After finishing the dovetail grooves, I started on workholding and clamps by designing and 3d printing some dovetail inserts and knobs.

Dovetail fittings and knobs

I tried a few different bolts, but settled on 40 and 50mm M5 hex bolts. Any longer, and I have trouble clearing them with my router (and extra spoilboard).

For clamping taller blocks, I can counterbore them to recess the clamping knobs into the material a bit, and this helps keep the clearance height down a bit.

The inserts and knobs went through a few iterations.

The inserts got a little smaller in width, so that they can slide in the dovetail grooves more easily, and a deliberately undersized nut diameter so that the bolt heads fit tightly in them, instead of being easily pressed in.

Most recently, I also made them a little bit shorter, so that I can surface the spoilboard a few times, but also to make sure that when clamping they don’t press directly against whatever it is I’m clamping, causing them to slide even when clamped tightly.

These are not perfect though. With tight clamping, these get stuck in the MDF. I’m not sure if the MDF is getting deformed and snapping back when pressure is removed, or if the layer lines in the 3d print are kind of biting into the MDF surface, or if they’re getting jammed by rotation.

After clamping tightly, I usually have to uncscrew the knobs, pull off the blocks or cam clamps, and then poke the inserts back into the slots with a screwdriver to free them up. I’m not sure how to solve this yet. I’ve tried a few variations so far.

• Sanding and polishing the inserts so that layer lines are soft and smooth
• Increasing the taper of the inserts, so that they’re tighter toward the bottom of the slots
• Rounding the top of the inserts so that the edges are less likely to gouge in
• Adding reliefs in the sides at 10 and 4 o’clock, so that they’re less likely to get jammed by rotation.

I haven’t notice any difference with these though.

Stop blocks

I started by just drilling 5mm holes in random bits of scrap wood. This works fine with enough lateral and downward pressure but quickly realized they work much better if they’re a little taller than the material being clamped, and also have a slight 15° bevel on them to help keep the material down. Seems obvious in retrospect.

These I just cut on a table saw, and then drilled a hole roughly in the center.

Cam clamps

These are simple spiral-shaped cam clamps that apply sideways pressure, but won’t hold anything down.

I cut these from 3/4” plywood, and they work great.

Round cam

The above picture also has my first pass at a round cam clamp, cut from scrap redwood. This one is one inch thick and has the same 15° bevel on it to help hold work down. Before cutting it, I drilled two holes through it surface and held it in place with flange nuts rather than clamping.

This was roughed with a 1/4” square endmill, and then finished with fine passes with a 1/4” ball endmill. This could have been made much easier and faster without the CNC, using a bandsaw and an a tall bevel bit, but I don’t have either.

Here’s what it looks like in use.

I refined the shape a bit, so that it has a smooth spiral from beginning to end, instead of having some lost space around the perimeter that can’t be used for clamping, and cut a new one from 1” plywood (really two 1/2” sheets sandwiched together).

Instead of bolting through it, I modeled tabs for it manually in Fusion.

Low profile clamp

One issue I’m having with these styles of clamp is that they have to be taller than whatever I’m working on to have any holding power (at least downwards).

I’m experimenting with low profile sliding clamps, and just finished designing and assembling this one (a rebuild of one I found on thingiverse to fit my hardware).

This uses a M5 18mm socket screw (I’m really using a 16mm but it’s a little short) for the sliding part, a M5 16mm screw to hold it to the dovetail insert, and a couple of 5x25mm steel dowel pins.

It holds fairly well, but I haven’t tested it thoroughly yet. It may not be better than any other side clamp, especially since the “teeth” are quite dull.

Files and downloads:

• Dovetail inserts and knobs
• Cam and circular clamps
• Low profile clamp

Some minor site updates (once every 5 years, whether its needed or not, imo).

Added pagination, because all of the posts on a single page used something like 84mb in images.

Added a projects section to track larger/longer term projects chronologically.

The stock spoilerboard included with the MDF version of the Mega V uses t-nuts for workholding, but they’re pretty sparse to begin with (example here)

I knew that I wanted to add a supplemental wasteboard that could be surfaced and replaced easily, and started looking for other options.

From what I can tell, the most common options here are:

• No special workholding: Screw, glue, nail, or even plastic pin nail in your pieces and/or workholding devices directly into the spoilboard. This means that setting up the wasteboard is easy and inexpensive, but it does suffer some extra wear.
• T-nut and holes: Pretty easy, plenty strong, not too expensive.
• Aluminum t-track slots: The track is fairly easy to set up, but does require some extra t-track hardware, as well as the tracks themselves. The board between the tracks can use strips, allowing better use of large material sheets.

I was planning to use aluminum t-tracks, which were only marginally more expensive than the t-nuts, but stumbled on a couple of examples of using dovetail grooves instead:

• https://wiki.shapeoko.com/index.php/V_slot_bed
• https://www.thingiverse.com/thing:3728184
• https://www.reddit.com/r/CNC/comments/fhftb9/my_spoil_board_work_holding_jigs/

These slots have a couple of cool features. They’re cheaper (depending on what you use for fixture hardware) and allow for very dense workholding, in any direction, at any spacing.

