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Thread: Replacement Change Gears for 12” Geared-head Lathe

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    Paul Jones's Avatar
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    Replacement Change Gears for 12” Geared-head Lathe

    This not exactly “homemade” because I started with manufactured spur gears and modified these to fit my lathe. I have the situation where replacement parts are no longer available and I have to either make or modify the parts.

    I have a used 12” x 37” geared-head gap bed lathe that came with the wrong change gears for cutting imperial or metric threads. The lathe has two spur gears located in the compartment behind the spindle that must be changed when switching between cutting imperial and metric threads. When I acquired the lathe it had an odd set of 32 tooth and 46 tooth spur gears for cutting only 11 ½, 23, 46 and 92 TPI and nothing else. Missing were the two 40 tooth gears required for imperial thread cutting and a 30 tooth gear for cutting metric threads. Luckily, the lathe still had the 120/127 combo gear essential for either imperial or metric thread cutting.

    My geared-head lathe was built in Taiwan in 1987 but it is very similar design to the 12” swing Grizzly lathes. I called Grizzly but they could not provide the specs to the gears other than the number of teeth. I took a chance and the ordered replacement gears. The Grizzly gears did not fit because they use a 14 ½ degree pressure angle and I needed 20 degree PA and a diametral pitch of 20. Boston Gear makes steel spur gears in their YA series that fit my specs and I ordered the gears with 0.500 bores.

    I machined the gears to be 10 mm wide on the teeth and 10 mm wide on the hub using an expandable mandrel with a slotted brass tube to fit the in between mandrel size. Next I bored to 18 mm ID by chucking the hub section and not touching the gear teeth. Finally I broached a 5.01 mm wide x 2.51 mm deep keyway to fit my lathe shafts.

    I made a “broaching” tool using a HSS cutting tool blank ground to cut the keyway using a boring bar and having the lathe chuck locked in place (and turned off). I used a digital height gage to align the horizontal direction and height of the broaching tool. After creating the keyway slot, a 0.1970" (5.004 mm) gage pin was used to check the slot width before removing the gears from the chuck.

    These are not exactly “homemade” from scratch but the gear modifications allowed me to install the exact parts I needed for this lathe. Now the lathe has all the necessary change gears and a quick change gear box combinations to cut a wide range of threads from 3 3/4 to 112 TPI and 7.5 to .25 mm pitch (see attached threading chart showing the change gear sizes and placement options). The two 40T change gears normally drive the 120T gear for most imperial threading and the lower 40T gear is reversed on its shaft to drive the 127T for metric threading.

    The change gears are lubricated using a high press grease and run almost silently. The grease product is "Dart LUBE CMD Extreme Pressure Lubricant" (see https://www.amazon.com/Dart-LUBE-Ext...sure+Lubricant ).
    Attached Thumbnails Attached Thumbnails Replacement Change Gears for 12” Geared-head Lathe-modified-40t-change-gears-ready-install.jpg   Replacement Change Gears for 12” Geared-head Lathe-modified-original-40t-spur-gear.jpg   Replacement Change Gears for 12” Geared-head Lathe-installing-adjusting-40t-change-gears.jpg   Replacement Change Gears for 12” Geared-head Lathe-two-40t-change-gears-installed.jpg   Replacement Change Gears for 12” Geared-head Lathe-machining-gear-hub-using-mandrel.jpg  

    Replacement Change Gears for 12” Geared-head Lathe-broaching-boring-bar.jpg   Replacement Change Gears for 12” Geared-head Lathe-custom-ground-hss-cutter-broaching.jpg   Replacement Change Gears for 12” Geared-head Lathe-setting-keyway-cutter-height.jpg   Replacement Change Gears for 12” Geared-head Lathe-aligning-boring-bar-keyway-cutter.jpg   Replacement Change Gears for 12” Geared-head Lathe-12x37-geared-head-lathe-thread-chart.jpg  

    Last edited by Paul Jones; 12-07-2017 at 10:21 AM. Reason: wrong TPI, should be 92, not 93; spelling corrections

  2. The Following 9 Users Say Thank You to Paul Jones For This Useful Post:

    Frank S (08-27-2017), jjr2001 (09-01-2016), kbalch (03-30-2015), LMMasterMariner (08-27-2017), PJs (10-23-2015), rossbotics (08-28-2017), Seedtick (08-27-2017), Workshopshed (03-31-2015), Y-geo (08-27-2017)

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    Thanks Paul! I've added your Change Gears to our Lathes category, as well as to your builder page: Paul Jones' Homemade Tools. Your receipt:


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    Very interesting post! Learned something.

