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Mini-Mill Improvements, A Companion WIP

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  • Ringo
    replied
    there is way to confirm and/or measure a accurate squareness without any standard square.
    it's an old wood tablesaw trick.
    take a piece you 'think' is square, on table saw lets say 6" sq,
    using your fence or mitre make a skim cut, rotate the part 90 degrees that the fresh cut is on the fence, take another skim cut.
    repeat this till you go around the part 5 times.
    the last skim cut is in fact a parellel if your fence/mitre is in fact square.
    Should be the same with your mill, the fixed jaw is your fence, and if you go around 5 times and the last cut is a parrellel, then you are square.
    What this does is magnify the error every time you place the fresh cut on the fence, turn it 5 times you magnify error 5x.
    Go around 10 times and you get 10x the error, this makes a small error measurable.
    If the last cut is a taper, you are not square

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  • epicfail48
    replied
    So, conclusion to this part of the project. I got all the bits and pieces from the old saddle moved over to the new one, no pictures of that process because franky, its boring. Theres like, 10 screws and you can find guides on how to disassemble a mini-mill anywhere, you dont need my hackjob version of it here. So, howd i do?

    Well, first impression was that the sliding surfaces felt a lot better. Honestly, thats probably confirmation bias, but it really does feel like everything meshes together just a tiny bit better and makes for smoother movement. As far as accuracy goes, huge success! Now, before i start going into my numbers i want to be very clear on a few things; I am measuring with the standards available in my shop, and i do not have fancy standards. My reference surfaces are 123 blocks and my screwless vise, i dont own a granite square or any other fancy gizmos, no super precise certification sheets are hanging on my walls, my tests are not NIST traceable. All these numbers are just measured with my basic equipment in my basic shop on my basic tools by my basic self.

    So, disclaimer out of the way, i started off by measuring on the machine. I got the fixed jaw of the vise trammed along the X axis, then swept a dial indicator along the side of the vise using the Y axis. With the original saddle, this test got me about .006" difference over about 4", so an error of .018" per foot. Not really an acceptable amount of error. Same test with the new saddle gave me about .0005" over the same 4" distance, so about a .002" per foot deviation. Hardly toolmakers accuracy, but frankly good enough for me, doing the math that puts the angle at 89.993 degrees, or 26 arc seconds off square. Could it be better? Yeah, probably. Do i need it to be better? Not for the work i do.

    Next thing i tried was squaring off the end of a bar of steel, then checking it over at the surface plate with a comparator. The steel was a piece of 1.5" wide 5/8" thick 1018, held in the vise, the end squared off by moving the Y axis. Took it over to the plate stood it up on the freshly cut end, used a 123 block as a self-proving reference square to calibrate the comparator, then checked squareness on the part about 3" up from the surface plate (making sure to measure the face of the bar that was up against the fixed jaw of the vise). End result? Bout the same as what i measured on the mill, about .0004" off from square.

    Too much detail that makes very little sense and doesnt prove anything to anybody but me? Probably. Bottom line is that my mill now cuts square to a decent enough tolerances, plus the overall smoothness and rigidity have had a subjective improvement from this. Time well spent to me. Now i just need to get the DRO scales reinstalled and im off to the races, at least until the next project to improve this thing. Already got some plans brewing. Unfortunately i dont have access to a larger machine so i cant get to work truing up all the other dovetails, id love to recut the base and table dovetails, so the next project will probably be something a little smaller. Ive got some ideas for replacing the leadscrews with ballscrews to start making steps to a CNC conversion in the distant future brewing

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  • epicfail48
    replied
    Now, heres the setup after being rotated:


    I have the same side of the saddle referenced against the fixed jaw, ive flipped the saddle vertically, and the saddle itself is referencing off a set of match-ground 123 blocks from the mills table, the vise is just holding it square and in place. Here again i trammed the part in along the X axis as fine at my tools allowed, and again, if my theory works then the X and Y axes on the new saddle should be as square to each other as the corners of my vise, so pretty square. The same sequence of cuts is made on these dovetails and thats it, were finishedL



    Got a set of nice, freshly cut, smooth, flat, parallel dovetails. A word of note, im saying flat but honestly i dont care enough to blue up a straight edge to see how flat. In this case, flat enough is flat enough for me. The scrape marks on the ground surfaces are intentional, its redneck flaking. Frankly i didnt care enough to fully scrape in those surfaces but still wanted to try to prevent any stiction. Works on the other saddle and the ground surfaces i did on it, so i figure it cant hurt here.

