Bridgeport for Beginners!

Discussion in 'Other metal working projects' started by Jason, Dec 10, 2019.

  1. Jason

    Jason Gold

    Thanks Mark, I'll check out those videos for my nightly machining lesson.

    Tonight, dumbass here tried to cut a metric thread. After watching Tom and a couple others, I thought I was ready to try it. Yeah I know about staying on the lead screw.
    I set up my machine, I discovered what I wanted (M8 1.25) looked more like a 32 tpi. I got something REALLY fine.:(
    Well, I start looking at my gears and YUP, I've got a 30 in there. This is what I saw on the tag so I'm guessing I should have a 50tooth installed. (a)

    I set C,R,Y on the levers and #1 on the dial. I didn't see the 50 at the top of this chart until after I realized things were amiss.
    So my guess is to have a complete setup, I need a 28,30,35,36 and a 50. Not that I have a need to cut a lot of metric, but it would be nice
    to see them in the drawer for when I do need something oddball....

    20210331_000932.jpg

    My owners manual shows this for options. So I'm guessing the previous owner kept the 5 gears this thing should have. Typical or they didn't get them when new, lost etc.

    20210331_013843.jpg

    So I searched the net for the usual's like grizzly and their change gears don't look like mine. Why do I have a feeling I'm about to learn about gears and broaching??
    I've got that indexer so I guess I'd need a cutter, arbor and a clue or two? Would 4140 be good enough for these? I could probably ask my neighbor to send them
    through his oven for heat treatment if necessary.... Sure seems like a BUTTLOAD of work when grizz sells change gears for 4-7bucks a pop!:eek::rolleyes::(


    Anyone see anything like this for sale out there?? This is my 30tooth. The ones up on fleabay are all flat and don't have this flange.
    20210331_022111.jpg

    20210331_022122.jpg
     
  2. The change gears for my small Colchester are just cast iron, on the bigger Graziano they are hardened chrome steel. As far as the flange goes, just machine a spacer ring and so long as the gear has a key-way you're good to go, that's what my lathe has. I was missing some change gears for a smaller lathe and found the ones made for Myford ML7 were a perfect fit, so there's a chance of getting a workable substitute that will fit your lathe.
     
  3. Jason

    Jason Gold

    I'm liking the way your thinking. Here is my setup put back together.

    I think the 120/127 gets flipped around at sometime, but it's job is just to spin the bottom gear for the gear box... I'm guessing. I measured the shaft for my 30tooth at the top, it's 19mm.

    20210331_034818.jpg
     
    Last edited: Mar 31, 2021
  4. The way I read your diagram the 50 tooth gear should mesh with the 127 tooth gear and the 120 tooth should mesh with the 60 tooth gear. The way it's set up in that photo with the 127 tooth gear in the middle meshing with the other two just means it will cancel out mathematically; in any three gear combo, the middle gear cancels out so you'd have a 30/60 gear combo the way it's set up in the photo.

    At least with the 30 tooth you can cut some metric threads and check if the pitch is the expected one on the chart, like a 3mm, 1.5mm etc.
     
    Last edited: Mar 31, 2021
    Jason likes this.
  5. Jason

    Jason Gold

    AHHH... I think I see it now.. The 50 would spin the 127 and I'd have to flip over the bottom 60 to run off the 120.
    In this photo, I just put it back the way I had it for my imperial setup.. Now I know how this works. The manual didn't explain this.
     
    Mark's castings likes this.
  6. dtsh

    dtsh Silver

  7. OMM

    OMM Silver

    on some older machines that were designed imperial... but have metric thread cutting capacity, the split nut cannot be disengaged. On some of my Japanese lathes, you need to leave the split nut engaged, stop the lathe at the end of its cut, back out the cross feed, put the machine in reverse, put the cross feedback to its zero position, then advance the compound. And repeat...

    If the machine was designed imperial, the split nut dial indicator will designate threads per inch usually with a little nameplate. Usually the nameplate does not show metric pick up engagements on the dial.

    Metric is metric and imperial is imperial. If the machine was made Imperial but has dual function within the same gearbox this is the step pattern you should try to take.

    This might be more advanced then I can explain in words. I'll see if I can put a video together.
     
  8. Jason

    Jason Gold

    Don't waste your time Matt, there is a bunch of videos on yt demonstrating this technique. I know the drill.

    I did find a guy on fleabay with a gearset for sale. He's got 7 I think and I can only use 2 of them. :rolleyes: Maybe he will cut me a deal. Of course he has the 50 I just happen
    to need for this thread. I'm just thankful for the gear lesson. Looks like grizz sells gears for cheap, I'm betting they are plastic. Probably not really a deal breaker when just doing a simple
    threading job. I was just attempting this metric thread for S&G's and I actually needed it to boot.
     
