I'm puzzled by a "tramming" measurement

While I've got the table cleared off on my Tree Journeyman 325 (link here) I've been measuring the table/knee/quill movements. As you can see in the brochure photo the 325 is a rigid chassis machine -- what I've got is what I've got, without the typical ram/nod/shake adjustments as you'd find on a Bridgeport-style mill.

What I'm working with is one of those 12" x 4" OD cylindrical squares and a Interapid .0005" DTI held with a Noga jointed-arm magbase. I also used the probe for checking the table flatness.

Mostly, things are looking pretty decent for a 30 year old mill that was used in industry before I bought it.

As I mentioned in another thread the table slots seem to be very parallel to the X axis motion. If the quill is fully extended hand pressure on the end of it results in the DTI just barely moving enough to see so that seems tight. At 7" from center on the left side of the table when probed it is .0003" high on the back "land" and on the +7" (the right) rear side the back of the table is .0007" higher than the front.

Over 6" of Z movement the knee is out .0004" (X) and .001" (Y) which seems very respectable.

When I "sweep" the (centered) table (9.5" diameter circle) the back is .002" higher than the front of the table (with the knee locked). .001" is hit just before table center slot on the left side and just after the slot on the right. That seems like pretty good perpendicularity of the spindle to the table.

Measuring the quill movement is where I'm getting puzzled. On the sides of the square (X axis) I'm getting just a bit over .004" movement over 6" of quill travel. But on the front (Y axis) of the square I'm consistently getting .009-.010" over 6". The top of the square is tilted back towards the column.

I don't see how the quill can be .004" and .009" over 6" of travel out of square with the table when the spindle rotation gives .002" variation over 9.5" in the Y axis and 0 in the X axis.

Wouldn't that mean that the spindle bearing axis would have to be non-parallel to the quill axis? If so, that seems like a problem that would have occurred at the manufacturing stage and would have been caught before the mill left the factory or at least shortly after the mill was installed with the first customer. My Tree manual doesn't have any specs for inspection tolerances but I'd think that anyone who in the late 1980s had just spent $30K or so wouldn't have been to thrilled to find the quill being that far out.

Doesn't this mean that any hole bored using the quill is going to end up being out of square to the table? Boring with the knee would seem to be a work around, but shucks, this is a CNC mill and I wouldn't think I'd have to be cranking on the knee for a precision operation like that.

I'm also thinking that if I had a very long shank EM where the shank and flute diameters were the same and was milling a deep pocket there would be a chance of the shank contacting the upper wall of the pocket before the flutes contact at the bottom (this should only be a problem on one side and not the other).

There are two lifting eyes on the top of the ram. There is a crack (visible, not gaping open) in the bondo/paint on the column where the head casting is bolted to the body. The head casting is located and attached with 12mm x 60mm taper dowel pins, 12 x 45mm straight dowel pins, and M16x60 socket head cap screws. I suppose someone could have yanked hard on the lifting eyes at some point and stretched the bolts (having the body open up like an over-tightened C-clamp). Let's say that happened and originally the table was dead square to the spindle and is now two-tenths/inch high in the back. But the quill is about .0015"/inch out so wouldn't that still be an indication that the quill and spindle axes aren't parallel?

For lots of stuff it won't make a big difference. But if I wanted to bore (with the quill) some bearing pockets at Z0 and Z-6 I think the measurements would mean that the bottom one would be .009" off the intended Y position, and that's not too cool.

ETA: I did both rotate the cylindrical square and check at three different quadrants and also stood it on both ends as well as having it sit on a couple of completely different spots on the table so I don't think the square is the issue.

cheers,
Michael

Try this, loosen the bolts for the head casting. Then, while tightening back up test the tram of spindle to table. You may end up in a better place.

Hi donie. I thought about doing that (since loosening the bolts is what I had to do on my manual mill) but I'd like to hold off until I've exhausted all other possibilities. Those bolts are buried down in the column and I would have to pull the spindle motor out to get to them. I've done that once and found that pulling the motor by myself is a fun way to spend a couple of hours terrifying myself as I've got 15" from the top of the mill to the ceiling in which to work (by myself, standing on a step ladder) and I think that motor weighs about 80 lbf.

What do you think about the appearance of the spindle and quill axes not being concentric? If they are and the quill is straightened up then the spindle would be farther out of tram. But if they aren't off axis then why are the numbers so far off?

cheers,
Michael

Michael- Check the quill travel to the vertical ways. That eliminates the squares. You need a long and rigid gooseneck. I can guarantee you that it was better than you measured when it left the factory.
Lost

Can you extend the quill and mount the indicator on an arm on the spindle folded around to indicate the concentricity of the spindle and quill? If you do it at the top and bottom of the exposed quill area, you will have a measurment of the angle, if any, between them.

