Cncfusion Lms Upgrade Kit #5

[JimDawson]

Consider that you are probably not going to be doing work for NASA, so a small amount of error is not likely to significantly affect the end product. The place where this does become a problem is in a bearing pocket or something like that. Even with my mill that has 1 micron magnetic scales on the table and is thus self correcting, I normally pocket bearing bores undersize and bore to the final dimension. I have to do this because I have a small amount of backlash in my Y axis, about 0.002, so I can count on a pocket to be about 0.001 out of round.

It is possible in Mach3 to ''map'' the leadscrews to correct for errors over the length, but I'm not convinced that this works very well.

The most important thing in my estimation is: Can the machine return to 0,0,0 consistently after an operation? If you lose your ''0'' position then you have no idea where you are at.
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[RJSakowski]

Wow. I'm surprised that works. I would think that if the measured backlash was off by even a little, cumulative error over many operations could be significant.

It only compensates once at the point of each reversal in direction. When the direction changes again, the compensation is applied in the reverse direction so it the two comps cancel. The cumulative error will be the difference between measured and actual backlash at worst .

There is a problem with backlash compensation if the backlash is excessive though. When a coordinated move is taking place as when cutting on a diagonal, the compensation creates a hiccup in the movement. For this reason, it is recommended that as much backlash as possible is removed by mechanical means rather than software.

 

[RonGinger]

Backlash is one thing I always harp on. Yes, Mach3 will turn the screw so that the backlash is accounted for. No, it does not really solve the problem. While the adjustment is happening the table is unconstrained by the nut in either direction- it is free to move. If you are in luck all that will happen is it leaves a divot in your part, if not lucky it grabs the work and digs in and breaks the tool. Backlash compensation is something every software guy adds, but it is less than useless in my view.

You must do everything you can to eliminate all mechanical sources of backlash. Loading the ball nuts with oversize balls can help, but I think it is more tricky to accomplish that you might think. The more common method is to place two ballnuts back to back with some adjustment between them so that the lash can be adjusted out. I did that on my Jet mill conversion and it works pretty well, but the Y nut is in a place that makes it very hard to reach and it keeps coming loose.

I used the CNCfusion kits in the 3 build class I ran at CNC workshops. They are good quality and work well. I am now designing a CNC lathe conversion for the next CNC workshop and have found a Chinese source of some unbelievable ballscrews. I got two sets of samples and we have built the first two machines and they are proving to be amazing, and surprisingly inexpensive. I found them on Amazon, with prime shipping, from a vendor called TenHigh.