MWF FEED
7th February 2021, 03:00 PM
Well .. it's been an interesting week. My AL-960B has a standard BXA-clone QCTP, and I made a quick bodge-up mounting post for it to attach with way back when I bought the lathe. It's always been a bad fit, partly as I hacked the job and partly as the hole in the post had a nasty finish that wore down over time. The result was that if the post wasn't locked it would suddenly move a couple of thou at the worst possible time, ruining a tolerance fit. I finally had enough and got off my lazy ass to bore out the QCTP and make a properly fitting mounting post.
Of course, that meant going back to the four way toolpost, and that's been an eye-opener, so much so that the QCTP might only get used on rare occasions. I'm really loving that original post. Why this Neanderthalic change of heart? Well.....
I got a set of 12mm carbide tools with the lathe as part of a deal (same as these: L0099 - L0099 Lathe Turning Tool Kit - 7 piece Insert Type | Hare & Forbes Machineryhouse (https://www.machineryhouse.com.au/L0099)), and dismissed them as "the usual Chinese junk" at the time and never used them. FYI, they're the wrong size. 5/8" tools would be a tiny bit too high and 16mm well too high, but no sweat, I'll make some shims. Measured the difference to centre height, thinned down some 5mm BMS to 3.65mm, done. And you know what? They cut great. The WNMG tool took 3mm cuts off 1045 (I had a lump of 35mm I decided to use) throwing tiny little blue C shaped curls, just like the book says. The DNMG did a lovely job on the finish cuts, and the parting tool did a great job of the thread relief and a beautiful parting cut under power feed at the end (smoother than my facing cuts!). So, smart-ass Chinese dismissal gets stuffed down my throat.
Now, I like to thread away from a shoulder with the lathe in reverse and an upside-down tool. I had a left-hand 12mm threading tool, and wondered, "If I use another 12mm tool as a spacer, will it work"? Now, something in my brain said the geometry was right, but I still can't put it on paper. Anyway, I gave it a run, and you'd never believe it: the tool was dead on centre height with another tool and it's standard shim as spacers. See attached image.
Inverse threading tool.jpg (https://metalworkforums.com/attachment.php?attachmentid=390596&d=1612664775)
The standard 4-way is really rigid as it places the tools right over the compound rather than hanging them out in space. I suspect that helped the parting no end, and with solid dedicated shims a tool change takes the same time as with the QCTP. Even my Eccentric Engineering Diamond Tool holder fits without a shim (don't try turning the 4-way on the compound :oo: ). The only pain is for boring bars, but I could always make a square mount with replaceable sleeves that puts them on centre, or just mount the QCTP for boring operations, as a boring tool is always hanging out anyway.
OK, that would have been a good week had that been the end of it, but no....
I bought a 90 year old Brown & Sharpe grinder from another member recently. I've been working at de-rusting the table (another lesson learned vicariously: if you wet grind, you MUST clean the grinder. The mag chuck was rusted solid to the table and the table T-slots were filled solid with rust, all old grinding dust mixed with water based coolant. Still grinding it out with a Dremel two months later). Anyway, the Mag Chuck was basically immovable, so I tore it down to refurbish it. I won't go into it, but others had been there before me, and it wasn't the previous owner, I know. But someone was in there: screwdriver gouges in the inner plates made that clear.
Anyway, I needed to resurface the inside of the top and bottom plates of the chuck. On my mill I was going to flycut them, but the geometries just weren't working out. No way I could do it in one pass and even my smallest flycutter has a 60mm swing and would have had to be lowered onto the job to start the cut or lifted off while still cutting as I only had 52mm of travel left beyond the length of the part. Eck! But, I have an old 50mm Chinese face mill that I've always disdained as rubbish. It would just fit to start passes and feed back before moving.
