Desktop Not Cutting Accurately Anymore....

I have had my Desktop for right around 10 months now. All of a sudden I noticed that it was no longer cutting accurately. I went through all the maintenance, made sure everything was tight, but that didn't seem to help. Any ideas on what might be causing this issue? I have attached 2 pictures, one that I originally cut back in April that turned out perfect, and the most recent cut that looks absolutely terrible. Lines that are supposed to be straight are crooked, and also at the wrong angle.

Attachment 32111

Attachment 32112Attachment 32112

Are all the lines on the same cut later? It looks like the larger object outline and the text and smaller objects are on 2 different layers (or 2 different grouped components) and one layer was bumped slightly? I have inadvertently moved a layer or group by accident just by not being careful moving the mouse around. Just a guess without seeing the actual file.

It is on the same layer, it somehow lost position as well.

I used the same program to cut both, nothing has changed except one was cut in April and one was cut last week

Are you sure that everything on your machine is tight? With the machine on do you feel any play when you grab on the bit and wiggle it?

I'd try and cut out a 6" square and see what happens.

Quote:

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Originally Posted by EricSchimel

Are you sure that everything on your machine is tight? With the machine on do you feel any play when you grab on the bit and wiggle it?

I'd try and cut out a 6" square and see what happens.

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You used the same file to cut this as you used back in April?

I'd bet that your Y axis bearings are all jammed up with MOP grit etc. On the newest DTs. the bearings are somewhat covered, but prior to this, they were very susceptible to getting plugged up with swarf and chips.

Move the gantry in and out using keypad mode while simultaneously feeling how smooth movement is from one side to the other. Do it over and over again until you are sure the bearings are running smoothly. If you suspect that one or both sides are jamming up, disconnect the leadscrew from the tombstone under the bed (just lift it up you'll see it) - then move the tool at will with no screw to hold it back. It should move smoothly without binding when pushed at the center of the gantry front to back.

Report back and let us know what you found.

thanks for the help everyone!

what i've done so far- i checked the bearings, they feel like they are running smooth. i looked underneath to see about disconnecting the leadscrew but i couldn't figure out how i could do that.

as far as the 6" square goes- i cut it- the x dimension measures right on 6", however the y dimension measures 5.975" on the right and 5.980" on the left

I've never seen a desktop,so assuming a couple things,
Check setscrews on motor to screw coupler,
also,is there a jam nut against bearings on the motor end of the lead screw? I have seen those loosen and allow the screw to shift under load

First of all - what Brady said!
I have had the same problem with my desktop. To check alignment of the screw underneath the machine do this. On the front of the machine you will see some screws that hold the end of the ball screw in place. Loosen them. Run the carriage all the way forward and tighten them. Now loosen the screws holding the motor at the rear of the machine. Run the carriage all the way back and tighten them.
On each side of the machine you will see two linear bearings. Take off ONE AT A TIME and clean them. I used WD-40 on mine. There will be a collection of fine dust and gunk in the channels that the ball bearing run in. I have had to do this a couple of times and so I have some extra bearings to make this go a little faster. If you take off both bearings on one side you are going to have a jolly time getting the first one back on. Trust me on this!
I also made a couple of pieces that attach magnetically to the sides of the carriage and help protect the bearings from flying dust and debris.

There are no couplings per se on the motor to screw. The motor drives the screw directly, but is sort of double nutted in the motor itself. It can loosen, but it is rare...and adjustment is tricky. There is no documentation on this...You can verify slop/slippage by powering up and working the screw by hand. If you feel rotational slop it needs adjustment. Otherwise, it is good.

I would recommend NOT removing the bearing blocks from the rails, unless you have a short piece of rail to transfer them onto from the rail on the machine. You will most likely scuttle some of the balls inside and you will play hell trying to get them back in again. My advice would be to free them up from the gantry so they can be moved in & out without the gantry beam moving, then douse them in WD40 and work them back and forth, repeatedly dousing them to flush them out. They are really supposed to be greased, but there are no fittings on them...so delouse them by flushing them out and working them along the rail to move the balls around. Then - as suggested - make yourself something to keep debris from falling on the rail and fouling them up again.

I assumed (as did others) that you have one screw on the Y axis. I believe the new ones have 2. Which does yours have? Pics are worth thousands....