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  1. #1
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    Manual to CNC Lathe conversion..Pictures

    I bought this Pratt Whitney Type C Tool room lathe in the early 70's at a US Government auction.The lathe had never been used, had no tooling, chuck, motor or belts, but was damaged as the shipping pallet had wasted away and broken or bent all the controls in front. At the time I was going to college on the GI bill,working full time at a machine shop and raising a growing family.Having neither the time or resources to equip or repair it, sat for another 4-5 years. In fact I almost went broke paying for transport to my garage, as this "little" 12X30 lathe is 3200 lbs !

    Sometime after graduation, suffering through my 1st layoff in the GREAT Aerospace industry, I did repair the broken handles,clean,install a 10hp, 2 speed motor and belts and started doing prototype work, sub contract and small lot pieces. We quickley found out that this is a very accurate, smooth lathe, with a very good finish capability.My customers were happy.

    We have kept good care of the lathe over the years, I did not allow any other employees to operate, never used a tool post grinder on it, did only prototype or small pieces. Got tired of the horrible Government green paint and refinished with a 2 part epoxy Grey in the 80's..have touched it up, but the paint is still holding up.

    I believe the machine was manufactured in the mid 1950's as one thing that I got with the lathe is an updated wiring diagram dated 1952 ( The paper is parchment, really old) The auction reciept did not list a year, only model and ser.#. Wow that makes it 50 yrs old or so..!

    The gearedhead has 32 speeds ( with the 2 speed motor) has its own oil filter and oil pump. I did have Caterpiller ( Empire Machinery,Phoenix ) do an oil analysis on the gearhead oil...came out real good.. no metal, bronze, chrome or other suspect metals in any excess amounts .

    The decision to retrofit to CNC was easy.Due to an accident I'm in a wheel chair and cannot stand in front of a lathe very long to build goodies (blower systems, pulleys, contours, threading etc) very long. I have a good Le Blond 17X60 manual lathe if needed, in fact will be used to build parts for the Pratt Whitney.

    Getting with the program to retrofit:
    1)Clean up and spot paint the old girl
    2)Remove the apron drive shaft,threading feed rod compound acme screwand nut, along with the taper attachment.
    Attached Thumbnails Attached Thumbnails jsw_jse_start_of_cnc,_pratt_whitney_lathe_016.jpg   jsw_jse_start_of_cnc,_pratt_whitney_lathe_005.jpg   jsw_jse_start_of_cnc,_pratt_whitney_lathe_007.jpg  

  2. #2
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    Here are the items purchased and delivered so far. Machine Tool camp servos with US Digital encoders, ( 672 oz/inch) Desk CNC Motion Control Card and their Software,encoder cables with a US digital encoder for the spindle RPM.I chose Machine Tool Camp as I used their program for my 3 axis Tree Mill retrofit,have had NO problems, and Scott's help in the electronics and software was invaluable. I'm also using Vector 3d CAD/CAM from IM Service that matches Desk CNC, and I have become comfortable with the system, even being a complete computor KLUTZ.Fred Smith and Jackies help have kept me sane learing the system.
    Rockford rolled Ballscrews and double nuts were my choice for both axis, will machine the ends myself on my manual Le Blond lathe.Taking my own advice, I also purchased the Fixed angular bearing mount for both the Z and X axis, will use one simple bearing mount for the Z axis, but made the mount for the X axis.
    I made the large timing pullys ( 72 teeth) out of 6061 Alum and had them hard anodized, bought the 10 teeth smaller ones which will give me a 7.2 to 1 ratio..the servos are rated @ 4200 rpm, but will reduce to 3500 rpm. This gives a final G00 rapid of 90ipm with the 5tpi ballscrews, which is a lot faster than I can think at this age.(actually that means the entire Z axis transverses in less than 30 seconds) Misc electronics will include 2 electronic relays to control coolant and a four position tool changer that is in "design" stage..for now my goal is to construct the 2 axis,with no backlash or problems and use the lathe in CNC untill I'm comfortable .Then possibly a 3rd axis and tool changer.
    Not pictured is the 12 amp 70 volt power supply ( Machine Tool Camp) and the electronics cabnet and misc wiiring and electronics.
    Building the front x axis simple bearing mount:
    1st picture. Using my PowerMatic Verticle automatic band saw to cut the 6061 t-6 material. ( If I concentrate this saw will cut accuratley to .030-.050 and saves a lot of machine time..)Then using my Retrofited 3 axis Tree Mill to "square "the part and machining the male and female bosses . The bearing fit is tight slip fit ( used oil and both thumbs to push in ). Also the 4 mount holes and counter sink.
    You will notice the mounted manual oil ( way) pump. I drilled and tapped fittings for the Z axis carriage,and the compound slide,in addition both Ball nuts will be lubricated by this system.
    Next will be the rear bearing ( fixed angular ) mount.
    Attached Thumbnails Attached Thumbnails jsw_jse_start_of_cnc,_pratt_whitney_lathe_010.jpg   jsw_bearing_spacer_block,front_x_axis_001.jpg   jsw_bearing_spacer_block,front_x_axis_004.jpg   jsw_bearing_spacer_block,front_x_axis_009.jpg  

