Magnetic Chuck for Surface Grinding on my Lathe?

Magnetic Chuck for Surface Grinding on my Lathe?

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neil what are you up to is that a magnetic plate   i hope this isn't going to be one of your  sketchy setups don't twist too hard why not turn it off try turning it off more crikey i've got a regular need to make thrust  washers of a very tightly controlled thickness   and flatness but i don't own a surface grinder  however i do have a tool post grinder for my lathe   in one of my increasingly rare lucid moments i  decided that rather than having a surface grinder   table moving forward and back why not have it go  round and round especially as most of the parts   i need around anyway and then drive a grinding  wheel across the face of the part with a cross   slide using the y axis of the lathe to set the  thickness it might have ended there but i was   looking for some parts on a website and a very  attractively priced fine pitch round magnetic   chuck scrolled up the screen i was hooked but i'd  need to make a d1-4 mount and pins and all that   malarkey a quick google to find the dimensions  triggered the NEIL IS SHOPPING AGAIN algorithm   and bam! an advert for a very attractively priced  part finished d1-4 cast iron chuck back plate hove   into view of my mouse hand it would have been rude  not to click on the buy me now button wouldn't it   the chuck had a shallow 100 millimeter  diameter inset but no mounting holes the magnetic face of the chucks made  from a stack of alternating iron and   brass plates clamped by two transverse pins  which are machined flush with the outside face it probably has the usual internal  cam system and magnetic magic   but i wasn't in the mood  to dismantle it to find out a quick test with a tiny toolmaker's vice showed a   remarkably powerful grip and some  considerable residual magnetism i guess the holes in the mount were intended to  take 5/16 inch cap bolts because they were about   nine millimeters diameter trying to decide where  to make the threaded mounting holes is amusing   i've got to avoid the two transverse tension  pins and the six clamp bolts and the actuation   mechanism i picked an orientation with two holes  halfway between pairs of clamp bolts and away from   the actuation pin and lock pins just hoping there  isn't anything delicate in my chosen spots fingers   crossed firmly step on the mount's about 131  millimeters diameter it's also a little too tall spindle nose hygiene is so important neil  that sounds like an advert for intimate wipes   i did the usual setup for camlock chucks fitting  the pins so the reference line was flush with the   face of the mount checking the fit to ensure  the cam locks had about half a turn of travel   one of them needed an extra turn once sorted i fitted the set screws  which are there to prevent the pins   from falling out but still  allow a bit of wriggle room   so the cams can seat nicely against the  curved sections machined into the pins before doing any machining of the mount  i thought i'd better check it for axial   and radial run out using a dial gauge  on an Noga arm with a magnetic base face run out's pretty good at 15 micrometers,   that's six tenths in imperial but  i can do a lot better than that run out of the raised step's not important  but it isn't very accurate at the moment   once machined it should be concentric  to within a few micrometers just for completeness i'm also checking the  bore run out and the face of the raised step   which i'm going to machine off soon don't know why  really seemed like a good idea at the time perhaps   for a self-inflicted false sense of security  yay measure all the things as the meme goes next steps to machine the face  of the raised section then start   reducing the diameter of the  boss down to 100 millimeters as the fit's critically important i'll do fine  finish cuts to get the fit exactly right it's not   trivial to measure the size of that housing  on the chuck to great enough precision so   cut and try will be my tactics when  you overshoot the mark there's plenty   of meat on that mount so you can  try again loads of times ha ha huzzah it's a splendid fit time for a  bit of a clean up to break any sharp   edges then we'll be ready to drill and tap  the mounting holes in the back of the chuck i'm taking a fine skim off the outside simply   to pretty it up a bit there  wasn't much run out anyway i'm doing a quick debur of the central hole  just so that i don't slice my fingers again i do love these sure shot sprayers i  got one after i saw adam booth using one   product placement is a marvelous thing cost me a  fortune to import it it's pneumatic so i part fill   it with brake cleaner and then give it a squirt  of compressed air instant aerosol not sponsored   lol hey neil hack my avatar an add a Quinn  Dunki cap and safety specs i wanna