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Thread: The "Schulte Dimension"--A Useful Spec for Translating CAD Dimensions to Reality

  1. #1

    The "Schulte Dimension"--A Useful Spec for Translating CAD Dimensions to Reality

    When I was at ISS in March, I had a rather interesting conversation with Paul Schulte from Invacare/Top End. We were discussing their upcoming 7000 series aluminum box frame and how one would be able to get reasonably accurate measurements without the benefit of a demo.

    One idea he had was to have the end user push their current chair against a wall so that the footrest was touching and measure the distance from the front of the back post to the wall. Giving credit where credit is due, I'll refer to it as the "Schulte Dimension".

    To my knowledge no manufacturer, not even Top End, includes the SD routinely in their CAD drawings. "Why should they?", you ask. Since it is easy to measure this accurately on an existing chair, including this spec on the CAD allows one to make a fairly direct comparison of where the footrest will be on a proposed chair relative to the footrest position on an existing chair.

    A colleague and I recently requested this dimension on a CAD for a ZRA S2 for an end user who had an 18" deep TiLite Evo with a 70 degree frame angle that was roughly the same dimensions as a Scion xB. He did require a longer than average frame length because of limited knee flexion and posterior pelvic tilt. We arrived at the closest approximation of an optimal fit using our 18" deep 85 degree classic frame Q7 demo with the footplate reversed...



    We initially thought that going with a 16x18+2 85 degree frame would be enough (16wx18 deep with the 2" longer custom frame depth option). Since we had some uncertainty, however, we requested a CAD with the spec for the SD included...



    I'm glad we did, when I compared the SD's, our proposed specs would have been almost identical to the Q7 without the inverted footrest. We are changing the specs to 16x18+3 and keeping the 85 degree frame angle. We will be replacing the TiLite angle adjustable footplate with another manufacturer's design to provide multiple sets of mounting holes to ensure optimal support under his feet without having to add another inch to the frame.
    Will it be a long chair by most standards? Yes.
    Will it be any longer than necessary? No.
    Length relative to the "USS Evo": The SD of the ZRA S2 will be 2-3 inches shorter.
    Did requesting the Schulte Dimension on the CAD keep us from making a major mistake on this particular chair? Absolutely.
    Should it become a standard spec on any manufacturer's CAD drawing? Absolutely. Until it becomes standard, it is definitely something one should request on their CAD for a new chair.
    Last edited by SCI_OTR; 07-16-2011 at 01:41 PM.


  2. #2
    Interesting stuff SCI_OTR. (It seems like we had a similar discussion here in the past.) Curious, why did you stay with the 85 degree front and + 3 rather than a different degree front and less +?
    C5-6 Complete - 8/13/1982

  3. #3
    Quote Originally Posted by Brianm View Post
    Interesting stuff SCI_OTR. (It seems like we had a similar discussion here in the past.) Curious, why did you stay with the 85 degree front and + 3 rather than a different degree front and less +?
    To preserve static vertical stability for transfers. Going 85 +3 keeps the caster in closer to the footrest--making it less-likely to tip forward. It also provides useable frame tubing before the bend to grab onto.

    Dipping into the repository, these drawings illustrate the difference between 80 and 85+1 on two chairs having 16" seat depths (The drawings were scaled to allow comparison using the length of the upholstery for reference). If one were to scoot to the front edge of the upholstery, which chair looks like it would be less-likely to tip?


  4. #4
    Humm, interestiing; I sure would like to see a CAD for both I have always liked how my casters lined up well with my footrest, allowing the casters to roll up things without my (low) footrest rubbing. I had assumed this was something TiLite calculated on purpose. From the two CAD's you give, they are in different locations, yet when I look at my CAD in the repository and compare it to others, it seems we are the same local and my chair being an 80 degree front and the others, laidbackben and peteran, being 85 degree.
    C5-6 Complete - 8/13/1982

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