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  1. #21
    Hi Irving

    Don't 'learn' too much, this is just my way, room for improvement :heehee:

    I use an ER32 chuck, much bigger overhang than you've got, but you need to hammer to change a tool. Swings and roundabouts.

    I use a drill chuck because it is so much easier to change the bit and I don't end up scrunching a 5mm collet down to a 4.2mm point contact. That's got to hurt

    Holding the work down is the big problem. I have other methods but that's my favorite.

    You can clamp alternate ends from above but it makes the G code complicated. You can leave mounting lugs and saw them off afterwards. You might mill through holes first (if it has them), then run a big bolt down before removing the other clamps and milling the external. You might not be milling full depth and have excess that you can clamp sideways but space is limited if you don't want to compromise the splash guards. Water mess that makes :heehee:

    Changing fixture part way through usually means cleaning out the tee slots with the work in situ and moving stand-offs. Not easy without losing X,Y or applying a tilt.

    Don't use stand-offs and you hit the bed.

    Cutting a sacrificial spacer for every job would be expensive.

    Using scraps doesn't hold it true IMHO.

    I cut my bolt down standoffs all from the same 3/4" thick bar and I don't face the top. That way I can make more and they are all very close to the same height. They are sort of pear shaped. The fat end just allows them to pass by each other in adjacent tee slots. The thin end, with the screw thread, is offset so they reach just past half the tee slot separation when turned 90 degrees.

    I put the centre drill in deep when I drill for the thread so I get an annulus for alignment.

    3/4" thick is pleasantly chunky, allows me to countersink an 8mm cap head flush to hold it down while still having some meat left to relieve most of the top so it stands proud around the threaded hole. The smaller sizes do get a bit chewed on occasion.

    If you can come up with a better idea I am all ears

    Robin

  2. The Following User Says Thank You to Robin Hewitt For This Useful Post:


  3. #22
    Thanks Gents,
    It will be a while before I can comment on much of this, but….

    I had not included a release in my Z axis, which is similar to Robins (but not as pretty … no surprise there!), so you have saved me from myself, and a time consuming re-make. (two Hobgoblins).
    I am using a smaller motor for the Z, as it will be geared and therefore should be approx. the same torque ( although slower).

    Irving (Hi ), said you would not use a boring tool on a CNC, why not?

    I don’t have one and have been cutting large holes using a mill and my rotary table, but I would have thought that having a fine a constant feed down would be beneficial, giving a more accurate (round) bore, with a better finish, would you enlighten me?
    I remembered watching a program on TV, where a company building Drag Racers had received a part with a bore (about a foot across) cut in it, which was not round.
    The chap commented that it must have been cut using a CNC machine (and therefore circular interpolation).
    I am concerned that my bores for the Z bearings will not be very accurate, so I was intending to buy a boring bar.

    I have just received my MT3 collets today, so haven’t tried them yet.
    I use an Osborn Titanic collet chuck, which seems quite sturdy, so I will compare the cuts with the collets and see how much difference there is.

    It seems that we have the wrong spindle for CNC, are we stuck with it? The R8 is presumably not any different in operation.
    I guess the proper CNC machines have much larger quills, allowing the larger tapers to be used, is the lower bearing the limiting factor?

    Cheers for now.
    Mark

  4. Quote Originally Posted by Tweaky View Post
    Thanks Gents,
    It will be a while before I can comment on much of this, but….

    Irving (Hi ), said you would not use a boring tool on a CNC, why not?
    Well I've not got my mill CNC'd yet, but done a lot of boring (badly - my problems are getting the centre accurate after drilling because I need to move the mill head and not rushing it so as to end up on the diameter I want and not just over! - I've learnt that you need to take roughly the same amount off each time to allow you to estimate/compensate for the movement of the bar). The point about a boring bar is that you have to adjust it and creep up on the final diameter, so the CNCability of it is limited to just driving the vertical movement (ignoring the intial XY placement). When I said 'not on a CNC machine' I meant 'not under full automated XYZ control'. Of course you could use the z-jog or a bit of g-code to get a constant Z feed to a fixed depth and that would ease things a bit. I dont know why a milled bore would not be round assuming the final cuts were done light enough not to bend the tool/quill..

  5. #24
    Quote Originally Posted by Tweaky View Post
    It seems that we have the wrong spindle for CNC, are we stuck with it? The R8 is presumably not any different in operation. I guess the proper CNC machines have much larger quills, allowing the larger tapers to be used, is the lower bearing the limiting factor?
    You can get a Warco Major with an R8, it's an option. Now't wrong with MT3 though, apart from needing draw bars in 3/8", 1/2" and M12.

    Production CNC requires an auto-tool changer so they prefer shorter fatter tapers.

  6. #25
    Auto tool changer would be nice though, complete the system, …..next time.

    Cut my first metal using the X Y controlled by Mach. I faced the blocks for the Z axis, and cut shoulders on each.
    What a difference, simply having DRO on the screen is a huge improvement, but coupled with little or no backlash (as opposed to half a turn on the X and a quarter of a turn on the Y) and a “go to” facility and constant federate it is a million miles from how it was.:dance:

    I used a newly acquired ripper cutter, 0.5mm side cut, 12mm deep, feed rate 700mm/min. I like this too, fast removal of metal and small chips of swarf, I have not finished these surfaces yet, so have not encountered the “print through” that Robin talked about.

    This was the first time I had used G-code as well, and that is not a daunting as I first thought (only simple stuff so far) but this is fun.
    Back down to earth though, when I measured the blocks.
    Not square by a long way.
    I am still using my vice, as I don’t have many clamping bits yet, so I put a parallel in the vice with the DTI on the spindle, blimey, I can file squarer than that!

    Before I started on the Z axis, I should have trued the column, so I’ll start there.

    Set the DTI on the spindle, with a bar, so that I could measure the compass points, so about 3 ½” from the spindle.
    Starting with West set to zero, South was +3 thou., East = +7 thou. and North = +5thou. So that is an error of 0.001” per inch! on the East West axis.
    Four hours later, it was zeroed.
    Cranked the head up and extended the quill to max, then repeated the tests, OMG.
    The quill lock moves the spindle to one side by 0.005” (on a 10” extension from the spindle)?
    Removed the quill lock, it is not even cut to fit the column, just an angle each side.
    Re-ground the contact surfaces as they were a bit rough.
    Now 0.003”, not good, but this must be wear in the quill housing, bugger.
    Whilst doing this, I noticed that the head is actually quite well balanced, and if it still had the single phase motor, which is much heavier, I think it would have been near perfect.

    Next, I put the vice back on, parallel in the vice and ….. still not square.
    Stripped the vice, yuk, made in Poland, but exactly like Chinese machinery, a reasonable collection of bits, but completely un-fettled.
    Re-assembled and back on the table it is better to operate, but still not square.
    So the next step is to turn the vice over and machine the base, then maybe I can make my Z axis.
    Hopefully my finish will have improved with things a little truer.

    I have a day off tomorrow, so will hopefully get some actual progress on the machine.

    Fursty Ferret time.
    Last edited by Tweaky; 22-02-2010 at 01:19 AM.

  7. #26
    Robin,
    I have replied on your post "heads up Ebay", but I guess you are not very likley to read that.
    Have you had any joy modifying your touch probe to incorporate the Z?
    Also, how do you mount it?
    Could it be rotated 90 deg. on it's mount?

    Regards

    Mark
    Last edited by Tweaky; 22-02-2010 at 01:20 AM.

  8. #27
    Quote Originally Posted by Tweaky View Post
    I have replied on your post "heads up Ebay", but I guess you are not very likley to read that.
    Hi Mark

    It sends me an email if you post on one of my rants.

    You are having teething troubles. When it misbehaves, figure out what went wrong, fix it, try again, find out if you were right. Nemo repente sapit

    Robin

  9. #28
    Hi Robin,
    of course it does, sorry, I am new at this.

  10. #29
    Fettled, filed and stoned my vice, did not skim the base (it was late and I was tired) because it swivels.

    Tried my Z axis bearing blocks again, lots more G-code, swarf and finally ….. square, plus a much better finish.

    Now for some more complex code, as I want angles on the outside and three different bore diameters.

    “Apparatus est amo a infantia, totus Ego operor est nutritor is quod tarsus is”

  11. #30
    My Latin isn't very good, "Gizmo's are the child's friend, thereby all work is food for the hands" ?

    Nemo repente sapit, "Persevere and win".

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