I'm not sure yet. I have some 2-5/8" aluminum stock on hand which will work fine for a quick test and is easy to turn, but is smaller than I'd like to run long term. I may have some 4" stainless I could use, but I'm rather dreading boring out that much 304!
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Grinder wheel axle flex/wheel alignment
- Thread starter REK Knives
- Start date
How long do you think aluminum would last before it has to be trued up? It sounds a whole lot easier, especially if you start with a tracking wheel and just remove the crown. I have thought about doing that but was concerned that the aluminum would not last too long.
Please, post your results when you try this out, I'm very interested in what you find.
6204 bearingI always have the same belt tension on my SGA (I have tool-arm stick out marked for repeatability) so the few thou of deflection in my wheel is mapped onto my chuck and I can grind very precisely if I'm careful but this raises an interesting question: when grinding aggressively the belt is being pinched between the wheel and your work piece with the motor pulling the belt through with a very large amount of force, far greater than the static belt tension. This will cause further deflection and pull the wheel out of square with the chuck. I'm fairly sure this is why my SGA always removes more material from the work piece at the bottom of the wheel than the top when hogging. As the cuts get lighter this evens out and thus isn't an issue but I had never made the connection before. I'm currently experimenting with a few solutions but it will be a little while before I'm ready to share the results. I turned a stainless steel 20mm shaft with a flared base to use to mount my wheel. It will be screwed into the tool arm from below and a wheel with 6204 bearings will be a very tight slip fit or very light press fit onto it, then clamped with a screw from above. This should make the wheel more than an order of magnitude more rigid and decouples the two jobs the 1/2" bolt does in a normal assembly: preloading the bearings and securing the assembly to the tool arm. I'm currently waiting for bearings to arrive and I need to turn another wheel to fit them.
Ok , i make some test on several grinder and with different Dia. wheels .Note , some are ratchet some are off center cam belt tension system and i can tight belt as guitar string ! .And I can t see any movement on dial under the maximum belt tension. What I managed to do is this ,I used M12 bolt with allen head on one wheel , then I put belt on tension and used straight allen wrench and some tube over that and hang on my weight ...well dial moved , I flex 12 mm steel frame !!
I have nothing more to say here , sorry to interfere
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Was it just a bolt, or a much larger sleeve around the bolt? The area moment of inertia is proportional to the fourth power of the OD. A 20mm OD sleeve with a 12mm ID hole has about 14 times higher stiffness than an M12 bolt with a minor diameter of just under 10mm. What you show in your picture is a completely different setup from the OP's.6204 bearing
Ok , i make some test on several grinder and with different Dia. wheels .Note , some are ratchet some are off center cam belt tension system and i can tight belt as guitar string ! .And I can t see any movement on dial under the maximum belt tension. What I managed to do is this ,I used M12 bolt with allen head on one wheel , then I put belt on tension and used straight allen wrench and some tube over that and hang on my weight ...well dial moved , I flex 12 mm steel frame !!
I have nothing more to say here , sorry to interfere
You did not know that there is no gravity in Macedonia?
Okay, let's try this then ! Do you have some money to throw away ? We'll bet, I'll put two on one of your dollars , serious bet .
Look this picture , you will know what is what .I will ADD weight on belt until it breaks . Which means a much higher load on wheel than in normal use of grinder . I will setup two dial indicator , one under the wheel one on top of wheel in the middle of wheel .IF we have ANY /no matter how small/ movement on any of that two dial indicator BEFORE belt break I lose ?? Of course I will record everything so that it is clear what I am doing.
Are you IN ?
Drew Riley
Knifemaker / Craftsman / Service Provider
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If I had to guess, most of the flex is somewhere in OP’s frame. The bolt likely has minimal deflection, though as you state, some of this depends on tightness/rigidity of setup, as well as fit tolerance between parts.Yes , everything flex if we apply required force .
I will waste my time but i will make some test tonight !
Drew , where would be flex in our case ? Can you show me on this drawing . If bolt is tightened properly what will flex ? Bolt ? HOW and where ? All parts are tightly tightened together so to get wheel to flex , spacer between tool arm and wheel has to raise on one side . I can not see any other way to get flex in that setup ? I f I explain right what I mean ?
As for why any gaps are changing, the bolt likely isn’t straight, and/or something is not square.
