Acme Threaded Rod
When you design for ShopNotes Magazine you can’t help but develop an appreciation, even an obsession, for hardware. Not just flashy hinges and knobs, but mundane bearings, springs, brass rod, plastic sheets, cranks, pipes, motors – even threaded rod. There are more bits, parts, and stuff out there than you can believe. (Just sit down with all 3,602 pages of the McMaster-Carr industrial supply catalog. You’ll be amazed. And you’ll be inspired.)
A few years back in ShopNotes, we did a version of an English carving vise that appeared in Issue No. 71. (Editor’s Note: This issue is available as part of ShopNotes Annual Volume 12, a hard-bound collection of Issues 67 — 72.) I have an early prototype in my home shop that I use often. At the time we designed this project, the only reasonably priced and available option for the screw mechanism was to use standard threaded rod. The size I used was 3/4″-10 NC threaded rod. It works well, but you know how it can be if you need to go a distance on regular threads, spin, spin, spin, yawn, spin, spin some more. Standard V- thread is more for sealing and fastening applications rather than quick movement. What I really wanted to use was ACME threaded rod.
So what’s so great about ACME thread? This stuff has the guts you want for strong clamping and it won’t put you to sleep spinning the handle. What sets it apart are the shape of the threads. The threads are large, broad, and square, which provides great strength. And, because there are fewer threads per inch, it offers rapid lateral movement. ACME threaded rod and fittings are available in two grades: general-purpose grade or precision grade.
General-purpose ACME thread has one start, or one continuous thread, the same as standard thread on bolts and screws. Precision acme thread can have up to five starts delivering much more lateral movement per revolution.
General-purpose ACME threaded rod has a looser fit, better for dusty shop environments. Precision ACME threads are made to much higher standards as it’s often used for lead screws in lathes, milling machines, and industrial equipment requiring great precision and durability. This precision and durability can cost 3-4 times as much as general-purpose ACME rod.
General purpose ACME rod is the type we’re interested in. It’s now available through two of my favorite suppliers (McMaster-Carr and ENCO) and priced reasonably enough for projects in the home shop.
Of course, there needs to be something for the threaded rod to engage. Square, hex, and cylinder nuts are available for general-purpose use. Brass and bronze nuts are also available. They’ll travel move lightly than steel, but I find that plain steel hex nuts are the best option as they are versatile and also inexpensive. So, I don’t have to cry over a nut buried in epoxy that didn’t work out.
A few simple design rules. First, when I build any mechanism out of wood, I don’t strive to build with perfect precision. Instead, my aim is to build the structure around the mechanism, altering and adjusting to it to accommodate the movement that I want.
What I mean is rely on accuracy rather than precision. (Precision means building to a tight standard. Plus or minus 1/8″ might be precise for a house. Plus or minus .0001″ might be precise for a wristwatch.) Accuracy is building toward what’s right or true. In the case of a shop made vise or clamp, this means it should work smoothly and effectively.
The second rule is to design mechanical projects from the beginning with a bit of float in them. If it rattles a bit more than you like in winter be satisfied by knowing it will still work fine in the summer.
Finally, just like a powered machine, moving parts benefit from lubrication. In a dusty shop environment greases and oils collect dust, dirt, and other shop grime. So, the best choice is a dry lubricant. There are convenient spray dry lubricants available, but I prefer the old-fashioned paste wax I use on my woodworking projects. Is it the best choice? No, but I always have some around and it’s easy to apply.
“Working tools” such as vises, hold downs, and clamps are great projects for your shop. Not only will you get the satisfaction of using a tool that you’ve made, but, the tool can be built specifically to suit your requirements and style of work. Additionally, there will be a whole new range of things to learn including the strength of individual materials, the strength of assemblies, and principles of simple mechanics. Designing and building tools can be a fun challenge to your ingenuity.
If you decide to build one of these working tools take some time to consider all your hardware options. Even a small upgrade like using ACME threaded rod will make a huge difference in how your project will turn out. Your project will look and work like a “real” tool.
Spoiler Alert: I’m in the early stages of designing a benchtop vise that will possibly appear later this year in ShopNotes Magazine. I’d like to hear what you’d include in the way of design, materials, and features.
James Alguire said,
Tearing out what little hair I have left. I have been a subscriber since issue one of both Woodsmith, and Shopnotes magazine and file(pile) them faithfully. Guess which issue I can’t find? Yep, # 71.
(posted on December 1st, 2009 at 5:38 pm)