Idler wheels: "Sharp" or rounded corners?

[Drew Riley]

I noticed that when I'm using higher grits belts, particularly j-flex, that they're not laying flat against my platen. I get a little hump on the outer edges, and I'm wondering if this is due the the radius/round over on the corners of my idler wheels. I normally position my plate at least 1/16 to 1/8" proud of the wheels, but I'm still not getting as flat of a belt as I'd like for sharpening and such.

Would non radiused wheels solve this problem?

 

[AVigil]

Same here, I went to the norax engineered ceramic for sharpening because they run dead flat and not belt hump.

 

[WhitleyStu]

The platen wheels on my Reeder have 1.75" of flat and .125" of 45° bevel on each edge of the wheel. All of my 3M Trizact belts run flat on the platen. I keep the platen set even with the upper and lower wheels and run the belts pretty tight since almost everything I do is sharpening or stropping at 20-40% speed.

 

[coldsteelburns]

I have the same issue, even before I'd "break" in the edges of the j-flex belt for getting into the plunges they still wouldn't lay completely flat so I'd try to keep the blade moving back and forth even when getting into the plunges.
Sometimes it's the edges of the belt and sometimes it's the center. I just kinda thought it possibly had something to do with the crown on the drive and tracking wheels stretching out the center of the belt more so than the rest of the belt (i.e. the sides), or something like that.

I also did the same as Adam and switched to the Norax ceramic belts which has really helped keep things nice and even when I'm convexing/rolling in the bottom of the bevel or applying an edge since they're thicker and stiffer than the j-flex, and thus they lay nice and flat, even on the slack portion above the the top idler on the platen.

As to your actual question I honestly don't know (sorry bout that), but I'd also like to know if there is a way to fix this issue and avoid possibly grinding in any grooves on my the bevels when using these belts for plunges.


~Paul
My Youtube Channel
... (Just some older videos of some knives I've made in the past)

 

[mike-E]

Check your top platen wheel for any dishing. If you plan on making new wheels, make them 2 1/8" wide. My platen wheels have almost zero chamfer. Basically just broke the corners. They are 2" wide and I have the same issues with thin belts.
I think it all comes down to the crown on the tracking and drive wheels to be honest. When on the machine, the center of the belt gets stretched and takes all the tension. The edges just get pulled along for the ride.

 

[Drew Riley]

Check your top platen wheel for any dishing. If you plan on making new wheels, make them 2 1/8" wide. My platen wheels have almost zero chamfer. Basically just broke the corners. They are 2" wide and I have the same issues with thin belts.
I think it all comes down to the crown on the tracking and drive wheels to be honest. When on the machine, the center of the belt gets stretched and takes all the tension. The edges just get pulled along for the ride.

I see that OBM makes some 2.25 wide flat wheels. I'm thinking about trying a pair of those, though I'm also wondering if the crowns on the drive and tracking wheel are contributing.

 

[Natlek]

Check your top platen wheel for any dishing. If you plan on making new wheels, make them 2 1/8" wide. My platen wheels have almost zero chamfer. Basically just broke the corners. They are 2" wide and I have the same issues with thin belts.
I think it all comes down to the crown on the tracking and drive wheels to be honest. When on the machine, the center of the belt gets stretched and takes all the tension. The edges just get pulled along for the ride.

These are my thoughts also .I never understand why they make that much crown on wheels ? On my grinders crown is almost invisible to the eye and tracking is perfect .

 

[Drew Riley]

Well, after thinking about it, and looking at things a little more closely, I do believe it is mainly the crown that's contributing to the lighter weight belts not laying flat:

With a straight edge just touching the high spots of the belt, you can see that this just about mirrors the crown of the tracking wheel, and it makes sense now that the middle would be tighter, since there's more "wheel" in the middle of the tracking and drive wheels.
Now you can also see that where the corners of the platen idlers are radiused, the belt does "turn in" a small amount. I'm thinking that a better idler wheel design would be a 2.25" wide wheel with a .125" radius on the corners. That would keep full contact on the belt when centered, but still give you a chance to curve the belt when tracking off the edge of the platen.

That still doesn't address the inherent issues with the wheel crowns though... I think I may flatten them out a bit and see if that helps.