They do have some (significant) disadvantages though, some I recognized during planning, and some only later.

Disadvantages

Tearout

When using these grooves with MDF wasteboard, you must, 100% of the time, use clamps which press directly against the wasteboard surface at the clamping point, or the MDF can absolutely shear out. I was easily able to tear out an entire 4” square section by hand with the clamping pressure spread away from the slot. This eliminates many of the most common types of clamps.

Available space

I’ve reduced my available space a few ways with this board. First, by putting another 3/4” board on top of the existing wasteboard, I’ve lost a pretty good chuck of my machinable Z height. I’m already planning a new stock and secondary wasteboard to reduce the height.

In order to route the slots with the CNC itself, using a 1/2” dovetail bit, I needed a little clearance on all sides for the bit to enter and exit the edge of the board, so this reduced my X and Y range as well.

Lastly, I wanted the router to overhang the end of my spoilboard a bit so that I can (hopefully) cut dovetails in upright stock, so I slid both spoilboards back a couple of inches, which reduces the Y range a little more.

Resurfacing

I have a bit of extra room, but I’m limited it how many times, and how deeply I can resurface my wasteboard before the inserts no longer fit correctly. I can reprint them easily when that happens though.

Ease of use

While these can be easy to set up, they rely on a pretty good fit inside the slot. This means, though, that they’re harder to get in and out when the slots fill up with chips.

They get stuck

More on this later, still trying to figure it out, but I often have to unjam these from the slots after use.

First attempt (spoiler)

First, I cut a section of MDF, a bit oversized, and temporarily fastened it to my wasteboard using drywall screws around the outside edge. I really want to find a better fastener for this but haven’t yet.

Then, I set up some operations in Fusion 360. First, I surfaced the area of the wasteboard that the CNC could reach, enough to take care of any real high spots and/or warping. This also showed just how out of tram my router was, with a huge nod forward. After some investigating, most of this nod was coming from badly off-square router mount. Once that was shimmed back to square, there was enough play at the router to get it close to trammed using a simple tramming tool.

Then, using a 90 degree chamfer bit, I made some spot markings for the holes that would fasten the new spoilboard to the stock one.

These I then hand drilled, deeply countersunk, dropped some CA glue into for a little more longevity, and finally fastened down.

I then ran a 2D contour toolpath to cut the excess MDF free and removed the temporary screws.

After the wasteboard was fastened and cut free, I made some relief cuts for the dovetails just under the final depth with a 1/4” downcut endmill, and then ran the dovetails in the same slots.

Here I had some trouble, and had to start over.

First, with the relief cuts and dovetails, the MDF wanted very badly to curl up. Some of my screws were around 5” from the edge of the board, and that was enough for it to want to lift.

Secondly, somewhere along the way, I lost some steps in the Y direction, and a couple of my dovetail slots were both the wrong shape and size (due to them not being centered on the relief cuts).

Second attempt

I went back to fusion and moved the screw holes around. I increased the density of the screws, and made sure they were fastened close to the edge as well.

Since the process of manually drilling these was such a pain, I also set up a toolpath to bore these down to final depth instead of just marking them, leaving me to only need to countersink, drill, CA glue, and screw each of them, which was still a pain, but one step fewer.

Afterward, I ran through the same steps as before. I’m not sure when the missed steps happened. Maybe I crashed something. At any rate, I didn’t end up with any missed steps for the second attempt.

I also took the time to set up an extra toolpath to cut beveled openings in all of the slots. It was really satisfying to see these run successfully.

After assembling the Mega V, I ordered some endmills and MDF for a supplemental wasteboard, and while waiting for those to arrive, I made a few pen holders to get a feel for the machine and sotfware.

For software, I settled on CNCjs because I had a spare raspberry pi available, and it’s open-source and easy to modify.

I’m currently connecting to it with my phone, but have tried with an old android tablet with mixed success.

For small touchscreens, this pendant interface is probably your best bet: cncjs-shopfloor-tablet. It features a simplified interface designed for touchscreens, making it harder to crash while jogging with tiny buttons (though I’ve still managed to).

Pen holders

I ziptied a sharpie to the router first. This kind of works, but since I hadn’t surfaced my spoilboard yet, and it’s a bit warped, the pen can’t follow its contours. Heres what slowly destroying a sharpie looks and sounds like.

To add a little more flexibility (and because I was still waiting for endmills), I modified a design for quick release router mount to allow for some modular attachments, and then started iterating on pen holders for it.

And here it is with a small bracket to hold a sharpened nail (I used it to measure and calibarte motor steps).

Pen holder the first

This one is very simple. It uses a collar with a set screw to keep the pen from sliding out, and a cop with a slot to hold a rubber band for tension. The pen can move up and down a bit in case of uneven surfaces, and getting the heigh zeroed out exactly isn’t critical.

