Grinder wheel axle flex/wheel alignment

REK Knives

REK Knives

Moderator
Knifemaker / Craftsman / Service Provider
Joined
Apr 3, 2011
Messages
5,753
I am pretty sure every grinder uses bolts to secure the wheels to the tool arm/platen and bolts are precision ground. I recommend checking multiple angles as well (not just from one side). Now given, this is a 2.5" wide wheel and this is the far side of the wheel but it's a .005" gap (checked w/ feeler gauges).

*update: axle flex is apparently a significant issue for any of the wheels

i-cG7KcKv-L.jpg


When I rotate the axel/bolt around I get this:
i-ZHpNgTB-L.jpg


Fortunately I was able to use an indicator and bend the bolt straight so it's good to go now! I am thinking about trying a step bolt as those are likely more precise.
 
Last edited:
Interesting. Now I'm curious what happens when you apply belt tension...

Is this a steel wheel for an SGA? If yes, can you tell me who made it? I have been looking for one for an SGA I'm building.
 
REK Knives said:
Not here to call anyone out as I am pretty sure this is common across the board since most every grinder uses bolts to secure the wheels to the tool arm/platen and bolts are precision ground. I recommend checking multiple angles as well (not just from one side). Now given, this is a 2.5" wide wheel and this is the far side of the wheel but it's a .005" gap (checked w/ feeler gauges).

i-cG7KcKv-L.jpg


When I rotate the axel/bolt around I get this:
i-ZHpNgTB-L.jpg


Fortunately I was able to use an indicator and bend the bolt straight so it's good to go now! I am thinking about trying a step bolt as those are likely more precise.
Click to expand...
Is that bolt screw tight ? If it is , bolt can not be reason for what you show us .
 
Last edited:
Hubert S. said:
Interesting. Now I'm curious what happens when you apply belt tension...

Is this a steel wheel for an SGA? If yes, can you tell me who made it? I have been looking for one for an SGA I'm building.
Click to expand...
Wow now you got me thinking... I just checked and have about .006-.007" flex when under tension!!

Yeah this was a proto aluminum wheel I had made before the steel wheel... I ended up having a hardened A2 steel wheel made. I'll pm ya
Natlek said:
Is that bolt screw tight ? If it is , it can not be reason for what you show us .
Click to expand...
Yes it's very tight. I'm not sure what else it could be... When I rotate the axel 180 degrees the light gap switches. And when I bent the bolt straight I check 4 different directions and the light gap is gone
 
REK Knives said:
Wow now you got me thinking... I just checked and have about .006-.007" flex when under tension!!

Yeah this was a proto aluminum wheel I had made before the steel wheel... I ended up having a hardened A2 steel wheel made. I'll pm ya

Yes it's very tight. I'm not sure what else it could be... When I rotate the axel 180 degrees the light gap switches. And when I bent the bolt straight I check 4 different directions and the light gap is gone
Click to expand...
spacer between wheel and tool arm is machined on lathe ?
 
REK Knives said:
Wow now you got me thinking... I just checked and have about .006-.007" flex when under tension!!

Yeah this was a proto aluminum wheel I had made before the steel wheel... I ended up having a hardened A2 steel wheel made. I'll pm ya

Yes it's very tight. I'm not sure what else it could be... When I rotate the axel 180 degrees the light gap switches. And when I bent the bolt straight I check 4 different directions and the light gap is gone
Click to expand...
That mean that you also have spacer between bearings right ?
 
REK Knives said:
Not here to call anyone out as I am pretty sure this is common across the board since most every grinder uses bolts to secure the wheels to the tool arm/platen and bolts are precision ground. I recommend checking multiple angles as well (not just from one side). Now given, this is a 2.5" wide wheel and this is the far side of the wheel but it's a .005" gap (checked w/ feeler gauges).

i-cG7KcKv-L.jpg


When I rotate the axel/bolt around I get this:
i-ZHpNgTB-L.jpg


Fortunately I was able to use an indicator and bend the bolt straight so it's good to go now! I am thinking about trying a step bolt as those are likely more precise.
Click to expand...
On first picture you have not used that red color spacer ? Why you used it in on second picture ?
 
