Cutting bed is out of plane with the cutter

[hualon]

I bought a simple 3-axis machine that uses a rotozip as a spindle. The machine is perfectly adequate for my needs in terms of power. I've noticed a problem lately, however.

If I have the gantry all the way to the extreme of the Y axis and then move it to the other extreme of said axis at the same height, the distance between the bit and the material increases! I've tried to get in touch with the manufacturer to get some troubleshooting but he's been slow to respond.

The problem may have existed the whole time but I usually cut very small parts that require less than 5 inches of travel in the x or y axis... bigger items are the problem now.

So I was thinking that I could fix this out-of-parallel problem by putting on a new bed (or a sacrificial bed), chucking up a big straight mill, and planing the work surface parallel to the bit. Would that be enough or are there adjustments to be made?

Thanks!
Jonathan

[GeeksGoneBad]

I'm no expert but I've seen people talk of doing that as a standard thing I think... I guess it really depends on how much difference it is - for instance - my machine has a .03 difference in height on the extreme opposite side and I think that's "planable" - but an inch probably wouldn't be...

I'm sure others will respond though

[hualon]

Originally Posted by GeeksGoneBad I'm no expert but I've seen people talk of doing that as a standard thing I think... I guess it really depends on how much difference it is - for instance - my machine has a .03 difference in height on the extreme opposite side and I think that's "planable" - but an inch probably wouldn't be... I'm sure others will respond though

Oh it's not an inch... maybe a quarter inch over the 20 inch travel. It seems to have a bump in the middle though.

I plopped a slab of MDF as a new sacrificial bed on the machine and planed it. That's when I noticed that the machine bumps in the middle. I'll try to machine something tonight and see what happens. I'm getting so infuriated with this machine!

[GeeksGoneBad]

Yeah - that would really upset me as well if I bought a machine and it wasn't perfect... I built mine so I'm responsible for all it's glitches hehe

Got a picture of the linear rails? or of the machine at all? that might help in figuring things out... the "bump" sounds odd for sure (and frustrating)

[hualon]

Originally Posted by GeeksGoneBad Yeah - that would really upset me as well if I bought a machine and it wasn't perfect... I built mine so I'm responsible for all it's glitches hehe Got a picture of the linear rails? or of the machine at all? that might help in figuring things out... the "bump" sounds odd for sure (and frustrating)

Here's a picture of one from the guy's website:


Mine is very similar except for the cutter and the bed has two 1/4" aluminum tracks for holding stuff down.

So if I move the gantry from the left (as pictured) to the right here's what happens:

1. The bit depth changes indicating that it's sagging in the middle (shallower cuts)
2. Sometimes the machine when moving in the longest dimension will get stuck and not actually MOVE even though the motor continues to spin. This, obviously, screws up the controller so it now thinks that it has moved X inches when, in fact, it hasn't moved a smegging millimeter.

[GeeksGoneBad]

for #2 that's just the motor stalling or loosing steps - it happens to me when I try to go too fast... could just be a tuning issue - did you have to tune the motors or did you get the computer and software all in the same deal?

I only have experience with Mach3 as well - so if you're using that you should be able to go into the motor tuning and take the speed down some and avoid the motor stalling (unless it's the linear stuff binding) but if you slow way down and it still stalls then that should "say" that it's binding or is blocked or something

[hualon]

Originally Posted by GeeksGoneBad for #2 that's just the motor stalling or loosing steps - it happens to me when I try to go too fast... could just be a tuning issue - did you have to tune the motors or did you get the computer and software all in the same deal? I only have experience with Mach3 as well - so if you're using that you should be able to go into the motor tuning and take the speed down some and avoid the motor stalling (unless it's the linear stuff binding) but if you slow way down and it still stalls then that should "say" that it's binding or is blocked or something

Very astute. Even at slow movements (6.0, for example) the machine binds in that long direction. The motor and screw continue to turn but it's almost as though the screw is not threaded right on the gantry.

[GeeksGoneBad]

really? wow - if the motor and screw still turn then whatever holds that linear nut is loose - hopefully it's just a few bolts or screws that need tightening...??? can you get under there and see or is it unaccessible? what if you take that sacrificial board off again, can you get to that nut?

[hualon]

Originally Posted by GeeksGoneBad really? wow - if the motor and screw still turn then whatever holds that linear nut is loose - hopefully it's just a few bolts or screws that need tightening...??? can you get under there and see or is it unaccessible? what if you take that sacrificial board off again, can you get to that nut?

I'll take the sacrificial board and the permanent board off and then I can get to the bed. I hate having to do surgery on something I didn't build! At least I'll know how to repair it in the future!

I went to the Shopbot open house on Saturday and I was just drooling over their $6000 "Buddy" CNC. I think I'll save my pennies!

[GeeksGoneBad]

I hear ya - that sucks... you should send a repair bill to the guy you bought it off of

yeah - Shopbot rocks! I wish the wife would let me spend $6k on that hehe

[ger21]

The bearings are probably binding due to the shafts sagging. Not sure what you can do to fix it.

[hualon]

I just got a reply from the builder:

Go to Home Depot and buy two steel angles and screw them on the sides of the table top, that will prevent it to sag. When you remove the table top also remove the motor/lead screw and replace the nut(the part that I sent you) on the base of the gantry.

So that seems pretty reasonable. That will help to normalize the bed...