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  1. #1
    Join Date
    Feb 2014
    Location
    Werribee, Melbourne
    Posts
    159

    Default Macson Autofeed Gearbox

    My old Macson uses a floating gearbox arrangement that sits on the power-feed shaft and is moved horizontally in the apron to select carriage feed or cross-feed and lifted slightly to lock on the appropriate gears to drive each feed.
    It has always been tricky to engage and I eventually worked up the enthusiasm to look into some excessive up and down play in the bushes that support the gearbox on the feed-shaft.

    Not a minor undertaking as the easy way was stymied by what appears to be a major burr from a tapered pin so rather than risk damage to the cross-feed shaft I removed the quick change gearbox, banjo etc in order to slide the power-feed shaft out that way with the gear installed.

    I removed the two bronze bushes from the gearbox today and these are worn soooo close to damaging the housing on the gearbox it isn't funny but as luck would have I have escaped that misery.

    These are the long suffering bushes (an impressive 0.122" out of round) - not sure if they are originals but I suspect they are so not bad service for 76 years.

    IMG_1815.jpgIMG_1816.jpg

    Remaking these would require a spendy piece of bearing bronze given they are each almost 2" in Diameter, 1.6" long with 1.25" bore so I am contemplating making the replacements from Delrin given the application that might be OK.
    The bushes could be made 1/2" longer on the thicker section without clearance issues so that would allow a bit more support.

    Does anyone have experience using Delrin as a plain bronze replacement to suggest it would be worth a try?

    Ray

  2. #2
    Join Date
    Jul 2016
    Location
    Melbourne
    Age
    34
    Posts
    1,474

    Default

    I probably wouldn't bother with delrin, it might go okay but with something painful to dismantle id just buy LG2 hollow bar, you will be able to get something pretty close to those net dimensions without wasting too much.

    Sent from my SM-G973F using Tapatalk

  3. #3
    Join Date
    Nov 2007
    Location
    melbourne australia
    Posts
    3,164

    Default

    Ray,
    Ertalyte TX is a plastic substitute for bronze bushings in some cases. Machines just like Delrin. I managed to get a couple of offcuts from Datco Plastics in Carrum Downs.

    https://www.datco.com.au/materials/ertalyte/
    Chris

  4. #4
    Join Date
    Apr 2012
    Location
    Healesville
    Posts
    1,911

    Default

    Ray for a fairly long term fix could it be possible or easy enough to bore out the housing a and fit sealed bearings?

  5. #5
    Join Date
    Nov 2017
    Location
    Geelong, Australia
    Age
    55
    Posts
    2,163

    Default

    Canít help with your Delrin question, but the flange on those bushes doesnít look like itís a wear surface. If thatís the case and itís only for location purposes you might be able to use a plain bush without the flange. That would reduce the OD/cost of the material. Loctite or a thin circlip would be options if you were still concerned about them moving.

    Another cheap option might be to use a steel outer bush with a thin bronze ďlinerĒ as the bearing material. Concept is common in engine plain bearings.

    Steve.

  6. #6
    Join Date
    Feb 2014
    Location
    Werribee, Melbourne
    Posts
    159

    Default

    Appreciate the replies gents - plenty of food for thought.

    Ralph, you are correct about the difficulty of accessing these things - I would prefer not to have to repeat the exercise too often.

    Jack, being a hobbyist I wasn't even aware of Ertalyte TX - I have made a few spacers out of Acetal but that's the limit of my exposure.

    Shed, I don't have the equipment to bore out the housing anyway but I think the issue with sealed bearings would be the ID of the bearing would be wearing against the power feed rod as the apron moves back and forward.

    Steve, you are correct in that the flanges look like they only act as stops at either end of travel of the gearbox so definitely don't need to be as big in OD and are held in place laterally by grub screws in shallow dimples in the bushes so definitely an opportunity to start with smaller diameter material.
    So as per your suggestion about standard bushes I found a mob in Melbourne (Refast) that supply standard size imperial LG2 bushes for very reasonable prices (a lot less than buying a chunk of LG2 hollow bar) so I think my best bet is modify a couple of the closest sizes they have.

    Ray

  7. #7
    Join Date
    Jul 2016
    Location
    Melbourne
    Age
    34
    Posts
    1,474

    Default

    I have quite a bit of bronze kicking around but I'm just in the process of moving workshops, you are welcome to swing by and have a dig through but its not very organised right now.

    Sent from my SM-G973F using Tapatalk

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