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Thread: Cutting gears?

  1. #1
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    Default Cutting gears?

    This purely hypothetical, suppose I wanted to cut a couple of gears, say a 100 tooth and a 127 tooth matching set.

    1. How do I determine the tooth profile?
    2. How do I determine the pressure angle?
    3. How do I determine the gear blank diameters?
    4. What else should I be asking?

    I see that CTCtools sell gear cutters, about 8 in a set. I presume that once the above questions are resolved, then the right choice of cutter will become apparent.

    I'm hoping Pipeclay, our gear guru, will help here, and others of course.

    Needless to say, a mill with dividing head is a pre-requisite.

    Ken

  2. #2
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    Lets assume they are Involute gears of either 14/12 or 20 PA.

    Firstly measure the diameter of an existing gear,if there are no existing gears make them whatever you like as long as they will fit.

    Lets say you have an existing gear,measure it ,for this we will assume they are 16,18 or 20 DP.

    Count the Number of teeth on the existing Gear and ADD 2 to the total,then divide the result by 16,18 and 20 and see if the answer comes out to your measured Diameter.

    Hopefully it has or is within a few thou or hundredths of a mm.

    If you get an answer that is right that will be the DP of the Gear and the DP of the cutter/s you will need.

    Once you have determined the DP of the cutter/s required working out the OD of the blank will be (teeth + 2) / DP,eg 36+2 = 38,38/18= 2.111. 2.111 would be the OD of the Gear blank,to cut 36 teeth.

    Can you or do you know if the gears are 14 1/2 or 20 PA,if not sure and you allready have an existing gear count the number of teeth on it and let us know,chordal calculations can be made to determine whether 14 1/2 or 20 PA.

  3. #3
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    Lets say they are for a Hercus lathe, the DP would be 18,the PA would be 14 1/2,the OD of the 100th would be 5.666",the OD of the 127th would be 7.166".

  4. #4
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    Pipeclay, many thanks. The gears I was thinking of are in fact for a Hercus 9" lathe.

    You reckon the PA is 14.5 degrees for Hercus lathes? Is it easy to tell the difference by eye between one gear with a PA of 14.5 degrees, and the other 20 degrees? Would the two mix?

    The reason I ask is that Southbend transition gear sets are available in the States, and
    I have a feeling that Southbend lathe gears are 20 degrees, but could be wrong.

    I shall sit down and digest your replies.

    Ken

  5. #5
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    Pipeclay.

    By your reckoning, a 100 tooth gear is 5.666", and 127 would be 7.166".
    Is this the OD of the gear, or the diameter of the pitch circle?

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    Ken read the answer.

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    Hi Pipeclay,

    Gotcha, just wanted to make sure.

    Ken

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    If you use a magnifying glass and overlay the gears you might be able to see a difference in the shape,you can measure full depth that will also indicate PA,just check with the seller before purchase as to the way in which the compounds are held together,also ask how thick the compound set is.

  9. #9
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    Quote Originally Posted by pipeclay View Post
    Lets assume they are Involute gears of either 14/12 or 20 PA.

    Firstly measure the diameter of an existing gear,if there are no existing gears make them whatever you like as long as they will fit.

    Lets say you have an existing gear,measure it ,for this we will assume they are 16,18 or 20 DP.

    Count the Number of teeth on the existing Gear and ADD 2 to the total,then divide the result by 16,18 and 20 and see if the answer comes out to your measured Diameter.

    Hopefully it has or is within a few thou or hundredths of a mm.

    If you get an answer that is right that will be the DP of the Gear and the DP of the cutter/s you will need.

    Once you have determined the DP of the cutter/s required working out the OD of the blank will be (teeth + 2) / DP,eg 36+2 = 38,38/18= 2.111. 2.111 would be the OD of the Gear blank,to cut 36 teeth.

    Can you or do you know if the gears are 14 1/2 or 20 PA,if not sure and you allready have an existing gear count the number of teeth on it and let us know,chordal calculations can be made to determine whether 14 1/2 or 20 PA.
    Pipeclay
    I noticed some time back you could supply a compound gear 60 tooth to 63 tooth for Hercus lathes.
    I have a Hercus 260 model A imperial lathe & looking for the above compound gear for cutting metric threads.
    Please lets knoe if you still supply this item.
    regards
    Abratool

  10. #10
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    Yes I still either have them or can make them or any of the others,63/60, $90.00 plus post or pickup.
    Hercus or other suppliers might have them cheaper.
    Last edited by pipeclay; 9th Mar 2011 at 09:44 PM. Reason: more sence

  11. #11
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    Quote Originally Posted by pipeclay View Post
    Yes I still either have them $90.00 plus post or pickup.
    Hercus or other suppliers might have them cheaper.
    You should get a job at a certain machinery retailer - might improve their reputation substantially

  12. #12
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    I allways give people the option to find an allternate source,I charge what I think something is worth.

  13. #13
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    Default Change Gears for Hercus 260 Model A

    Quote Originally Posted by pipeclay View Post
    Yes I still either have them or can make them or any of the others,63/60, $90.00 plus post or pickup.
    Hercus or other suppliers might have them cheaper.

  14. #14
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    Hi Ken,

    If you are abput to cut gears the following link may assist.
    There are three separate pages and its basically for the late but still lots of good applicable info that will posibly help.

    Cut a lathe change gear

    cheers
    Grahame

  15. #15
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    I need a replacement cross slide driven gear for my Nuttall Lathe and have been researching gear making for a long time. I found that site a few months ago and am now in the slow process due to other commitments of making a setup as shown. When I read this thread, first I thought I would have to find this site again but it has already been done. I also need to finish my metal casting forge to cast brass blanks for this job.

    Dean

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