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  1. #1
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    Default Gears, gears and more gears

    Been playing with this program a bit...Looking at the difference pressure angle makes..

    I remember a short time ago someone was wanting to determine the PA of a gear they had..

    Here are two 16dp gears 17 teeth... The circular line of the pitch circle diamater line

    First up the 20PA one spur20pa16dp.jpg



    Now the 14.5PA one spur145ps16dp.jpg
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  2. #2
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    Default gears

    Thanks for the info RC

    You may help me out. My Premo lathe is in need of a replacement spindle gear ( pictured ) The Diam. pitch of this gear is 4 and it has 24 teeth . Im not sure if its 14.5 or 20 PA ?

    Before I buy a cutter Id like to know !

    What would be a suitable metal to use as the gear blank ? Would cast iron suffice ?

    Mike

    PS I have to remove the spindle first ,
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    Default

    Are you sure about that DP Mike? If the gear were 4DP for 24 teeth I would expect something over 6" diameter and the spindle gear (the one with the missing teeth) does not look that. What is the OD?

    Michael

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    Default

    If you print these out as no scaling, they should be the right size
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    Default gear

    Quote Originally Posted by Michael G View Post
    Are you sure about that DP Mike? If the gear were 4DP for 24 teeth I would expect something over 6" diameter and the spindle gear (the one with the missing teeth) does not look that. What is the OD?

    Michael
    Hi Michael

    Its about 4" diam I think. I measured along the pitch circle and I counted 4 teeth per inch . Ive got Ivan Laws book . He writes the 20PA teeth are more chunky looking compared to the 14.5 teeth

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    Default 3"

    Ok I tried to measure the gear , but its not easy as its in situ . Looks like it has a PCD of 3" .

    which with 24 teeth , this would be a PD of 8 ? Mike

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    That sounds/ looks more within the realms of possibility.
    The equations for a Gear are OD = (no. of teeth +2)/DP and PCD = (no. of teeth)/DP
    so if you have 24 teeth on a gear around 3" in diameter that would be 8DP. Gears made to this DP have a circular pitch of 0.393", so you would expect to see 2 1/2 teeth per inch of (PCD) circumference.
    If you were counting 4 teeth per inch of circumference then you may have a 12DP gear, but the OD of that would be 2.167"

    Michael

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    For a Cone pully gear running in back gear it wouldnt really matter if it was 14.5 or 20 PA.

    The amount of use it would get would not be detrimental to the gear profiles.

    What is your method of repairing this going to be.

  9. #9
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    Thanks for posting this RC. I was wondering if the program was worth it but for checking PA it may just be.

    How old is the Premo Mike? I would say 90% that it would be 14.5deg, normally DP gears, especially older ones are. However as i have found out with the holbrook there are always exceptions. Once you are sure of the DP you can easily check the PA with a gear cutter. I disagree with PC and would say it is worth getting it right. If you see how 2 different PA's mesh it is not very nice.

    Ew
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    Default age

    Quote Originally Posted by Ueee View Post
    Thanks for posting this RC. I was wondering if the program was worth it but for checking PA it may just be.

    How old is the Premo Mike? I would say 90% that it would be 14.5deg, normally DP gears, especially older ones are. However as i have found out with the holbrook there are always exceptions. Once you are sure of the DP you can easily check the PA with a gear cutter. I disagree with PC and would say it is worth getting it right. If you see how 2 different PA's mesh it is not very nice.

    Ew
    Ewan I'd say the Premo is early to mid 1950's . I believe these PREMO lathes were made by Brackenbury & Austin til the early 60's . Mine has T slots on the cross slide which later examples dont seem to have . A company in West. Aust. took over the design and the Premo lathe was reborn as the VEEM .

    Yes I'd like to get the PA correct . What metal would you suggest I use as a gear blank , 4140 or cast iron ? Mike

  11. #11
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    Quote Originally Posted by morrisman View Post
    Ewan I'd say the Premo is early to mid 1950's . I believe these PREMO lathes were made by Brackenbury & Austin til the early 60's . Mine has T slots on the cross slide which later examples dont seem to have . A company in West. Aust. took over the design and the Premo lathe was reborn as the VEEM .

    Yes I'd like to get the PA correct . What metal would you suggest I use as a gear blank , 4140 or cast iron ? Mike
    Hi Mike,
    I'd think they were just cast. I doubt those teeth were broken in the course of correct use. More likely someone using the backgear to lock the spindle.

    The age puts it in the ?? category, 20PA gears were made in that era but i'd still say its would be 14.5PA.

    Ew
    1915 17"x50" LeBlond heavy duty Lathe, 24" Queen city shaper, 1970's G Vernier FV.3.TO Universal Mill, 1958 Blohm HFS 6 surface grinder, 1942 Rivett 715 Lathe, 14"x40" Antrac Lathe, Startrite H225 Bandsaw, 1949 Hercus Camelback Drill press, 1947 Holbrook C10 Lathe.

  12. #12
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    Some years ago I found a gear train animation that was very good at showing their exact working. It had a line showing the changing pressure angle(s). I wish I could find it again, but repeated searches have come to naught. My knowledge of gears is almost non-existent.

    Dean

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    Quote Originally Posted by morrisman View Post
    Ewan I'd say the Premo is early to mid 1950's . I believe these PREMO lathes were made by Brackenbury & Austin til the early 60's . Mine has T slots on the cross slide which later examples dont seem to have . A company in West. Aust. took over the design and the Premo lathe was reborn as the VEEM .

    Yes I'd like to get the PA correct . What metal would you suggest I use as a gear blank , 4140 or cast iron ? Mike

    You would in my opinion be better off removing the cone pully from the machine before deciding on what material to use as a replacement.

    Once removed then you can decide the material type,have you as yet thought of how you will replace it.

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  15. #15
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    Looking at the original gear, the way it's broken would suggest it's cast iron. A steel gear is unlikely to break like that.

    A steel spindle gear would be a better setup, as used in most modern lathes (it's the hardest working gear).

    Rob
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