Cheap Tool Length Sensor Options

Generally I try and machine a job with a single cutter to avoid tool changes. But recently I have had jobs that needed a number of different tools and so have started thinking about adopting a more streamlined process for tool changing by adding a tool length switch.( I have a touch off puck for setting Z and use the Z zeroing macro in UCCNC).

Proper Uk sourced ones seem to be about £75 (Link)
There are cheap Chinese copies on ebay for around £35-40 (Link)
Though not entirely clear what the compromise is: This guy seems unimpressed but mostly by the waterproofing (not an issue for a woodworker). Where as this guy demonstrates considerable accuracy is available though how 'low cost' his particular model was is hard to guess given the outsides all look alike.

At the more hobby focused end of the market, there are more options
Topcom.cz seem to have some nice products but around £80 (Link)
Stepcraft and BZT have a little one around £45 (Link)
and Carbide 3D do there own Bitsetter but that comes in at over £120! From the Shapeoko forum this appears a popular option even at this price

Then there are things like this on ebay for £18 (Link) which I believe is just a sprung loaded touch plate (but add a magnetic connector to replace the crocodile clip and that might be accurate and safe if switches are the source of cost and accuracy)

Interestingly when I looked at DIY options I came across this guy and he used a £6 metal push button! A high spec, metal 'Anti Vandal" non-latching switch. (Is that what Carbide 3D also use and mark up!)

It became clear the possible selling features of a tool length sensor were:
Coolant proof (Not interested as a woodworker)
Compressed air blow off to clear sensor surface (not an issue if you are manually changing tools)
Overtravel sensor - estops before breaking tool, (seems a reasonable backstop)
Sprung loaded - so it wont break tool immediately giving chance to manually press e-stop
No need to attach earth wire to tool (sensor uses switch rather than contact to ground like my touch off plate)
AND
Accuracy and repeatability........vital yet only looking for +/- 0.05mm, and most low cost products dont make promises

So at the moment I am rather tempted to start at the cheap end and mount a metal panel switch to the corner of my waste board. With the switch between the probe line and ground as normally open to act as the sensor. I don't get over travel protection but then I don't with the touch plate. A further enhancement could be to add an LED circuit to indicate the switch is triggered, givig a moment to react before it goes beyond full travel.

There is surprisingly little about fixed position tool length sensors on the forums (except Shapeoko one). Do most of you manage without? They seem strangely expensive for a switch but then perhaps I am missing something. I've shared what I've found, please enlighten me further please.

Provided the probe is using a reasonable quality switch, switches are generally fairly repeatable.
Plus for woodworking, you generally don't need that high an accuracy.

I'll admit I personally use a mechanical tool setter on my mill, despite having a circuit board made up for adding a tool length sensor, but it does have a toolchanger, so I only have to set tools when changing them in holders.

I probably wouldn't get too hung up on emergency back up switches. Just make sure you have a screen that shows when the switch is actuated, and give it a quick press manually to check it's working before running the automatic tool setting routine.
Sometimes you can overthink things (I know I can be bad for it!), but simple is more often than not more than adequate.

Thanks M_C, having a toolchanger does rather change the game! Your advice to not overthink it is noted. It was my concern that things are more complex than I thought that made me post.

Why on the one hand do savvy builders on this forum appear to have no interest in a tool sensor that can save them so much time when it can be as simple as a £6 panel switch yet the market supports solutions at £50-100 and Shapeoko hobbyists go mad for the benefits and pay £120?

Quote:

---

Originally Posted by Andrewg

Why on the one hand do savvy builders on this forum appear to have no interest in a tool sensor that can save them so much time when it can be as simple as a £6 panel switch yet the market supports solutions at £50-100 and Shapeoko hobbyists go mad for the benefits and pay £120?

---

My spindle is grounded, which seems to also ground my bits, so there is nothing to clip on, and I have a block of cast aluminium which I use as a Z touch off puck on a coiled wire which can reach anywhere on the bed. I do my tool changes manually, and it's really no extra trouble to do a new touch off. Sometimes I even change touch off references during a job deliberately. The time saving (if any) of a fixed probe which would take up usable bed space is of zero interest, because I'm there anyway and it literally takes seconds. In three years I've broken a single £4 Vbit through accidentally driving it into my touch off puck (I got a cable stuck around my hand pendant which unexpectedly drove the Z down and made a whoopsie) so it's not a massive safety issue, other times the tool is strong enough and it just stalls the Z axis.

Soo, yeah, don't see the point. If I had ATC that would be a completely different story.

Quote:

---

Originally Posted by AndyUK

Soo, yeah, don't see the point. If I had ATC that would be a completely different story.

---

Thanks Andy. Having an earthed tool so no crock-clip needs attaching before probing is clearly a huge advantage (I did check, mine isn't). I can also see that the need to travers all the way to a fixed sensor and back is a waste of time that could out-weigh the need to position the probe. You make me reconsider the solution of leaving my touch plate permanently plugged in, change to a coil wire to reduce wire tangles and make a holder for the touch plate so it is safe on the machine when not in use and perhaps replace the tool crock-clip with a magnet so that connect/disconnect is easier. That is even easier and cheaper than wiring in a £6 switch!

