Easy DIY CNC Workholding Clamps

Photography by Andy Lee
With every CNC router, strong and secure workholding is critical for a successful job. At Sienci Labs we’ve tried many designs, and created these universal clamps to be easy to use and make on any CNC router.
The goal for these designs is to allow folks to make their own clamps using cheap and easily available materials. For these projects, you’ll need plywood, ¼-20 fully threaded hex bolts of various lengths, ¼" washers, and ¼-20 threaded inserts. Depending on the T-track you have, you may need T-bolts that fit as well, but if you’re looking for a T-track for the first time, I’d recommend finding some that have a profile that fit ¼" hex bolt heads instead.
I’ve designed the clamps to use 11mm or ½" plywood because these are easiest to come by, but if you want to use other thicknesses, the Onshape design documents (hold down and toe clamp) are publicly available and can be adjusted to the materials you have on hand by changing the #thickness
variable in Part Studio in Onshape.
General Cut Settings
All of these clamps can be milled easily on a CNC machine and assembled by sliding the parts together. While the downloadable designs are made for 11mm and ½" material, variations in the thickness of your material may affect how well parts slide together. For the most accurate fit of parts, I recommend measuring your material’s thickness with calipers, then using that thickness plus 0.1mm on the #thickness
variable in Onshape. That being said, some gentle persuasion with a mallet will usually do the trick as well.
Everything is designed to be cut with a 1/8" bit, as that’s what I’ve added reliefs for the radiuses on the inner corners for. Here are the DXF, sample G-code files, and other design notes.
These are the settings I’ve used to cut these parts out:
- Feed rate: 2000mm/min on the X and Y axes, 300mm/min on the Z axis
- Depth of cut: 3–4mm per pass, with the last pass being set to cut 0.5mm
- Spindle/router speed: Around 20,000RPM
- End mill: ⅛" downcut 2-flute end mill
If you want to get the cleanest-looking cut, a downcut bit will work well and a compression bit will work even better.
For the sake of accessibility, these designs have been made to work with ⅛" bits. But when I make slot-together projects, I actually generally use a 1/16" corncob bit because:
- It leaves a fairly clean top and bottom edge
- It has a thicker overall body, which makes it less prone to breaking than a fluted 1/16" bit
- It leaves most of the dust in the cutting path, so most of the time I can get away without needing tabs or other methods to keep the piece from flying out
- Since the radius is pretty small, a relief on the inner corner radius isn’t necessary for parts to fit together, and
- The cuts are thinner, so it also makes less dust and waste overall.
Since ⅛" straight bits are almost ubiquitous, I’ve just made the designs work with those, but if you can get some 1/16" corncob bits to experiment with, I highly recommend it.
Hold-Down Clamps
Hold-down clamps are versatile and simple to use. This design is unique as it uses a rounded support at the back to allow for the right angle to apply downward pressure against your material. The optimal angle for securing your material is at a level or slightly angled down position. Based on the thickness of your material, simply flip the clamp upside down to use the side that offers the most optimal angle.
Since these clamps are made of wood, even if you have a bit of an “oops” and run into them while carving, you’ll minimize the damage to the machine, and since you can make them on your CNC, you’ll basically have an unlimited supply!
Tips:
- Threaded inserts are super handy in adding threaded holes to wood. Simply fit a hex head driver or Allen wrench into the top end of the insert and screw it into the pilot hole.
- The knobs and the semicircles are prone to flying out after cutting, so I recommend milling them a little slower on the final pass than you would on the body of the clamp.
- You’ll need different length bolts to accommodate different thicknesses of your project workpiece, but I’ve found that 1½" and 2" bolts are suitable for most applications.
- If you make the toe clamps in the next part of the article, make sure to make extra knobs as you’ll need them there too!
Toe Clamps
If you don’t want to have clamps in the way of the top surface of your material, toe clamps are the way to go. By pushing in from the side, they stay away from the top of the material, and by angling the force downward, they’re able to keep the material from lifting up as well.
This clamp must have a hard stop for the other side of the material to butt up against. I’ve also included some designs for corner stops that can be bolted to a T-track table, but any solid stop for the material will work fine.
Tips:
- If your clamp can’t get close enough to your material, try using scrap blocks to fill the gap. This can also help if your clamps are getting in the way of your spindle or router.
- Watch out that your clamp doesn’t slide away on the table when you turn the toe knob. Because of the mechanical leverage you get in the screw, the amount of force you’re putting on the material may be enough to slide away the clamp as well.
Final Thoughts
I hope you find these designs useful as a starting point in building up your CNC workholding arsenal! Since these designs are freely open for you to use and modify, please feel free to make changes to the original design to make improvements and fit your needs.
Designing in Onshape
Onshape offers a free, hobby and education use license for full functionality of their program on the cloud, with the exception that all projects made on the free plan are public and searchable. This means that derivatives of these designs will also be available to the public.
To modify a design, you’ll need to create an Onshape account and duplicate/copy a new version to make changes.
Most CNC users will likely want to export all of the parts as DXFs. This is a very easy process. Simply right-click the side of the model whose planar faces you wish to export, and select Export as DXF/DWG. Then import the vectors into your CAM software.
Visit cad.onshape.com/help/Content/exporting-files.htm for more detailed information.
This project is from Make: Volume 85.

