Machsupport Forum
Mach Discussion => General Mach Discussion => Topic started by: bigjim on December 25, 2009, 06:36:20 PM
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I have a Town Labs CNC mill and it has no features to square any part of the mill and it's off by quite a bit. The mill's manual speaks of some kind of compensation settings inside Mach3 to remedy this...I can't find those setting options...does anybody have any clue what to do in Mach3 to do this??
Please help!
JD
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You can define formulas (in Function Configs->Formulas) to modify how Mach3 moves. But you're FAR better off actually fixing the machine if you can.
For example, if your Y axis is tilted to the right by 0.003"/inch, you could enter a formula like this:
X = X - (Y * 0.003)
Y = Y
On a "straight" machine, when you tell Mach3 to move from Y0.000 to Y1.000, Y will move 1.000", and X will not move at all. On this hypothetical crooked machine, that same move will cause Y to move 1.000", but X will also move to the right, off-true, by 0.003", due to the error in the machine. Entering the above formula un-does this error. So, now when you command a move from Y0.000 to Y1.000, Mach will actually do a two-axis move, from X0.000, Y0.000 to X-0.003, Y1.000, "un-doing" the error in the machine.
Regards,
Ray L.
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Thanks for the fast reply.
It's odd, when I do a sweep of the table...it's off by .026 over a 3" sweep front to back on the Y axis and .042 over 3" on a side to side x axis sweep...the table is way off. I thought just bolting a piece of aluminum to the table and milling it flat would give me a surface to work with, but it too is off in the same way. So, I'm not sure what's going on. There are no adjustments on mill for anything to fix this...so, I'm hoping to figure out what I can do in Mach3 to fix this....any suggestions?
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Are you meaning it is off on the table surface when you sweep with a dial in the Z axis? If so you need to tram the head if there is adjustment for that. If there is no adjustment then you may have to try and make some but without knowing what your mill is like its hard to say if that would be easy or not.
Hood
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The table surface is off when I do the sweep with the z axis. The mill is a 512 Town Labs model. It basically is a Harbor Freight Mini mill head/column bolted to an iron cross slide table...and has no adjustments at all. I can post an picture of it or even do a quick video post on youtube to show you the sweep and the mill if that would help....
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Looks lie it will take some delicate shimming or re-machining of some of the components.
The spindle centerline might be angled to the z ways too which would cause it to tram out of wack.
Is this it ?
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First thing to find out is if its the head that is out of square or the Z axis or both.
Hood
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My model is the previous generation and is different than the current Town Labs model. Here is a video of what my problem looks like:
http://www.youtube.com/watch?v=mhGuCXJZeNo
tell me what you guys think??
Thanks!
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Assuming that the actual spindle is square to the column then it looks like you are going to have to loosen these two bolts and shim to get the column true.
If the spindle is also out of square to the column then you will have to true that as well if you can, not sure how it attaches.
Hood
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First, you have to get the column perpendicular to both X and Y, probably by shimming where the column bolts to the base. You'll need a *good* machinists square or large right angle block to check this. This will ensure the head moves straight up and down, and doesn't move along X or Y when you change the head height. Next, you need to get the spindle parallel to the column, in both X and Y, by shimming where the front part of the head bolts to the dovetail part. If X and Y are not perpendicular to each other, you may be kinda screwed there, since the only fix would be re-machining the X/Y dovetails.
Regards,
Ray L.
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Jim,
If your X-Y slide assembly is like the one pictured, can't see yours for the shield, you might be better to shim IT true to the column as it will have a much bigger footprint than the flange on the column making it a bit less sensitive and easier.
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Like Ray said, find yourself / borrow a good machinist square ( accurate one and not some piece of junk ) and make some measurements. I think you can shim it and get it acceptable. If possible take it over a friends if they have some precision stuff and do it there. Fortunately it's a small machine.
RICH
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I have shimmed it up as good as I can and it's not off nearly as much...but still off by about .003 over a 4" sweep on the X and about .002 on a 4" sweep on the Y. Now, for some reason, the mill is now stepping over on the X axis on each program cycle. I thought maybe the timing belt was slipping, but that doesn't appear to be it and the code is fine. It will complete a cut and when it goes to start the same cut over at a lower depth, it's stepping over to the left and will do so everytime. So, now I have two sets of challenges...any suggestions?
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Sounds like your head is off compared to the Z axis, is there any way you can rotate it?
Hood
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You were able to get it a whole lot better than you started off with. I think you need to just slowly modify the
shimming and you can do better. I will assume that the table is ground flat in the x and Y direction and you can check it easily if you have a straight edge ( just use a feeler gauge and see if it will go under at any point (stone the edge of a piece of .001" shim stock or see if you can detect any light under the straight edge ) say for 6" circle under the center of the collet.
