[wmgeorge]

BTW I am on here too much and I have never read of an issue with the gear rack binding up the gantry without the rail being involved? Can someone else check and see if its so? The Chinese way.... looks like it could work. https://www.youtube.com/watch?v=k5kdWaTM_14

[GME]

BTW I am on here too much and I have never read of an issue with the gear rack binding up the gantry without the rail being involved? Can someone else check and see if its so? The Chinese way.... looks like it could work. https://www.youtube.com/watch?v=k5kdWaTM_14

Interesting video, Bill. Thanks for sharing it. One observation. So much for precision milling of an edge for rail mounting. Nevertheless, they are at least making the corrections, rather than leaving it up to the customer to worry about it.

Gary

[ger21]

I would pull the motors, and mark the shafts, and make sure they are both turning the same amount.
What you are describing would lead me to believe they are not.

[wmgeorge]

I would pull the motors, and mark the shafts, and make sure they are both turning the same amount.
What you are describing would lead me to believe they are not.

Thats why your getting the big bucks, Gerry. If its not binding. it could be pulley slipping on shaft.

[he1957]

Drop the R+P engagements.
Check the gantry is square as described elsewhere.
Manually check spindle and gantry motion over length of X and Y

If there is binding on Y (the longest edge) , Loosen slave side of gantry to column mounts (to easy possible twisting/warping caused by difference between master and slave rails).

Check motion. If it no longer binds, issue is in this area. Shimming the sliding truck between bearing block and gantry riser plates would be preferable to trying to shim a profile rail. Let the bearing run true to the rail and offset the mounting between the bearing block and the gantry support. This can be done on both sides to allow for non-parallel/co-planar (ie tapering inwards (or other) on one or both sides) rail mounts.

If not binding, remove belts between motor and pinion drive and engage pinions

Check motion. If binding, problem is between R+P. Drop slave, retest. If problem it is master side. Repeat for slave. Measure teeth heights for R+P. Ensure teeth do not bottom-out when engaged.

If binding, then problem is meshing between R+P's.

If not binding, attach belts and repeat as above. If binding, problem is in a motor. Disconnecting motor wires from driver module will remove any electro-mechanical/magnetic resistance and make motor turn easier.

If all of the above checks out OK and still binding, problem is non mechanical.

Somewhat in order but E&OE :-)

[GME]

I would pull the motors, and mark the shafts, and make sure they are both turning the same amount.
What you are describing would lead me to believe they are not.

+1 for Gerry's idea.

Leon,

Just curious, but do your stepper shafts have a keyway, a flat, or are they just round? If a keyway or flat, could it be that on one of the motors (the one running short), the set screws are a little loose? That could account for a the consistent difference in movement at 30". I believe it would also deliver a consist differential at any distance. Like backlash on steroids. Of course, if you have a keyway with a key in it, it must be something else.

Gary

[GME]

+1 for Gerry's idea.

Leon,

Just curious, but do your stepper shafts have a keyway, a flat, or are they just round? If a keyway or flat, could it be that on one of the motors (the one running short), the set screws are a little loose? That could account for a the consistent difference in movement at 30". I believe it would also deliver a consist differential at any distance. Like backlash on steroids. Of course, if you have a keyway with a key in it, it must be something else.

Gary

Oh, one other thing, and it's a huge long shot. The R&P drives Fineline (and CNCRP) sells come in 2 versions; one for nema 23 and one for nema 34. The same body is used for both, so outwardly, you wouldn't notice a difference. I belive the only difference is the size of the timing pulley. The nema 23's ratio is 3.1:1 and the timing pulley has 60 teeth. The nema 34's ratio is 3.2:2 and the timing pulley has 64 teeth. Could it be that you got one of each and that's the problem? I really doubt it, but it's worth a look. I didn't do the math, but I believe you would have a differential of more than 1/16" over 30 inches of travel. Still, easy enough to check and rule out.

Gary

[wackocrash5150]

I very much appreciate everyone's input here. I only just last night sent Nate an email describing the issues and asking for suggestions. So unless he's been reading this thread, last night will be the first he's heard of my issues. That being said, let me answer a few questions here;

Yes I had problems with an axis changing directions which a narrowed down to a faulty drive which has since been replaced with no issue.

