on the machine.
    I found i much better to cut all the way through the material on the edge so the cut can be seen and it reduces the load on the machine.

    As the wheel diameter decreases I found it's easier on the machine, and to see what is happening, to cut not quite all the way through and then flip the work piece, and do that back and forth - the blade will follow the previous cut pretty closely.
    I have cut up to 25 mm material with this arrangement - yep its slow but it works.

    But, for practical purposes 99% of those cuts are now done by the BS and plasma cutter, the sorts of cuts I'm look at with this saw are things like tool steel, cuts into the ends of rods and bars, and small pieces of sheet metal. It's much quicker to cut small pieces of sheet metal on this setup than convert the BS to upright cutting for sheet metal, or setup the plasma cutter.
    Attached Images Attached Images

  6. #21
    BobL is offline Member: Blue and white apron brigade
    Join Date
    Feb 2006
    Location
    Perth
    Posts
    7,183

    Default

    An example of what I cut with this saw was a small cover for the old switch position on the grinder.
    It's 1.2 mm thick steel, I even de-burred and rounded the corners on the side of the wheel!!

    Attached Images Attached Images

  7. #22
    BobL is offline Member: Blue and white apron brigade
    Join Date
    Feb 2006
    Location
    Perth
    Posts
    7,183

    Default

    Quote Originally Posted by BaronJ View Post
    Hi Bob,

    Couple of questions. What is the disc diameter that you used ? I have some 115 mm X 1 mm ones and they seem a bit small. Are 6002 bearings ok for this application. My grinder motor runs at 2850 rpm and I was thinking 2:1 step up in speed using a flat rubber stretch belt from a vacuum cleaner for the drive. It would avoid the need to adjust belt tension.

    Thanks
    When I had the thin kerf cutting wheel in the table saw the limit of wheel exposed and available for cutting was determined by the 45mm diameter pulley and the thickness of the table saw top so I lost around 55 mm of wheel.

    So, available f I used a 125 mm wheel this left (125-55)/2 = 35mm of exposed wheel ( for a 115 mm wheel it was only 30 mm) available for cutting. Grinders typical have 40 mm on a 125 mm wheel.

    On grinders the amount of wheel is determined by the size of the wheel holding collars, which on my grinders are 45mm
    It's not worth trying to get much more as the collars have to be able to hold the wheel and as the wheel gets smaller it gets weaker so I made my collars 40 mm.

    6002 (no suffix) bearings are good for 32000 rpm so you are well covered.

    A 2:1 step up will give you about 6000 rpm. This is still in the "wheel wear region" i.e. significant wheel wear (grit/dust) relative to cutting. However given your grinder is not variable speed it seems like a good compromise. It looks like I will be using mine @ 40Hz (~9000 rpm) as this is where my setup has the lowest vibe and good cutting speed relative to wheel wear.

    Wheel wear is more related to the speed of the cutting edge rather than the RPM. Users of narrow kerf wheels on angle grinders will notice this i.e. as the wheel gets smaller it wears faster. I also notice this on tiny Dremel wheels. So ideally the speed should be kept as high as possible.

    OTOH wheels are cheap and greater control of the cutting process is possible with reduced cutting speed.

    Stretch rubber belt are suited to vacuum cleaners because if the inlet becomes blocked the motor can still turn the impeller which will just cavitate.
    Is it a flat belt? If so on something that can be completely locked up like a cutting wheel I'd be looking at something a bit more positive. But it probably cost you nothing so you have nothing to lose by trying it

  8. #23
    Join Date
    Sep 2012
    Location
    York, North Yorkshire UK
    Posts
    6,444

    Default

    Hi Bob,

    Quote Originally Posted by BobL View Post
    When I had the thin kerf cutting wheel in the table saw the limit of wheel exposed and available for cutting was determined by the 45mm diameter pulley and the thickness of the table saw top so I lost around 55 mm of wheel.

