Touch Off Light for my Probotix CNC

No touch off plate came with or is available for my CNC (yet).   I've been using a piece of paper to set my Z axis origin height. I put the paper under the bit, then slowly (.005") step it down until the paper is trapped. Set Z at 0 there then lift up to remove the paper. Paper is generally from .0025 to .005" thick so I know I'm within .005 using this process.

A Probotix.com User Forum member KLWestfall posted his idea of using a light bulb, thin metal plate, and an alligator clip to signal when Z has touched down.   That idea intrigued me so much I knew I had to make my own version.

I went to my local Radio Shack (which sadly has now closed down thanks to internet competition) and picked up a battery case, 3v green LED bulbs, and some AAA batteries to go with the unused touch puck and alligator clip (Link) I've had for awhile.

I drilled a 5mm hole in the battery case for the LED, then wired the LED in line with the batteries and contacts. Now the LED glows when the plate and alligators touch.

To use I clip to the router bit and place the plate underneath it atop the material I'll be cutting. I jog the bit to within 1/8" or so of the disk, then set my step increment to .005".   I'll then step down until the LED glows. I'll move up one .005" step, then reset my increment to .001".  Now I step until the LED glows again, and I know I'm within.001" of the top of my material.  I've carefully measured my plate.  I enter that value when touching off Z in LinuxCNC.

This solution isn't as automated as it could be if the touch plate was wired into my CNC controller, but so far I haven't found any info on how to go about that.  The LED that glows on contact will be more accurate than using paper was. The led is easy to see from back at the keyboard/PC station and makes it easy for one person working alone to handle setting Z.

The only problem to this point was that my touch puck wasn't consistently thick.  I had my CNC mill a hole to tightly fit the metal disk. then press fit my puck upside down in that level (to the CNC) hole. I had the CNC mill a flat plane across the plastic bottom of the puck to make it uniformly thick.  The photos here show a simple bar of aluminum used for the touch plate,  The numbers on the battery box remind me how thick the plate is.

If you don't have or want to buy the puck I linked to, then any small chunk of conductive metal and an alligator clip lead can be used. You'll need a way to hook one wire from the battery case/LED  to the plate, then solder the other wire to the alligator clip.  I drilled a 5/32" hole in my plate and used a speaker plug inserted into it to connect from the battery. I was inspired by how the touch plate for my CNC Shark connects.

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Simple Overhead Camera Rig

Inspired by several videos I've seen on YouTube, I thought I'd take a crack at making a simple rack to hold my camera vertically above what I want to photograph or video record.

My solution has as few parts as possible.
It maximizes the structural interaction between all parts.
Mount/dismount of the camera is quick and easy.
The camera position adjusts up or down, and left or right.
The camera stays plum above the base on its own.
The base of the rack minimally imposes on the surface it sits on.

Material I already had or acquired quickly:

- Salvaged, white painted metal pipe from an abandoned tent kit. 29.25" long and .625" diameter.

- 1/4-20 x .75 knobs bought from Amazon.com.  These knobs arrived 3/30/2016 and are all metal with knurled rim.  Nicer than I was expecting them to be for their low cost.

- Lighting is yet to be determined.  I've started with the LimoStudio Photography Light Set from Amazon.  These come with their own stands.

- Two vertical posts.  Strong/stiff connection to overhead pipe. 36" tall.

- Two feet for the vertical posts.  Just enough to let each stand securely on their own or together.

This rack disassembles easily, relying on gravity and clever joinery to stay together when in use.

A quick inspection of my lumber supply reminded me I had some 1" x 2" hard maple scraps that are long enough for the posts and feet. Already rounded over on two corners, so that was considered when planning the joints/connection to their adjacent parts.

With a little testing, it turns out a hole that the pipe fits snuggly into is all that is needed to hold it there.  For joining the posts to the feet I drew up and cut a 4-tenon joint. Although the tenons were tight in the matching mortises I cut for them they did go together.   So far "simple" is where I remain.

I drew up and used my CNC to cut out this vertical camera hanger bar.  I had a pretty crappy looking scrap of 1/2" Baltic Birch plywood which was big enough to use for this part.  Scarred as it is, it will still do the job fine. The stepped hole was perhaps not my best idea, as it requires completely unscrewing of the top adjustment bolt to raise or lower the camera. The initial conceptual advantage is 1/8" stepped height adjustment, and once the bolt is in place, even loose, it won't slip down.

The final part is a bracket to hang on the top rail. I had a 1/4-20 t-nut for the camera slide to bolt into. My idea for front to back adjustment for plumbing the camera works, but there may be a simpler more useful solution in this rack's future.  I should have added a little tolerance between the fingers and the slots between the back plate and the side plates of the bracket. They went together under duress, requiring a heavy hammer and a bench vise.  While I enjoy using this finger joint I can cut on my CNC, a simpler rabbeted edge in the oak into a slot in the plywood would have been a fine way to connect this oak backplate to the plywood sides.  Expansion/contraction of the oak part may lead to self destruction.   Time will tell.  These are the scraps I had available to use.

