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Thread: Goodell Pratt Hand Drill Repair

  1. #16
    Kevin, Rob, Richard, Thanks for taking an interest. I think the gears are different - from the pictures I've found on the web one has 21 teeth and the other has 20 teeth. From my own measurements I think that the angles are different too.

    Jim, Richard - I'm obviously too much of a hoarder. I needed some springs for the chuck too - but when I chuck stuff out I save useful bits like springs - so I looked in the tin marked springs and found three - I've no idea what they came from.

    Thanks all for taking the trouble to comment.

    Russell

  2. #17
    Guys, I guess I am better at lurking than posting!! You're right, the gears are different:
    IMG_0049_1_1.jpg

  3. #18
    Hi Kevin

    But you inspired a couple of other people to comment.

    Russell

  4. #19
    I am shocked to see how long it is since I last reported progress on this. There has been a lot of procrastination going on.

    I set up a search on eBay which only found me drills that were in better condition than mine. I read up on gear cutting and mitred bevel gears in particular. All that revealed were that these were not theoretically correct gears.

    So having exhausted all avenues of procrastination I decided to try making a pinion. I decided to try making one in plastic first as it would be much quicker to machine and it would be an experiment.

    I measured two angles from the drills handwheel. One was the angle the top of the teeth made with the axis of the drill and the other was the angle the bottom of the gaps between the teeth made with the axis. Because of limited space around it I had to make a sort of mini bevel gauge but I ended up with angles of 39 degrees and 28 degrees.

    I made a gear blank on the lathe with an angle of 39 degrees and setup the milling machine to cut 20 gaps between the teeth at an angle of 28 degrees using a home made dividing head (another product of procrastination) which used a lathe changewheel to index 20 positions.

    At this point I had to confront the main problem that had been putting me off this job. What shape should I make the gaps between the teeth. Best approximation methods for home cutting of bevel gears suggest three cuts for each gap would be needed so I decided to make a cutter the shape of the smallest part of the gap using the other pinion as a model. At this point I realised that the gaps between the teeth are parallel sided and the wider gaps are created by deeper cuts at the larger end of the pinion so only one cut should be needed.
    tooth.jpg

    I made a cutter out of silver steel and mounted it to an arbour and cut the teeth so that the gaps between teeth were about the same size as the teeth.
    cutter.jpg


    The only remaining difficulty was the diameter which was difficult to measure. It turned out to be too small - but since it's tapered I could make it seem larger by removing material from the small end and much to my delight it actually meshed quite well with the existing gear although it was now too thin.
    plastic1.jpg


    I made a second one using the same technique but using measurements from the first attempt. This time the teeth seemed to mesh a bit too deeply so I skimmed the top of the teeth in the lathe. It fitted reasonably well and the drill worked.


    I have assumed the missing gear was originally made from cast iron as if it were steel it wouldn't have broken so I bought a piece of cast iron and made another gear blank.
    blank.jpg

    I hardened and tempered the home made cutter and tried again on the milling machine.
    milling.jpg

    Then I cut the slots on the back to engage with the dogs on the drill. Can you spot the mistake here?
    pinion.jpg

    Then I assembled the drill.

    drill.jpggears.jpg


    It works. I drilled a few holes using both speeds. Success. I'm really pleased with that.

    Russell
    Last edited by Russell Talbot; 10-29-2019 at 7:59 AM.

  5. #20
    That's very cool Russell. I'll bet it was very satisfying to take on that challenge, make the gear and then see it work so well. Good for you!
    Fred
    "All that is necessary for the triumph of evil is that good men do nothing."

    “If you want to know what a man's like, take a good look at how he treats his inferiors, not his equals.”

  6. #21
    Russell, I just bought one of these and it is missing a couple of things. The side handle (like the one you made. What size are the threads? I get a bolt to match I hope (I don't have a metal lathe). The springs in the chuck are also missing. Do you know what size they are and how long.
    Thanks in advance,
    Tad

  7. #22
    Quote Originally Posted by Tad Englund View Post
    Russell, I just bought one of these and it is missing a couple of things. The side handle (like the one you made. What size are the threads? I get a bolt to match I hope (I don't have a metal lathe). The springs in the chuck are also missing. Do you know what size they are and how long.
    Thanks in advance,
    Tad
    Hi Tad

    I found a bolt to match, but I don't know what it came from, it measures 5/16 with 20tpi. I suppose there is a possibility I found a worn 8mm x 1.25mm bolt.

    I had to have a couple of goes at the springs. First I used three that looked the same but the jaws didn't close evenly. I eventually bought a 100mm length of spring 3.18mm (1/8) diameter with 0.5mm wire diameter off ebay and cut three matching lengths of that. I used the longest length that I could fit into the holes in two jaws and still squeeze the jaws together. It should be possible to calculate that by measuring the depth of the holes in the jaws and working out how many coils will fit in the two jaws but I just used trial and error.

    Good luck with finding the bits.

    Russell

  8. #23
    Join Date
    Jun 2010
    Location
    twomiles from the "peak of Ohio
    Posts
    12,120
    Springs out of three Bic Lighters should also work.....the ones under the flint.

    Millers Falls liked to use regular, off the shelf hardware sizes....rather than go with what Stanley used. So...SAE bolts should fit...

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