Clamping techniques

TECH NOTE 26: Torque screw vs toggle clamp. The Club Scout comes with a slip clutch clamping assembly, which always provides a constant force regardless if it's a raw shaft, regardless of its diameter, or if it's a gripped club. The disadvantage of the toggle clamp is that its clamping force varies depending on how it's set up and the diameter of the shaft. The toggle clamp can provide tremendous force and can even crack a shaft if a little care is not taken. The toggle clamp has its advantage however and that is with gripped clubs. The slip clutch is basically a screw that comes down on a set of V blocks and slips when a certain torque is reached. To test a gripped club this screw must be backed off a number of turns to get the back end of the grip through the V blocks and then re-tightened a fair number of turns. This takes several seconds. The Toggle clamp has a very large throat and is therefore very quick to use with gripped clubs. There is little difference between the two with raw shafts.

If you are going to measure a lot of gripped clubs the toggle clamp may be advantageous. The Club Scout's slip clutch is held in place with a U shaped bracket that bolts over the top of the clamping unit and is attached with two bolts. It can easily be removed. I've developed a toggle clamp that attaches to these two bolt holes. The change over from slip clutch to toggle clamp takes about 60 seconds. This accessory might be useful if you measure a lot of gripped clubs.

The toggle clamp is no longer available due to lack of interest. Contact me if you are still interested.

To keep the cost down the new Club Scout Junior does not come with a complete clamping unit. It's do-it-yourself project (see Tech Note 33: Jr Club Scout Clamp). Some of the required pieces are provided however. To apply the clamping force between the V blocks a T handle bolt is provided. I was concerned initially just how uniform a clamping force could be applied by hand. Using a 305 cpm PCS Equalizer calibration shaft I tested the T handle bolt. First I removed the T handle and just tighten the bolt as best I could with my finger tips. I got readings of from 300 to 302 cpm. I then slid the T handle in place and gave it 1/4 turn. The frequency rose to 305. Another 1/4 turn and the frequency still read 305. Another 1/4 turn and I was up to 306. Based on these tests it became pretty easy to hand clamp a shaft accurate to 1 cpm or less.

The best and most uniform clamping system is with a pneumatic cylinder. The pneumatic cylinder has an internal piston that the air pressure impinges against. The force on the shaft can be very precisely control. The force is merely the area of the piston times the air pressure, psi, applied. I've been fooling around with cylinders from Bimba Corp. Their model number is actually the area of the cylinder and is therefore the psi multiplier to get to force. Their two-inch diameter cylinder is model 314. The multiplier is 3.14. (Pi times radius squared) I've asked a couple of shaft manufacturers who use pneumatic clamps, how much force they put on the shaft. In each case I was given a psi value. When I asked what size air cylinder they used nobody seemed to know. I guess these manufacturers have no clue how much force they're putting on their shafts when they test them.

I built two clamps one with a 1.5" diameter cylinder and one with a 2" cylinder. Both were simply a Club Scout clamp with the torque screw removed and replaced by the pneumatic cylinder with the upper V block attached to the ram of the cylinder. I gave the smaller one to a local clubmaker to try out and I have little information on the results. It appears however you need about 100psi or more to get a good solid hold of the shaft especially if you're twanging horizontally. I did play around with the 2" clamp briefly and it really worked well (I twang vertically with my Club Scout). The clamp base has a three way valve attached to its front face. In one position the valve allows the air pressure to enter the cylinder and brings down its ram on the top of two V blocks to clamp the shaft. In the other position the valve stops the air from going to the cylinder and bleeds off the air that's already there. These cylinders are spring-loaded so the upper V block which I've attached to the cylinder's ram automatically raises back up out of the way.

My compressor is homemade and less than desirable. I'm reluctant to run it much over 50 psi. But using the 2" cylinder at 50 psi, equivalent to about 160 pounds of clamping force (50 times 3.14) it worked great. Its operation is very slick. Slide the shaft into the lower V block, flip the valve lever (very little effort needed) twang the shaft to get a cpm reading and just flick the lever back to the open position. It's by far the best clamping system I've tried yet. Cylinders, three way valves and the mods to the Club Scout clamp are not inexpensive but for the large shop I would think it would be a very desirable system. The pneumatic clamp would add about $200 to the price of a Club Scout III. If you have any interest give me a call.