be a cool kid   uh nope made sets of four dots with my gorgeous  starrett automatic dot punch to prevent idiot   mistakes so the chuck mount and spindle nose  will stay in the same relative positions   even if i take it to bits to  fiddle with something or other   there are four dots on the spindle nose of all  my other d14 mounts it's all about repeatability the holes in the mount appeared to be  on 142 millimeter pitch circle but i   wasn't prepared to trust the positional  accuracy of whoever drilled those holes   so i clamped the chuck to the back plate  and used a 10 millimeter transfer punch   to make a dot where i needed to drill the holes  in the mag chuck off camera i drilled the eight   and a bit imperial millimeter holes out to 10.25  millimeters it did not go smoothly there was lots   of swearing including such choice expletives as bleeeep bleep bleeeeeep  and bleeeep, not advertiser friendly i'm advised the body of the mount is pretty tough stuff so i'm   using a center punch to make  the dots a little more obvious although i use the transfer punch to make marks  in the right places i'm still doing an idiot check   after all there's an idiot at large in my shop  and that looks fine actually one of the holes is   a little bit off so it's a good job i marked the  exact orientation isn't it haha you're fooling   nobody you straight up forgot now you'll have to  guess which way round it goes good luck with that right as a final idiot check i've  calculated the radius of the pitch circle   from the distance between the dots and it  actually matches up with the real radius   i might have to have a little sit  down after all that arithmetic at this point i made a strategic error  one two three blocks are great nice and   flat and parallel except they're also full of  non-magnetic holes can a thing be full of holes   the chuck being magnetic can hold itself  down while it's drilled and tapped   except for all those flipping holes reducing  the grip a bit still i got away with it just i used a wiggler to set the spindle directly over  the center of each punch mark using a c-spanner to   center it very precisely it's ancient technology  but it's self-correcting and totally idiot-proof   unless you try to align it using your fingers just  don't the sharp point drops in nice to the center   punch mark and you can see a tiny deviation if  the dot isn't right in line with the spindle discretion being the better part of valour and  this chuck not being inexpensive i used a center   drill for once instead of just going for it with  a stub drill see i can be sensible on occasions the tap drill for m10 by 1.5 is 8.5  millimeters so i used one of my cobalt   stub drills which worked nicely in this  material i set a stop at 21 millimeters this is just a debur rather than a full chamfer  to clean up the edge of the hole so i can use   the depth micrometer to confirm how deep  the hole is call it nominative determinism   if you like but the name does kind of imply  that's what it's for depth micrometer it's apt Moor and Wright solid British  made up the road in sheffield   actually i like my mitutoyos more sorry sheffield well that looks like 21 millimeters to me a nice fat chamfer on each hole should prevent any   distortion of the face of the  chuck when the threads are cut i used an m10 spiral flute tap to start the  hole using the chuck on the mill under power   and then finish the hole with a hand tap wrench  and uh spiral point tap to complete the thread   the lovely brown earwax stuff CT90 which is  normally the consistency of grease but it's been   so cold in the shop that the dratted stuff's more  like candle wax although a less attractive colour   i always think the chips that come  off spiral flute tap should yell   WHEEEEE sadly i've snapped the cheap m10  plug tap that i normally use to do   a finish cut on the last two threads  of blind holes must order a new one i want to get these cap screws to fit with the  maximum possible thread engagement without them   distorting the brass insert or hitting anything  important so 21 millimeters is the maximum depth   and about 18 millimeters is the  best thread depth that i can achieve   i'm measuring each cap screw to be totally certain   that they'll bear on the counter bores in the  back plate rather than bottoming out in the holes after a trial fit i found the heads of the cap  bolts i'd chosen were too large for the counter   bores there were also a teeny bit too long it  appears my luck's running at its usual level   i held them by the threads in a 10 mm ER40  collet and machined the heads to 14.6 millimeters   diameter so they'd be a loose fit in the counter  bores and then chamfered the corners a little after sorting out the heads i grip them tightly  in an er 40 collet and neil we've already spoken   about your sketchy setups this is not going  to end well if you're as clumsy as