Putting it all together and adding a photo camera reveals two mistaken assumptions I made.  First, the balance point was closer to the inside than I expected.   I left enough adjustment room to get the camera to hang vertically, but having added that adjustment the camera now will swing like a pendulum  with any breeze or slight bump.  Pressing any button on the camera gets it swinging.

A rubber band provided a simple way to clamp the current bracket to the pipe,

I noticed that my current camera has an HDMI output.  It requires a  mini HDMI-to-HDMI cable which I don't have, so I ordered one from Amazon. I have a spare monitor with HDMI inputs so I'll see if the camera shows real-time video out that cable when on.  It would still be nice to have a remote control for it though.

The tendency to swing when bumped I have now minimized by wrapping a couple of rubber bands around the pole and bolt head.

The digital 8 video camera I have also mounts fine on this rack.  It has the same 1/4-20 tripod socket as almost all photo and video cameras have. Larger than the previous photo camera I tried it needed the top bracket slid to its outmost point of balance to hang the camera vertically.  I found I could keep it in that position using a rubber band wrapped around the pipe and bracket.  With its own pivoting fold-out viewfinder screen I don't necessarily need to run video to a larger monitor.   I'll see if it works with the TV I already have though.   I'll have to find a video cable that works with both the camera and the TV.

I've got a wireless remote controller that works with this video camera.  Using it should eliminate wiggling the camera to start and stop recording.  I will have to order a more modern video camera that doesn't use 8mm tapes. It is a pain to rewind and copy video files to my PC.

Update:  I now have added LED lights to the posts, one on each side. Info on the brackets I made to hold the lights is ( here ).

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Advanced Compound Angle CNC Clamping Fixture.

The need to clamp parts beneath our CNC router at an angle or compound angle has increased each semester as more and more of my students realize the potential of our CNCs.  I had previously designed and built a simple angle clamping jig to fit between the rails of our Meteor CNC.  This worked, but was difficult to install and align.  It also would flex in the middle when heavy boards and clamps were hanging on it.

I came up with this advanced fixture only after seeing the weaknesses of my original design and contemplating how to solve those issues over several months.  Components of the final solution came to me slowly.

My first realization was that bolting the jig into the TOP of the frame members would be far easier than bolting into the inner side of them.  I made a few small prototype angle clamping jigs to prove my assumption, and they are indeed easy and quick to install.

Using the front rail (rather than both side rails) to clamp the fixture to was my second "aha!" moment.  The front rail is always parallel to the gantry, so using it would eliminate any need to "square" this fixture when installing it.

Setting and holding the jig at the desired angle was the third challenge.  Locking the fixture angle needed to be quick and accessible. To measure the fixture angle we use a magnetic digital angle gauge attached to a metal bracket that hangs on the fixture.   Locking bolts hold the bar securely in position once the angle is shown on the gauge.

This version has connection ribs that extend in an arc beneath and behind the jig.  A handle/bolt through this arc into nuts embedded into side plates permit easy locking of the angle.  All photos here are of my personal version.

I have since replaced the knobs that tighten the fixture with cam levers. Quicker to lock or release to adjust the angle. 

Cam Levers VS Twist Knobs

First cuts using the jig happened this day. A student project needed a slot cut through the two end boards of a wood box.  Slots needed to be at 7.4 (82.6) degrees rather than straight through.   The jig held securely.  The slots turned out great.

The support plate of the fixture has an array of rectangular holes to pass c-clamps through for clamping parts to it.  Other "assist" brackets can be attached to the support plate for unique clamping needs.   I like using c-clamps through the plate, and will borrow this strategy for future CNC bed and fixture configurations.

Two CNCs in the small CNC lab where I taught also have larger versions of this jig:

Last CNC

The last CNC was bought specifically to use my jig with.  It adjusts from vertical to horizontal.  Mounted on a taller stand to permits tenon cuts on the ends of longer stretcher mounted vertically.

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Comments and questions welcomed and appreciated!

Supporting Assembled Projects Beneath the CNC.

The open frame design of Probotix' CNC machines  proved useful when this challenge came up.  A student of mine had already assembled the body of her cabinet. We needed to cut a circular array of holes at each corner on the bottom board.   The only way to cut this hole array accurately was to use the CNC.

Her design has no back panel.  This permitted using bridging supports I designed that could pass through the body to hang it from the CNC frame. 1/4" dowels were installed along the top of the bridges to position her bottom board square and centered in the frame. C-clamps locked the cabinet to one of the bridging supports.

The bridges are made of 3/4" plywood.  A 6" tall side piece joined to a 2" wide top piece. The vertical piece is an inverted arch, thicker in the middle of the span where the greatest load would be.  The top pieces have holes in the ends so they can be bolted into the side frame members of the CNC.

First test of these bridges worked perfectly. The cabinet was lifted up into the frame, the bridges passed through it then dropped onto the side frame members. We slid the bridges to either end of her cabinet to be right under where the CNC work would happen. The bridge ends were locked into the frame, and the dowels held the cabinet securely in position on the bridges.

The tapered legs in this photo were cut using the rotary axis on another Probotix CNC. The pin arrays on the top end of them were cut using an adjustable angle clamping jig I designed that also fits into this CNC t-slotted frame.

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