[boboxx]

Hello guys,
I just terminated my Joes hybrid look alike. This is my first built and it when fairly smoothly.

I ran my first part tonight, I was pretty excited event dough it did not come out as nice as expected… as you can see from the picture attached, I’m having some sort of skewing problem on my Y axis, I have double check everything and it should be ok but it’s not!! Anyone know where I should start looking? Both sides are the same…





Thanks

[ger21]

If the part you cut is a parallelogram, then your gantry is probably out of square.

[boboxx]

yes it is... what would be the easiest way to square it out?? I just used my 30 year old carpenter (was my grandfather) square to square it up... I know I can use the 3,4,5 rule but it won’t be precise enough....

[joecnc2006]

Machine looks very much like my CNC 4x4 Hybrid from gantry rail down, I suppose you built it from seeing the many machine completed now, a skew problem has not arised as of yet with people building the machine.

Use the Router bit to square the machine up, mark the lines with the square on the table and jog the machine to each side, then rotate the leadscrew manually on that side until it is on your square line, then lock the motors into place.

We have quite a few machines built already with great success, when they were following the plans. Plus allot of support on the forum. We have 4 others in Canada building the machine already

Hope you are able to get the machine running the way you want, It is a proven design and robust, not to mention flexible.

Joe

[Richster]

Yes if you're ending up with a parallelogram then the X and Y axes are not at 90deg to each other as previous posters have mentioned. Another similar way of resolving which worked for me is to mark the 4 extreme corners using the router bit. Measure the diagonals - any non-squareness between x and y will give an enlarged error here. Basically you want to adjust one side of the gantry until the two diagnoal measurements match.

Good luck...

[ger21]

Mount home switches on each side and let mach3 square it with a homing command.

[joecnc2006]

Mount home switches on each side and let mach3 square it with a homing command.

I think if the motors are slaved, then mach3 will shut down that axis when it hits one of the homing switches, not sure as i do not have home switches on mine.

Joe

[boboxx]

ha thanks guys, this is all good info :c) I don’t have homing switches yet as I didn’t not really how to align the ends of my 2 rails on my Y, plus I wanted to have a touch probe and would not have enough inputs to support all of them on a single board. I will have a look again tonight.. I'm sure i will be able to do something with all the recommendation that were given.
I hope it works out, the machine is sweet, I just have 2 slaved 260oz motors on my Y and 1 260 on my Z and a 280 on my X, this was a kit from Probotix. The table is about 36x48 and I can jog at 90IPM…
The cost of the table was a little under 1100$ including the Bosh trim router. I have not bought or followed joe’s built plan, plus this is my first machine so I can understand that I might have issue that payed members would not have! Joe, by the way this is a really nice machine and should be really easy to build using the pans as mine was still fairly easy without plans. Some inspiration was taken from the first and second generation of the 4x4 hybrid and some other bits and piece here and there from other machine I have found here on CNC central hope you don’t mind guys :c)


Thanks
Christian

[ger21]

I think if the motors are slaved, then mach3 will shut down that axis when it hits one of the homing switches, not sure as i do not have home switches on mine.

Joe

Joe, Mach will home each side together (they'll move towards the switches together), but each side will trigger it's switch separately, allowing the axis to be squared to the switches. There is also an option to home them together to a single switch.

[boboxx]

ha ok that is good to know but then I still have the same problem, how could I make sure that both of my switch are equal???

[M250cnc]

I can use the 3,4,5 rule but it won’t be precise enough....

Bob that statement is incorrect.

I am planning a router at some stage and this concentrated the mind in how to square the machine.

The next point is your square is that correct ?

The next problem i can see in the design of an axis that is slaved, in that you may lose steps on one motor of the pair then you will be out of square again. And you will need to be able to readily reset the machine back square.

So now the fix, cut some strips of MDF say 2" wide x 1/2" thick. These will need to be long enough to do the 345 over the longest length of your machine.

You will then parallel to the edge of the strips put in accurate holes at the centres of your correct 345 dimensions these will need to be dowelled together. It will not matter that the machine is out of square at this stage.

You will then have the correct 345 triangle for setting your machine you could set the homing switches to achieve this using your jig.

HTH
Phil_H

[jcoats]

I really like your computer cabinet ... great for use in the shop!

