My Lathe - 9x20

Central Machinery Model 45861 9x20 Lathe

[Sept. 7, 2015]

[Sept. 30, 2015]

[Feb.4, 2021]

[Feb 10, 2021}

I'll be adding information and additional references to this page as I gain more experience with my "new" lathe.

The drawing below is a detail from the Grizzly manual (see references below) showing the idler pulley (#212), the bushings (#207), and the retaining ring (#215). The right hand picture below shows the 9x20 pulleys - the idler pulley is the pulley on the middle left.

Sacrificial "White Plastic Gear" for 9x20 Drive Train

There is a white plastic 80 tooth gear in the gear train that drives the lead screw; it's called a "sacrificial gear" because the idea behind using plastic for this gear is that if there is a jam or similar problem the plastic gear will strip out and save the rest of the gear train from worse damage. If you bought your lathe new, you probably got one or two spares for this gear; if you bought your lathe used, you may or may not have a spare. If you don't have a spare, it;s probably a good idea to have one or two on hand, but they seem to be very hard to find.

In searching the web, I have found some possible sources:

1. Jet lists what I think is the same part as GEAR 80T BD-920N, but it's a whopping $40.69 (2015 price).

2. Grizzly no longer provides the plastic part, but lists a metal replacement as P4000119A - GEAR 80T METAL for a more reasonable $18.50. The downside here is that being a metal gear, you lose the protection provided by the plastic version, and risk serious damage to your lathe in the event of a jam.

In a related note, this page provides code for 3D printing 9x20 change gears, and states that the gear parameters are as follows:

• Thickness: 8mm

• Bore Diameter: 14mm

• Keyway Width: 5mm

• Keyway Depth: 2.5mm

• Pressure Angle: 20

• Diametral Pitch: 1 (MOD1 Gears have a DP of 1) [Note: Not sure here whether the original author simply means that these are Mod 1 gears, and has confused this with DP. I'm pretty sure he means Mod 1, but I'm still learning about gears so don't take my word for it.]

Note: As of this date (Sep. 10, 2015) I have not purchased any of the above, so I cannot say for certain if they are the required replacement. When I eventually make a purchase, I will update this note.

[Update Feb. 4, 2021]

Since I originally wrote the above, I have acquired a 3D printer and was able to design and print the sacrificial gear. You can find more details and the required print files here:

https://www.prusaprinters.org/prints/30043-9x20-lathe-sacrifical-80-tooth-gear

References

This model of 9x20 lathe is sold in a number of variations by a variety of vendors and is very popular, so many people have written about its pros and cons, and have offered numerous modifications and improvements. The links below attempt to collect some of the best references for the 9x20 lathe.

A note of caution: Not all 9x20 lathes of this type have identical components; in some cases there are even significant differences between different model years from the same manufacturer. In addition, the manuals are not always accurate. Check and measure the components on your own lathe before ordering replacements or additional accessories.

• Belts, replacement :

  • According to this link, the the HF45861 takes a p/n: 5M710 v-belt - 710mm (note that the Grizzly G4000 takes a 5M730); the belt is available from MRO Supply and other sources. An alternative suggested in the link cited is the Gates K040275 Multi V-Groove Belt, a wider belt with three grooves which can be sliced into four usable belts.

  • Additional information on replacement belts can be found on Steve Bedair's website.

  • It has been suggested that reducing belt tension can reduce belt wear; done by inserting an S-hook into the tension spring (see photo here).

• Gears

  • Gear Ratio Chart : Downloadable PDF - feed rates and setting for SAE and metric threads.

• Manuals

  • Manual for 45681 : Central Machinery 45861 9 x 20 manual from Harbor Freight Tools.

  • Manual for Grizzly G4000 : A much better written manual. The Grizzly G4000 is essentially the same lathe as the Central Machinery 45681 (but be aware there are some differences); this manual is better written and is worth reading.

• Modifications

  • Chucks and Backing Plates

    • 39x4mm Backplate : Steve Bedair shows how to make a backing plate from scratch, including cutting 4mm threads.

    • 4-jaw Chuck and Back Plate : akpilot shows how he fitted a pre-threaded back plate from Grizzly. On the same website is a downloadable PDF on Fitting Lathe Chucks.

    • Backing plate : Jeff Davis shows how to cut 4mm threads for the backing plate.

    • Chuck Backplate : Tools and Mods shows how to make a steel backplate with front mounted chuck.

    • Fitting a Chuck and Making a Backplate : Very thorough discussion on fitting a backplate.

  • Crossfeed modification : "This modification changes the lead screw to a thick 7/16-20 thread, a larger mount, adds a deep grove ball bearing and a thrust bearing. Plus the hand wheel diameter has been increased from 2" to 3"."

  • Mods and Repair docs : A good collection of documents relevant to the 9x20, including rebuilding, modifications, and installing a DC variable speed replacement motor.

  • Quick Change Tool Post (QCTP)

    • Jerry's Metal Working Links : See the link on Tricking Out the 9x20.

    • Micro-Machine Shop : "Adapted a Phase2+ wedge-type QCTP, Model 250-111. Wedge-type tool posts are purportedly more accurate & repeatable than the piston type."

    • Phase II Quick Change Tool Post Installation : "The fly in the ointment with this tool post is that you have to modify your compound slide to accept the tool post. Or, I should say to accept the tool post mounting stud."

    • Steve Bedair's 9 x 20 Lathe Site : A method for the Harbor Freight 39083 Quick Change Toolpost is found at this link. Sadly, Steve has died and his site may go offiine; fortunately a copy of the site has been archived here: http://web.archive.org/web/*/http://bedair.org/9x20.html

  • Tumble reverse gear : "A tumble-reverse gear changes the direction of the 9x20 lathe's lead screw so the carriage can feed left to right with the part still turning CCW. This allows selection of automatic feed right to left, neutral, & left to right as well as enabling left-hand single-point thread cutting, if so desired."

  • Variable Speed DC Spindle Motor : "Baldor Model CDP3440 DC motor (USA): ¾ HP, armature 90VDC, 7.6A full load, 1750RPM, Permanent Magnet (PM), & Totally Enclosed Fan Cooled (TEFC)."

• Websites related to 9x20

  • BedairMachine Works : Steve Bedair's website has lots of information on 9x20 mods and projects.

  • 9x20 Discussion Forum : https://groups.io/g/9x20lathe

  • Home CNC Technologies : Jeff Davis's website is not just CNC; follow the Enco 9x20 Lathe link as well as the More Modifications link for a DC motor install.

  • Introduction to 9x20 Lathe Operations : [PDF] An overview of basic operations for the beginning lathe user.

  • Jerry's Metalworking Links : Discussion and downloads related to the 9x20 lathe.

  • Stellar International : The original site no longer exists, but fortunately the site was archived at the link given. Various 9x20 mods and improvements discussed include: Gear Clutch, Chipguard. Dog Clutch, Saddle Lock Lever, Power Cross-Slide, Digital Read-Out, Reverse Tumbler, Phase II QCTP Mount & Rear Toolpost, DC Motor, Hand Crank, Tap Holder, Phase II Flange Nut Lever, Revolving Tailstock Drive, Coolant Pump, Hand Wheels, Tailstock Lock.

  • Smitty's 9x20 Lathe Homepage : Includes modifications, projects, and a useful links page. (Update Feb. 2021 :link is now to archived site)