Facts Only

* Clamps are designed for use with CNC routers.
* Materials required include plywood, ¼-20 hex bolts, ¼" washers, and threaded inserts.
* Designs accommodate 11mm or ½" plywood, with Onshape documentation allowing adjustment for other thicknesses via the #thickness variable.
* Milling is suggested with a 1/8" bit, with reliefs added for inner corner radii.
* Recommended feed rate is 2000mm/min on X and Y axes, and 300mm/min on Z axis.
* Depth of cut should be 3–4mm per pass, with the final pass set to 0.5mm.
* Spindle speed is around 20,000RPM.
* The author suggests using 1/16" corncob bits for slot-together projects instead of standard ⅛" bits.
* Hold-down clamps use a rounded support at the back to apply downward pressure.
* Toe clamps are designed to stay away from the top surface of the material when force is applied from the side.

Executive Summary

Designs are provided for creating universal clamps for CNC routers using readily available materials like plywood. The designs facilitate making custom workholding, requiring materials such as plywood, ¼-20 fully threaded hex bolts, ¼" washers, and threaded inserts. The designs can be adapted for different material thicknesses by modifying a variable in the Onshape design platform. Milling settings are recommended using an ⅛" bit, with specific feed rates, depth of cut, and spindle speeds provided. The author recommends using 1/16" corncob bits for slot-together projects due to advantages in edge quality, body strength, dust management, and material removal efficiency. Hold-down clamps feature a rounded support at the back for optimal angle application, and toe clamps allow workholding without obstructing the top surface.

Full Take

The content functions as an accessible, practical guide for bridging the gap between theoretical CAD design and physical CNC fabrication, focusing heavily on material interaction and process optimization. The pattern observed is a structured delivery of specialized knowledge—specific hardware requirements, nuanced milling techniques, and material handling tips—all framed around empowering the user to create functional tooling rather than simply consume finished designs. This approach leverages the authority derived from specific procedural details (e.g., feed rates, bit selection) to establish credibility while democratizing complex engineering concepts. The implicit implication is that mastery in CNC workholding stems not just from geometric modeling, but from understanding the physical constraints of the materials and tools. The shift toward advocating for alternative tooling (corncob bits) suggests a challenge to conventional industry standards by proposing practical alternatives based on superior material interaction and reduced waste. The core tension lies between the generality of the design files and the specificity required for flawless execution across diverse user setups, pushing the reader toward active, iterative application rather than passive acceptance of digital files.
Bridge Questions: What are the limitations in the design documentation when applied to exotic or extremely thick materials? How can the concept of "optimal angle" be mathematically formalized outside of empirical trial-and-error measurements? Does this emphasis on accessible tooling inadvertently create a new standard that bypasses established, potentially more rigorous, industrial standards for workholding?

Sentinel — Human

Confidence

This text reads like an experienced craftsperson providing detailed, practical advice for a specific technical project, blending theoretical design with empirical machining experience.

Signals Detected

Erratic sentence length and highly specific, practical technical vocabulary interspersed with informal instructional tone.

Clear, goal-oriented exposition of a practical DIY/engineering process, marked by necessary caveats (e.g., material thickness variation).

Structure flows logically from general necessity to specific tool settings and then to component details, suggesting deliberate instructional writing.

The inclusion of highly specific, context-dependent recommendations (e.g., using 1/16" corncob bits vs. 1/8" straight bits) that reflect direct user experience is difficult to generate without prior domain knowledge or real-world testing.

Human Indicators

Use of highly specific, nuanced advice regarding material handling (plywood thickness adjustments), cutting tool selection (end mills vs. corncob bits), and mechanical tolerances demonstrates practical, experiential knowledge.

The narrative shifts tone effectively between design presentation, machining settings, and tips, exhibiting a natural flow typical of an enthusiast sharing a project walkthrough.