usual   as i was saying before i was so rudely interrupted  i carefully removed three millimeters from each   bolt and chamfered the end of the threads nobody  died no parts went into orbit no tools were ruined   for a change it did scream a bit sadly my  lantern chuck's too small to take m10 bolts i'd be hugely cheered if you could prod  that like button it really helps me a lot having failed to have any disasters i gave  the threads a good polish with garryflex   abrasive rubber Cratex or bright boy would  be a much better choice but i've got loads   of Garryflex in rather fetching autumnal shades  or is that fall shades mostly mud brown anyway   it's always safest to run the lathe in  reverse when polishing threads so the   abrasive and your fingers are pushed  away from the whirly finger mangler   note the nakedness of the hands no gloves for  anyone to complain about this is one of those   cases where even flimsy gloves are definitely  not advised sorry i sounded like an "elf an'   safety" nut for a moment there let's go and do  something dangerous off camera to compensate   i stoned the rear face of the chuck to remove  any burrs then cleaned it very thoroughly to   remove any remaining abrasive using brake cleaner  and compressed air same treatment for the mount   if i had any marketing sense i'd label the  next segment asmr peace and tranquility pink   noise and relax feel that tingly  autonomous sensory meridian response well as the late john peel once said you  couldn't possibly talk over that could you   hey wakey wakey oh heck i nearly nodded off  there right i've mounted the completed chuck   so let's check the run out first the mount looks  like 30 micrometers that's a thou and a bit for   anyone listening in the 1950s as expected the  peripheral run out's not exactly stellar but i'm   not going to fix it it'll never be spun fast and  the internals are probably out of balance anyway   the face is a critical element that really must  be flat and perpendicular to the lathe axis   so i'm taking a fine clean up cut  using a polished carbide insert off camera i cleaned the surface and  stoned it run out looks reasonable   this is after i removed and replaced the  chuck twice to check for repeatability i reckon less than two micrometers or about a  tenth whatever that means i found a two inch   square by half inch thick piece of cold rolled  steel deburred a face degreased it and put it   in the center of the mag chuck that ought to  be a decent test of adhesion and what happens   with interrupted cuts i stood well back from the  danger zone wore a hard hat with a full face guard   and kept one foot on the emergency stop brake bar  then depressed the lever on the make-it-happener it machined perfectly so i de-energized the chuck  remove the part deburred the machined face and   fixed it back the other way around roughly in  the center of the chuck stood well back cocooned   in my ppe and lit the blue touch paper once  more it machined perfectly with a nice finish quick check with the dial gauge showed no  significant run out so i checked the thickness   of the part at four places where the cut was  continuous the mic showed around five micrometers   of variation across the surface i tried fixing  the block near the edge of the chuck face and   spun it at 750 rpm with ppe and a polycarbonate  shield it worked perfectly even at 750 rpm   this is definitely not intended for a use  at any more than about 80 rpm for grinding   but it's good to know that i can also do  machining so long as the parts are significant   size and perfectly flat on the lower face throwing  what little caution i have left to the four winds   i've protected the way, fitted the tool post  grinder and fired it up with the lathe at 275 rpm   and the grinder at 10 000. as well as covering  the lathe ways i'm using the shop vac to suck up   most of the grinding dust and sparks i'll make  a proper fixture for the vac pipe at some point in upcoming videos i'll make a super glue  chuck around 120 millimeters diameter   with a sacrificial aluminium surface on a smaller  d14 mount to hold very thin steel parts that can't   be gripped with a mag chuck and stainless brass  copper and aluminium parts that can be glued   but are non-magnetic after that next job's going  to be a vacuum chuck to hold dielectric plastic   parts such as lenses and Fresnel Zone Plates that  finish makes this little project worthwhile the   grinding wheel i used was slightly unbalanced so  there are some harmonics the real parts will be   done with a much better wheel and spindle once  i get it machined lots more projects are in the   pipeline if you'd like an irritating reminder  when the next one's published please consider   subscribing and clicking the bell i know asking  is unfashionable these days but then so am i

2022-02-23 00:02

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