I had some keyboard switches left over from a previous project, and wanted
a more convenient process for changing bits during a job.
This is a simple switch, wired in parallel with my touch plate, that is used before and after changing router bits.
When changing a bit, a macro offsets the Z height by the difference between the first and second tool length, and
work can continue with the new bit.
This process is much faster than manual zeroing after changing bits, or using the touch plate. The tool can overshoot the switch’s trigger
position slightly without damage, so the probe speed can be much faster than a touch plate, and it doesn’t require connecting the probe clip.
Additionally, if the original zero position has been carved away by the previous job, the tool setter can still be used.
It’s promising, but has some issues.
First, it has moving parts exposed to cnc dust and chips. I added a magnetic cover for it to help with that
Second, though it’s much lower profile than commercial options, it’s just about flush with the surface of my wasteboard. For surfacing, when I’m cutting off the edge, I’ve been pulling the
cap off and taping it down. I’m planning to move it out in front of the wasteboard instead.
Third, repeatability isn’t amazing (around 0.02-0.04mm) because the 3d-printed button top I’m using isn’t a perfect fit on the switch,
and the switch has some play as well. I’m looking to replace it with something with less play, but haven’t found the right thing yet.
To drive the CNC, I’m currently using CNCjs, installed on a Raspberry Pi 3b+.
The system is currently headless, because I don’t have a dedicated laptop for it, and my CNC lives in my garage where it’s too cold to leave an LCD screen.
CNCjs is fine, and a good fit for this use case, but pretty clunky on a small screen, and lacks some of the features available in other gcode senders, like autoleveling, basic gcode generation for simple operations like facing, cancelable jogging, angle deviation probing…
I find jogging via the default web interface really uncomfortable. It’s very easy to hit the wrong button among the tightly packed buttons, and do something bad, like rapid moving to zero when things are in the way. I’d like to say I only did this once, but…
The other issue with jogging like this, particularly with a small screen is that button presses may be queued, and delayed, and then may execute in series unexpectedly. There’s also no real way to quickly cancel dangerous moves.
I saved myself some pain by enabling soft limits in GRBL, but I need to tune these better.
For small screen use, there’s a much better interface at https://github.com/cncjs/cncjs-shopfloor-tablet, which I used for a little bit. It too has some issues; It’s much better suited to a tablet display than a phone, and you cannot run macros from it.
I started down the path of making the interface more responsive, but stopped using it before finishing.
I also ran into this issue which drove me crazy for a few days before discovering that, if I left the interface open on my phone, and the phone went to sleep, whatever job was running would halt.
To transfer gcode from my machine to the raspberry pi, I’m currently using https://github.com/efeiefei/node-file-manager
to upload the gcode to the CNCjs watch folder. It would have been easy to set up network shares for this also.
I’ve also written (hacked together) a utility to upload gcode files to node file manager, as well as opening them in my default editor, and have set this utility as my Fusion 360 editor.
Now, these are automatically uploaded after post processing.
It now uses node-hid like cncjs-pendant-keyboard so it doesn’t require focus,
and works with the Logitech K400 plus.
I have it set up to jog on X and Y with the arrow keys, Z axis via I and K in 0.1mm increments.
Ctrl + direction will move 10mm at a time. Alt + direction will move 1mm at a time. Shift + direction will move continuously in that direction until shift is released.
Ctrl + H will home the machine.
I’ve also added a few macros via keyboard:
Ctrl + P will run an XYZ probe Ctrl + Z will just run a Z probe Ctrl + 1 will initialize the bitsetter for the first tool Ctrl + 2 will use the bitsetter for tool changes Ctrl + Shift + Return will continue after pausing for toolchanges.
With an easier setup for jogging, I’m only using the default CNCjs interface on my phone to start jobs.
Eventually, I’d like to replace the keyboard with something more specialized, but most of the commercial ones I’ve seen aren’t compatible with GRBL.
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.
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.
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.
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.
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:
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.
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.
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.
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).
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.