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  • epicfail48
    replied
    Behemoth of a dovetail cutter finally showed up, so im back to work on the saddle. Quick refresher for anybody who doesnt feel like reading through, im presently finish machining a replacement saddle assemble to correct the X and Y axes not moving square to each other. Ive already got the outside bits surface ground flat to use as reference surfaces, now im machining the 55 degree dovetails.

    Now, in this next part im going to be explaining how and why im cutting these dovetails and what im focusing on. I realize that a lot of people already know how to cut a dovetail, if you do feel free to skip this part. This is more for Joe Newbie who stumbles across this thread. Now, some visual aids:



    Some color-coded photos of the saddle, both as its own thing and installed on a mill. Itll make explaining easier for me. Now, first face we want to look at is the black face, what im going to call one of the working faces. This face is going to be what makes direct contact with the dovetails on the base of the mill and underside of the table. These faces, on top and bottom, need to be parallel to each other, otherwise the face of the table wont be parallel to the travel of said table. Flatness and parallelism of these faces has already been taken care of at the surface grinder, and theyve been ground as flat and parallel as i can measure in my shop.

    The red and green faces make up the portion of the dovetail that ill be milling in this setup, and can be referred to as the actual dovetail. In this instance, the red face is a working face, it makes direct contact with a mating face on the table or base, depending on which side of the saddle youre looking on. This red face needs to be parallel with the other half of the dovetail making up one axis, and perpendicular to the dovetails on the opposite side of the saddle. The green face is clearance in this application, it has no real bearing on anything.

    Now, to re-cut the dovetails ive got the saddle clamped in my milling vise, with the ground faces of the dovetail trammed in to be perfectly parallel to the table, and the vise trammed in the X direction. In order to get the new saddle square on a mill that doesnt presently move square, im not going to make any cuts along the Y axis, instead im going to rotate the vise and attempt to transfer the accuracy of the vise onto the part. Now, the first setup:


    Ground face up against the fixed jaw, long edge of the vise trammed along the X axis. The cutter ill be using:


    Thats a 50mm 55 degree dovetail cutter. Yes, the angle is bolded for a reason. The dovetails on these machines are 55 degrees and require a non-standard cutter, as i found out to my detriment. Bit of a pain to find, only ones i could find were cheap imports, and yes, thats the bad cheap. This one is HSS, ran me about $30, and has an annoying amount of runout. Still, the angles proper and it cut well enough. Its being held in a 5/8" er32 collet, which is interesting for me because my mill doesnt like the stickout that collet game me. At least, my mill didnt used to like it, after upgrading the column, 0 problems. Money well spent im feeling. Anyways, lets move on to the part:


    Thats a closeup of the dovetail as i got it. It doesnt show up quite as bad in a photo so youll have to take my word for it, the surface was pretty rough and franky didnt feel flat at all. Color the surfaces of the dovetail with a sharpie and take a quick pass to see what gets cut:


    Surprising nobody, its not flat. I wont bore you with the step by step on how to cut a dovetail, ill just skip to the end where i got the entire surface remachined and looking good:


    Actually got a bit of reflection going on the machined surfaces, i was pretty happy with that. Thats one half of the dovetail done, now im going to step over and cut the other side to be parallel to the first, and just as smooth, before breaking down the setup to work on the other side

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  • epicfail48
    replied
    Originally posted by RB211 View Post
    Nicely done. The one advantage I can think about the mini-mill is that most parts of it would fit on my surface grinder, if I ever had a need to get one.
    one of the reasons I'm very happy I stumbled across a 6x18 grinder instead of the more common 6x12 actually, it's just big enough for everything on the mini mill to fit, I think. I haven't tried the column though I'm fairly certain it would. Someone skilled enough could certainly regrind everything, dovetails and all, without horribly much issue.

    Originally posted by BCRider View Post
    A nice job on analyzing and correcting items as you've found them. And nicely written up too.