Natlek said:
spacer between wheel and tool arm is machined on lathe ?
Click to expand...
Yes, but when I rotate the bushing by itself the light gap does not change, it's only when I rotate the entire axle
 
REK Knives said:
Wow now you got me thinking... I just checked and have about .006-.007" flex when under tension!!

Yeah this was a proto aluminum wheel I had made before the steel wheel... I ended up having a hardened A2 steel wheel made. I'll pm ya

Yes it's very tight. I'm not sure what else it could be... When I rotate the axel 180 degrees the light gap switches. And when I bent the bolt straight I check 4 different directions and the light gap is gone
Click to expand...
That is a lot of flex. I guess you grind in the chuck under (approximately) the same tension, so maybe the error is a whole lot less.

I ordered a rubber wheel for my SGA with 20mm bearings so I can use a beefier shaft and hopefully minimize flex. I am still interested in the metal wheel down the road and look forward to hearing from you.
 
Natlek said:
That mean that you also have spacer between bearings right ?
Click to expand...
Yes that's correct
Natlek said:
On first picture you have not used that red color spacer ? Why you used it in on second picture ?
Click to expand...
I was swapping bolts around - I have 3 axles. Just took pictures with different bolts but they all do the same thing. For some reason the other bolt has slightly less thread - guess it's within the bolts specification but it wouldn't allow me to get it quite tight enough (so there was play) without it
 
JDWARE said:
Nathan Carothers posted here in 2018 explaining the details of his C-Plates for flat and rotary platens that he built. It showed the importance of proper drilling and tapping and high quality precision made axle bolts:

https://www.bladeforums.com/threads...-attachment-c-plates-and-other-stuff.1555503/

Saludos
J
Click to expand...
yeah it's quite important for sure!! I actually have Nathan's C-plate and use his axle bolt set up and it's really nice. But the flex part is inevitable to some extent, even on that with bolts cranked tight I am getting .005" flex out the outer rim of the wheel. But I don't have any issue in operation. I just hadn't really thought about it before!!

The reason this all came up is because I'm getting ready to grind my chuck on my SGA w/ a new wheel so got to thinking about it haha
 
what brand is the arm and wheel? i am confused you call it flex when there is no belt or tension on it in the photo, it would seem the axle is bent ? i wonder if it will be worse with belt and tension applied.
 
john april said:
what brand is the arm and wheel? i am confused you call it flex when there is no belt or tension on it in the photo, it would seem the axle is bent ? i wonder if it will be worse with belt and tension applied.
Click to expand...
Sorry it started out as a wheel alignment thing but then I ended up finding that the wheel flexes .007" when under tension so the alignment thing isn't as big of a deal as long as you have it flex back into alignment lol
 
REK Knives said:
Sorry it started out as a wheel alignment thing but then I ended up finding that the wheel flexes .007" when under tension so the alignment thing isn't as big of a deal as long as you have it flex back into alignment lol
Click to expand...
Again , I don think that that flex come from bolt and wheel , impossible .Check tool arm
 
Natlek said:
Again , I don think that that flex come from bolt and wheel , impossible .Check tool arm
Click to expand...
I did the calculation for a cantilever beam with circular cross section and the numbers Josh saw in his test appear very plausible to me.
 
Hubert S. said:
I did the calculation for a cantilever beam with circular cross section and the numbers Josh saw in his test appear very plausible to me.
Click to expand...
Just to check that we are on same page . Do you mean wheel flex like this when it is bolted to tool arm from belt tension ? Just wheel not whole setup ?
ZoFxgpB.png
 
Hubert S. said:
I did the calculation for a cantilever beam with circular cross section and the numbers Josh saw in his test appear very plausible to me.
Click to expand...
What approximations were you making about the stiffness of the wheel and where it was supporting the cantilevered beam? I just measured the 2" idler wheels on my D-plate and found they deflect about 2.5 thou at the far end under belt tension. I could throw my SGA with 5" wheel on to see what it does in a bit; I'd expect it to deflect even less because I'm using a shorter (and steel) spacer for it.
 
You must log in or register to reply here.
Back
Top