DIY Laser Alignment (kinda' long)
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Thread: DIY Laser Alignment (kinda' long)

  1. #1
    crv|oc Rank: Member
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    DIY Laser Alignment (kinda' long)

    Wheel Alignment 2011

    I align my own vehicles and have for over 10 years. My alignment tools have gotten better and easier to build, maybe this one will interest some CR-V owners.

    http://www.advantagewheelalignment.c...h_Article.html

    To start off with, this is a very good article on why a home improvement store laser level will not work for wheel alignment. All of their points are valid, however, all of these points can be worked around to build an inexpensive and highly accurate wheel alignment system using a commonly available (that means cheap) laser level.

    Some of the points in the article are:
    1 - The beam is not aligned with the level.
    Oh, so true! Some are not bad, some are *really* off. Fortunately it doesn't matter. Even if the beam is off by 2 degrees (or more) as long as it is off by the same amount and same direction for both wheels the worst we will get is a steering wheel that is not centered (and this is easy to correct).
    A typical figure for accuracy is 1/2" @ 50'. Since alignment requires about 5' this would give 0.05" accuracy, good enough for our purpose.

    2 - The laser line cannot be calibrated.
    Sort of true. It cannot be calibrated to the level surfaces *but* it can be calibrated to some spacer blocks and that is all we need!

    3 - The beam line is not straight.
    Again, very true. The lens that changes the spot into a line introduces a slight curve into the line. If we only use a small portion of the curved line (and that is all we need) it very closely approximates a straight line so this is not an issue.


    4 - The inexpensive 650 nM, <5 mW lasers are not very bright.
    They are not but in a garage they are still easy to see. Working outside in sunlight would probably be a problem though.

    Absolute accuracy is not required for front wheel alignment, relative repeatability is. Even if our beam is crooked, as long as it is crooked by the same amount every time then we can easily correct for it later. The worst that can happen is the steering wheel is not centered and that is easy to correct (turn the tie rods the same direction, same amount). Rear wheel alignment adds another problem because we don't usually have a tie rod or a steering wheel to let us know the wheels are aligned but off center.

    For rear wheels we need *absolute* repeatability. The key to this is that the spacer between the laser level and the wheel must be the same on the front and rear of the rim ("same" means within 0.010" in this case, not difficult to achieve) *relative to the laser beam*, not the level. Side to side does not have to be the same, in fact if the laser port is not centered on the laser level then the spacers can be different lengths in order to center the beam. The Harbor Freight laser level I used has about a 7/8" offset from the laser to the level surfaces, so my spacer blocks are offset by 7/8" to make this work out.

    The spacer blocks are the key to this project. They must be square, accurate, and properly fit to the laser level. I used dowels to connect the two sides so they would always go together exactly the same. Bolts are for clamping, dowels are for positioning. The spacer blocks were made with about 0.030" greater cutout than the height of the laser level to allow for calibration. To calibrate, place the laser on a flat surface and aim the laser at a wall about 5' away. Mark the spot/line, flip the laser over and check it again. Shim the spacer block gaps until the spot/lines are in the same place no matter which way the laser is placed. Now do this again at a 20' distance. When the spot/lines are always in the place same the laser is aligned with the spacer blocks. Don't get carried away, 1/8" @ 20' is as good as we need.

    Besides the laser level we need a toe scale. This can be as simple as a 2x4 with two 1x4 uprights set at the track width of the car, just something to mark where the laser beam hits.

    Camber is easy to check with a bubble or digital level, toe is not much more difficult with our new tool. Caster is a real pain *but* it is not adjustable on most cars anyway. The only reason for caster to be off would be if the suspension pieces were bent or if we made some major changes to the suspension. Also, for most FWD cars caster is not critical. Most of the time it is not worth checking caster.

    Now for the math: 1 degree of angle causes 1" of deflection at 57-1/4", some Greeks figured this out about two thousand years ago and no one has disproven them yet. Since we can detect about 1/8" we can then detect about 1/8 degree, which is good enough for alignment (and about as good as most shops will do). If we want more accuracy then we can double the distance but the laser line gets wider and the whole process doesn't really improve much for our troubles.
    So, the idea is to make sure the laser level assembly is resting on the front and rear edges of the rim, take a reading from each wheel at some distance from the wheel (24" works well), take similar readings at 57-1/4" further, and compare the difference. Again, 1" difference means 1 degree of toe. If the readings are taken in front of the car and the further readings are greater then this means toe out.

    Some manufacturers give alignment specifications in degrees, some in inches (or mm). Degrees does not depend on the tire size and should be the preferred method. Changing from inches to degrees is simple trigonometry.


    Parts list:
    24" laser level - Harbor Freight or Craftsman
    spacer blocks - custom made from ABS plastic
    3/8" hollow dowels (can be brass tubing)
    1/4-20 x 2-1/2" nylon bolts
    1/4-20 nylon nuts

    The alignment tool:


    The spacer blocks:

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  3. #2
    crv|oc Rank: Sophomore
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    Brilliant!

    And thank you.

    Now to figure out how to set the rear tracking?

    Maybe attach the device to the front wheel and shoot past the rear?

    Thanks again for a great write up.

  4. #3
    crv|oc Rank: Member
    Join Date
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    I was thinking of maybe using the jacking flanges as reference points for the rear tracking, they are probably close enough tolerance for that.

    After all this I found the rear wheels have too much negative camber (after the H&R spring installation) so now the CR-V needs camber links (SPC links are on order).

  5. #4
    crv|oc Rank: Sophomore
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    Is this a better price?

    Quote Originally Posted by bobquincy View Post
    I was thinking of maybe using the jacking flanges as reference points for the rear tracking, they are probably close enough tolerance for that.

    After all this I found the rear wheels have too much negative camber (after the H&R spring installation) so now the CR-V needs camber links (SPC links are on order).

    The picture is wrong but the SPC number is correct, I believe:
    http://cgi.ebay.com/ebaymotors/SPECI...Q5fAccessories

    (The links to Whitney below don't seem to work. They take me to their splash page instead of the item. But the search is fast.)

    And I stumbled onto these Camber Gauges:
    http://www.jcwhitney.com/alignment-t...04d9015y2007j1

    I intend to put camber adjusters on all four corners. I thought I had found some Ingles rears for about $50 but cannot find them again.

    The best price I have found for fronts is Raybestos at Whitney for about $15: http://www.jcwhitney.com/professiona...04d9015y2010j1

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