This video documents the process of machining a 5-pitch Acme thread on a manual lathe as part of creating a replacement spindle for a hard tail vise. Key steps include purchasing and modifying a new right-handed Tool-Flo carbide insert tool holder (MTV-VR) by milling its base to achieve the correct center height on a Precision Matthews lathe. The video details the lathe setup, including setting the compound angle to 14.5 degrees, indicating the tool holder for perpendicularity, and configuring the lathe's gearbox and thread dial. The threading process itself uses a TNMA 54 carbide insert, flood coolant, and a follow rest. Challenges encountered, such as managing burrs that interfere with the follow rest and adjusting the infeed strategy from compound to straight feed for final passes, are shown. Thread depth and fit are checked using calipers and the mating nut. The video concludes with the successful completion of the Acme thread and discusses future steps, including CNC machining of the spindle's ball end and modifying the mating nut.
Machining a 5-Pitch Acme Vise Spindle Thread
0:00:15 Project Introduction: The goal is to machine a new 5-pitch Acme thread for a vise spindle, leveraging experience and tooling (Tool-Flo MTV holder, TNMA 54 inserts) from a previous project.
0:00:55 New Tooling: A right-handed version of the tool holder (MTV-VR) was purchased specifically for this job, complementing an existing left-handed one.
0:01:14 Carbide Insert Advantages: Carbide inserts offer convenience for threading, allowing easy indexing or replacement if damaged without losing thread alignment, unlike regrinding and realigning HSS tools.
0:02:04 Tool Holder Modification: The new 1-inch shank tool holder must be milled down on its base to sit low enough for the insert to be on the lathe's centerline. About 0.175 inches needs removal.
0:02:50 Milling the Tool Holder: The tool holder base is machined using a Walter face mill on a milling machine, taking multiple passes due to the tough tool steel.
0:08:31 Lathe Setup - Center Height: The modified tool holder is mounted, and its center height is verified using the tailstock live center point.
0:09:34 Lathe Setup - Compound & Perpendicularity: The compound rest is set to 14.5Β° (for Acme flank angle infeed), and the tool holder is indicated to ensure it's perpendicular to the workpiece axis for accurate thread form.
0:12:48 Acme Thread Basics: The video explains key specs: 5 TPI (Threads Per Inch) = 0.200" lead. Tool geometry (flank angle, nose width) can be checked with specialized Acme thread gauges. Thread depth is nominally half the lead (0.100") plus clearance (0.010"-0.020").
0:15:31 Fit Verification: The mating nut will serve as the final gauge to ensure proper fit and clearance.
0:15:42 Initial Setup & Test Cut: The follow rest is positioned, DROs/dials are zeroed, the tool is touched off, the lathe gearbox is set for 5 TPI, and a light scratch pass is taken to confirm the pitch with a gauge.
0:19:40 Thread Cutting Begins: Flood coolant is applied, and the first real cutting pass is taken using compound infeed (20 thou depth of cut). A dial indicator is set as a visual stop reference at the thread relief.
0:21:14 Follow Rest Management: Cutting produces significant burrs, which interfere with the follow rest's bronze pads, requiring careful monitoring and adjustment. Filing the burrs between passes becomes necessary.
0:30:35 Infeed Strategy Change: Towards the end, the infeed method is switched from compound angle feed to straight-in (cross slide) feed to ensure both flanks of the thread are cleaned up properly by the insert's full profile.
0:30:58 Depth & Fit Checks: Thread depth is periodically measured with calipers, aiming for ~0.110"-0.120". The fit is tested with the actual nut. Passes are taken (approx 5 thou DOC) until the nut screws on smoothly.
0:35:28 Thread Completion & Finishing: The Acme thread cutting is successful. Final steps involve deburring and softening sharp edges with files, Emery cloth, and Scotchbrite for a finished look and feel.
0:37:55 Result & Comparison: The newly threaded spindle is shown next to the original. Minor chatter occurred near the thread relief but is deemed acceptable.
0:38:43 Next Steps - Spindle: The "meatball" (ball end) needs to be machined on a CNC lathe.
0:39:16 CNC Machining Prep: A custom spindle liner (bushing) will be required for the CNC lathe to support the long spindle and prevent whipping at high RPM due to slight runout.
0:40:13 Next Steps - Nut: The new nut blank needs modification: parting off the threaded section and joining it precisely to the original vise nut body.