    An interesting option for some future time with the solid column would be the addition of an external brace to give an increase in stiffness if you think the scale of the machine would warrant the effort. Something to consider at some point?
    I appreciate the compliments! My hope is that if someone happens to stumble across this thread they'll be able to use my misadventures as at least a source of ideas.

    With the solid column I doubt that any sort of external brace would add enough stiffness to justify the effort. With the tilting column the brace makes sense as the tilting mechanism sacrifices a massive amount of rigidity, and an external brace serves to fix that. With the solid column the column and based are fixed solidly together and any rigidity issues are with the casting itself, not the fastening method, if that makes sense. Adding to the rigidity of the column would require either filling the column with something like epoxy granite or just bolting massive plates of steel to the sides to try to build up the thickness. Either way I feel you'd hit really diminishing returns. As it is now, the weakest link in the system, rigidity wise, is probably the spindle assembly. Still has the stock radial bearings, and the head castings are a bit on the thin side. New bearings are probably going to be the next thing on the list, still get a bit more tool deflection under heavy load than I'd like and bearings seem like the next logical step. Still though, the column assembly was the biggest weak link in the system, with that replaced it's honestly a different tool

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  • RB211
    replied
    Nicely done. The one advantage I can think about the mini-mill is that most parts of it would fit on my surface grinder, if I ever had a need to get one.

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  • BCRider
    replied
    A nice job on analyzing and correcting items as you've found them. And nicely written up too.

    An interesting option for some future time with the solid column would be the addition of an external brace to give an increase in stiffness if you think the scale of the machine would warrant the effort. Something to consider at some point?

    Leave a comment:


  • epicfail48
    replied
    And here we are after grinding:




    Forgot to get a picture of both sides. Ah well, take my word for it, both sides look passable, and are miles better than what i had at the start. Anyways, now i have 2 flat, parallel, non-working surfaces on the side to grip in the vise on the mill, and 2 flat, parallel surfaces that the table references off of when its installed. Speaking from experience, if i were to install this saddle on the mill as-is the table would be perfectly parallel to the movement of the X and Y axis, and smoother in movement. Ive actually done this same grinding on the saddle installed in the mill, i just didnt machine the dovetails in the original saddle. Speaking of the machining on this saddle, heres how i plan to do that:


    The vise is rotated 90 degrees from normal operation and trammed in along the X axis to as perfect as i can get it. I think i measured in the neighborhood of 3 tenths across the length. The saddle is clamped in the vise with what will be the Y axis dovetails facing up. My theory for this is i grab the part like this, machine the Y axis dovetails, then flip the part over so the X axis dovetails are facing up, rotate the vise 90 degrees, then machine in those dovetails. This entire time im only moving the X axis, never the Y axis, with the reference for squareness being however square the fixed jaw of my vise is to the body. Im taking a risk here and assuming my vise is square, but my vise is the only thing i have in my shop that actually has certification paperwork. Its a risk im willing to take. Again, i know that my mill will cut acceptable flat and straight along the X axis, so ill be able to re-machine the dovetails without issue, and im just transfering whatever the squareness of my vice is onto the new saddle. This was the best method i could come up with with the materials i have available. Hopefully itll work out, just have to buckle up and see.

    Anyways, onto machining. Now, im aware that the overhang on the part is a bit much and frankly asking for problems, but in this case i feel its a necessary evil. Im limited in space for how i can set up this cut, and im honestly not removing much material, just barely skimming the surfaces, so i dont imagine ill hit any snags. First thing i did, since i already had the face mill installed from the last project, was to skim the clearance surface in the center of the saddle. If you skip back a few pictures you can see what that surface originally looked like, a chainsaw wouldve left a better surface. This is just clearance so the surface finish doesnt matter in the least, but id still like it to look nice and again, face mill was already mounted up and ready to go. Added bonus, this gives me a chance to see how this piece will react to machining and gives me another surface to reference off of if i need it. Final thing to note before the cut, i swept a test indicator over the freshly ground surfaces of the dovetail, just to make sure everything was trammed in and i wouldnt create any weird dovetail geometry. Quick pass with the face mill:


    Much, much nicer finish. Not perfect mind you, but a far sight better than what it was. Plus, the 45 lead in of the face mill leaves a nice chamfer on the sides of that relief valley, just looks all around better to me. Now, from here i can move on to actually recutting the dovetails, which i would love to show you if it were for the fact that for some bloody reason Seig ignored convention and made the dovetails 55 degrees instead of the 60 degree standard. I dont have a 55 degree dovetail cutter, not yet at least, so here the project sits until i get that in...