Here it is running some gcode. I generated the paths for this by passing a photo to blackstripes, and then importing the SVG into Fusion 360 and then running a contour toolpath with no cut compensation.

This pen has a bit of a taper though, so the holes that guide it are a bit oversized, and this causes pen backlash when drawing.

Also, lots of little dots without much sideways movement prevents the ink from flowing a bit. I’d want to find a way to easily skip paths under a certain minimum distance.

Pen holder the second

To reduce some of the backlash, I used a couple of bolts with smooth shafts to guide a pen assembly up and down, without relying on the pen’s diameter. I also tried adding a bit of an angle to the pen, more in line with a natural writing angle. However, this applied a lot of friction between the bolts and the 3d printed plastic when pressing down due to the torque it applied, and the pen got stuck very easily.

Pen holder the third

I reused the sliding base for this one, but turned the pen back to straight upright, so that it can slide up and down more easily.

This gave the best result so far, but you can still see some of the play in the system as it “flicks” back into position at the end of each line.

Here’s a comparison of the line quality

Next steps

The issue with this last design is that it both relies on a tight fit between the sliding plastic carriage and the bolts, but is also hampered by any friction there. To reduce play, these holes should be as tight as possible, but then pen won’t be able to move up and down smoothly.

I’ve purchased some teeny, tiny linear rails and will attempt to replace the moving components of this last design with them instead when I get the chance.

Files

Files can be found here:

• Modular quick release router mount
• Nail holder
• All pen holders

I preordered the Millright Mega V CNC router in October, and it feels like I should write something about it.

I have a small workspace in the corner of my garage, so naturally I ripped out most of it to make room for the 35” machine instead of something smaller and more practical for my space.

When I bought it, it wasn’t scheduled to ship for a few months While waiting, I took a stab at a basic table design to keep the machine at a comfortable working height, and to allow some storage for tools and dust collection.

This is a very simple 2x4 and 4x4 box (in line with my woodworking ability), with a plywood top and MDF sides. Eventually, the front will have cabinet doors, and the top will be enclosed with a hinged lid to keep the sound level down.

I went back and forth about putting the whole thing on casters, whether they should be raisable so that the box is sitting on solid wood when stationary, how much the box and table would weigh, and most importantly how well they could be used with the table tucked into a corner when only of the feet/casters might be accessible.

Eventually, I settled on these: https://smile.amazon.com/gp/product/B07V1NTLDP

They work well, but are difficult raise and lower once weighed down. I’d like to replace them but haven’t yet found an alternative.

Parts arrive

Got all my parts. I think I was missing a couple of screws, and there was a little shipping damage to the MDF spoilboard

I put together what I could before building a cabinet for the CNC but it didn’t take long.

Table assembly

I started building the table right around the time of my state’s stay-at-home order. I let my local big box store select and deliver some of the worst warped, cupped, and twisted, wet wood, I’ve seen. It was still cheaper than my local lumberyards (by a lot) but quality isn’t great unless you can spend time picking through their stacks.

Mega V assembly

Assembly was easier than I expected, largely owing to the prebuilt control box. I think the longest part was just running cables through the cable chains.

There are some issues getting the Mega V set up that I (and other people) have run into, that I wish I’d known about when I started.

Instructions

At the time of building (and writing), the assembly instructions are limited to two assembly youtube videos. They’re not bad, but some sections are not clear, or slightly out of order (esp related to the endstop switches) and in general it’s a pain in the butt to watch video, pause, assemble, rewind and repeat, when written instructions with diagrams would have been easier in most cases.

Bearing insertion

The instructions call for hammering these into the v-wheels. I found it was much easier to use this 3d-printed bearing press. I printed this ages ago, and I use it for all kinds of things now. This may be be the first time I’ve used it to press bearings into something though.

Wiring

There are a couple of issues I ran into and have seen other people mention regarding the wiring, particularly for the endstop switches. The crimped connectors are low quality and badly crimped, and the wires themselves are going to be too short to reach the control box when routed through the drag chains as instructed (at least on the 35” model).

The solution to both of these is to rewire them. I ended up running new wire for one and resoldering the aviation connector, and then just spliced an extension onto another.

Rack and pinion meshing

This isn’t really an issue with the machine, per se, but there doesn’t seem to be a good way to determine whether the rack and pinion meshing on the X and Y axes is correct, or correct enough. It’s easy with hand pressure to warp the rack slightly where it’s fastened to the aluminum extrusion, and the gantry can lock up or miss steps.

Router mount squaring

I’ve heard that the aluminum router mount is waterjet cut, instead of machined, but can’t speak to that with any confidence. What I can say is that it was somewhere in the neighborhood of 89° when I measured, causing the router to nod further forward than I could adjust anywhere else to compensate. I ended up taking apart my Z axis and shimming the mount using shim stock.

You can save time by getting this close to square to begin with before fully assembling the Z axis, and/or reshaping the mount where it bolts to the Z plate if you have the tooling.

Done

The bulk of the assembly was pretty easy, just going slowly and carefully.