Power Pro Case

[mickyd]

FWIW the part protruding above the top of the countersink is contributing little if any additional strength.

Now if the countersink was deeper and the heads went in further, that part in the countersink does add strength.

In other words, that part of the head that is not contacting the surface contributes little to the shear strength. Of course if the head gets too small,there are other factors determining the holding capability.

Well Mike does that pass the sanity test?:)

Well, shear is kind of mute. There is negligible shear force on the fasteners in this type of application. What's holding the load (motor) is the frictional force at the interface between the motor mounting bracket and motor pan, caused by each socket cap screw applying a HUGE compression load.

[JPG]

Well, shear is kind of mute. There is negligible shear force on the fasteners in this type of application. What's holding the load (motor) is the frictional force at the interface between the motor mounting bracket and motor pan, caused by each socket cap screw applying a HUGE compression load.

OK! I said shear when I should have said tensile. Pls forgive a old sparky!:rolleyes:

[mickyd]

OK! I said shear when I should have said tensile. Pls forgive a old sparky!:rolleyes:

That's OK. Your batting about .999.

With that out of the way, grinding down the heads down would work great. I'd wouldn't hesitate doing that. Alloy cap screw are the strongest commercially available off the shelf fastener.

[horologist]

Mike,

Somewhere I have a chart with a curve for calculating the transfer between layers due to friction. We aren't allowed to take credit for this as there are too many variables.
However this is most certainly a shear application. The tensile load is entirely due to tightening the fastener. As you said there will be a fair amount of shear transfer between the layers, and either way the loads are relatively small.

My only concern with milling the head of the screw is that the depth of the hole for the Allen wrench might be reduced sufficiently that it may make it hard to tighten the screw without rounding the corners.

What is the Ftu or Fsu for a commercially available cap screw? For my guesstimate I was using values that were about half of the standard alloy steel bolt we use. (Fsu = 95ksi)

Troy

[JPG]

Mike,

Somewhere I have a chart with a curve for calculating the transfer between layers due to friction. We aren't allowed to take credit for this as there are too many variables.
However this is most certainly a shear application. The tensile load is entirely due to tightening the fastener. As you said there will be a fair amount of shear transfer between the layers, and either way the loads are relatively small.

My only concern with milling the head of the screw is that the depth of the hole for the Allen wrench might be reduced sufficiently that it may make it hard to tighten the screw without rounding the corners.

What is the Ftu or Fsu for a commercially available cap screw? For my guesstimate I was using values that were about half of the standard alloy steel bolt we use. (Fsu = 95ksi)

Troy

My original concern was with the decrease in tensile load capability caused by decreasing the head size by grinding it down closer to flush. The portion above the top of the counter-sink does not contribute to resisting that tensile force. I did mistakenly refer to it as shear(as Mike has pointed out). The application load is a shear force(the weight of the motor etc. is against the side(top) of the bolts).

Although I was also concerned re tool surface area, I assumed the amount ground off would be small compared to the tool 'hole' depth.

Any who, ss apparently will 'fix' it under warranty(only the inconvenience remains as a 'problem').

[dusty]

Shopsmith may well render a fix 'under warranty' but in the long haul that does not eliminate the total problem. In my mind there needs to be an analysis of the problem to determine whether or not there needs to be a redesign.

Shopsmith may well be doing the analysis, we don't know that.

The bottom line: I will probably not do a DIY upgrade. When I finally decide to acquire a PowerPro it will most likely be a factory built unit.

I feel differently about the Mark 7 upgrade. I believe that the casual user probably has the tools and skills required to do a quality job.

[mickyd]

Mike,

Somewhere I have a chart.......

What is the Ftu or Fsu for a commercially available cap screw? For my guesstimate I was using values that were about half of the standard alloy steel bolt we use. (Fsu = 95ksi)

Troy

What's Ftu / Fsu? Haven't dealt with that in my QC world.

[JPG]

What's Ftu / Fsu? Haven't dealt with that in my QC world.

Failure Shear ????

Failure Tensile ????

Mike You are supposed to be making/selling them, not destroying them!:D

[dusty]

Failure Shear ????

Failure Tensile ????

Mike You are supposed to be making/selling them, not destroying them!:D

That may be Mike's job but my job in Quality Control was to test until they break. It was my job to ascertain just how good our product was. I was in design engineering though and not production.

[mickyd]

Failure Shear ????

Failure Tensile ????

Mike You are supposed to be making/selling them, not destroying them!:D

Gotta destroy 'em to QC 'em. Only do destruct tests on aerospace and militiary spec fasteners.