    jsw_bearing_spacer_block,front_x_axis_finished_and_installed_001.jpg  

  3. #3
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    Here are the rest of the pictures for the front x axis bearing mount
    Attached Thumbnails Attached Thumbnails jsw_bearing_spacer_block,front_x_axis_finished_and_installed_003.jpg   jsw_bearing_spacer_block,front_x_axis_finished_and_installed_007.jpg   jsw_bearing_spacer_block,front_x_axis_finished_and_installed_008.jpg  

  4. #4
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    Machining and assembly of the rear X axis fixed angular bearing mount.
    The real problem here is to establish a true center line of the compound ball shaft both vertical and horizontal. There is a machined hole that had located the rear compound bearing for the acme rod, and also located the the taper attachment. The center line of that machined hole will be the center line of the ball screw. I turned a "plug" that fit in the hole, (1.125), then cut, surfaced , drilled the 4 mount holes and counter sunk for allen bolts on the spacer block.
    Mounting the spacer block on the lathe, I used my depth mic from the top of the bearing block ( machined) to the top of the compound ways ( machined) then to the top of the plug I just made, added that together plus the radius of the plug and I should have centerpoint ( should) I measured three times and had a friend of mine who is a very good machinest come over to the house/shop with his depth gauge and his answer was withen .0003 of mine.
    This gave me the depth for the fixed angular bearing mount, the center of the bearing block is the center of the bolt pattern(horizantaly)
    Using Vector Cad Cam made a short pocket program, but added .015 to the width of the pocket for a little "fudge factor". and also drilled the 4 holes (oversize by .020) for the bearing mount.When I know everything is in good alingment,then I will install 3/16 locating pins on both the spacer block and the fixed angular bearing mount and correctly torque all of the fastners.
    The reason I left some fudge factor is due to "stack of tolerance",which believe me ,has gotten me in trouble before.( I.E. assuming everything was perfect and would fit just right )I'm not discounting that we may have to use shims, or surface the fixed angular bearing mount.
    Next will be the mount for the double ball nut on the compound, then to machining the ball screw and a very small knurled "positioning" knob on the front of the machine for the X axis.

    Adobe ( old as dirt)
    Attached Thumbnails Attached Thumbnails jsw_courtyard_and_rear_bearing_block_x_axis_010.jpg   jsw_courtyard_and_rear_bearing_block_x_axis_014.jpg   jsw_courtyard_and_rear_bearing_block_x_axis_012.jpg   jsw_x_rear_bearing_block_installed_008.jpg  


  5. #5
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    Nice. Do I see the leightweight pulley on picture #1? Big reduction?

  6. #6
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    yes ,but the belt is not the correcrt one..also you can see the tensioners, as I use two per belt to tension and to keep the correct "wrap" on the small pully. By the way how is your conversion going ?any pictures yet ?

    Adobe (old as dirt )

  7. #7
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    Where did I say I was doing a conversion? I already did a CNC mill and software with a friend in 1986. I can only be accused of updating. But my main fixation at the moment is threading.

  8. #8
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    yes the software I have does have a threading program, all you do is fill in the length etc, and immediatly the G code is written.This covers metric, us and if you need an odd ball ( like .472X 32) you can build that type also.
    O, and sorry I thought you were building a cnc lathe.

    Adobe (old as dirt )

  9. #9
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    I worked on a CNC lathe. Threading was just fantastic at 800-1000rpm, it is the big difference. I also did worms with circular intrapolated starting points. But, what is the reason for the big reduction?

  10. #10
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    Its just 7.2:1. This also helps increase torque, which I need as the spindle is limited to 2000 rpm .At axis servo speed of 3500 rpm, this calculates to 90 IPM. The total Z travel is only 30 inches, so it could go from Z 30 to Z0 in 20 seconds which to me, is just real fast. Any higher ratio,it would gain speed and lower torque. Also, if I do not like the axis performance,it is not much of a job to make another pully. Thanks for your reply

    Adobe (old as dirt )

  11. #11
    Moderator Switcher's Avatar
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    Adobe Machine,

    I noticed that your new thread here is posted in the "Test Forum".

    You might want to move to a more specific catagory. I'm not 100% sure, but I think that all the post in the "Test Forum" are deleted after a short period of time.

    Jerry




    .

  12. #12
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    er, your right.how do you switch to another forum ? and thanks.


