(Temporary) Spindle mount materials recommendation

Ok, I'm finally trying to get back to this- it's just so easy to get distracted when you're having so much fun cleaning up after failed hard drives. So... time for some catchup.

First:
MDF. Yes, it's squishy, unsuitable, and altogether tacky - thus the fact that it was never meant to be more than a temporary mount to cut something more suitable out of something more suitable. Continuing to discuss it's appropriateness is (and has been) just a distraction at this point.

Second:
Everything else.
(quick - there's still time to run!)

I don't think variables are really an issue at this stage - or at least not a significant one. Rubber's squishy, but there's a lot less there than it looks like - it's a single thickness of maybe .05" thick before being compressed, so it's not a significant contributor. MDF may squish & flex under load, but for the load produced by a dial indicator - or even the dusting cut on (other) MDF that started me on the adjustability kick in the first place - it might as well be a rigid body. The issue isn't even that the spindle is currently crooked on the MDF mount - it is, certainly, but less than it initially was, and little enough that I'm not concerned about it for cutting the next version.

The problem I'm hung up on right now is that the spindle is going to be crooked on the next version for exactly the same reason it's crooked on this one: because while I can measure said crookedness, I don't have fine enough control over the position to actually correct it. It doesn't matter whether I make the final (or not-quite-final, or next) version out of aluminum, or delrin, or hardwood, or plywood, or more MDF when I can't control precisely where the drop-in T-nuts are going to pull the mount as they tighten, or adjust the mount and/or spindle afterwards to compensate. I suspect using standard T-nuts would cause less movement, but considering the hassle of disassembling the axis to get them in, it'll probably take more than "I think I might improve things incrementally" before I find the motivation to try.

Yeah, probably without those - instead of making the mount easier to adjust post-assembly than the current design, the holes behind the spindle would make it impossible (also, there are four slots in the rail, not three... but who's counting?)

Also, I may be misinterpreting the picture, but I'm not so sure about those square bosses. I'm assuming they're meant to ride in the slots for alignment (since if the drop-in T-nuts are going to tighten properly, the bosses would have to be somewhere less than .04" tall & lending little bossy strength to the holes). To make any difference in alignment, though, they seem like they'd have to be precisely mated to the V-slots - at which point adjusting for your-B axial twist becomes impossible, and your-A axial shimming could only happen between the mount & spindle (whether that last matters, I don't know).

The whole assembly could be machined to be inherently aligned by cutting the back side & filing the bosses to a perfect fit, bolting the mount to a chunk of C-beam, aligning that perfectly to the X or Y axis, and then cutting the channel... but by that point the "easy to machine" has probably gone out the window (and I'm also not sure whether the Lead has enough Z travel to do it without removing the spoilboard).

Without the bosses, though, yes, it should be easy enough to machine. It neatly sidesteps the question of whether the two or three separate mounts are correctly aligned with each other, too. But without the bosses (and specifically without the bosses fitted to the rails) it doesn't seem to do any more than the two-mount design to make sure the top of the mount is aligned with the bottom, or to allow any more adjustment of whatever misalignment there is (whether from that, or anything else).

As Gary points out, though, it's entirely possible - or even likely - that I'm over(under? sideways?)thinking this, so I stand ready to be corrected.

I didn't explain it well - the idea (and the reason it was such a pain in the things-the-forum-will-turn-into-*'s) was to make an eccentric that would stick out on the outside of the corner, instead of between the corner and C-beam where it would cause overhang, increased leverage, a drastically reduced bearing surface, indigestion, and bad breath.

Something more like this:

( yes, that's actually a #10-32 not an M5. good eye! it was the closest screw McMaster had a model for )

It still keeps the wide bearing surface of the corners, and doesn't move the mount or spindle any farther from the C-beam than before - it just relocates the hex portion of the eccentric out of the corner where it can actually be gripped/turned. It's just a pain to make, a pain to enlarge the slots in the corners to accept an eccentric instead of just a screw, and I can't get rid of the nagging suspicion that the long screw would still introduce new weaknesses - but so far it's the only thing I've come up with that would allow finer adjustments than "tighten down the drop-in and hope it shoves everything to the right position this time".

If I wasn't so sure I'd end up kicking myself as soon as it came time to put everything back together with the new mount, the temptation is mounting to just go with the industry standard Machinery's Handbook-recommended method of high precision adjustments: "just keep whacking it with a hammer until it goes where it's supposed to".