[boboxx]

hehhe yes it's even on wheel :c)

I was home at luch and I think I manages to square it up... man I have so much to learn :c)

[joecnc2006]

Joe, Mach will home each side together (they'll move towards the switches together), but each side will trigger it's switch separately, allowing the axis to be squared to the switches. There is also an option to home them together to a single switch.

Thanks Ger21, this is very good info to know.

The next problem i can see in the design of an axis that is slaved, in that you may lose steps on one motor of the pair then you will be out of square again. And you will need to be able to readily reset the machine back square.

This is a very good point, especially using 260oz motors, and not knowing the power supply used, (hopfully now just 24vdc), This is why I used a min. of dual 425oz motors as well as placing a belt between the motors as called for in my CNC 4x4 Hybrid Plans for just this type of instance, a safety net so to speak only not for driving them, but just to makesure gantry stays sq.)

Joe

[boboxx]

This is a very good point, especially using 260oz motors, and not knowing the power supply used, (hopfully now just 24vdc)

Joe

I know the motor are small but they where already ordered when I started my machine... they are powered by a 24vdc/6.5A powersupply. I will be upgrading these on the first chance I get.

I cut some parts last night and my problem is gone! thanks guy :c)

[boboxx]

I just added a small video of my cnc in action for anyone interested:c)

http://www.charetx2.com/_cnc/

[JerryFlyGuy]

I built a larger router [10 x 20ft] which has a slave driven X axis [20 ft]. Across the gantry is the Y direction =10ft.

The best way I've found to sqr my machine was as follows:

I know that when I do cuts in purely the X direction they will be straight and parrallel to only the X axis. So I put a pc of mat'l on the bed of my machine, placed it right tight against the -Y side of the bed.

Next I machined a reference edge on the pc so I know it was parrallel w/ the X direction.

Then I placed another pc of material which was sqr'd [placed against] w/ my reference edge.
I would machine one edge of the material purely in the Y direction. [Keep in mind that this pc was ~24" wide in the x and 8ft in the Y]. I would then cut a second pc of material exactly the same.

Lastly I would place the two pc's of material on the reference edge w/ the cut faces/edge towards each other [you'll need to flip one of your pc's- Rotate it only along the "Y" axis]. They can touch at one end [or use a spacer block of a known width] and will have a gap at the other end. By using a caliper I can measure the 'gap' accuratly. 1/2 the width of the gap is my 'out of sqr error' over 8 ft. W/ some quick math I was able to nail down how far I was out over the 10ft on my machine.

I am using prox switches for either end of the gantry [so Mach3 will auto sqr the gantry every time I home the machine] the sensing 'flag' is on an adjustable slide w/ a 20 pitch bolt. I can then move the 'flag' fairly accuratly to adjust for the out of sqr.

Repeat the test cut in only the Y direction again and I was off by a few thou.. Adjusted it again and it was perfectly sqr.. or as sqr as I could measure.

I haven't found a more accurate method than this.. and it took a bit of head scratching to figure out

Btw if this isn't too 'clear' let me know and I'll post some 'paint' pictures..

Fwiw

[wyldesyde007]

I'm probably stating the obvious here but I would apply the gantry corrections to the areas circled in red. If you try to correct the skewing at the areas circled in blue it would cause binding on your screws and misalign the bearing trucks on your rails.

also as mentioned above, I traced a line on my table using a drywall square (being sure to make sure it was indeed true) I then clamped a fine pointed V-bit in my router and jogged it along the line to check for trueness. My router was out about 3/16" I have a cabling system on my rig to make my gantry rigid and I just tightened one of the tensioners until it brought my gantry square. I did have to reshim my rail bearings though.

[ger21]

If you're using Mach3, you can compensate for this in software. Not the best way, but it might work for you.

http://www.cnczone.com/forums/showthread.php?t=63776

[flyboy1015]

I had the same problem with my machine. I used a scrap piece of plywood and cut short slots where the ends of my carpenter's square would lay out and then cut short slots where the corner of the square would go. When I finished, I'd lay the square on the board and see if the slots lined up with the edges of the square. If not, I would know which way to adjust a lead screw. Hopefully, the explanation and drawing are enough to convey the process.