OK , I will add weight on wheel equal to your weight ? If dial move I lose ?
If you have a sleeve ?? Of course that there is sleeve between or thru bearings ? You don t use them ? How you will tighten wheel without sleeve ?
10.9 M12 bolt can be tightened quite a lot ,that is a lot of force on spacer ,sleeve....
Of course that will gain some additional stiffness .That is what I am talking about here .........
Never mind , I am out of here .Enough braggadocio whatever that mean .............
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Would you mind doing a video for me so I can see how you are achieving no flex? I'm quite curious now! I'll try to do a video soon of how mine is set upYou did not know that there is no gravity in Macedonia?
Okay, let's try this then ! Do you have some money to throw away ? We'll bet, I'll put two on one of your dollars , serious bet .
Look this picture , you will know what is what .I will ADD weight on belt until it breaks . Which means a much higher load on wheel than in normal use of grinder . I will setup two dial indicator , one under the wheel one on top of wheel in the middle of wheel .IF we have ANY /no matter how small/ movement on any of that two dial indicator BEFORE belt break I lose ?? Of course I will record everything so that it is clear what I am doing.
Are you IN ?
Look at Callum's post #37 above, or your own drawing (configuration #1) in the thread you referenced in post #33. A "sleeve thru bearing" as you call it is nothing but a bigger shaft where you combine the function of securing the shaft to the tool arm with the function of preloading the bearings. What you show in post #43 is a 20mm hollow shaft with a 14 times higher bending stiffness than an M12 bolt.
The amount of force you can apply to the spacer does not have anything to do with its resistance to bending, please look at the wikipedia page about deflection to see the equations. The sleeve effectively increases the diameter of your beam and thus the resistance to bending. Because the resistance to bending increases with the fourth power of the shaft diameter, a slightly larger shaft/sleeve has a huge effect. For the pictures you showed in post #43 with the 6204 bearing, the cantilever beam equations do not predict any appreciable deflection with typical belt tension, which is consistent with your experiment. It is, however, not the same as bending an M12 bolt with the same load.
You already said that in post #43, yet here we are.
Stacy E. Apelt - Bladesmith
ilmarinen - MODERATOR
Moderator
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OK everybody. Let's let this one go. There is only one set of physics and only one set of mechanical engineering rules that work on earth.
We all agree that a larger diameter flexes less.
We all agree that the bolt needs some type of a solid shaft to tighten against the frame.
We all agree that the frame is often what flexes.
We all agree that the holes through the tool arm have to be a perfect 90°.
If you want rock solid and minimal deflection you could:
Custom turn the wheels in a fairly hard material with the bearing pockets at .0025mm/ .0001" tolerance.
Use a 25mm/1"precision hardened axle bolt.
Use a good grade large diameter bearing with a through sleeve.
Make the grinder frame from 12mm/.5" stainless steel.
Make grinder arms from 75mm/3" stainless steel.
Drill and tap all holes on the mill that has been trammed as close to 90° as your setup will allow.
True the ends of the sleeve and use perfectly parallel washers.
However, most of us do fine with the 12mm/.5" bolts and the bearings we have been using. The wheels from places like Reeder are precise enough for most of us. Proper mounting of the wheels, bearings, sleeves, etc. work sufficient for most of us.
We all agree that a larger diameter flexes less.
We all agree that the bolt needs some type of a solid shaft to tighten against the frame.
We all agree that the frame is often what flexes.
We all agree that the holes through the tool arm have to be a perfect 90°.
If you want rock solid and minimal deflection you could:
Custom turn the wheels in a fairly hard material with the bearing pockets at .0025mm/ .0001" tolerance.
Use a 25mm/1"precision hardened axle bolt.
Use a good grade large diameter bearing with a through sleeve.
Make the grinder frame from 12mm/.5" stainless steel.
Make grinder arms from 75mm/3" stainless steel.
Drill and tap all holes on the mill that has been trammed as close to 90° as your setup will allow.
True the ends of the sleeve and use perfectly parallel washers.
However, most of us do fine with the 12mm/.5" bolts and the bearings we have been using. The wheels from places like Reeder are precise enough for most of us. Proper mounting of the wheels, bearings, sleeves, etc. work sufficient for most of us.