I've always had an issue with this cutter: if I cut one way, moved the Y, then cut the other way I'd always get a ridge between cuts. Not my head tram, it's perfect (I mean perfect: the needle barely moves on a 0.01mm indicator). I had always assumed that the cutter was off on the arbour and, again, just "Chinese Junk". But I figured that I had to take a full 1.5mm off one plate, so I'd give it a go and still have plenty to go if I got those damn longitudinal ridges and could see if I could come up with something else.
Did the cuts, but the geometry meant I'd have to lift at one end, and obviously that's an awful idea if you want a flat surface, so I made one cut in x then fed back to the start, moved y and made another cut in the same direction, moved back, and so on ... and no ridges. Huh? Sat and stared and tried to figure thing out and the lightbulb went off. The cutting force when moving left to right was lifting the cutter towards me (on some radius centred somewhere in the middle of the head) and lifting it away from me when feeding the opposite way in x. Making all the cuts in the same direction eliminated those ridges, and resulted in a nice, flat surface. I would like to surface grind them, but they're fine as they are for what they do (let a magnet stack slide on them). Some stoning, clean things up, new high pressure moly grease and the mag chuck runs smoothly now. I still have a couple of things to do to it, but it works nicely now. I may send the magnets off for re-strengthening, I'm not sure. It's about the same strength as those Chinese fine-pole ones at the moment.
So, it wasn't the Chinese face mill after all. It's the Chinese mill! :D Now, my first thought was the Z way gibs, but it's not that, they were locked, so it must be a simple issue with rigidity, but it can only be in one direction, so some serious investigation needed there. The head was way down low to the surface for this operation, as the face mill in on an R8 arbour. If it's a one way rigidity problem then it should be able to be fixed. It's not bad - the ridges that 50mm face mill produced were only 0.01mm or so (I could just feel them with a fingernail), but that's a cliff in my book, so it has to be fixed. One day..... now that I can work around it, I'll probably be too lazy to ever fix it.
So, that was a week of learning! Hope I didn't kill anyone from boredom who may have tried reading all the way though. If you made it, then you deserve a medal!
Attached Images
https://metalworkforums.com/images/attach/jpg.gif Inverse threading tool.jpg (https://metalworkforums.com/attachment.php?attachmentid=390596&d=1612664775) (149.3 KB)
Read the full thread at metalworkforums.com... (https://metalworkforums.com/showthread.php?t=206258&goto=newpost)
Of course, that meant going back to the four way toolpost, and that's been an eye-opener, so much so that the QCTP might only get used on rare occasions. I'm really loving that original post. Why this Neanderthalic change of heart? Well.....
I got a set of 12mm carbide tools with the lathe as part of a deal (same as these: L0099 - L0099 Lathe Turning Tool Kit - 7 piece Insert Type | Hare & Forbes Machineryhouse (https://www.machineryhouse.com.au/L0099)), and dismissed them as "the usual Chinese junk" at the time and never used them. FYI, they're the wrong size. 5/8" tools would be a tiny bit too high and 16mm well too high, but no sweat, I'll make some shims. Measured the difference to centre height, thinned down some 5mm BMS to 3.65mm, done. And you know what? They cut great. The WNMG tool took 3mm cuts off 1045 (I had a lump of 35mm I decided to use) throwing tiny little blue C shaped curls, just like the book says. The DNMG did a lovely job on the finish cuts, and the parting tool did a great job of the thread relief and a beautiful parting cut under power feed at the end (smoother than my facing cuts!). So, smart-ass Chinese dismissal gets stuffed down my throat.
Now, I like to thread away from a shoulder with the lathe in reverse and an upside-down tool. I had a left-hand 12mm threading tool, and wondered, "If I use another 12mm tool as a spacer, will it work"? Now, something in my brain said the geometry was right, but I still can't put it on paper. Anyway, I gave it a run, and you'd never believe it: the tool was dead on centre height with another tool and it's standard shim as spacers. See attached image.
