Belt slides on platen

johnnyjump

Well-Known Member
I’m trying to decide if the belt sliding on the platen when applying pressure while grinding is an equipment or operator problem. I have an Origin Blademaker Grinder with a one horse power motor. The wheels are all crowned and aluminum with the exception of the top platen wheel, which is a rubberized contact wheel. The wheels are all in alignment and the piston on the arm is completely compressed while grinding. But whenever I apply a fair amount of pressure while grinding, especially right to left, the belt has a tendency to shift right to left with the blade. I’m thinking either the piston is not putting enough tension on the belt or maybe the motor is too weak? Anyone else run into this issue? It’s kind of annoying because I end up chasing bad grind lines as a result. Thanks
 

billyO

Well-Known Member
the piston on the arm is completely compressed while grinding.
I'm not sure if it matters, but I was always under the impression that these work best in the mid-range, not fully compressed or extended. I, too, have an OBM grinder for the past 7 years and this happens to me occasionally, and only with really high pressure, like when I'm grinding a billet flat. I find that it happens more in cold weather than in the summer, too. I've been thinking about replacing the piston on mine with a spring, but it doesn't happen often enough for me to go through the trouble.
 

johnnyjump

Well-Known Member
I'm not sure if it matters, but I was always under the impression that these work best in the mid-range, not fully compressed or extended. I, too, have an OBM grinder for the past 7 years and this happens to me occasionally, and only with really high pressure, like when I'm grinding a billet flat. I find that it happens more in cold weather than in the summer, too. I've been thinking about replacing the piston on mine with a spring, but it doesn't happen often enough for me to go through the trouble.
Thanks for the feedback. I’ve wondered about replacing the piston myself with a heavier duty one.
 

EdCaffreyMS

"The Montana Bladesmith"
My immediate gut instinct says belt tension. However, if memory serves, isn't that one of the machine that the motor is mounted separately? I mean the motor is not mounted to the machine's frame? If it is that type of machine, then the belt slipping can also be due to the motor not being mounted properly (squarely to the machine). Because it's a spring cylinder type tension, it's likely NOT the cylinder....those things never fail slowly..... they either work, or the don't.
 

SS369

Well-Known Member
Norton calls for 15-25lbs per inch of belt width.
Without a belt tension gage, how would one go about measuring this? I ask because my grinding belt will also move to my left when really pushing hard. I would replace the spring, but I don’t want to exceed what all belts can handle.
I am wondering how tight the grinders with a ratcheting system get? Or is this still determined by what the spring pressure is?
 

EdCaffreyMS

"The Montana Bladesmith"
They might have changed things (I've got one of the early models) but I'm pretty sure mine is a pneumatic cylinder (or gas spring).
That's what I was referring to..... industry generally refers to them as "Spring Cylinder." The term "pneumatic" is generally used to describe air cylinders. Either way.... we're talking about the same part/item. :)
 
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EdCaffreyMS

"The Montana Bladesmith"
Without a belt tension gage, how would one go about measuring this? I ask because my grinding belt will also move to my left when really pushing hard. I would replace the spring, but I don’t want to exceed what all belts can handle.
I am wondering how tight the grinders with a ratcheting system get? Or is this still determined by what the spring pressure is?
Usually those spring cylinders have a rating printed on them. I've tried them everywhere from 15-90lbs. Most commonly I see 30-50lb rated ones on grinders. I doubt you'll exceed the belts pressure/tension limits.

If the belt is diving off both directions when pressure is applied, there's more wrong then just the tension. Something is out of kilter somewhere. The tough part is figuring out what, especially if the belt diving came on so slowly that it took some time to notice it.

I own a KMG TX which had the ratcheting system, and I find to be a bless/curse thing..... I can tighten a belt as much as I can physically move the arm to the next ratchet/lock position. It's a bless with "Y" and "X" weight belts that don't stretch much as they are used. But it's curse with "J" and finer weight belts that stretch significantly during use.....the ratchet type tension doesn't compensate for the stretch like a spring or cylinder would..... so you have to be wary of belts slipping, stop, tighten, and go again. Hence...the "curse" part.
 

SS369

Well-Known Member
Mine is a grinder by Pheer that has a tension arm with an exposed spring. Would be easy to replace, but I would not like to replace it and find I am shortening component lives or breaking belts. I usually compress the spring close to completely, but not all the way.
The going left only happens on the flat platen, not the 10 inch wheel. Best I can tell, using an machinist’s square, the platen is 90 degrees to the arm.
Really, not a big deal, I don’t generally grind with that much force.
 

johnnyjump

Well-Known Member
Ed’s astute observation could be the answer to my problem. The motor is mounted on a wooden bench and is attached separately to the machine. I’m thinking it might be slightly off in alignment with the machine. I’ll check it out and report my findings. With regard to the spring cylinder that came with the machine, it’s rated at 20 lbs. I’m thinking I might also purchase a 30 lb. cylinder.
 

Gene Kimmi

KNIFE MAKER
I noticed you said all wheels are crowned but one. If I remember correctly, I read somewhere that only one wheel should be crowned or it could cause problems with the tracking.
 

BossDog

KnifeDogs.com & USAknifemaker.com Owner
Staff member
Sounds like belt tension is a bit low. A belt should sound like a bass guitar string when plucked. I really crank down on them to minimize squirm.
 

EdCaffreyMS

"The Montana Bladesmith"
Gene makes a good point with having multiple crowned wheels on the same grinder/machine. UNLESS the crowned wheels are PERFECTLY aligned/squared to each other, they will fight against each other.... one will try to "pull" the belt one way, and the other will try to pull another.

Usually the top end machines will have EITHER a crowned idler wheel, or a crowned drive wheel....but never both. Something else to possibly consider.
 

KenH

Well-Known Member
With regard to the spring cylinder that came with the machine, it’s rated at 20 lbs. I’m thinking I might also purchase a 30 lb. cylinder.
Remember, unless that cylinder is mounted directly under the tracking wheel, the 20 lb cylinder might be putting more, or less actual pressure on the belt. Like other folks have said you really need a good bit of pressure on belt for heavy grinding - say "middle C" when plucking belt? :)

Moving the motor a tad in alignment is the way some grinders adjust the belt tracking. If the belt is running true when not grinding the motor "should" be in alignment - note I did say "should".
 

johnnyjump

Well-Known Member
I took some time to realign the motor, and believe that may have solved the problem. I’ll know more when I begin my next grind tomorrow. But it doesn’t move like before when applying pressure to the platen. Regarding the crown on the wheels, I misspoke before; the drive wheel and tracking wheel are crowned but not the idler wheels. Thanks so much for all the expert advice!
 
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