This small wheel is attached with M8 bolt , no flex i can measure with dial indicator . Then I used M12 thread in tool arm and attached M12 10.9 bolt , tightened with two nuts from both side of tool arm and tightened belt over bolt so i have clear two inch length of bolt body without nut and bolt head . What do you think , did I measured any flex?
Most grinder use steel spring or gas spring for tension .I don t think that they can apply that much force on belt .Even with ratchet tension 22 kg is questionable.
Edit - Just out of curiosity I will try to apply 22 Kg weight on that bolt to see what we will get .I leave shop half hour ago so i will try tomorrow .
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50 lbf .
Don t you think that it is to much to use it as belt tension on wheel ?
I just watched your youtube here ................. https://bladeforums.com/threads/my-sharpening-jig-set-up-for-my-2x72.1833562/
and I noticed that you have LOT of play between tool arm and slot in frame .You have one bolt to tighten tool arm .Your tool arm is Al so you probably don't use to much force to tighten that bolt .Even if you tighten it hard that bolt is still pivot point to tool arm and belt tension on wheel would use that pivot point to rotate tool arm and maybe there can hide your 0.000 flex ?
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From weight of wheel and because of play inside slot your tool arm will sit like this in slot before you tighten it with bolt .Then when you add tension on wheel .................Maybe ?
In the meantime I make many other test and I still can t measure any flex in my setups
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That's an excellent, thanks for pointing that out!!I just watched your youtube here ................. https://bladeforums.com/threads/my-sharpening-jig-set-up-for-my-2x72.1833562/
and I noticed that you have LOT of play between tool arm and slot in frame .You have one bolt to tighten tool arm .Your tool arm is Al so you probably don't use to much force to tighten that bolt .Even if you tighten it hard that bolt is still pivot point to tool arm and belt tension on wheel would use that pivot point to rotate tool arm and maybe there can hide your 0.000 flex ?
.
From weight of wheel and because of play inside slot your tool arm will sit like this in slot before you tighten it with bolt .Then when you add tension on wheel .................Maybe ?
In the meantime I make many other test and I still can t measure any flex in my setups
But I'm not sure if that is it... When I take the tension off it springs right back to 0 and when I put it in it goes up to .006" or whatever. It may be tool arm flex though... I have a steel tool arm, I'll try that and see what happens
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Flex, bend, and deflect appear to be used interchangeably, even though they do not all mean the same thing. Maybe this is where some of the disagreements in the thread come from? The thread started with pictures of a wheel whose axis was not square (perpendicular) to the arm, but used the word ‘flex’. One does not remove flex in something by bending it straight.
It could be hard to tell whether deflection of the wheel axis under load is the result of flex in the shaft or clearances in the assembly allowing movement.
In the engineering I do, it is a given that you do not use threaded joints to control position or perpendicularity. Also, anything that fits together with easy slide clearance fits will have enough clearance to allow parts to tip over, as in Natkek’s diagram of the tool arm.
Bolts generally have rolled threads. Even if the shank has been ground (something I am sceptical about), it would be dumb luck for the axis of the thread to be aligned with that of the shank to any fine degree. This is all geometric tolerance stuff (GD&T).
If precision was needed, you would not use bolts as shafts. Custom machine the shaft with an anti rotation feature in the middle and a turned thread at each end used with nuts so bearings could be clamped independent of fixing to the arm. A ground diameter going into a reamed steel insert in the arm, hole axis defined by GD&T. Bearings clamped with a defined torque.
Chris
It could be hard to tell whether deflection of the wheel axis under load is the result of flex in the shaft or clearances in the assembly allowing movement.
In the engineering I do, it is a given that you do not use threaded joints to control position or perpendicularity. Also, anything that fits together with easy slide clearance fits will have enough clearance to allow parts to tip over, as in Natkek’s diagram of the tool arm.
Bolts generally have rolled threads. Even if the shank has been ground (something I am sceptical about), it would be dumb luck for the axis of the thread to be aligned with that of the shank to any fine degree. This is all geometric tolerance stuff (GD&T).
If precision was needed, you would not use bolts as shafts. Custom machine the shaft with an anti rotation feature in the middle and a turned thread at each end used with nuts so bearings could be clamped independent of fixing to the arm. A ground diameter going into a reamed steel insert in the arm, hole axis defined by GD&T. Bearings clamped with a defined torque.
Chris