squaring

[lutchman]

hi guys,
after cutting some pvc sheets i realized that our machine is not square, so, i tried squaring it using the following method,
1. i used a .25em mill and etched a line .05 deep, one inch from zero along the x axis,
2. i drew a perpendicular line to the line i had cut in step one and placed a straight edge on the line i drew,
3. i placed a .25" rod into the collet and (with the motors off) i pulled the y car to the furthest point on my right and had the rod just touch the straight edge,
4. did the same thing to the furthest point on my left, i am about 1/8" off square.
so i carried the y car back to the right side of the machine and set it against the straight edge and clamped the right side of the x car, then i carried the y car to the left side of the machine and nudge the x car so that the .25" rod touches the straight edge, and turn the motors on.
so now i am perfectly perpendicular, but when i switch the machine off it go back to its original, non-square position, so the question is, isnt the gantry supposed to be perpendicular even when the motor is at rest? how do i fix this? i almost forgot, we have a 48x96prt alpha. any help will be very much appreciated.

[bleeth]

See next post-PRS directions deleted here

[bleeth]

When you square it up you need to loosen the four bolts holding the y carriage to the x plates. You should clamp one side and adjust the other till you are square, then clamp the other side and then tighten the bolts.

Best to unplug your motors and do this with no power, although I have done it by unplugging the clamped side and moving the other by relative mode movements so I could move it exactly the out of square distance I wanted.

[lutchman]

thank dave, you have always been a great help. unfortunately, i dont know where the x plate is, can you clarify please?

[bleeth]

That is the side plate that has the wheels for the x rails and motor mount at the bottom. The Y rails are bolted to it at the top. You need to loosen the bolts a bit when you square it and then re-tighten them so it stays square. Make sure you maintain the even distance between the y rails so your z car keeps riding smooth in the y direction.

Once you do that it is a good idea to make sure the stop blocks at the zero end of the rack gear are aligned with each other so both sides touch them simultaneously. Then next time if you go out of square it is easy to re-square

[bleeth]

In the attached photo I circled the bolts. You may have to loosen the ones under them a bit also.
Quite a few guys tack welded those corners after getting them square for the umpteenth time. You just need to be very sure you have it square when you weld them.

[lutchman]

great thanks, i will proceed with your method and i will post back with the results. thanks again, you have been a great help.

[Brady Watson]

Before you loosen them....You can re-square most of the time by clamping one side, changing your MS to 1 IPS and commanding the tool to go in the direction it needs to go about .25-.5 inches. The clamped motor will stall, but the loose motor will not. You REALLY don't want to loosen up the gantry bolts if you can help it. Since they are not only trying to keep it square, but parallel as well as holding the whole deal together. Think of resquaring one of those things like a chiropractor would...lock one side and 'adjust' the other - by hand or under power - WITH CARE! Little nudges at a time. You'll get it.

-B

[lutchman]

thanks brady, a bit too late with that suggestion, i already undid the bolts and squared the x carriage and re-tightening, with everything tightened and in place i cut a rectangle 30x40, and measured diagonals and came up with exactly 50, so i think i am good for now, i am going to adjust the stops so i can square using the stops next time.

[lutchman]

Before you loosen them....You can re-square most of the time by clamping one side, changing your MS to 1 IPS and commanding the tool to go in the direction it needs to go about .25-.5 inches. The clamped motor will stall, but the loose motor will not. You REALLY don't want to loosen up the gantry bolts if you can help it. Since they are not only trying to keep it square, but parallel as well as holding the whole deal together. Think of resquaring one of those things like a chiropractor would...lock one side and 'adjust' the other - by hand or under power - WITH CARE! Little nudges at a time. You'll get it.

-B

brady, i tried that at first but it always goes out of square once the motor is off.

[bleeth]

Glad you got it going Lutchman-PRT's are like a big Erector set (If you're old enough to remember what that is!) and reworking the alignments is an occaisonal maintainence task!

[lutchman]

lol..yup, i am old enough to know what an erector set is but i never built what was on the box,...lol....thanks again, i figure i'll have to check it about twice a month or so, depending on the usage.

[frank]

For future reference there is document for squaring the X car. http://www.shopbottools.com/ShopBotDocs/files/Squaring%20PRS%20gantry%20tools%202008%2009%2030.p df. On page 3 there is a description on how to set the end stops so that you have a reference point for when the gantry is square.

[bleeth]

I was going to refer Lutchman to that and also Gary's web article until I looked closer and realized he has a PRT.

As far as either the PRT or the PRS going out of square when you power down, I have to respectfully disagree with the SB article. Having had a PRT for years and then rebuilding it to a PRS I can tell you that when properly tweaked, possibly with a strategic shim or two, they will both stay square barring catastrophic incident.

I've even had the PRS go out of square due to an electrical gremlin causing only one x motor to be powered up when cutting and not noticing, and once the bit is out of the material and I am powered down my gantry returns to square.

It is a sensitive adjustment and time consuming to get it this way but in the long haul it has been well worth it.