Setup for squaring twin X-axis gantry

[JAZZCNC]

Yes I was thinking about using a hall effect sensor, seeing as I cut wood they would work for me, thanks for the info.

To be honest it's not worth doing unless you buy the sensor and Led resistors etc cheap has you can buy inductive prox switches for approx £2.80 from Ebay.

I bought these to try and they are fine giving repeatabilty much better than mechanical switches and simple and easy to adjust. They also allow higher voltage so can be used with 24V and kept in line with rest of system. They are more than good enough for a Wood router without the hassle of soldering and making holders etc.
UK 10pcs Inductive Proximity Sensor Detection Switch NPN DC6-36V LJ12A3-4-Z/BX | eBay

[EddyCurrent]

You also have to consider switch hysteresis because that determines how much Mach3 backs off once activated.
These switches for example have to be backed off 5mm before they reset.
TZ-8104 Rotary Roller Lever Arm Enclosed Limit Switch | eBay

[Neale]

Do these need a magnet to trigger them, something magnetic, or what? Looks like a cost-effective device, in any case.

[JAZZCNC]

Do these need a magnet to trigger them, something magnetic, or what? Looks like a cost-effective device, in any case.

If your talking about what I posted then No they just need a Steel target to trigger them which the sensor detects as it passes the face. Adjusting the distance from target to sensor face as the affect of adjusting sensitivity.

[EddyCurrent]

I've been thinking about this gantry squaring issue when two motors are used for the X axis.
If the gantry design consists of two tall end plates with unsupported rails between or maybe aluminium profile and supported rail, I can understand there might be a fair amount of flex between the two ends and in this case it might make sense to have two home switches.
In my case where the gantry is like this http://www.mycncuk.com/forums/gantry...html#post55076
it's rock solid and virtually no way it can go out of square as it's like one big lump of metal. With this in mind I'm proposing to use just one home switch for the X axis because I think the steppers will stall if they try to home independently and the AM882's will then trip out.
Any thoughts ?

[Ger21]

Clamp one side so that it can't move, then push very hard on the other side. I wouldn't be surprised if it moves at least 1 mm.

Another thing to consider, is that when you apply power to the steppers, that they'll usually "jump" to the nearest full step. If one moves one way, and the other moves the other way, then they'll be twisting the gantry out of aquare, although the amount would be very, very small.

If it's as rigid as you say, then one switch would be fine. But you need to make sure that the gantry is perfectly perpendicular to the axis is moving along.
If you go with two switches, you need to position them so that they get the gantry perfectly square. Both methods require very precise measuring and fabricating.

[JAZZCNC]

I wouldn't be surprised if it moves at least 1 mm.

Wow Gerry your getting all Metricated now, Watch it you'll be speaking with Yorkshire Mans accent before you know it. . Lol

Eddy every thing Gerry says but I'll also point out the affect of inertia pushing the gantry can lead to error that without home switches on each axis you'll never know about untill the error as accumulated enough to rack the gantry and stall ONE motor. The Mess that can come from this is sickening if it happens at high speed which it often does because that's when torque is lowest.!!

Another way and one I know Gerry used or maybe still does is to bump upto a hard stop on each axis which squares gantry and use this as machine Home position. Then just occesionally bump upto stops to realign.!!

Another way is to permantently fit cheap dial indicator at each side and use these to check if it's losing position.

[Clive S]

Wow Gerry your getting all Metricated now, Watch it you'll be speaking with Yorkshire Mans accent before you know it

And I thought it was the official system over there, but I have had a few glasses of vino http://www.nist.gov/pml/wmd/metric/upload/1136a.pdf ..Clive

[EddyCurrent]

The only time you are going to know it's moved out of square, unless it stalls, is when the gantry is back at the home switches. So with this in mind I'm going with one switch and will create a datum point each side to enable checking with a DTI as suggested. If upon the first attempt at homing the machine I can see that Mach3 moves it only a very small amount I may then consider using two switches but the last thing I want is for the homing procedure to gradually 'loosen' the gantry structure.

[Ger21]

The only time you are going to know it's moved out of square, unless it stalls, is when the gantry is back at the home switches.

Or when your parts don't fit together.

Yes, I used to just bump into the stops before I had home switches. But it's much easier to just push a button and let the machine take care of it.

With 25 years of using 32mm cabinet hardware, and damn Italian machines, knowing a little metric comes in handy.