Question First CNC

Hello All..

My name is Joe, and I am in the middle of building my 840. So far, things are going pretty smooth, and I like the product overall (albeit with a couple recommendations for tweaks to design).

I am a general tinkerer of all types, and enjoy working on anything mechanical. Besides this first CNC, I have a full machine shop at my home. Currently I maintain a Bridgeport Mill, Hardinge Lathe, Cazeneuve Lathe, Miller Dynasty TIG, a pair of Brown and Sharpe surface grinders. Besides these, I have a slew of other metal working machines.

I am also a car/motorcycle enthusiast, and have a good bit of tuning experience. For the last decade, I made my career in e-commerce, and in motorcycle design/fabrication; however I am now a school-teacher.

I live in the Philadelphia suburbs, with my two giant dogs, in a pre-revolutionary farm house.

Hopefully this is the beginning of a great new hobby!

Hi Joe, welcome!. I look forward to see your projects posted in the forum

Hi Joe,

Welcome to the club from the UK.

You mention that you are mid build on your 840 - if you are not too far forward, might I suggest that you run a couple of extra ground wires alongside the stepper wiring so as to connect solidly to the X and Y axis metalwork. Connect these back to the 0 volts of the power supply on the electronics board.

There have been various forum reports of possible static effects causing difficulties in the past, and there is no guaranteed path to ground from either of these assemblies ( powder coating and hard anodising of guide rails). I think someone even reported getting electric shocks from their machine - not good for fragile modern electronics!!!!

Also connect the O volts to the internal metalwork - the attached picture shows how I did it. I wasn't aware of possible static problems when I built my machine, so properly grounding X and Y hasn't been done yet. Pleasures to come threading wires through X and Z cable trunking!!

When it comes to tuning, be cautious about over tightening the adjustments on the moving rollers - my experience was that following the +1/4 turn suggested in the build manual is far too much. My machine Y axis virtually locked solid with the suggested preload. I slackened everything off and then tightened each very carefully until no relative movement could be felt between roller and the guide rail when the assembly was rocked. The kinematic design in this area could definitely be improved - potentially 16 points of contact on the Y axis is not ideal.

Time spent "tuning" will be well repaid later on - in fact I did a complete mechanical assembly and initial tune before getting into the wiring.

As far as grounding is concerned, on my machine there is continuity between the mains 240V/30V power unit connector ground pin, machine Y axis metalwork though to the USB connector on the laptop computer (I'm using the UC100 + UCCNC combination) and then to the ground pin of the laptop supply. Yes it is a ground loop, but operationally everything has been solid with no unexpected events over the last year of operation

peterg1000 wrote: Hi Joe,

Welcome to the club from the UK.

You mention that you are mid build on your 840 - if you are not too far forward, might I suggest that you run a couple of extra ground wires alongside the stepper wiring so as to connect solidly to the X and Y axis metalwork. Connect these back to the 0 volts of the power supply on the electronics board.

There have been various forum reports of possible static effects causing difficulties in the past, and there is no guaranteed path to ground from either of these assemblies ( powder coating and hard anodising of guide rails). I think someone even reported getting electric shocks from their machine - not good for fragile modern electronics!!!!

Also connect the O volts to the internal metalwork - the attached picture shows how I did it. I wasn't aware of possible static problems when I built my machine, so properly grounding X and Y hasn't been done yet. Pleasures to come threading wires through X and Z cable trunking!!

When it comes to tuning, be cautious about over tightening the adjustments on the moving rollers - my experience was that following the +1/4 turn suggested in the build manual is far too much. My machine Y axis virtually locked solid with the suggested preload. I slackened everything off and then tightened each very carefully until no relative movement could be felt between roller and the guide rail when the assembly was rocked. The kinematic design in this area could definitely be improved - potentially 16 points of contact on the Y axis is not ideal.

Time spent "tuning" will be well repaid later on - in fact I did a complete mechanical assembly and initial tune before getting into the wiring.

As far as grounding is concerned, on my machine there is continuity between the mains 240V/30V power unit connector ground pin, machine Y axis metalwork though to the USB connector on the laptop computer (I'm using the UC100 + UCCNC combination) and then to the ground pin of the laptop supply. Yes it is a ground loop, but operationally everything has been solid with no unexpected events over the last year of operation

Thanks for the tips on this. I wish that I had read this a little earlier, but as it happens, one of the leadscrew carriers was drilled off axis, so I'll have to wait a couple of days to get the machine fully built regardless.

One thing that has me a bit perplexed is tramming the spindle to the bed. I was figuring on doing a rough setup, seeing it in action, and determining a list of desired tweaks/tuning. While it is a pretty good setup overall, it certainly lacks a little in this regard. I am also not a big fan of the integrated wiring. To replace a stepper, quite a bit of work is needed, in a relatively specific sequence..

Hi Joe,

The only tramming (if you can call it that) I did was to make sure that the Z axis extrusion was at 90 degrees to the X axis using a square. Adjustment was by loosening off the fixed Z rollers and tapping until square.

The rest is what it is!! However I did subsequently check against a silver steel rod held in the spindle collet and was surprised to find it spot on as near as I could tell. Beginners luck I guess.

I fully agree about the wiring - a real nightmare to replace an x or Z motor. Fortunately they do run very cool, so hopefully will prove reliable. It is important to make sure that the cable trunking doesn't flex close to the ends too, this could rapidly fatigue the cables towards failure.

At least you have the equipment and experience to rectify your problems - I feel sorry for those without the tools or knowledge to do so.

THE major problem on my machine was the spacing of the Y axis leadscrew bearings at the free end. I ended up filing out the bearing housings so that they matched those at the driven end - crude, but the Y axis now runs sweetly end to end, even when hand driven with power off. It took me many hours of abortive "tuning" before I realised where the problem lay. I've some pictures somewhere if you are interested.

Peter