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  1. #1
    Join Date
    Apr 2018
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    Drouin Vic
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    633

    Default Have to laugh or I'd cry.

    It was all going so well.....I decided yesterday arvo to do a job I'd been wanting to get to for ages- properly bedding in the mag chuck on my surface grinder. I took the chuck off, had to remove a few other bits as well to enable the spindle to come down a lot lower than usual and grind the surface that the chuck mounts on. It was quite bowed and I probably had to grind about a couple of thou off the ends before the wheel touched the middle; took a while but I finally got a nice flat surface to mount the chuck to.

    The next stage was to mount the chuck upside down, clamp it down lightly with the magnet off and proceed to grind the bottom of the mag chuck. It's a 150 x 450mm chuck. Again took quite a few passes before I was contacting over the whole surface, finished up with a couple of .002mm passes then a 'spring' pass and congratulated myself that I had a decent starting point and called it a night.

    Got back to it this afternoon. Turned the chuck over and clamped it down lightly, dialed in the back edge, tightened it down, turned on the magnet and dressed the top surface of the mag chuck to the flattest, smoothest most perfectest ever. Very very happy with the finish and confident that it was flatter than a dunny man's hat. With the final spring pass I think I was splitting the molecules in the coolant.

    I decided it was time to try it out on a couple of 100 x 25 x 14mm parallels that were looking a little worse for wear. I mounted the pair on the mag chuck and took a few light passes on one side. The cross-feed wheel started to develop a tight spot that puzzled me a bit; checked that nothing was fouling anywhere and pressed on with the job. Flipped the parallels over and got half-way through one pass when the cross-feed handwheel started freewheeling without moving the table. Removed the feed screw assembly and discovered that the thread is stripped across a goodly section of the middle of the screw. Completely cactus. It appears to be a 3mm trapezoidal thread (didn't measure the diameter, probably 25mm). Obviously the nut will also be stuffed but the thing that hurts is that to get the nut out, I'll have to remove the chuck AND the table or whatever the side-to-side moving part is called. So all my good work of the last 2 afternoons will have to be done again.

    The other fun thing is that I don't have the change gears to cut metric threads on my lathe. And I don't have all the necessary change gears for my universal dividing head to make the 127-tooth gear for the lathe. So, I can either finally get around to making the 20dp gears for the dividing head so I can finally get around to making the 12dp 127 and 60 tooth gears for the lathe so I can make the 3mm thread for he SG....or I can just make a 8tpi ACME feedscrew and nut for the surface grinder.

  2. #2
    Join Date
    Nov 2017
    Location
    Geelong, Australia
    Age
    57
    Posts
    2,651

    Default

    What a bugger!
    I can easily print up some gears for the dividing head if it helps.
    Could do some for the lathe too, but not as confident they’d hold up. Should be fine for the DH though as there’s no load/speed.
    Can’t get onto it until Tuesday though.

    Steve.

  3. #3
    Join Date
    Apr 2018
    Location
    Drouin Vic
    Posts
    633

    Default

    That's a very generous offer Steve, had never considered 3Dprinted gears for the DH but I'll get back to you about that.

  4. #4
    Join Date
    Aug 2008
    Location
    Melbourne
    Age
    34
    Posts
    1,075

    Default

    I salvaged a near complete set of 20DP 14.5PA change gears from work, what numbers do you need?
    Gear cutting specialists and general engineers www.hardmanbros.com.au
    Fine pitch gear cutting from 0.1 Module www.rigear.com.au

  5. #5
    Join Date
    Apr 2018
    Location
    Drouin Vic
    Posts
    633

    Default

    Quote Originally Posted by elanjacobs View Post
    I salvaged a near complete set of 20DP 14.5PA change gears from work, what numbers do you need?

    Here's what I have figured out....
    to complete the 12dp change gear set for my lathe, I need 35, 45, 60 and 127. To cut the 3mm metric thread i need the 60 and 127.

    All of the above with the exception of the 127 can be cut by direct dividing. To cut the 127 I need 24 and 56 for the dividing head. I have the 24.

    so I would need to a 20dp 56 tooth gear to be able to complete the lathe set and repair the surface grinder. I have no idea what the pressure angle is of the gears I have, I picked up a toolbox full of gears a few years ago that appear to be from a lathe, maybe a hercus. I am well shy of the complete set for the universal dividing head but that has been a backburner project for several years.

    I could always cheat and make the new feedscrew and nut 8tpi ACME, would actually be easier all around as (correct me if I'm wrong) I think the leadscrew has to be kept engaged throughout the job when doing metric threads with an imperial leadscrew, i.e. can't use the threading dial.

    Need to get the involute cutters as well of course if I'm going to go the long route.

  6. #6
    Join Date
    Aug 2008
    Location
    Melbourne
    Age
    34
    Posts
    1,075

    Default

    Quote Originally Posted by Pete O View Post
    so I would need to a 20dp 56 tooth gear to be able to complete the lathe set and repair the surface grinder. I have no idea what the pressure angle is of the gears I have, I picked up a toolbox full of gears a few years ago that appear to be from a lathe, maybe a hercus. I am well shy of the complete set for the universal dividing head but that has been a backburner project for several years.
    If it's just the 56, you can have it for $10 to cover postage. If you want a bunch, let me know and we'll sort something out They're 16mm wide with a 5/8 bore and 3/16 key so you might need to modify to suit

    For a dividing head the pressure angle doesn't matter, it only becomes an issue at higher speeds where you start to get excessive noise and wear. If they're old, it's probably 14.5 degrees anyway.
    Gear cutting specialists and general engineers www.hardmanbros.com.au
    Fine pitch gear cutting from 0.1 Module www.rigear.com.au

  7. #7
    Join Date
    Apr 2018
    Location
    Drouin Vic
    Posts
    633

    Default

    Well there would be something pretty badly wrong with me if I wasn't happy to part with ten bucks for that gear.
    What I should do is see what I need to complete the set for the paradisi dividing head, I bought it as just the bare dividing head and tailstock and made a start on recreating the missing gear train, including banjo and spindles, but that project has been stalled for a couple of years. I'll have a look and get back to you.

  8. #8
    Join Date
    Nov 2007
    Location
    melbourne australia
    Posts
    3,228

    Default

    Quote Originally Posted by Pete O View Post
    ...or I can just make a 8tpi ACME feedscrew and nut for the surface grinder.
    That does look like the solution. I'm ignorant about surface grinders, but I don't think they have a graduated dial on the cross-feed? If not, does it matter if the table moves ⅛" instead of 3mm with each turn of the handle?
    Chris

  9. #9
    Join Date
    Apr 2018
    Location
    Drouin Vic
    Posts
    633

    Default

    Quote Originally Posted by jack620 View Post
    That does look like the solution. I'm ignorant about surface grinders, but I don't think they have a graduated dial on the cross-feed? If not, does it matter if the table moves ⅛" instead of 3mm with each turn of the handle?
    Yes there is a graduated dial on the crossfeed wheel- the first time I ever noticed it was this week when I was removing the screw after it stripped!

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