    Adobe (old as dirt)

  13. #13
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    Wow, Nice machine Adobe. Warms the heart to see one of these beasts find a caring home
    Regards,
    Mark

  14. #14
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    er, your right.how do you switch to another forum ? and thanks.


    Adobe (old as dirt)
    You could just start a new thread in a more specific catagory, then copy and paste what you have here into the new thread.

    Or, maybe ask a Moderator to move the entire thread for you?

    Jerry



    .

  15. #15
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    A note on the small pulley: for the inch timing belts, the factory recommends that there are at least 6 tooth in contact with the pulley. I cite: "Befinden sich 6 oder mehr zahne in eingriff, so ubertrifft die festigkeit der zahne normalerweise die festigkeit der zugkorper"(catalog Uniroyal). Translated: If there are 6 or more tooth in contact, then the total rip force of the tooth is greater than the ripforce of the belt. I have never seen this recommendation again, but I think it is a sound advice. It is imaginable that under load you introduce flex, through overloading off the (few) tooth. Theoretically I would say, that you lose precision with a small pulley.

  16. #16
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    RotarySMP, thanks, that lathe has been good to me, might be the oldest CNC lathe around when I'm finished.

    Fka.Carel Yes, you are correct.Before my "enforced" retirement (wreck) we designed and manufactured specialty Asphalt machinery, and in the last 6 years began using large timing belts (in place of chains)in certain situations.
    The belt supplier always recomended a 50% or better wrap.Because of space constraints and ratios we had to use 2 tensioners ( or 1 idler and 1 tensioner) to acheive the correct wrap. My initial design will use one idler and 1 tensioner placed so that the small pully will get at least 50% engagement.
    But, if I do not like the design then can be changed quickly. ( thats what nice about being retired, nothing has to happen quickly)

    Would also like to point out that the timing belts held up 3-5 times longer than chains, as they withstood shock better. ( Actually we called them Gilmer belts )I have seen some German asphalt machines that also used Gilmers( in situations where they were not exposed to heat or hot asphalt)
    and they used the 50% warp too.

    Adobe ( old as dirt )

  17. #17
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    Beautiful machine and a good looking conversion...One question...What are the "T" slots down the side of the way for? I think it's in picture No3 on your original post. :beer:
    Keith

  18. #18
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    Those " T " slots were machined at manufacture for the Taper attachment.
    I checked them for parallel to the Z axis ways and they are spot on. They are an odd ball size so I made 4 "T" nuts( 4 came off the machine ) and they will support the bearing blocks for the Z axis ball screw.Pretty handy ,huh.
    Thanks for the comment.

    Adobe (old as dirt)

  19. #19
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    Quote Originally Posted by Adobe Machine View Post
    Those " T " slots were machined at manufacture for the Taper attachment.
    I checked them for parallel to the Z axis ways and they are spot on. They are an odd ball size so I made 4 "T" nuts( 4 came off the machine ) and they will support the bearing blocks for the Z axis ball screw.Pretty handy ,huh.
    Thanks for the comment.

    Adobe (old as dirt)
    Thanks for that and I like the email notifications for this thread Keep going and never stop Sir :tiphat:
    Keith

  20. #20
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    Machining the X axis ball nut carrier: There is not a lot of room under the carriage cross slide to install a carrier for the double nut, and there is the alingment problem too. After removal of the old acme screw nut ( and what an engineering marvel that is ,will explain in next post ) I copied the gross deminsions. I cut a square of 6061-t6,& squared up in the mill . Using Vector CAD / CAM drew the boss and placed the mount holes as per the old acme nut, plus drilled and tapped 3/8 -16 hole in the center of the boss, also milled some 3/8 grooves on the bottom for clearence, then milled an .800 hole thru the carrier for ball screw clearence.

    I will not actually assemble the carrier to the carriage untill the ball screw has been machined..I have to assemble the ball nuts to the screw "in place" then assemble the rear fixed angular bearing mount to the machine bring the ballnut flange up to the the carrier just made, mark the holes, ( everything

    tight, carriage in place and gibb correctly adjusted) pull it back apart , drill and tap 1/4-20 ( the flange holes will be sized to .266 for fudge factor again)
    this will also be pinned with a 3/16 steel pin when everthing works smooth.( I have no doubt that will take time and be a little frustrating)

    1st picture : the squared and flat piece in the mill and milling the boss circle.
    2nd picture: the completed part with fastners
    3rd picture: showing the double ball nut and the new carrier
    4th picture: fit to crossslide ( off the machine )

    next post will explain the very innovative acme screw not for the cross slide.

    Adobe ( old as dirt )
    Attached Thumbnails Attached Thumbnails jsw_ball_nut_carrier_(old_and_new)_014.jpg   jsw_ball_nut_carrier_(old_and_new)_023.jpg   jsw_ball_nut_carrier_(old_and_new)_019.jpg   jsw_ball_nut_carrier_(old_and_new)_022.jpg  


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