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Thread: Mill tram sanity check please

  1. #11
    Join Date
    Jul 2015
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    S.E. MI, Metro Detroit
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    Little Machine Shop sells a 2" riser, should fit your mill, check first.
    https://littlemachineshop.com/produc...5127&category=
    Larry

  2. #12
    Join Date
    Nov 2017
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    Watford, UK
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    Aw damnit. I was thinking that BCRider was barking up entirely the wrong tree because he'd not spotted that I'd swapped out the stupid tilting part for a solid column....and then I went and measured what he suggested It looks like there is some taper to the table - about 0.12mm. I was smugly taking some comfort that winding the table side to side was showing no movement at all....and then it started moving and got up to about 0.08mm from end to end of the travel. Mostly in the latter half so I guess that it could be as the weight of the table shifts?
    By the sound of it the right way to go about it is to scrape all the ways and the dovetails and do it properly.....I also know that's never gonna happen! Partly due to laziness - hey, let's be honest here! - but also, I just don't have the time, required spare sanity or the tooling to do it (no surface plate, for a start). There's a good chance I'd end up making it worse too. So I think I'll go down the route of making the best of what I've got...but I'm glad I'm aware of an error I wasn't previously.

    The riveted-on angle scales aren't graduated in degrees, they're in "degrees", same as the lathe. Trust them about as far as I can throw 'em….and the lathe's 15 stone, so that's really not very far!

    Bob: You're right, it shouldn't be hard to get....but it seems to be. I'll grant you that I should have specified 'for a price I'm willing to pay' as part of that though! Best I can find so far would be 50x30x250mm bright mild steel (EN3) that I could do two risers with - one for the left two mounting points (4-point mounting) and one for the right. I can find ground flat stock in 2"/50mm thickness but only in 500mm lengths that they want an arm and a leg for....and if I'm going to cut it to cancel out the tramming errors, it rather negates the benefit of paying for it to be nicely ground anyway.

    BCRider: The mounting has four raised pads on the base casting that have been milled 'flat' so relieving the middle of the riser shouldn't be necessary.
    I was thinking a fly-cutter should cut a nice plane co-planer with the plane of the head and with the bottom being co-planer with the table.....but I didn't think about the effect of cranking the table to get it to cut more than a circular groove; which you obviously have.

  3. #13
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    Nov 2017
    Location
    Watford, UK
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    282

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    Quote Originally Posted by metalfixer View Post
    Little Machine Shop sells a 2" riser, should fit your mill, check first.
    https://littlemachineshop.com/produc...5127&category=
    Larry
    Thanks Larry. I've not checked with LMS but I reckon that with the cost of shipping it to the UK and then the customs charge we get slapped with and the admin charge for taking the money off me (that's what really hurts!), it'd work out uneconomical. Interesting to know that it exists and that 2" is a sensible amount to go for.

  4. #14
    Join Date
    Jul 2015
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    S.E. MI, Metro Detroit
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    I had to make my own, they weren't available from LMS. I use a Procunier tapping head
    and went 4", 2 2" blocks.
    http://bbs.homeshopmachinist.net/thr...l+riser+blocks
    I had the stock, if you make your own, drill and tap 2 new holes for the rubber chip protector.

    Larry

  5. #15
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    May 2002
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    SE Texas
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    11,596

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    "Tram" is not the only thing. It is only ONE factor in a well aligned and adjusted mill. And it is NOT the first step.

    This is not a complete alignment check, but before assuming that the tram is off, I would check the table height across it's width and depth (X and Y). Mount a DI in the quill lower it into contact with the center of the table, and lock it down. Then do a nine point check by moving the table and locking both X and Y feeds at each point before reading the DI. The nine points are the four corners, the centers of the four edges (front, back, left, and right) and, of course, that center point where you started. This places each measurement point at the center of both ways (X and Y) for the measurement and also, by locking it down at each point, eliminates any changes from an off center weight raising that center, measurement point above the "real" position with the dovetails tight. This is a good, rough check to see if the table top is parallel to the ways. Admittedly, it does not check to see if the cross ways (Y) are parallel in the front-back direction to the long (X) ways. But that is not a big concern.

    If any errors are detected in the table thickness with the above procedure, then they should be corrected first. Only when the table measures the same thickness at all points (nine at least) should by worry about the tram.

    If you think this is a trivial concern, I found large to medium discrepancies in the table thickness in at least three mills that I have checked. My Unimat, when set up as a vertical mill, had an error greater than 0.010" across the top of the cross slide (where the milling table mounted): this was a distance of less than 2 inches. This produced some very obvious errors when milling thin parts. I had to mill it down flat. And my present, full sized, Grizzly mill had an error around 0.004" to 0.006" across the horizontal (X) travel. It also had local irregularities. A fly cutter worked wonders with this table.

    Once the table thickness is correct, you can tram for the proper angle of the column. If it is made perpendicular to the table top then it will be perpendicular to the ways also. Most vertical column mills have the vertical column bolted down to the base and shims can be inserted under the corners, where the bolts are. On import mills you may have to scrape off some (a lot) of putty under the paint, at the junction of base and column. You do not have to remove the column to do this. I was able to just loosen the bolts one or two turns and insert the shims by tilting the column. Be very careful doing this: do not loosen the bolts too much. Make sure there are at least four or five threads in engagement at all times. You can take ONLY ONE bolt all the way out at a time to check their total length. Keep the other three COMPLETELY TIGHT while checking this. After adding the shims you should tighten the bolts with a torque wrench to equal values to recheck the tram. When you get within the limits of what you can do with the shims, you can make some smaller adjustments by increasing the torque on one side or the other or front to back.