Bill

Bill, I dont why I didnt think of that. Otherwise, I would pull the quill set it up on a surface plate and test the whole thing with a test bar mounted in the spindle.
If somehow the spindle bearing bores are not true with the quill, that would be a major problem to fix.
If that is the case, and you went with what you had, it would be better to true the quill to the table, rather then the spindle.
Never seen that happen.

tramming/sweeping table is not the test for

perpendicularity of the spindle to the table. Tried to explain this to many people, but not many ever understood. (too many varibles to mention) short explaination is that you need granite surface square to achive this and you have to know the reversal error of all the axis involved. the cylinder square should work but with a worn table top might be off that much. remember 4" is gonna move 12" 3 times as much, so .002" can be .006"

If the quill and spindle are out of true, whatever you do sucks. I had essentially the same thing happen on my Boston Digital mill. A heavy cut knocked the head out of line. The head still moved up and down square to the table because the Z axis was right, but changing cutter length changed the X axis location of the end of the cutter. I cut out a piece with an end mill chucked up close, then bored a hole with a longer boring bar and head. The hole came out in the wrong place and was a bit oval to boot. That was an expensive piece of scrap.

Bill

Bill and Lost, I think I should be able to reach much of the quill/knee ways that way with the Noga magbase holder. I'll check that on Monday and report back.

gentle, probing the table makes it appear like it is very flat **as it passes under the spindle**. I suppose the whole top of the table could be bowed but I'm not sure how I'd identify that with what I have. The cylindrical square is supposed to be square to +/- .00015" over 12" and I've tried to rule out problems with that by using both ends of it and rotating it as well as moving it to different spots on the table.

I hope you'll appreciate that I'm reticent to try major disassembly of the mill for fear that I'll far surpass my level of incompetence and not be able to get it back together. I'd guess that the spindle bearings were not bored grossly off center in the quill because .009" over 6" would likely have been hugely obvious to any QC person at the factory.

I can see how any mill, under enough force, could do the "overstressed C-clamp" opening up trick. I'd just expect that any nice mill with the quill and spindle running concentrically would have both measurements off by similar amounts if that had happened and the anomalous readings are what are throwing me for a loop. I can't think of what could be causing that if the spindle and quill weren't machined incorrectly.

cheers,
Michael

All good advice is written above. I can only add the "If it were me doing the job" to it.

I would remove the bolts that hold the head in place and clean the both mating surfaces and run a fine stone over them to clean off any burrs. At the same time I would clean both the attaching bolts and tapped holes and lightly lubricate both.

Reassemble the unit and torque the bolts in two stages in an X pattern. This should remove any error caused by uneven torque, dirt or burrs, which except for pure mechanical wear or error is responsible for most of things driving you

Sort of like building a house. If you have a bad foundation, no matter how well you build the structure it is sure to end up crooked.

There is no "head" as you might find on a Bridgeport. There is a large casting that comprises the upper third/half of the chassis that contains the spindle motor, Z servo and quill, but it isn't a normal maintenance adjustable/removeable type of thing (otherwise they probably wouldn't have bondo/painted over the joint).

In any event I don't have a crane system that would allow me to pull the top third off of a 4600 lbf mill, especially when there's only 15" or so between the top of the mill and the ceiling/second floor joists. If it comes to that I'm in big trouble.

http://www.eurospares.com/graphics/metalwork/treebrochure/treebrochure5line.jpg

the purple line is where I can see the crack in the paint. The only thing that comes off the top of the mill is that little sheetmetal box that allows the quill space to move up/down.

If it seems absolutely necessary I can probably get someone to help me pull the spindle motor so I can try to reach and retightening the clamp bolts between the castings, but that will be a loosen/tighten without dislodging the castings deal, not a "let's take it all apart" process.

I'd be pleased as punch if I had a high ceiling and gantry crane etc to allow me to strip the thing completely down (and a skilled machinery repairman/millwright/scraper hand to tune everything up perfectly), but the thing is in my garage and it was a tight fit doing that. If I didn't have the space concerns I'd probably have some sort of small VMC that might be more amenable to disassembly.

cheers,
Michael

If you can see a crack that developed in the paint and bondo along the parting line then is very likely that it was stressed in some way by lifting and that is the source of your errors. While you don't want to do it you may have to lift the "head" of the machine and clean the joint of dirt, etc. and rebolt it.

