New to me lathe need of new gear
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  1. #1
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    Default New to me lathe need of new gear

    I just bought a new to me lathe, and I am missing at least one gear 40t, that is ofcourse one of the most important for the threads I want to cut... How can I determine what gear specs I need ? It is the drive gear first changable from the top in the picture.... ANy ideas?
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    Without the manufacturer name and more/better photos, it's difficult to offer any suggestions.

    If it's a generic Chicom manufacture, be prepared to not like the suggestions.

    jack vines

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    Take one of the bigger change gears and measure the outside diameter and count the number of teeth. If the lathe is American, you can easily calculate the diametral pitch and assume the pressure angle is 14.5 degrees. If it is European, probably depends on age, but might be metric (module).

    Larry

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    I am living in Sweden, and this is a Swedish made lathe, so probably metric as we use metric system... The mfg is "OB Maskiner Mariannelund" but I have searched everywhere in Sweden for someone into lathing / machining and nobody had heared of this mfg. SO probably an odd one....

    But is there a way of measuring a gear? I have almost all other cears according to the the gearing table, but the nr 40 is missing... :-(

    Or is it possible to "play arround" and calculate a different gear ratio thus not having to use the 40t, and change also another gear ?
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    Yes, it is possible to determine the diametral pitch or module of your gears. Measure the outer diameter of at least one of the larger change gears and count the teeth. Then look up online how to do the calculation from just those two numbers. Once you figure out the tooth size, you can look for a 40 tooth gear with that size tooth, so it will mesh with your other gears.

    I see from your thread chart that your lathe uses the 127 tooth gear to cut metric pitches. That means the lead screw has an inch pitch. So I have to wonder just how metric the other parts of your lathe may be.

    I had the misfortune to buy a Volvo 164 sedan in 1969. I well recall that almost all the fasteners in that car had standard American inch threads and hex sizes. But the Z-F German-made brake and steering parts had metric threads and hex sizes. So I have my doubts about how metric an old Swedish machine is.

    Larry

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    For instance - a gear with forty teeth might be "1.5 Module" in which case the pitch diameter will be 60mm and the O.D. (The outside of the gear teeth) will be 63 mm

    A good one to play with measuring is your 100 tooth - if it is a 1.5 Module, the pitch diameter will be 150 and the outside will be 153mm

    If your lathe turns out to be "Imperial" on this end, the 100 tooth could be 8.500" OD and 12 Diametral Pitch - or "DP". A forty tooth 12 DP will be 3.500 OD

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    It looks a lot like a south bend.

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    Quote Originally Posted by johnoder View Post
    For instance - a gear with forty teeth might be "1.5 Module" in which case the pitch diameter will be 60mm and the O.D. (The outside of the gear teeth) will be 63 mm

    A good one to play with measuring is your 100 tooth - if it is a 1.5 Module, the pitch diameter will be 150 and the outside will be 153mm
    And if the diametral pitch is 16, the outside diameter of a 40 tooth gear will be 2.625 inches. If the DP is 20, the OD will be 2.10 inches. And so on.

    Larry

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    OK, thanks for all the input, I will have to go outside measuting some ODs, pitch etc... Really thank you for this input.

    OK bear with me now, as I am new to lathing, and this being my first "real lathe". (I had some smaller mini lathes before)... I have attached a picture to explain my headache. Next problem is that I can not engage the separate feed rod. In the pic I place a doubble gear call it 4/5 in the pic in order to get the correct pitch for threading and correct feed rate on the feed screw. I removed this in the pic for easier viewing. The lowes set of gears is on a bracket that pivots upwards and is driven by gear nr 6/7. The problem I have is that the bracket itself has no room to be pivoted upwards to engage because of gear nr 4. (Gear nr 4 / 5 is a doubble gear being nr 5 is inwards the bed). In the pic I numbered them in the order the should be connected to eachother.

    I think that something is missplaced here but after trying to figure this out myself for a week I am stuck here...

    So all suggestions about this is also appriciated...
    Attached Thumbnails Attached Thumbnails img_20200502_104903_fel.jpg  


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