    One more caution. If you have to mill the table top and you use a large diameter (fly) cutter, then you may produce a stepped top surface where the several passes meet. If this is the case, you can do a rough tram first, then mill the table top, then do a second tram, then a second milling pass, and then a final tram. This should get you real close to a flat, parallel table top and a good tram. After that is done, just re-tramming will suffice for decades of further use. I would suggest a medium diameter cutter, perhaps one that will take three or four passes to reach the full table width.
    Paul A.

    Make it fit.
    You can't win and there is a penalty for trying!

  6. #16
    Join Date
    Dec 2015
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    Chilliwack, BC, Canada
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    As Paul says above the tram is just about the last check that you use to set the final aligning factor. Lots of other stuff ahead of that.

    I saw the solid column bit but I didn't realize that the "solid" meant removing the tilt feature. I was thinking solid core column bar with the vertical dovetail mounted to the tilting joint.

    It was in one of the chapters in Guy Lautard's Machinist's Bedside Readers that I read his write up on flat vs nice looking. A flycutter CAN do just fine on a machine which is in perfect alignment in every manner. But if you want a flat face on a machine with any degree of questionable alignment then the smaller the end mill you use the better. The rotational movement of the end of the end mill's cutting edges will still form a slightly concave track. But with the width being lower the degree of distance between the edges and the dip or the amount of saw toothing going on will be very minimal. And the smaller the end mill the less noticeable it becomes and the "flatter" it is. Downside is that the tracks end up looking like an acid drooling worm crawled over your workpiece as far as the appearance is concerned. It'll look like hell but it'll be much flatter than a fly cutter used on an out of tram machine.

    Be sure your gibs are snug and that you can feel a touch of drag. It doesn't need to be a whole lot. Just noticeable means you've removed all the play. That'll stop the table from sagging on the ways as it moves from side to side and cantilevers off each end of the travel.

    If the base and the cross feed "block" measures out well for the dovetail ways being parallel to the lower face of the base and the issue seems to be strictly in some taper of the table perhaps consider taking the base, cross slide block and table with the gibs bound up snug into a shop that can run it on a surface grinder to true up the table's upper face to the other stuff. It'll cost. But you'll have a nice performing machine to work with from then on.

  7. #17
    Join Date
    Nov 2017
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    Watford, UK
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    Ah, you guys kill me with the stuff I don't want to hear!
    Gibs are a touch on the snug side at the moment if anything. Was having issues with the leadscrew being aligned I think.
    I've not done as large a sample as Paul suggests but a drag from one end to the other does suggest that it's not parallel to the ways in the x axis. I have found there is a surface grinder fairly local so I'll take Paul's survey and see if they're able to assist without mortally wounding me in the wallet.

    nickel-city-fab: Thanks for the video link. Interesting to know of its existence but I'm not sure I'd use it for this as I think that taking it apart again may be next to impossible.

    Larry: Thanks for that link. Interesting to see two different approaches. Is it still rigid enough with 4" risers or is it noticibly better with 2" or 0"?

  8. #18
    Join Date
    Nov 2017
    Location
    Watford, UK
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    Well, I found a small place that will do surface grinding fairly locally. Might have to wait in the queue for a week or two but, that's life. Marked out the table and it varies by 0.12mm across the section I can wind under the spindle. I'm hoping that if I take all of it down there, they might skim the bottom of the column and the top of the base to bring them true and give better seating than the milled finish that makes my worst roughing look like a millpond!
    Went to lift the mill off the table; it's only small.....nope! Now it's in three pieces ready to load up tomorrow. Will probably leave the head and attached electrics at home unless they say they want that too - can always drop it off.

  9. #19
    Join Date
    Jan 2004
    Location
    Missouri
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    It's all very well to go on about all the checks to be made in what order to do everything right.

    Bottom line is that IF the spindle is perpendicular to the table in all positions, and the table is the same height under the spindle in all positions, the tram will read right in every place. And that will be fine.

    So you can in fact just check tram at some positions of the table, and at different spindle locations. If tram reads right, and moving the table does not change the readings, that is what you want, there is little need to go further.
    1601

    Keep eye on ball.
    Hashim Khan

  10. #20
    Join Date
    Nov 2017
    Location
    Watford, UK
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    Got the mill table and base back from surface grinding. Have discovered that there are.....NO useful datum surfaces in an SX2 mill. The nicely ground surface is not a sliding surface and isn't co-planer with anything. The impressive thing is how they got it even vaguely accurate in the first place!
    Table has been surfaced co-planer with the 'feet' of the y-axis dovetail, then mounted back on the base. Whole lot flipped over and the bottom of the base casting skimmed flat. Flipped over again and the column mounting pads surfaced. Should make the whole lot co-planer with the y-axis which was only out by 0.01mm over the width of the table.
    Column may still be out, I'm not sure yet. It was too long to get on their grinder.
    Have spent a while dismantling it all and cleaning the grit and coolant out. Getting there!

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