Arbor Nut Clamp Load?

[MBG]

I was wondering how much clamp load is required to hold say a 3/4" width dado set on a 5/8" arbor with a 2.4 max. HP TS (no load speed of 3450RPM).

When I do the calculations I come up with some very small clamp load values.

Thanks

[gsmittle]

Hmmmmmmmm

I was wondering how much clamp load is required to hold say a 3/4" width dado set on a 5/8" arbor with a 2.4 max. HP TS (no load speed of 3450RPM).

When I do the calculations I come up with some very small clamp load values.

Thanks

I'm not a Math Guy, so I've never calculated the exact torque requried on an arbor nut. I just get mine fairly snug, and the rotation of the arbor tightens up the nut a little more.

I'm sure somebody can tell you--I've never worried about it.

g.

[LCHIEN]

I was wondering how much clamp load is required to hold say a 3/4" width dado set on a 5/8" arbor with a 2.4 max. HP TS (no load speed of 3450RPM).

When I do the calculations I come up with some very small clamp load values.

Thanks

I've always just tightened my blades a little, single blade or dado stack.
By that I mean I snug the nut by hand and then use about 1/8 to 1/4th more turn (estimating, here) to lock the nut with the wrench.
The nut is inherently self tighteneing once snugged by virtue of the direction of the blade load.

I think personally most people overtighten their arbor nuts.

[MBG]

More info.....I'm looking to apply clamp load to a dado stack with a modified arbor (to essentially lengthen the arbor) that has a 1/4-20 thread tapped in it. A 1/4-20 bolt can apply around 2000 lb. of clamp load. Just wondering if this is enough load.

Mike

[onedash]

I think personally most people overtighten their arbor nuts.

I over tighten mine!!!The washer has to be screwed off and on....I should probably get a new one because its a royal pain in the A@# to get it off. Then it has to be screwed back on....

[LCHIEN]

More info.....I'm looking to apply clamp load to a dado stack with a modified arbor (to essentially lengthen the arbor) that has a 1/4-20 thread tapped in it. A 1/4-20 bolt can apply around 2000 lb. of clamp load. Just wondering if this is enough load.

Mike

well, mechanical engineering is not my training.
But, I'm guessing that I put maybe 5-10 lbs force on the end of my 8" wrench so that's about 5 ft-lbs of torque.

A screw thread is an inclined plane.
I can't remember the pitch which will be in threads per inch and
the circumference is somewhere around Pi x D or 2"
so there's a mechanical advantage.

Help - I need a Mech E.!

Forget the ME. I love the internet.
http://www.pdhonline.org/courses/s149/s149content.pdf

It turns out that the tension in a bolt (or arbor in this case)
is simply Tension = Torque *12/(.2 x D)
where D is the major dia. in inches and Torque is in Ft. pounds.
So assuming my 5 ft lbs and 5/8" diameter
I get ~460 lbs tension in the arbor which should be the force with which the blade is clamped. Assuming my estimation of torque is +/- 50% then it could be anywhere from about 230 to 700 lbs of tension.

So that's less than 2000# capacity of your 1/4-20 bolt. But don't overtorque it. 5 ft pounds is very low. You don't want to break off your bolt in the arbor. Frankly, I'm not wild about your drilling a hole in the end of the arbor, Even if you extend the arbor this way the outer dado blades will still be riding on the threads.

[MBG]

Thanks, Loring.

I put a long (borrowed) extension onto my torque wrench and found I apply around 10 ft-lbs of torque to the arbor nut.

A 5/8-11 bolt will give 14,400# load at 150ft-lb of torque unlubricated. Using this and 10 ft-lbs gives 960#.....the 1/4-20 should be plenty.

(With the full stack of dado blades and the adjusting dial I still have 1-1/2 threads exposed - enough to pilot an arbor spacer on the OEM arbor.)