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  • epicfail48
    replied
    New column in place, time to address the next big issue with this mill; squareness, or the lack thereof. Unfortunately, the X and Y axis arent square to each other, thanks to a defective saddle. I kicked around with a few ways to fix this for quite some time, before finally deciding on what i think to be the easiest way to get the best results. To that end, i went down to Grizzly, bought a new saddle casting, and im going to completely remachine it to hopefully better standards. Making this just slightly more challenging, ill be doing the machining on this mill as it currently is. I know that my mill can make something flat and straight enough as it currently is, it just wont cut square, so it just became an issue of figuring out how to do all the work with only 2 axes being used, X and Z. Ill try my best to explain along the way what im doing, to start with lets take a look at the new saddle:




    As you can doubtless see, its pretty rough for a 'finished' part. Theres the baked on layer of cosmoline, to say nothing of the sliding surface that looks like it was milled with a chainsaw. Ive got it sitting on my surface plate, while i was taking these pictures i was also doing some preliminary checks on the geometry, seeing if the sliding surfaces were parallel and flat, if things were square, etc. Sparing you the gritty details, they werent. Neither side was flat, nothing was square, but thats okay, this is a rough casting for my purposes. A few quick sharpie marks for explanation purposes:


    Im going to start off at the surface grinder to get myself some flat surfaces to use as a datum for the machining. Starting at the sides with the red Xs, im going to get those flat and parallel. Once i have both of those sides ground, im going to grab the whole thing in a milling vice with the freshly ground flats up against the jaws and get the flats of the dovetails (black X marks) mostly square to those sides. I say mostly because theres no need to have those 2 surfaces perfectly square and i suck at grinding, so the extra effort id need to put in would be completely pointless. I ended up getting the 2 surfaces square to about .003" worth of deviation measured with a squareness comparator at about 3 inches up the part. Again, not a critical thing, so thats close enough for me. The more important thing was to get the flats of the dovetails flat and parallel to each other, which they now are, pics to come on that

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  • epicfail48
    replied
    Alright, been a while but i did a bit more work on the mill. Most noticable, i finally scraped together enough to get the solid column conversion kit from Little Machine Shop:


    As with all things from LMS, its ridiculously overprices for what you get but still absolutely invaluable for these machines. Before i get too deep into that, lets talk about the why, because i know someone is going to ask; I made the switch to eliminate the tilting mechanism as a source of deflection in the machine. Im well aware of the fact that i couldve made a bracket to stiffen the existing column, rather than buying the new column. I discarded that idea for several reasons. First off, i dont have a supply of scrap steel i couldve made the bracket out of, so i wouldve had to buy it new, and between the cost of the steel plus the cost of the time, i wouldntve saved any money. Its also worth mentioning that the solid column is custom made to higher standards for LMS, so in addition to it lacking the pivot, the walls of the casting are also twice as thick. Cant do that with an extra plate.

    Anyways, moving on to quality, its... Well, its better than stock. Still needed some shimming to get things into alignment, had to drill a hole in the column to mount the gas spring. Absolutely baffled me that i needed to drill into the LMS column to install the LMS gas spring kit thats a default option on the LMS version of this mill that takes all the same parts. Not difficult to do, but odd. The most irritating thing about installing was the paint job, for some reason they painted the mating surfaces too:


    Easy enough to correct, but again, irritating. For the price i shouldnt be scraping paint off. Anyways, got everything installed, got the appropriate shims to get everything within tram to about .001" on a roughly 8 inch circle. Not perfect, but anything finer than that needs sub-thou shim stock and i only have .001" stuff. So, hows it perform?