Although I have not measured the rack pulleys, they all appear identical and like the Nema34 ones. From what I've seen, the Nema23 ones are noticeably smaller in size than their Nema34 counterparts.

The motor pulleys are indeed keyed.

No, I have not pulled the motors off to see if they move exactly same distance, but that's not a bad idea. I believe they do but have physically checked. I should try to eliminate that as a variable.

The drivers do have an interface port but I do not have the interface cable or software to confirm settings. I can confirm that dip switches are all set the same at 2000 steps/rev

The encoders are 1000 line/rev spec.

About a week or so ago, I thought it might be a driver/motor issue so I swapped the X and Y whole R&P assemblies (motors included) and found no change. I did not however swap the slave axis.

I swapped the Y and X physical rack thinking it might be a manufacturing defect. No change.

I will make a note to measure the diameter of the pulleys and confirm tooth count.

There are indeed washer shims between the gantry and the aluminum gantry mounting plate.


I'm now curious to know what would happen if I loosened all 20 gantry bolts and measured again using the same procedure I described earlier. I am after all measuring from hard-stop plate to gantry mounting plate, which should not be loose despite loosening the gantry itself. Perhaps I can find some time to do that tonight.

Again, I am truly grateful for all the help and suggestions posted here. I am absolutely not trying to ruffle any feathers by any means.


Leon

[wackocrash5150]

Didn't have a lot of time this evening but I loosened all 20 bolts on the gantry and the aluminum gantry mounts did indeed move exactly 30" on each side when I repeat my previous test.

I should also add that when I disengaged the R&P while the gantry was loose, the rails seemed to slide with less effort. It wasn't night and day but, noticeably different in a good way. Perhaps the binding that I was told to look for? Was difficult to tell when I had nothing previously to compare it to.

Sent from my SM-G950W using Tapatalk

[he1957]

Engaging the R+P with motors belted will significantly increase resistance. Disconnect the motor power plugs (when no power applied) and it will be a little easier. Feel for sticky/binding spots but the travel length overall should have even resistance/constant pressure/effort to move it.

[GME]

The immediate problem has been diagnosed, i.e., binding appears to be the root cause of the distance moved disparity between the Y and A (Y Slave) axes.

I believe the real test will be when the gantry mounts are shimmed and mounting bolts tightened. The linear rails are out-of-parallel between 1/16" and 3/32" (up to 94% more than the maximum allowable spec). That means binding and premature wear/failure are givens, and accuracy must suffer. It isn't a question of whether there are multiple signifcant problems. There are, and all may not yet be known. The bigger question is what can be done to remediate them, and at what cost. The rails being tilted inward can be remediated to some extent by shimming between the steel gantry mount and aluminum interface plate, but that doesn't address linear rail parallelism. IMO, addressing the issue more holistically would involve designing some sort of new linear rail mount that would allow both parallelism and a flat, even plane, i.e., the Y and Y Slave axes would be coplanar . That, in turn, would take care of the tilt issue, and eliminate the need for shimming, except as might be required to adjust for weld warpage to the gantry mounting plates. Easy to describe conceptually. Not necessarily so easy when it comes to execution.

Gary

[wmgeorge]

The rails being tilted inward can be remediated to some extent by shimming between the steel gantry mount and aluminum interface plate, but that doesn't address linear rail parallelism. IMO, addressing the issue more holistically would involve designing some sort of new linear rail mount that would allow both parallelism and a flat, even plane, i.e., the Y and Y Slave axes would be coplanar . That, in turn, would take care of the tilt issue, and eliminate the need for shimming,

So once again as I suggested weeks ago. A flat 3/8 or 1/2 thick cold rolled plate, as wide or slightly less in width as the top square tube. Attached with Allen bolts, to the top of the tube, adjustable because of slotted holes. The linear rail attached to it. Fully adjustable to make parallel, shimmed as required. And you saw how the Chinese did the alignment, that is only one way of course. The plates can be made in a machine shop.

Too many calculations, just do it.

