Grinder/Belt Question

Discussion in 'New to Knifemaking' started by Jellis11, Apr 3, 2017.

  1. Jellis11

    Jellis11 Well-Known Member

    Why would my blade be rattling and banging all over the platen face when I'm using finer grit belts? Smooth as silk with 60 and mostly 120g.....It is not a chattering or skipping, but more "knocking" and only when the blade is on the platen. Brand new belts, so I don't think that is the issue. I recently added a face to the platen (courtesy of Ed Caffrey) with some 2" 5160 stock and glued on some of the cloth backed graphite with 3M adhesive spray until I can get a glass face. I'm using an old Wilton, and it runs FAST. (Still working on acquiring motor/VFD upgrade.
     
    Last edited: Apr 3, 2017
  2. Boss70

    Boss70 Member

    I think what your feeling is the tape that joins the belt together at the seam. Finer belts have thinner abrasives than coarse belts which cushion where the joint is. Some of the higher end belts run a bit smoother but on a hard platen even glass you will probably still feel the belt joint.

    Hope this was helpful

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  3. John Wilson

    John Wilson Well-Known Member

    splice bump, just as Boss70 says. You'll also notice that it eats little zigzag dips in your finish that you have to grind out again. I have no idea how guys run 220grit or higher j-weight belts on a flat platen for grinding bevels. I switch to Trizact Gator belts at 220 for this very reason.
     
  4. Jellis11

    Jellis11 Well-Known Member

    Thanks! If that's the case, it makes sense!
     
  5. Jellis11

    Jellis11 Well-Known Member

    Great information John! I actually tried to order a few last week, but unfortunately out of stock
     
  6. John Wilson

    John Wilson Well-Known Member

    TruGrit will have them
     
  7. Joe Cabaup

    Joe Cabaup Member

    Once you are able to slow the belt down to 40%, adjust the tracking so the j weight belt hangs over the side of the platen. Start in the middle of the blade and gently push towards the bevel. I finally tried this last night and it put in equal bevels!

    The less weight (thinner) of the belt, the slower you need to go to avoid the belt splice bump. Just like speed bumps.

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  8. Jellis11

    Jellis11 Well-Known Member

    Yeah, I need to make that modification a priority! I've sourced a brand new ABB VFD mini for 130.00, just need to find a decent motor now.
     
  9. EdCaffreyMS

    EdCaffreyMS Forum Owner - Moderator

    Everyone has nailed it on the belt joint issue.

    Personally, I would think twice about the VFD you mentioned. It's not a matter of IF that particular variety will give you grief, it's a matter of WHEN. It's simply not suitable for a grinder application. I know it's pricey by comparison, but it you want something that is going to last and be trouble free, go with a KBAC (model 24D, 27D, or 29D depending on motor HP) and a 3 phase TEFC (totally enclosed fan cooled) motor. That is assuming that you have 220V power available.

    I can't count the number of times I've fielded phone calls and emails from folks having difficulty with those type of VFDs..... they are just not built/intended for use in a "dirty" environment such as grinding. The "open" design means that steel dust can readily enter the units, often causing them to "burn out". They are also NOT intended for the frequent/routine speed changes we generally use in a grinder application. Whatever route you decide to go, both the VFD and the motor MUST be totally enclosed/dust proof. Otherwise it's just a matter of time before they go out in a loud crack, or a puff of smoke.
     
  10. Jellis11

    Jellis11 Well-Known Member

    Good point on the NEMA 4X enclosure Ed...although I was fully aware of the need for the TEFC motor, I hadn't even considered the enclosure for the drive. Its too bad the ABB isn't highly regarded for grinders...one of our reps is an ABB dist. so I can get them at cost.
     
  11. Joe Cabaup

    Joe Cabaup Member

    I had an ebay VFD. It was good for a couple of months and went up in smoke. Tried enclosing it in a tupperware container but kept overheating. I finally bit the bullet and got the KBAC with a 2hp motor. The control is great.

    I know for a while this expense was off the table so I used a step pulley system. I was able to slow things down enough to avoid the bumps (still didnt switch to J weight belts yet). I also used a 1750 rpm motor. If I needed to hog things off I used an angle grinder.

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  12. EdCaffreyMS

    EdCaffreyMS Forum Owner - Moderator

    Certainly step pulley are an option, especially if cost is the overriding consideration. It took me a few years before I could justify a VFD setup, but after doing it, I kept asking myself "Why didn't I do this sooner." :)
     
  13. Jellis11

    Jellis11 Well-Known Member

    Which is why I have pretty much set my mind to the motor/VFD option....in the meantime, I have to believe that working with the insane speed of that Wilton, I have no choice but to learn some control and patience (to a certain extent).
     
  14. Kev

    Kev Well-Known Member

    You could also reduce the size of the drive wheel, and slow it down considerably. That may be the best cheapest option for now. You could always sell the leftover wheel when you get a VFD setup. There's always someone looking for that stuff. Reducing the size of the drive wheel could get you down in a manageable speed range.
     
  15. EdCaffreyMS

    EdCaffreyMS Forum Owner - Moderator

    That was the idea I had many moons ago when I first realized my Square Wheel was way too fast. It comes from the factory, with a cast 10" drive wheel that moves the belt at 4600 SFPM, and is the major problem with the machine being a "knifemaking" machine.

    The factory drive wheel cannot be reduced in size because of it's factory configuration (there is only a "web" of material connecting the outer hub and the arbor hub), therefore you're left with the option of either obtaining a "slow down" wheel from somewhere....and for a while that was an option, but as the Square Wheel sorta "died" away, those who offered the slow down wheels ceased to offer them.

    About the only choice a person has these days is to find an 8" dia (or larger) X 2" thick chunk of aluminum (can't use steel, the weight tears up the motor's braking system, and destroys the motor), and have a drive wheel machined out. The smallest drive wheel that can be used without modifying the tooling arm's position, is 8 1/4".
    You can go down to a 7 1/4", but that requires re-positioning the tooling arm as far outward as possible....meaning you have to drill/tap new holes into the grinder's frame. (This is what I did to my Square Wheel).
    A 7 1/4" drive wheel slows the belt down to approx. 2800 SFPM. It's not ideal, but it makes the machine a far cry better then the factory 4600 SFPM.

    At the time there was no such thing as a commercially available VFD.... In the current time, a 2hp/3ph motor and the associated KBAC VFD is about the same cost as having a new drive wheel machined out...... considering that the costs are approx. the same, there's no question that I would go with a VFD setup if I had it to do over today.
     
  16. Kev

    Kev Well-Known Member

    I didn't realize it was so complex. I can't say that I've ever seen a square wheel grinder, so my comment was obviously from a "this should work" standpoint. I didn't consider machine specific issues. I was just thinking of it in context of the machine I have. Makes sense what your saying though. Too bad it won't work. Seems like a cheap and easy fix, but apparently not. Good to know.
     

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