    Night and day difference. With the tilting column i could get things to work, but not well. I was limited to a D.O.C of about 1/4", and thats on a good day, in steel no matter the radial engagement, otherwise chatter would leave an flat out unacceptable surface finish. Aluminium and softer metals werent much better. Face milling was about the same story, my 2 inch face mill was limited to about .010" D.O.C in steel, and that was assuming i could live with a bit of chatter and the machine sounding like it was about to fly to pieces. With the solid column, no problems at all on either from, Im pretty confident id stall the motor now before i outdid the rigidity (Motors tiny, keep in mind). I was able to take a .060" D.O.C slotting pass in mild steel with an acceptable surface finish on the walls and floor, a facing pass with the 2 inch face mill at roughly 70% engagement at a .025" D.O.C, and side mill off about .020" from a bar of 5/8" cold roll. Little bit of noise from all those cuts, but again, passable surface finish on everything, no chatter, and the machine didnt sounds like it was going to explode. I was even able to get some really nice chips off the face mill:


    Aluminium inserts in an SEHT mill, so the surface isnt super shiney, but seriously, those chips are nice, especially since i used to get dust and flakes instead of nice little lines. Overall, pretty stoked about this. Still need to get the DRO scales resinstalled, and finish washing the taste of dealing with LMS out of my mouth, but overall im pretty happy with this. Tool was already useable, now its just nicer to use.

    And before anybody says it, even factoring in all the upgrades ive done, ive still got barely $500 in this thing, counting the cost of the machine, and ive been able to make parts from day 1. Good luck managing that with a craigslist special, especially in my area

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  • RB211
    replied
    Do you trust these Chinese factories are paying a professional tool scraper to make sure these hobby grade machines are scraped in perfectly at the price points the importers demand? If anything, they feel more pressure today to produce at a lower price point.

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  • Cenedd
    replied
    Not sure any of this is of use to you but I suspect I have a similar mill to you and have done some of this myself. I've got an SX2 with the gas spring (from factory/reseller) and I added the fixed column a while back. Two things that may be of interest. Firstly the fixed column kit comes with a new longer leadscrew for the Y axis and secondly you may find that once you put it together you have to start again with truing up the table and the column.

    The pads on the base for the column to mount and/or the bottom of the column are not perpendicular to the Z axis so shimming is going to be necessary unless you're damn lucky or can fix that on your surface grinder. I contemplated mounting the column it on the lathe to true up the bottom of that but chickened out when I realised it would have to be held off the dovetails and not just a flat side.

    I don't think I'd measured it before I made the change but definitely afterwards I had the same issues with the table. The way I went about it was to tram the head as close as possible, mount three bars of 20x10mm steel square to the T-slots (or running in the Y axis) with counterbored screws and then mill the surface of each bar flat using the Y axis - if I remember correctly, the X was more off for mine and the Y not so bad but also shorter. I then sent the table out for surface grinding and had them chuck it upside down (milled bars against the mag chuck) and skim off the bottom of the dovetails. This then made that true to the plane of the mill and it was then just a case of flip it the right way up, remove the bars and skim the top. If I remember correctly it came out with less than 20 microns (take with consideration for the precision of the cheap import DTI used!) variation.

    Pretty sure we also cleaned up the base casting by assembling the table to it (one trued), mounting the whole lot to the mag chuck upside down, skimming the bottom of the casting and then flip, dissemble and skim the pads for the column that were very roughly milled and quite far from true.

    All the ways should probably have been scraped true (there's definitely a bow in the Y axis ways) but I didn't have that much spare sanity!

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  • epicfail48
    replied
    Been a while, time for an improvement by necessity! In the way that things go, i manage to finish up part of a project, and the second i did, something broke. In this particular case, it was the Y axis, the leadscrew completely seized in the bearing block. What i think happened is that, somehow, a tiny chip managed to migrate into the block, wedge itself between the leadscrew bearing surface and the block, ball up and gall the hell out of everything. Had to press the pieces apart, the results were... not pretty:

    The leadscrew, and this is after a cleanup cut on the lathe to take off the worst

    The bearing block, complete with crater and massive score mark

    The rear of the bearing block has a collar on the leadscrew running against it as a bearing surface. Honestly, poor design

    Clearly, i need to do something to fix this. I couldve just cleaned up the leadscrew and bearing block, gone in there with a flex hone or something and taken off the burr, thrown it back in service and called it good, but that seemed kinda hacky to me. I wouldve liked to make an entirely new bearing block, but that would require a working mill for parts, and clearly i do not have a working mill. I ended up deciding to just clean up the leadscrew, which wasnt damaged too badly, and then bore and bush the bearing block.