You could build up a frame on each side and lift the "head" from the sides and bottom enough to clean the surfaces. I am beginning to feel reasonably sure that is where your issues are coming from.

Michael - I'm not so sure that the disturbed paint means a problem exists there. The knee on a Bridgeport for example is fitted to be slightly high at the front when new, because it's expected to droop slightly with age (and wear). The .002 high at the front is fine, assuming all else is well.

Another way to check your quill is possible before you draw any conclusions. To verify your results with your cylinder square, try this: Clamp a part with a known round bore flat to the table. A bearing race perhaps or a ring gage would be ideal. Extend your quill all the way, raise the knee until the part is reasonably close to the spindle and indicate the bore concentric to the spindle. Retract your quill all the way and extend your indicator to reach the bore and re-indicate. Do not move the knee or the X or Y axis. Use the top of the bore both times to minimize the effect of table tilt, head tilt, bore not perpendicular in the part, etc. If your spindle is parallel to the quill the bore in the part will still be concentric the second time regardless of the condition of the rest of the machine, if it isn't you'll have an exact indication of how much it's off.

BTW, What inspired you to check this? Are you getting odd dimensions on finished parts?

maybe the bearing bores are fine, but you got a bottched breaing replacement job somewhere along the way. where they used cheap bearings or did not install them in time.

As Mr. Mud says, it's usual to fit the tables on Bridgeport style mills somewhat higher from the factory, perhaps to allow for drop.

I've been cleaning and refurbishing my Webb 4VH Mill and I noticed that the manual has a note in it mentioning this.


I'll be checking for this soon when put the mill back in to operation. I sure hope I don't find much more than that.

Good luck or your issue.

He has a Tree, not a BridgePort type mill. The head on his mill is not adjustable in any way, it is fixed. He should not be getting the readings he is.

Carl Darnell said:

He has a Tree, not a BridgePort type mill. The head on his mill is not adjustable in any way, it is fixed. He should not be getting the readings he is.

Click to expand...

I understand. Mud mentioned that Bridgeports are sometimes set high from the factory. I was merely verifying that. Sorry..........

Mike

As gentle implied, it's problematic assuming a machine table provides a flat datum, especially when that table is a moving element.

Ideally it seems to me you would set up a surface plate on the table, supported on three machinists jacks. Adjust jacks until it trams at zero, then sit your cylindrical square on that and dial up the quill travel as you have been

Applying this concept to what you actually have: How about setting up your cylinder square so it's dead nuts for tram on the top surface,
A number of ways to do this: perhaps on three blobs of epoxy putty + saran wrap - then use cigarette papers and/or scraping of the putty when set - another option would be REALLY shallow angle wedges. It's obviously too risky using jacks for something so tall and narrow.

Once the top surface is normal to the spindle axis (with a tenths indicator) you can dial up the sides with quill travel, as you have done, with confidence in the story that tells.

Mr. Moore,

I'm sorry...I didn't realize the configuration of the machine when I wrote my reply. It is a gorgeous machine and I hope that you solve your problem soon.

Just one point. If the paint is cracked in that area..something moved. And PROBABLY therein lies your problem and solution.

You may have heard the saying about how magical thinking involves doing the same thing over and over and expecting different results. Maybe that is why machining seems like magic to me, as things seem to work that way some times.

This finicky metrology stuff makes me feel like I should take up woodworking instead of metal, except every time I've trued welding wood it has always been disappointing.

I'll try and respond to a few of your comments and then go into todays thrilling episode of "Michael measures and still is uncertain what is going on." If I miss someone's comment it isn't because I'm ignoring you or don't appreciate your comment, I've just not picked up on it or thought I might have already addressed it.

John, the issue hasn't shown up in any parts as I've not done anything with a deep bore or accurate vertical face. But I am working on a new frame for a vintage roadracer project and for boring the steering head bearings after welding my plan is to center on a plug (just undersized from the first finished pocket) located on either the table or an angle plate above it (depending on the clearance issues with the rest of the frame and the table) and then moving the position of the unfinished pocket 6.5" above that until it will let me clean up the entire bore. This is a technique that has been recommended to me by several people who've built frames professionally. That would require repositioning the knee no matter what as the quill has 6" of travel, but it does bring up the possibility that the upper pocket could shift if I bored with the quill at the opposite extreme from where it was when I centered off the lower plug.

There is a single lock-down lever on the knee but unlike many manual mills none on the table/apron so there is no issue of the tram of the table moving as table locks are tightened. When I had the table off the knee/apron ways and Turcite all looked in good condition.