Inverse threading tool.jpg (https://metalworkforums.com/attachment.php?attachmentid=390596&d=1612664775)
The standard 4-way is really rigid as it places the tools right over the compound rather than hanging them out in space. I suspect that helped the parting no end, and with solid dedicated shims a tool change takes the same time as with the QCTP. Even my Eccentric Engineering Diamond Tool holder fits without a shim (don't try turning the 4-way on the compound :oo: ). The only pain is for boring bars, but I could always make a square mount with replaceable sleeves that puts them on centre, or just mount the QCTP for boring operations, as a boring tool is always hanging out anyway.
OK, that would have been a good week had that been the end of it, but no....
I bought a 90 year old Brown & Sharpe grinder from another member recently. I've been working at de-rusting the table (another lesson learned vicariously: if you wet grind, you MUST clean the grinder. The mag chuck was rusted solid to the table and the table T-slots were filled solid with rust, all old grinding dust mixed with water based coolant. Still grinding it out with a Dremel two months later). Anyway, the Mag Chuck was basically immovable, so I tore it down to refurbish it. I won't go into it, but others had been there before me, and it wasn't the previous owner, I know. But someone was in there: screwdriver gouges in the inner plates made that clear.
Anyway, I needed to resurface the inside of the top and bottom plates of the chuck. On my mill I was going to flycut them, but the geometries just weren't working out. No way I could do it in one pass and even my smallest flycutter has a 60mm swing and would have had to be lowered onto the job to start the cut or lifted off while still cutting as I only had 52mm of travel left beyond the length of the part. Eck! But, I have an old 50mm Chinese face mill that I've always disdained as rubbish. It would just fit to start passes and feed back before moving.
I've always had an issue with this cutter: if I cut one way, moved the Y, then cut the other way I'd always get a ridge between cuts. Not my head tram, it's perfect (I mean perfect: the needle barely moves on a 0.01mm indicator). I had always assumed that the cutter was off on the arbour and, again, just "Chinese Junk". But I figured that I had to take a full 1.5mm off one plate, so I'd give it a go and still have plenty to go if I got those damn longitudinal ridges and could see if I could come up with something else.
Did the cuts, but the geometry meant I'd have to lift at one end, and obviously that's an awful idea if you want a flat surface, so I made one cut in x then fed back to the start, moved y and made another cut in the same direction, moved back, and so on ... and no ridges. Huh? Sat and stared and tried to figure thing out and the lightbulb went off. The cutting force when moving left to right was lifting the cutter towards me (on some radius centred somewhere in the middle of the head) and lifting it away from me when feeding the opposite way in x. Making all the cuts in the same direction eliminated those ridges, and resulted in a nice, flat surface. I would like to surface grind them, but they're fine as they are for what they do (let a magnet stack slide on them). Some stoning, clean things up, new high pressure moly grease and the mag chuck runs smoothly now. I still have a couple of things to do to it, but it works nicely now. I may send the magnets off for re-strengthening, I'm not sure. It's about the same strength as those Chinese fine-pole ones at the moment.
So, it wasn't the Chinese face mill after all. It's the Chinese mill! :D Now, my first thought was the Z way gibs, but it's not that, they were locked, so it must be a simple issue with rigidity, but it can only be in one direction, so some serious investigation needed there. The head was way down low to the surface for this operation, as the face mill in on an R8 arbour. If it's a one way rigidity problem then it should be able to be fixed. It's not bad - the ridges that 50mm face mill produced were only 0.01mm or so (I could just feel them with a fingernail), but that's a cliff in my book, so it has to be fixed. One day..... now that I can work around it, I'll probably be too lazy to ever fix it.
So, that was a week of learning! Hope I didn't kill anyone from boredom who may have tried reading all the way though. If you made it, then you deserve a medal!
Attached Images
https://metalworkforums.com/images/attach/jpg.gif Inverse threading tool.jpg (https://metalworkforums.com/attachment.php?attachmentid=390596&d=1612664775) (149.3 KB)
Read the full thread at metalworkforums.com... (https://metalworkforums.com/showthread.php?t=206258&goto=newpost)