    Some quick planning and i got off to the races. First was material, i needed something to make the bushing out of. Wouldve like to have used some bearing bronze, but i dont have any of that. What i do have is a big hunk of cast iron, and i figure for this application cast iron will work more than well enough. The materials assembled:

    Leadscrew, bearing block and a roughly 15/16" slug of cast iron. Dont ask how i made that, hole saws probably arent meant to be used like that...

    A quick, garbage sketch of what im planning. The pencil is a non-scale drawing of the existing block, the black line is what the bushing will take up. The flange on the bottom is what the collar on the leadscrew i mentioned earlier will now run against, figured thatd be better than the chinesium of the block. I need to get better at drawing up plans, they make sense to me but theyre really a mess... Basics are the OD of the busing is .625", with a 12mm running fit bore put in it for the leadscrew to run in. Bushing is the full length of the block, with a .125" thick .7" diameter flange on the bottom.

    Half hour of turning later and here we are:


    Cant see it in that photo, but the bearing block has been bored out to ~.625" (measured with a field-expedient go-nogo gauge as im lacking anything for internal hole metrology), and the bushing being turned to .6265" for a moderate press fit. Little much of a press fit actually, as it took a bit more force that any of my tools could put out to seat the damn thing... Hammers fix everything though. Got it all pressed together, and you can see that i screwed up the counterbore for the flange in this picture:


    And thats where it sits for now. Still need to bore out the bushing for the leadscrew, then true up the faces, but thatll be another days work. Managed to melt my lathe belt, have to fix that before anything now. Sorry for no photos of everything in action, my shops a mess and i probably wasnt doing things properly anyways. Picture a fixturing job done by a monkey and youll get an idea of how i turned all this

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  • epicfail48
    replied


    There she is, all reassembled and shiney, complete with a few marks already in that nice ground finish. Errors in referencing aside, the end result turned out okay, ive not got a flat table thats parallel to within a few thou of the direction of movement, and even the error is within the acceptable level of tolerance for my work. Once everything was put back together i checked for tram, which i didnt photograph because everybody photographs tramming a mill. Left-to-right rotation was easily dialed in to under a thou off on a 9 inch circle, but theres still about a .004" nod to the head. Adjusting that would require shimming the column, and being that i plan on replacing the column i didnt see it worth fussing with at this juncture.

    So, all the effort, was it worth it? Well, an indicator run across the base of the vise shows 0 misalignment, so it looks likely. Proofs in the pudding though, so time for a test:


    Bar of 1"x2" aluminium, tossed in the chuck tight against the parallels, then skimmed on both sides with a face mill. First thing i noticed was the double-cut pattern to the surface, where the cutter actually cut on both sides. First time ive seen that, and a nice confirmation that my mill is now actually in tram. The nod in the column didnt present as much issue as youd think either. Beyond subjective measurements, a micrometer read on on both ends of the bar showed a difference in thickness of .0012" across the 9 inch span of the part. Given that im used to seeing about 4 times as much change on a part 1/4 that length, im going to say yeah, it was worth the effort!

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  • epicfail48
    replied
    Omitting the assembly steps again, time to repeat the same measurement process from the start of all this. Indicator is zereod at the back left:


    And then traversed to the back right:


    Flat 0 across the full length of the travel. Against all odds, my idiot error actually ended up making things better, since the right side used to be >.004" lower than the left, which was what caused my thickness issues. Somehow i fixed the problem i set out to fix. With the indicator still zeroed, the front corners also need to be checked:



    As you can see, the front left of the table is high by ~.0025", and the right is high by ~.0035". This is where my referencing off the wrong face came back to bite me in the ass, once i realized my mistake in reference surface i went back and measure the thickness from the top of the table to the bearing surface of the dovetail. Sure enough, the table is thicker at the front, which confirmed 2 things; the top of the dovetail and the bearing surface were no coplaner, and i was an idiot for referencing everything off the wrong surface. On to the conclusion section

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