Right now tramming with the DTI is showing the back of the table .002" high compared to the front, which is backwards from that Bridgeport "high on front" number.

I agree that it seems like something had to move for the paint to crack. If anything I'd expect stretch taking place on the front of the column. But the bottom of the square is farther away from the column (relative to the quill movement) than the top which I think would mean that the bottom of the quill would be moving closer to the column. With the weight of the front part of the ram/head cantilevered off the front of the column it seems like there'd need to be a gap on the back of the column allowing the quill to droop down and arc around the front of the column.

I think I will plan on ordering up some big metric hex key sockets and som e long 1/2" ratchet extensions and see what tightening/loosening the clamp bolts between the castings does. If I can get a friend to come over we could probably pull the spindle motor up enough to get at those bolts. It seems like one of those "couldn't hurt" things to do. I'd like to keep completely detaching the head casting as a last resort as that looks like a real PITA project.

The first thing I did this afternoon was Bill's spindle/quill test (I can't reach from the spindle over to the vertical knee ways to see how they compare). That seems fine. Checking about 6" apart on the quill I got .0010 TIR at one end and .0011-.0012" (having to interpolate between the .0005" marks) at the other. The high spots were both on the same side of the quill. I think that lets me rule out some problem with the quill/spindle. The differences could be due to minor wear on the outside of the quill.

Now for the magical numbers. I often start off by suspecting my technique is not up to standard, so I did more measurements of the cylindrical square, flipping it end for end and putting it on different spots of the table. I'm trying to take care with the DTI to avoid the variance with the tip moving at some odd angle in relation to the measured surface (cosine error?) but I realize that it is a "test" indicator so the numbers are relative and not absolute. With the DTI today I seemed to be a consistent .0045-.0055" over 6" of Z travel on the square, and not the .0095" I was seeing the other day. Maybe I had a tiny bit of trash under one side then, or it picked up one today that offset the previous readings. I do live near the beach so there's lots of grit in the air and when the bus roars down the street several times an hour the whole house shakes so even with trying to make sure things are dead clean it is possible that something sneaked in. It looks like when the square is slid over the table the sharp corner will scrape a dusting off the table. I didn't see that on the table (which I'd stoned) but noticed it when I was flipping the square and cleaning off the ends.

But if today's measurements are "truer" than yesterdays that's cut the error by about 50%, but still would show close to .001"/1" quill travel which seems high, but maybe a mill like this isn't expected to be doing jig-borer accuracy of holes. I read comments in the various machine/CNC discussions that some of the new lower-end VMCs aren't expected to hold .0005" all the time so maybe I'm expecting too much from a 20 year old knee mill.

That looked encouraging but I still wanted to try something else to try and validate the readings.

I got out the probe and did a series of "boss" probes without moving the square from where it was during the DTI measurements. I did some right below the top edge of the square and the others 1.150" below that. Any lower and the tip holder was going to contact before the probe tip. I did note the readings on the DRO and probed both at the same Z, X and Y starting settings each time.

I'll note that the ballscrews are not perfect and there may be some backlash effects involved, but that's why I tried my best to duplicate the positions as best I could before hitting cycle start on the probe operation.

I started on the front of the square. The X number at both Z levels had a 2 tenths range. The OD measurement also had a 2 tenths range. Y also had a similar range but at the lower Z measurement Y averages out to about .0003" farther forward than the upper one.

That would be roughly .0015-.002" over the six inches of quill movement. Those numbers should be absolute instead of relative like the DTI (though I'd think the DTI numbers with minimal cosine error should be pretty good) and that would be about half as far off.

Here's one of those moving number issues. I don't know whether I should accept the probe or the DTI numbers as being the best indicator and I suspect I shouldn't mix and match them.

I don't have a really nice plunger dial indicator but I suppose that tomorrow I could get the one I have out and try and check both the table tram as well as the square with it and see how that does/does not match up with the other numbers.

Does any of the above make sense, or am I just stirring up more clouds of silt in the quagmire? Does anyone have a factory test sheet for one of the Trees, or maybe a rigid Boss or Shizuoka, where you could give me some idea of what kind of squareness these things were expected to have when new? If I can get enough different measurements that seem to center around "don't worry about it you can't expect better" numbers then maybe I can ignore any outliers.

I'm thinking that no matter what I'm going to have to pay attention to quill stick-out when probing/boring things that need to be accurately located. Is that something that would be a common practice on these "Z with quill" machines?

cheers,
Michael