[wackocrash5150]

As another note to what I did last night, I should also mention that when the gantry was loosened and the R&P disengaged, the gantry moved very smoothly. I then re-engaged the R&P, re-homed the machine and then moved the gantry to +25 inches. It did indeed move exactly 25". I then tightened the gantry back down at that position with motors still engaged. Now take into consideration that I'm not trying to square the gantry at this point. Only to get the Y and the slave to move the same distance. My mentality was along the lines of "splitting the difference" at +25 inches.
So after tightening the gantry back down, I then re-homed that machine. Now there was tension on the front end of the machine as it sprung back when I hit the estop at home position.
I then homed again and moved to +25 inches. I again measured and again I found a difference in distance traveled between Y and slave. Then with the gantry still tight on the mounts, I disengaged the R&P to test free movement. It was again "tighter" than when the gantry was loose. I loosened the gantry again and checked movement feel; nice and smooth.
So at this point I do believe that I am getting the binding that fellow members told me to check for, I just didn't realize it without something to compare it to. I have not yet checked movement with R&P engaged and belts off.

[Ntl]

Same problem as mine, my rails are parallel though just tilted a little bit. I was able to Loosen where the aluminum plate mounts to the bearing blocks. What I did was Loosen them until the plates were level and left them loose then squared up and tightened up the gantry. I didn't shim out the small gap because the rails aren't completely flat, so the blocks basically float under the gantry. So far I'm not seeing any issues with it this way and I'm not having a problem with binding any more. I think that if I shimmed it then I would have a problem with binding again once the travel hits the low and high points. I attached a dial indicator to the gantry and the rails on my router fluctuate between 0.01 to 0.03 in the worst spot. Also the paired side is worse than the main drive side. The only way to fix the problem is going to be as George was saying for Fineline to have 3" flatbar made that is pre tapped and drilled out that can be installed and leveld. The only problem with this fix is it would change the rack and pinion angle but I seriously doubt there was any engineering involved with the angle of the rack and pinion in the first place.

[wackocrash5150]

I have not been daring enough to actually lift the gantry from the mounts yet and access the bearing block bolts. Seeing that there are shims in mine between the gantry and mounting plate, one would assume that the shims are to compensate for the tilt as well as the unevenness of the bottom of the gantry at the mounting points.

[wmgeorge]

The only way to fix the problem is going to be as George was saying for Fineline to have 3" flatbar made that is pre tapped and drilled out that can be installed and leveld. The only problem with this fix is it would change the rack and pinion angle but I seriously doubt there was any engineering involved with the angle of the rack and pinion in the first place.

Absolutely it could be done at FLA or at a machine shop that will do it for him. Since the tubing is not straight and my guess why the rail is tilted in is because the tube is dished. The plate would span all that, have the predrilled holes for the rail, drilled and tapped. And slotted mounting holes for the plate to mount to the 3 inch steel tube. The user would need to drill and tap the screw holes to mount the adapter plate which could turn into a can of worms for some.

There is a time for pondering and calculating, and a time to just git er done.

[GME]

I have not been daring enough to actually lift the gantry from the mounts yet and access the bearing block bolts. Seeing that there are shims in mine between the gantry and mounting plate, one would assume that the shims are to compensate for the tilt as well as the unevenness of the bottom of the gantry at the mounting points.

You are correct. The shims are to compensate for the tilt. On mine, Nate just used garden variety flat washers on one side only, when both sides needed shims. Clearly, he wasn't trying to remediate the problem. It was just a sloppy attempt to get the machine out the door. Dan had the right idea in so far as checking for the linear rails being coplanar, and as he observed, his aren't. I agree that his situation presents another source of binding.

As far as the racks are concerned, I agree that no real engineering went into their placement. Rather, it is dependent on the squareness of the frame tubing. ger21 suggested that I check the tubing on mine for square. They weren't. I'll bet yours aren't either. Easy enough to check with a square.

As observed, a fix of the coplaner/parallelism issues will create a disrelationship between the interface plate/stepper drive unit and the gear racks. This presents another source of binding, excessive wear, and potential problems with discrepancies in distance moved. So, you fix one set of problems and are faced with the prospect of having to fix another one. Extending Bill George's proposal, you would need another plate on each side that was drilled and shimmed to restore a proper 90 degree angle.

