Placement of Critical Components

Dave Tutelman -- March 12, 2005

You will learn how to measure the placement of a few critical components:

How to measure beam length, and place the beam length rulers properly.
How to position the bolts that hold the toggle board.
How to align the three sets of bearings so they lie in the same plane.

Bear in mind that the photographs were taken after my NeuFinder 4 was completed. The beam length rulers were already in place, and I was not going to rip them off for the photo session. So it will look a little different from yours when you do these steps, especially the step in 1.2 below.

1. Beam length measurement

1.1. How to measure beam length

Beam length is defined from the centers of the pivot bolts supporting the rear (left) bearings and the front (right) bearings. But that definition is not easy to measure precisely. So here is a way of measuring the same distance precisely.

The distance from the right edge of the rear bearing block to the right edge of the front bearing block is the same as the defined distance. And it is easy to measure pretty precisely, using the technique shown in the photo above.

Butt a yardstick against the rear bearing block. Holding it against the block...
Measure to the right edge of the front bearing block. You are measuring from red line to red line in the photo insets.

1.2. Placing the beam length rulers

Before you start, check your measuring tapes against a good ruler, to be sure they were made properly. Believe it or not, some cloth tapes need to be stretched to get to the proper scale. Once you have two good tapes, you can proceed.

Using the method in 1.1 above, set the toggle board for a beam length of 30". Be precise in this measurement; try to get within 1/16", and do not settle for worse than 1/8".

With the beam length set at a measured 30", mark the backer board where the two indicators are (shown by the blue arrows in the photo).
If your measuring tapes are still inaccurate and need to be stretched make marks at a few additional beam lengths. You will then have to line up more than one mark when you mount the tapes.
Mount the two measurement tapes so that the lower tape has its 30" at the rightmost of the marks you just made, and the upper one has its 30" at the other mark. When you have done it right, the tapes will look as they do in the photo.

There are several ways you can mount the tapes. Here are some that have proven successful even before the beta test was completed:

Contact cement. Lines ruled on the backer board, or even masking tape, can assist putting the cement in the right place and getting the vertical position right.
Double-sided grip tape. Cut it a little narrower than the measuring tape.

2. Placing the toggle board

Start by removing the knobs that hold the toggle board to the T-slot beam. Loosen the T-nuts that hold the toggle board bolts just enough so the bolts can slide in the slots, but not wobble around. Place the toggle board on the bolts through the lower holes, but do not replace the knobs; the toggle board is just resting on the bolts.

Place the end caps on the T-slot beam. Slide the beam all the way to the left, so the cam-clamp's bolt is up against the beam's end cap, as shown in the picture.

Slide the toggle board all the way to the left, so it is almost touching the rotator board, as shown in the picture. The beam length in this position should be 19" or a little less. If it is more than 19", you have exceeded tolerances in placing a number of the holes you drilled.

Mark this position on the beam using a marker or pencil through the middle of the unused pair of holes.

Release the cam clamps, and carefully slide the beam to the right until the "wand" is clear of the rotator board. While you do this, use your hand as a "clamp" to hold the toggle board in the same position relative to the beam.

Carefully lift the toggle board off the bolts, being sure not to move the bolts in the beam slot.

Actually, it is no disaster if the bolts move a little in the slot. Remember, you marked their position on the beam. Compare the bolts' position with the marks you made on the beam and, if necessary, slide the bolts in the slot so they line up with the marks.

Being careful not to slide it along the beam slot, tighten one of the T-nuts in place. You have now determined the location of the toggle board.

The other T-nut should be just tight enough so the bolt tip does not wobble, but not so tight that the bolt cannot slide in the slot. That is because the clearance between the hole in the toggle board and the T-nut "bushing" is quite snug; it is tighter than the tolerance on the spacing between the holes. That means that there is no fixed position for the bolt that will work for both the upper and lower pair of holes. (If you have drilled the holes so accurately that it works for you, then you can tighten both T-nuts.)

Hold the sliding bolt's T-nut in position with some sort of thread-locking compound. (Actually I used a bit of contact cement for the purpose. Worked fine, but it took over a day to set up properly.)

