Spindle size for a 14" contact wheel

flatgrinder

flatgrinder

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Dec 20, 2005
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I'm building my own hollow grinder, and will be using a 14" wheel.

What spindle size do you guys recommend?

I'm thinking of going with 3/4", is 1" overkill? Or would 3/4" work?

Another factor is that the shaft will be keyed along the entire length (standard 3/16"), pulley on one end and contact wheel on the other. I'm thinking that this may weaken it, so should I go with the 1"? I'd prefer the 3/4" as it will be easier to put together as I have the parts already.

I won't be spinning the wheel faster than 500 to 1000 RPM to keep belt SFM's reasonable.

Thanks!
 
I'm building one too, but I'll use 2" tappered to 1 1/4 at the wheel
 
OK, Let's put on our engineering hats and think this one out. The wheel is 14" and the shaft is 3/4".That is a 18.6:1 ratio. Add to that the factors that the shaft is 3/16" keyed and is power driven (add torque to the equation) and the ratio expands to 25:1. It indeed seems that a 1" (or larger) drive shaft would be advisable.
Stacy
 
I didn't think that the shaft mattered because the wheel turns at the same speed the shaft does. don't you multiply the rpm by the circumference of the wheel to find the sfm?
 
I'm with Keith on this one, but be warned that my engineering hat is a few sizes too small, and makes my head hurt.
(Maybe that's why I like knives?)
 
RPMs are not the problem it is deflection. If the shaft deflects too much it puts undo strain on it and can cause a fatigue failure. This type of failure is not pretty with a shaft turning at 1000rpm. A 1" or larger shaft is in order. I would go towards 1.25 or even 1.5. Less deflection means smoother running also.

Chuck
 
I have an early incarnation of a KMG 14" attachment. The wheel is mounted on a 1" shaft and a pillow-block assembly attached to the toolarm.
 
It is not the mechanical advantage of the pulley that we are talking about here. It is the deflection and torsion on the shaft. Let's go to the other extreme - a 1/4" shaft. It would bend under load and probably twist in the middle. The 3/4" shaft has the same load and torque applied, it is just a little more robust, but probably not enough. 1" is just barely crossing the threshold, and 1.5" would be certainly sturdy enough.
Stacy
 
Interestingly enough from reading Tool Steels Simplified it is interesting to note that both hardened tool steels and mild steel will deflect the same amount up until thier plastic limit. All steels have the same deflection rate until plastic limit. The hardened shaft will probably break upon reaching its limit and the mild bend. Thier limits may be different also but, until the limit you will have the same amount of deflection with either steel with the same od.
 
called modulus of elasticity or Youngs Modules. This is were the bend test being more difficult unless the material is thicker gets me. Also using a torque wrench to measure how much pressure it takes to bend a blade...... According to Youngs Modules it should be the same. Same with a shaft. The benefit would be going larger dia rather than hardened and ground material. The only benefit to HG would be wear resistance if your fits are off.

Chuck
 
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