You need some reference to work to so make sure the table is ok as a reference. Now do one direction at a time
If your out in one direction over 4" by .003", then shim 1/2 of it, test and repeat,etc...get one direction correct, for example the y direction reads the same as the indicator is rotated 180 degrees. Now do the x direction. When you have them as good as you can do, then put a piece of ground rod / drill blank into the collet and check the spindle. A machinist square against the rod will quickly show you how square the spindle is to the table FOR THAT COLLET only.
You can have runout on the spindle or the collet and over say 3 or 4" you may have 1 or 2 thou.
You need to work from a known reference and then check everthing one.... step ..... at a time.
BTW, when shimming place a small piece near the bolt or edge only since a different size shim may be required at each of the four bolts in the column base.
Take your time, be patience, Have A Happy New Year,
RICH
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As mentioned in my previous post I think your head is off relative to the Z and actually it is most likely it was the main cause of the error rather than the Z in relation to the table.
Heres a sketch showing what I am meaning, in the left you will see as the Z moves up and down the cutter would still be on the same path.
With you shimming the Z to make the sweep better the head moving up and down would move the cutter path to the side each time you moved on the Z.
Hood
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Yup...like said in #5 and 6.
The spidnle / quill needs to be tru to the Z slide FIRST .. then tram the z assembly tru to the table.
If you have a quill, it's easy to check. Put your indicator on the quill, cycle it up and down while the indicator is on the face , then the side of the column slide. If you don't have a quill, it gets a bit tricky.
RC
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Yep, agree with both of ya. so here is another try at it.
If the head assembly is one piece your kind of out of luck. You would need to scrape the head way to adjust if the Z is not correct to the column ways. Not a task for most folks.
Check that when the head assembly is locked that there is not a gap between
the head face and column face as sometimes the head may have a sharp end on the V edge and it will ride up in the way and throw the Z out. Just try see if a 1/2 thou feeler will enter bettween the faces. Step #1
Then do step #2 to #5
The problem with using an indicator is that some times they don't go back to the same point after passing a crack/ table groove.
If the set screws are long enough you can lock them after all the adjustments and if you wish, with column and base "waxed" you can epoxy in the gap for a permanent as shim.
other steps in next reply
FWIW,
RICH
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other steps
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Also Jim,
In your first post, the compensation referred to by the mfg might be refering to backlash comp...which is there. What Ray describes would work well if the x and y axis's arent square to each other but it is not a function already set up in Mach like the backlash comp is.
Russ
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Rich ol' buddy, :)
With all due respect, I think you are out there a bit with this one. ::)
IF that is a quill, (and I will assume the spindle is true to it, otherwise I'm outta here)
indicate it true to the column ways...then
True the column to the table, (or V-V) by trammeling,
and DONE ! No squares, light gaps, feeler gauges or whatever.
Let the indicator do the work.....it can see better than the eye.
Respectfully,
Russ :)
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Russ,
Quit being nice to me ;D as I may be "goofy" on this one. ;)
I have seen where a sharp corner as shown in the pic will cause the head assembly to skew the Z axis / quill out of allignment with the column. As you tighten the gibbs the head will start lifting away and rotate by riding up the radius. Just knock off the sharp corner and all is well. So you thought the column wasn't right / perpendicular to the X and Y and the Z is scewed when actualy all is ok. I have seen this also on joiner tables where you couldn't get the two tables alligned ( hey , Rockwell actualy gave me $500 bucks for that one and a nice thank you letter ). So that was step #1 since if that was happening you could be there alll day and would never get the Z right.
RICH
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Hello All,
I also have a TownLabs TL521ACH-3-ER16 purchased in late 2012. Works pretty well for cutting shapes so long as you do not have to move the z axis very far to pick up a xy location. If you try to do precision work with this mill, parts that will be assembled, you will run into problems.
After analyzing the problem I came to the conclusion the the XY stage assembly would need to be re-machined since the surfaces are out of parallel, and as a result there is no way to shim anything to correct this problem. The top surface is out of parallel with one or more of the XY plane surfaces in the stack up. I was surprised to find this problem since so much of this design is pretty good (this is a quality problem, not a design problem, and the error is large).
The machine is pretty rigid compared to many of the other mills in this class, and is cast iron, far superior to the aluminum machines people try to sell on the internet.
The only mechanical weakness I found is the spindle column cantilever assembly, it is pretty flimsy and as a result vibrations do not get damped out, even though this is a sturdy cast iron design, it is difficult to get the kind of finish a design like this should provide (the vibrations get transmitted into the surface finish).
I have not contacted TownLabs about this problem but intend to soon.
Best Regards,
Karl