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    Paul Jones (04-01-2015)

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    Update to the gear head lathe change gear remake,

    Last week I cleaned and replaced the change gear grease on the gears at the rear of the lathe headstock with the product "Dart LUBE CMD Extreme Pressure Lubricant" (see https://www.amazon.com/Dart-LUBE-Ext...sure+Lubricant ).

    This is sometimes a recommended lubricant for lathe dead centers but the sound dampening effect it had on the lathe change gears was truly amazing. The gears went from making a reasonable whirling sound to almost no sound at all. Try it and I think you will see a major difference in the change gear sound.

    Thanks for looking,

    Paul Jones
    Last edited by Paul Jones; 12-07-2017 at 10:22 AM. Reason: New URL for product

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    Paul,
    that hi pressure lube would be nice but it's your side of the pond, trying to get it here via mail without doubling the price !

    any of of the brit / euro crew know of an outlet this side of the water? or a "local " equivalent ?

    I remember back in the day i used Bel Ray EP2 Termalene grease I brought a small pot back to the UK, but that has long since gotten used up. Tried to find a stockist in the UK but no luck (unless i want a drum of it :-)

    Ideas?
    Last edited by Y-geo; 08-27-2017 at 06:30 PM. Reason: memory fade
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    Hello Paul,

    Nice post. Thanks for sharing.
    You can also order gears via aliexpress. Unfortunately you can't buy them cheap in China like I do, but should be much cheaper than Grizzly - chinese gears.
    I am presently buying 1.5 module gears for my next project - external lathe headstock gearbox. 16 gears - 4 shafts - 18 speeds. These metric gears are coming as follows: M1 - width 10 mm, M1.5 - width 15 mm, M2 - width 20 mm and so on.

    Regards
    LMMasterMariner

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    To: Y-Geo,
    I was introduced to the Dart LUBE CMD Extreme Pressure Lubricant from a recent YouTube video by Keith Fenner. He mentioned that his tube of the lubricant was probably his second tube in a lifetime of machining because it is used very sparingly. Instead of paying $9.05 USD you might have to pay $20 USD with shipping but it is not going to brake the bank when it lasts practically a lifetime.

    To: LMMasterMariner,

    Thanks for the tip on buying from aliexpress for 1.5 module gears.

    I bought my spur gears based on the YA series from the company Boston Gear instead of buying from Grizzly because the gears from Grizzly did not fit my lathe (Grizzly had 14.5 degree pressure angle and I required 20 degree PA). My gear head, gap bed lathe was built in Taiwan in 1987 but I discovered it has some Imperial dimensioned parts including the gears while the shaft diameters are exactly metric (some 18 mm). At first I though the gears were based on 1.5 module gears because I thought a lathe built in Taiwan would be basically all metric. After careful measurements of the existing gears, I determined the gears were actually 20 degree PA with a diametral pitch of 20. The gears sold by Boston Gear are USA made and very high quality. Instead of buying directly from Boston Gear, I searched eBay, found the exact Boston Gear gears I needed, made a fair offer and purchased the gears from new stock for $20 USD each with shipping. I still had to machine the hub and tooth widths to be smaller and broach the gears using this method ( Broaching Keyways with the Lathe ) because I did not own a 5 mm wide broach.

    Thank you for the information.

    Paul
    Last edited by Paul Jones; 09-18-2017 at 08:37 AM.

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    A lot of machinery that came out of Taiwan in the 80 were made by companies that shared a partnership with US companies at that time the change over to module gears had not been fully implemented as many of the gears were made in the USA then shipped over the shafts were metric because the bearing industry had already mostly adopted the metric system having the bores and OD's staged in 5 mm increments widths were determined by service duty.
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    Frank S,

    Thank you for the information. Your explanation helps a lot. The bearings on the 1987 Taiwanese lathe were made with metric dimensions and made in Japan. Some of the gears are stamped made in USA and had to be shipped over for assembly. It is a nicely made lathe with lots of hand scrapped surfaces. Despite its age, the run out on the headstock bearings show no measurable TIR when measured with a 0.0001" Interapid dial test indicator.

    Paul

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    My 1979 Victor 16-40 gap bed lathe also made in Taiwan was the same way nice little tool room lathe and as Toolmaker 51 describes a good fit for me after I placed it on 4 inch pads
    Last edited by Frank S; 08-28-2017 at 10:15 AM.
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