    So, available f I used a 125 mm wheel this left (125-55)/2 = 35mm of exposed wheel ( for a 115 mm wheel it was only 30 mm) available for cutting. Grinders typical have 40 mm on a 125 mm wheel.

    On grinders the amount of wheel is determined by the size of the wheel holding collars, which on my grinders are 45mm
    It's not worth trying to get much more as the collars have to be able to hold the wheel and as the wheel gets smaller it gets weaker so I made my collars 40 mm.
    Right ! I'll get some 125 mm X 1 mm discs then. I do have a 250 mm angle grinder and some 250 mm x 1mm discs for it. So far I've never used it, its still in its box along with the pack of 10 cutting discs. But I think that 250 mm is far to big for this kind of tool.

    6002 (no suffix) bearings are good for 32000 rpm so you are well covered.
    At least I wont have to buy any bearings then.

    A 2:1 step up will give you about 6000 rpm. This is still in the "wheel wear region" i.e. significant wheel wear (grit/dust) relative to cutting. However given your grinder is not variable speed it seems like a good compromise. It looks like I will be using mine @ 40Hz (~9000 rpm) as this is where my setup has the lowest vibe and good cutting speed relative to wheel wear.

    Wheel wear is more related to the speed of the cutting edge rather than the RPM. Users of narrow kerf wheels on angle grinders will notice this i.e. as the wheel gets smaller it wears faster. I also notice this on tiny Dremel wheels. So ideally the speed should be kept as high as possible.

    OTOH wheels are cheap and greater control of the cutting process is possible with reduced cutting speed.
    I suppose that I could use a larger pulley on the grinder spindle, say 2.5:1.
    Though I must admit I'm a little wary of using such a high speed, and comments made about the risk of wheel shatter don't add anything to my confidence. But I will add suitable guards, just in case.

    Stretch rubber belt are suited to vacuum cleaners because if the inlet becomes blocked the motor can still turn the impeller which will just cavitate.
    Is it a flat belt? If so on something that can be completely locked up like a cutting wheel I'd be looking at something a bit more positive. But it probably cost you nothing so you have nothing to lose by trying it
    Yes those are the type of belt. I literally have several dozens of them of assorted sizes, including around a hundred round rubber belts intended for the Hoover Junior and Senior upright cleaners. They should have been thrown out years ago along with a load of other junk.

    Thankyou for all the valuable information given.
    Best Regards:
    Baron J.

  9. #24
    BobL is offline Member: Blue and white apron brigade
    Join Date
    Feb 2006
    Location
    Perth
    Posts
    7,183

    Default

    Quote Originally Posted by BaronJ View Post
    Hi Bob,
    Right ! I'll get some 125 mm X 1 mm discs then. I do have a 250 mm angle grinder and some 250 mm x 1mm discs for it. So far I've never used it, its still in its box along with the pack of 10 cutting discs. But I think that 250 mm is far to big for this kind of tool.
    Woah, 250 x 1 mm - I've never even heard of these.

    I suppose that I could use a larger pulley on the grinder spindle, say 2.5:1.
    Though I must admit I'm a little wary of using such a high speed, and comments made about the risk of wheel shatter don't add anything to my confidence. But I will add suitable guards, just in case. .
    Maybe have a re-read of this post
    http://www.woodworkforums.com/showth...50#post1881750

  10. #25
    Join Date
    Sep 2012
    Location
    York, North Yorkshire UK
    Posts
    6,444

    Default

    Hi Bob,

    Sorry my bad the discs are 220mm X 1.5mm. They are intended for cutting stone or concrete. The angle grinder is nominally 9"
    I've had it for a few years from new and never used it. Brought it back home from France. It was on clearance, I thought for 25 Euro it was worth buying. The job that I had in mind for it is still waiting for me to get around to it Maybe one day

    Thanks:
    Best Regards:
    Baron J.