Quote:

---

Originally Posted by Andrewg

Having an earthed tool so no crock-clip needs attaching before probing is clearly a huge advantage (I did check, mine isn't)

---

Damn. Did you measure where the continuity ends? Wondering if you could get lucky by connecting to the spindle mount? I'm using one of the Hyangyang 2.2kW spindles from fred, so everything is metallic and unpainted which probably helps.

The main issue is you're not guaranteed to get continuity through bearings, so relying on the spindle to still be in circuit via the bearings could result in problems.

When I built my router, I added an earth continuity wire through each cable chain, connected to the metalwork at each end, to ensure a reliable connection mainly for this reason. I use a normal water-cooled spindle and have never had an issue. I use a small piece of tooling plate on a length of wire as a sensor. I also installed a fixed touchplate just below bed level although it does occasionally get covered by larger pieces of work so can't always be used.

One reason for using both is that sometimes you lose the reference surface after a machining operation which makes it difficult to set the height for subsequent tools. I wrote a few macros to do things like pick up the work reference with a tool, then move to the fixed plate to record that height wrt the work, so I could use the fixed plate for second-op tooling. In practice, it all depends on the kind of work you do - if you use spoil board height as the reference, for example, there's no need for this approach as the reference surface doesn't go away! With a simple "complete the circuit" type of sensor, wiring the two together is trivial.

On my CNC mill, I use a simple 3D probe for height setting of the work or other reference, but also have a bed-mounted tool height sensor. I have added and modified macros to, again, probe work height then find the tool length via the tool height sensor. During subsequent M6 manual tool changes, tool height is automatically set off the bed sensor. Have to say that the two-sensor setup is used a lot more on the mill than the router.

Can't say what make the tool height sensor is, though, as it came with the machine and is unmarked.

Just a thought:- could a proximity sensor work here - Don't know how the tool geometry would affect the sensing distance.

Quote:

---

Originally Posted by AndyUK

Damn. Did you measure where the continuity ends?

---

Well I hadn't, and when I did, it was continuous from frame to tool, (or to acknowledge M_C's point, it was the six times I checked)
Previously I had just tried the touch plate without attaching the tool clip. So now I attached the tool clip to the frame.....and it works! So if I earth the -ve digital input for the probe my touch plate will (almost M_C?) always work without needing to use the tool clip

Not sure where that leaves me though. This might be worth while to streamline use of the movable touch plate. Still looking into suitable retracting or coiled wire to allow me to leave it permanently connected in a holder on teh machine (it is looking for it in the draw that adds the most time)

However it still leaves me weighing up the advantage of a fixed tool length sensor. Feedback here from people like Neale helps in that evaluation. It also helped looking at Ger21's screen set and the macros included for both approaches. If I have a fixed sensor, I certainly don't want to have to trigger it first to check it is working so a switch (With or without overtravel protection seems the way to go. I am now wondering if I can use my cheap panel switch to act as a touch plate by connecting the body to signal and use the switch as over travel protection (in case M_C is eventually proved right)

Thanks for your help

For what it's worth here are some pics of one I made years back for my Novamill.Attachment 31750Attachment 31751Attachment 31752Attachment 31753

Basically laminated from a MS block with an inset magnet, then layers of 12mm epoxy fibreglass (could be e.g. Corian). There is a machined cavity inside which contains a stainless steel slug at the botton (insulated from the base), then a strong spring, then a 12mm square carbide insert as a hard anvil. Most of the layers are glued with epoxy but the top is bolted on to allow assembly. The slug has a hole drilled from the side for a 4mm banana plug to connect to the probe input. It fits to the table with the magnet, and the top face of the anvil is measured at 38.84mm above the table surface which is input as the setting plate thickness. As the Novamill table is small I generally just place this for setting the tool then take it away, with a bigger table it could be left in one place. The spring has a few mm free travel to reduce the consequences of a tool crash. Of course it depends on the tool being grounded. Total cost negligible as made from the scrap box.

On my lathe I have a rather different system to do an equivalent job which is to find the end of the stock in the chuck and zero the z axis. That's another story, it still relies on electrical contact between tool and work but senses that magnetically.

Thanks John, nice solution for a real engineer. As a woodworker I need to buy or assemble from purchasable parts.

Coincidentally I noticed from another reply you are based in Cambridge UK, like me.

FWIW, My probing routine requires me to touch the plate to the tool to initiate the process. I touch it against the tool and then it pauses for a few seconds, then the machine proceeds to move downwards. This, hopefully checks that there is a working connection.

I'd always recommend testing the probe prior to any automated probing routines.
If you're manually changing a tool, then you're already at it, so for all the time it takes to trigger the probe/touch the plate against the tool, it ensures things are working, and eliminates the risk of a broken wire, or more likely, you've forgotten to plug it in :whistle:

If you fit a "loop back" connection within the probe plug, you can detect if the probe is(n't) plugged in and inhibit probing moves. Requires an additional input but equally it reduces the risk of a crash. Some probes also have a secondary (overtravel) switch that you can wire into the e-stop circuit in case the probe connection doesn't work.