3. Aligning the bearings

We will align the three sets of bearings, so they all lie in the same vertical plane.

The photo shows three possible positions of a shaft when it is seated in the rear and middle bearings. It can meet the front bearings:

In the middle, right between the bearings..
Inboard (toward the backer board).
Outboard (away from the backer board.

Of course, you want the shaft to meet the front bearings in the middle. So you need to adjust the other bearing sets so they point the shaft in the proper direction. Here's how.

To start:

Fix the rotator board in its most clockwise roatation. To do this, extend the position of the glider on the rotator board stop, to take out all the slack.
Remove the locking nuts that hold the bearings to the rotator board (indicated by the arrows in the photo). Temporarily replace them with ordinary nuts, that you can spin on or off easily. Spin them on so they hold the bearing arms from moving back and forth, but they can still rotate fairly freely.

You will adjust the angle that the bearing sets point the shaft by controlling each bearing arm's distance from the rotator board. Do this by adding or removing the washers (see photo) between the bearing arm and the rotator board. That's why you want the bearing arms held on by nuts that you can spin off easily; you may be removing the bearing arms several times during this procedure, to add or remove washers.

Place the toggle board in the upper (profiling) position. Set the beam length for 19".

Find a fairly long (46" or so) wood shaft, that is as straight as possible. Any residual bend will jeopardize the accuracy of the results. As you go through the process, you will be able to judge how straight the shaft is. You may choose to switch shafts in the middle, to find a straighter one. That's OK; you will not have wasted much time doing the early work with a less-straight shaft.

With the toggle clamp wide open and the tip stop out of the way, slide the shaft into the bearings from rear to front. Slide it in until the butt is within an inch or so of the rear bearings. There will be a lot of tip sticking out in front of the front bearings. The shaft should sit in the bearings of its own weight, since there is so much tip hanging out the front.

Sight along the shaft from the front. It should look something like the photo. Ideally, the shaft will be centered between the bearings of the front bearing assembly. The alignment in the photo is pretty good, but the shaft is slightly to the right of center.

Place your fingers in the position shown in the photo. Slide them crosswise on the shaft to spin it in the bearings, while you continue to sight along the shaft from the front. You will watch the tip move in a small circle. The straighter the shaft, the smaller the circle, but I have yet to see a shaft where the movement is invisible.

At the front bearings, the circle due to shaft bend will be a lot smaller than it is at the tip. But it may still be there. Estimate the middle of the circle by eye. That is the place that should be centered between the bearings.

If the shaft is not centered between the front bearings, move the middle bearing assembly in or out by removing or adding washers. Find the washer combination that gives the best centering. If your washers are of different thicknesses, you can use that for a fine control of the position. But don't get paranoid about it. Being within 1/16" of center is really good.

When the shaft is pretty well centered, remove it and set the beam length to 43". Insert the shaft again, and repeat the test you did at 19". But this time, adjust the centering by adding or removing washers from the rear bearings instead of the middle bearings.

Once the shaft is well centered, check it again at 19". If it is within 1/16" of centered, you are done. Otherwise, fix it again at 19" (with the middle bearings) and again at 43" (with the rear bearings). At this point, it should be fine.

Undo what you did in the first step:

Put the lock nuts back on the bolts, and adjust them so they do not allow back and forth play of the bearing arm, but do allow free rotation.
Retract the rotator stop glider, until about 1/16" of slack is available.

Now the shaft alignment is whatever it is going to be. The next step is to align the direction of the front bearing with the shaft tip.

With the beam length at 43, insert the shaft and close the toggle clamp to bend the shaft.

Rotate the shaft in the bearings (with your fingers as shown in the earlier photos), while you watch the bearings in the front bearing assembly. Each of the four bearings should turn in response to the turning of the shaft. If any of the bearings do not turn, the yoke needs alignment. Here's how to do it.

Use an open-end wrench to slightly loosen the bolt that holds the aluminum yoke to the tip of the toggle clamp. Rotate the shaft while you turn the yoke. Find the position of the yoke where all four bearings turn, and tighten the bolt in that position. Check to make sure it is still in position after being tightened.

The bearing alignment is now complete.

Last modified March 26, 2005