  11. #26
    BobL is offline Member: Blue and white apron brigade
    Join Date
    Feb 2006
    Location
    Perth
    Posts
    7,183

    Default

    Here is an interesting graph that users of thin kerf wheels may not know about.

    Its a plot of the RPM and Linear speed (m/s) versus disc size.

    All except the Dremel 77 mm disc are Flexovit branded
    The 100, 115 and 125 discs are 1 mm thick, while the 76 mm is 0.89mm and the 200 and 230 disc are 1.9mm.
    I don't know the thickness of the Dremel disc.




    Except for the 76 x 0.89 mm Flexovit disc, all of the discs have a max linear speed recommendation of ~80 m/s
    The 90 m/s limit for the 76 mm disc is probably a reflection that if it does break being so thin it's not going to do much.

    This means if you know what you are doing and you have a variable speed machine, to improve cutting efficiency you can increase the speed of the wheel as the diameter gets smaller.
    Attached Images Attached Images

  12. #27
    Join Date
    Jul 2010
    Location
    Melbourne
    Posts
    9,088

    Default

    Hi Bob,

    Am I reading this right? Your saying for 230mm discs their rated m/s is about double their rated rpm? and for 76mm their rated rpm is 50% more than their m/s?

    Stuart

  13. #28
    BobL is offline Member: Blue and white apron brigade
    Join Date
    Feb 2006
    Location
    Perth
    Posts
    7,183

    Default

    Quote Originally Posted by Stustoys View Post
    Hi Bob,

    Am I reading this right? Your saying for 230mm discs their rated m/s is about double their rated rpm? and for 76mm their rated rpm is 50% more than their m/s?

    Stuart
    Not sure I understand what you mean.

    The red squares (m/s) apply to the RHS axis of the graph - i.e. all the discs have a max blade edge speed of (80 m/s) except for the 76mm disc which is 90 m/s
    The blue diamonds (RPM) apply to the LHS, the RPM vary directly with the inverse diameter of the RPM = to more or less give a constant speed at the blade edge

  14. #29
    Join Date
    Jul 2010
    Location
    Melbourne
    Posts
    9,088

    Default

    thank you

  15. #30
    BobL is offline Member: Blue and white apron brigade
    Join Date
    Feb 2006
    Location
    Perth
    Posts
    7,183

    Default

    While I'm bluing the bearing housing I though I would knock up a little sled/slider for this thing using some more of that scrap 2mm SS plate.
    This would enable small pieces to be held more securely and held square to the wheel.

    I attached two strips of plate to the side edges of the table using 4mm CS SS screws, and then cut out and folded a slider.
    The outer tabs of the slider are folded forward and ride on the edges while a large fold at the rear rides on the table.
    The flat topped triangular part of the slider is where the wheel might penetrate through to the rear so I'm still thinking about what to do about this.
    Another thing I could also do is mount a bit of perspex on the top to act as a shield to reduce operator spark/grit exposure.







    Folding the slider was a bit tricky.
    I don't have access to anything that can bend 2mm SS so I just did it in the 6" vice.
    I started by annealing the flat cut-out piece in my furnace.

    Then, guess what? - Of course - major visit from the FUF and I bent it the WRONG WAY.

    So I had to anneal it again and bend it the other way.
    I wasn't expecting this to work but was really pleased there was not even a tiny crack in any of the the folds - that furnace sure come in hand at times.
    After all that bending and beating the slider looks a touch wonky but it sits flat and reasonably square on the tables and slides just fine so I don't have yay much to complain about.
    I can adjust the squareness to the wheel by lightly tweaking the outrigger table

    I'll have another go at tidying it up after I try it for real with a wheel in the saw.
    Attached Images Attached Images

Page 2 of 4 FirstFirst 1234 LastLast

Similar Threads

  1. SOLD: Linisher attachment for your bench grinder
    By azzrock in forum METALWORK - Machinery, Equipment, MARKET
    Replies: 4
    Last Post: 2nd Jun 2013, 07:57 PM

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •