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| Trials and tribulations with a 7x12 lathe |
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| modeldozer:
Thanks fo the replies guys, Stuart, Thanks for the link, back as an aprentice we called it a standart for some reason. Unfortuanatly mine is not that forgiving having lost 90% vision. As is to "read" the blue have to use electronic visual aids. But keep soldering on finding differt solutions to do things. Loply, The Saddle originaly had good contact on the edges, only a verry narrow line at the deepest end (very top of the bedway. The problem with lapping is as one moves up and down the bed nothing realy prevents the saddle to twist in different directons, progessivly widening the outer edges. In hindsight should have thought this through better before doing it. At the moment am trying a few things before going for a repacement. Abraham |
| loply:
Hi Abraham, Just FYI I had a fiddle with my lathe last night. I discovered that the fit of the gibs on the front of the saddle was not very tight, using a DTI and applying quite heavy finger pressure I could lift the saddle up about 0.03mm on one side and about 0.06mm on the other side. I adjusted the shims bit when it comes to these tolerances despite the shimstock being 0.01mm I generally found that it would seize up if I removed any - certainly removing the amount of shimstock equal to the free play wouldn't work. My approach was to remove enough shim so that the saddle just squeezed onto the bed, but could scarcely be moved more than a few inches. I then used a piece of flat brass with 600, 800 and 1200 grit wet and dry to remove material from the bottom of the bed until the saddle did slide on. By this means I was able to achieve a fit which was not possible simply by adding or removing shims, as the sanding can reliably and consistently remove a given amount of material, and can be adjusted by area according to tight spots. I now have the saddle with free play of about 0.02mm and 0.03mm when pushed quite hard with a finger, and this has resulted in around 0.02mm of rotation tangential to the ways when pushed quite hard with fingers. The rotation and free play does not come with any accompanying sound and feels like flex rather than anything else, ie I feel like something is bending rather than rocking around in free space. All in all I'm pretty happy with this, I got more or less chatter free cuts of up to 2mm in mild steel prior to this, and I'm sure it will be fine from now on. Cheers Rich |
| modeldozer:
Rich, Thanks for the feedback. A question if I may, where can I get some 0.01mm shim stock? Had to use various thicknesses of paper as I donīt have anything that thin. Have looked on the web but thinnest I found is 0.05mm. After spending the weeked filing,sanding,fiddeling,,,, I am now at final adjustments. Am also between shim sizes so am also tweeking the bottom of the bedways. Had to hand file and sand the gib mounting surfaces of the saddle to get them parallel to the bed (0.04mm difference left to right), surprisingly got them to within 0.01mm. At the moment (only front adjusted) I have no detectable play up/down but still get 0.02mm "rotational", and think my orriginal conclution of flex/deformation somewhere was correct. It would be interesting to know the measurements of some of the bigger heavier lathes for comparrison. BTW the adjustments and readings were done wth oil on the ways and I have a nice slightly dragging, but smooth slide. The final verdict will come when some test pieces can be cut. (Donīt know if after all the fiddeling it slill cuts square) Have also ordered some bits for some of the mods. Abraham |
| lordedmond:
to answer your question my Myford coni big bore ( Ģ 10k worth ) tested at the rear of the cross slide 250mm from the centre of the bed i.e. point of rotation in is 0.005mm that is after two years use with no adjustment from me , i.e. as supplied form Myford ( only 5 miles away :) ) so there you go mind you my cross slide is nearly the length of your bed width wise Stuart |
| modeldozer:
Stuart, Thank you for the info. I expected it to be a lot less. The narrow bed and short cross slide was always a bit of a concern to me. The other concern is there is not a lot of material on top of the "V" in the saddle and it might be speading under force. For the moment am finishin the rebuid so I can do some test pieces. Abraham |
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