I'm not criticizing Bill's proposal, and even went so far as to draw up a plate in Fusion 360. However, I am not a fan of all the shimming that would be required as a permanent, standalone solution. At a minimum, I would set the new plate, level it with shims, and inject epoxy (Hysol product) under the plate to provide a solid, even foundation. I toyed with first using epoxy to create a level surface, but it's a tricky process with a good possibility of failure. Ultimately, I scrapped the idea. Bill has solidly rejected any notion of using epoxy in any form, instead being satisfied with relying on shims alone. I don't understand his resistance. The explanation he's offered is that machines are commonly shimmed and epoxy isn't necessary. In contrast, I don't see a downside to having the new plate supported along it's full length.

Something else to keep in mind is your proximity to a machine shop capable of milling a plate some 60 inches long. While a standard mill with multiple vices could probably surface a plate in sections, the result will not necessarily be all that precise. Close enough? Maybe. Maybe not. Having the surfaces ground, and then move to the milling stage might be an option. I would be more concerned about the linear rail mounting plate than the racks. An off the shelf piece of plate that is drilled, shimmed, etc. may suffice. I have no idea what all of this would cost. I'm betting it won't be cheap, and you could end up putting a lot of time and money into trying to fix a flawed machine, and may end up with something mediocre at best. After the parts are all made, getting everything put together correctly is dependent upon your having the requisite skills and equipment. If you break off a tap??? Stuff happens. Only you know whether you could confidently pull it off, and whether, at the end of the day, you can live with the results. Not much worse than dropping all that money on a project only to have a machine you hate the sight of.

Dan's solution appears to work for him, but it's not for everyone. I admit that I probably worry more about accuracy than most, and for me, Dan's solution has too much potential for alignment problems baked in. I would think that heavy cutting, which should a breeze for welded machines would be out of the question. I suppose it all depends on what you want the machine to do, and how much error you can tolerate.

Seems to me you are at a cross road. Either all in, or all out. Some of the problems are known, but you haven't ferreted them all out. For example, you don't know whether there are dips and/or rises in the linear rails. Depending on the fix of choice, you may not need to know all of them. A given fix may take care of problems both known and unknown. You have some tough choice. I know how it feels.

Gary

[GME]

The only way to fix the problem is going to be as George was saying for Fineline to have 3" flatbar made that is pre tapped and drilled out that can be installed and leveld. The only problem with this fix is it would change the rack and pinion angle but I seriously doubt there was any engineering involved with the angle of the rack and pinion in the first place.

Absolutely it could be done at FLA or at a machine shop that will do it for him. Since the tubing is not straight and my guess why the rail is tilted in is because the tube is dished. The plate would span all that, have the predrilled holes for the rail, drilled and tapped. And slotted mounting holes for the plate to mount to the 3 inch steel tube. The user would need to drill and tap the screw holes to mount the adapter plate which could turn into a can of worms for some.

There is a time for pondering and calculating, and a time to just git er done.

Bill,

My tubing was dished, as is evey piece of tubing I ever seen or used. However, the tilt on my machine wasn't from dished tubing. I confirmed that tubes were welded at an angle, worse on the left than the right. I'm betting Leon's is the same. His machine and the one I had seem to share the same negative characteristics.

To take your fix a step further, I would add a mlled edge for the linear rail to mount against, which is the industry standard. It would give a good reference point to maintain straightness.

Gary

[wmgeorge]

Much more complicated than it needs to be. Cold rolled flats are made in common sizes, 2.5 or 3.0 inches wide and .375 or .500 thick. Cut a piece, its 60 inches long put on a DRO or CNC mill drill the holes for the plate to tube and for the rail. Bingo, its done. Mount on tubing shim up or down IF required. Shims can be changed if the machine is moved, or shipped epoxy can not. Why would you mill the plate when its going to be mounted and shimmed?

Gary you must be an engineer. It makes no difference if the tube is dished or welded out of square does it? You just need a solution what part of my plate does not fix it? Are there other Practical fixes, sure. Its a problem solving exercise.

[ger21]

People have vastly different expectations. What's perfectly acceptable to some, might be completely unacceptable to others.