  9. Jason

    Jason Gold

    Petee sent my this video and it should be mandatory watching for anyone that owns a screwdriver, wrench or ratchet! The channel has a lot of good stuff on it.

     
  10. Fulmen

    Fulmen Silver

    Spot on. The 127 is the smallest gear that will give the correct 1:25.4 conversion between metric and inch. And as OMM mentions you have to keep the half nuts engaged when cutting metric threads with imperial leadscrews (or the opposite). The thread dial doesn't work as well on metric treads, so I cut all my threads with the nuts engaged.
     
    Jason likes this.
  11. Here's a Loctite technical bulletin I scanned a while back: "The Technology of Threaded Fasteners", a lot of these documents are no longer available from manufacturers as the companies have changed hands over the years and the new owners are probably afraid of litigation. I'd love to get my hands on the technical documents about Araldite epoxy glues but these have disappeared. The Loctite booklet is full of a lot of dry math but the graphs showing effect of lubricant when torquing fasteners properly, or the chart showing various locking methods and how long they survive vibration are pretty interesting: spring washers are pretty much useless.

    Edit: ok it looks like the 10Mb PDF file size is too large for this forum so message me if you want me to email you a copy.
     
  12. Jason

    Jason Gold

    I offered 60bucks for 2 gears and never heard a word. He did come down to 150 for the stack and told me to sell the rest. If any of you needed the other gears, I'd give them away. But I'm kinda thinking I should attempt to cut my own gears.

    How hard could it be? Probably super tough for a beginner like me, but I think I have most of the stuff I would need except for the broach and the involute cutter. question is, to save ass pain, could I cut simple gears out of brass or would steel be preferred?? After all, these are only for threading and I thought I saw cheaper lathes use plastic gears?? Should I just buy plastic or take the time to DIY and get the lesson? The knowledge is more valuable than the money or time saved in this case to me.

    Thoughts?
     
  13. You have the diving head and milling machine already so with the right cutter, all it would take would be an afternoon to spit out a gear or two. You could measure an existing gears circumference and divide it by the number of teeth to get the tooth spacing and then multiply by the desired number of teeth to get your circumference and diameter of the blank for the new gear. Machining a plastic trial gear would be fast and let you test the result quickly before machining several at once stacked on a shaft (Two to keep and sell the rest on Ebay). That said, there are commercial gear manufacturers that may have an off the shelf gear to suit your application. I think Zahnrad Kopf over on Practical Machinist makes custom gears to order.
     
    Last edited: Apr 3, 2021
  14. Jason

    Jason Gold

    Brass okay to use?
     
  15. Whatever you have on hand to use, although something soft and fast cutting for the practice gear would be handy. You're going to have to use the sector arms on the dividing head to measure out some constant number of holes on the index plate with some concentration at least 50 times, once per tooth without losing count. Some lathes have phenolic/linen gears in the headstock meshing with steel to give quiet operation.
     
  16. Jason

    Jason Gold

    As Pete says, and it only takes 10grand worth of equipment to make it!

     
  17. Jason

    Jason Gold

    Well, I don't know if I am actually going to try to cut these. But so far I have learned my gears are 20degrees and I have sorted out the blank diameters for the gears I am missing.
    I'll work on trying to source the right cutters and maybe the broach. I see it would be smarter to just buy a mandrel to hold the gear and I found the tailstock for my spindexer. Next thing I will need to look at and see if it has the appropriate holed plate..... I believe I even have the tool to hold the gear cutter. :D

    To think this morning I knew none of this. So the way I see it, today wasn't wasted. ;)

    I do like the phenolic idea.
     
  18. This is also a pretty good into to gear making, the audio quality sucks, it's obviously a film to tape to digital transfer. I think the second film shows things like pressure angle etc. It's all pretty interesting but you'll find there's a specific cutter wheel that covers a range of gear diameters.

     
    Last edited: Apr 4, 2021
  19. Jason

    Jason Gold

    Am I missing something here? There is a 3rd number on this list and I have no idea wtf it's for?:confused:
    Lets say I have a 7/8" arbor. I see 20x7/8 28x7/8 or 30x7/8 What's the first number mean? Is this cutter depth? I was thumbing through the handbook and didn't see where it tells
    you how deep you have to go.

    Maybe this search list will work at KBC.

    https://www.kbctools.com/CatSearch/..."],["Pressure Angle","Pressure Angle","20°"]]
     
  20. You need to get an existing gear and use it to calculate the diametral pitch according the formula at the 4:23 mark of Mr Pete's video you linked to earlier. That gives you a relative tooth size.
     

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