(that was Machinery's Handbook, wasn't it? Or am I thinking of Short-Tempered Mechanic's Handbook again?)

The concern (at least on my part) had more to do with the long bolts bending than shearing off or otherwise catastrophically failing, but your point is well taken. I generally trust the extrusions (although the amount I saw the "C" close up on the end of a dropped rail that came in my first shipment should probably make me think twice), but wasn't even thinking about the wheels.

That being said, I still don't want my nice pretty build polluted with filthy MDF any longer than absolutely necessary.

It's "close enough" to recut the mount right now - but that's as close as I can get it. If I go ahead and cut a new mount that doesn't allow me to adjust it closer, though, it's only going to be "close enough" until the first time I need to surface something, at which point this starts all over again and/or I dedicate the next few days to sanding. Thus my current obsession with adjustability.

Because, well, otherwise the first time I'll realize I need to surface something will almost certainly be tomorrow afternoon. And only 'afternoon' because mornings and I don't get along. It's a bat thing.

"...just to spite them! Doubt me, will you?"

Oh. Or that.

So, since you're also using dual mounts (I like that split ring design, btw), how do you adjust your spindle for A/B axis misalignment?

Is that a vacuum table? I'm going to be pestering you with questions about it, somewhere down the line.

I was a little more excited about vacuums and CNC (whether vacuum tables or vacuum dust shoes) before a trim router ignited my MDF and I looked up some of the pictures of other people's CNC fires, though... and then thought about what would happen if the fire ended up inside the vacuum, instead of just fed by airflow to it. Of course, I suppose that's probably still preferable to letting thick clouds of MDF sawdust spontaneously blow my shop into the sky high (via the intervening first floor). Or to clamping everything down manually.

Also, despite the "300V" stamp on it, every time I look at the picture I keep thinking you're using Cat5 as a power cord. Maybe they've upped the wattage in the Power over Ethernet standard.


-Bats
( still waiting for 30A 3-phase over WiFi )

 

Unfortunately my imagination, like my beagle (who happens to be far smarter than I am), has decided that the world being buried in snow is a good excuse not to get out of bed - so I had to outsource the job to Autodesk.

If Autodesk is interpreting what you're describing right, it seems like it would look vaguely like this:

...although I suspect they're not interpreting it properly, since I think you described it being portrait rather than landscape, and and the slots ended up on the sides instead of the corners because... um... reasons... but I don't think either changes much for visualization purposes. I also couldn't track down the picture I'd seen of your machine, so I modeled it based on all the details I thought I could remember (ie, that there were two chunks of C-beam on the gantry, and... err... well, that's about it). Err... They. They modeled it. Not me. Nope. Nope. Totally Autodesk's fault.

Based on my extensive (more then fifteen minutes!) experience with the design, it seems like those slots (which I couldn't even be bothered to put in the right place) would work better as shallow arcs (of the same circle) if you want the one board to actually rotate relative to the other. I suppose two diagonal slots perpendicular to each other could accomplish the same thing, if you don't care about the rotation being around a stationary axis..

That may be trickier than it sounds, as you'd need something that could move freely in two dimensions while adjusting, only to bolt down solidly afterwards - unless you just wait until everything's in position before drilling the lockdown holes. The problem I stumbled across while modeling it was that it was easy to model the bolts & holes in one board, but as soon as I tried to figure out how they fastened into the other one, I'd suddenly lose my mobility. In the model, the only two bolts that can fasten into the X base are the ones in the slots (which, looking at it, makes those "pivot" bolts pretty much decorative). One possibility might be to move the arc slots back to the corners where they belong (but all four corners this time) and use them as lockdowns.

Another problem I see is that, due to the gap, tightening down any bolts going between the two boards will tend to make them bend. This may not be a problem in itself, but it could mean that your alignment shifts as you tighten it down, depending on just how flexible your material is. What might be a bigger issue is the amount of flex being mounted to a big sheet of ply would provide to the Z axis when cutting. I can't imagine it being a significant issue with aluminum at that thickness, but would definitely expect a fair bit of flex from plywood (I've never worked with Delrin on that scale, and have no idea how bendy it is).

Of course, in the unlikely event you've worked on the design for slightly longer than my admittedly extensive fifteen minutes, you may have already solved and/or dismissed both of these, or be able to spot the fact that my model actually bears absolutely no relation to what you're describing.

That sounds like an awfully large and expensive slab of Delrin to use for a mockup/interim piece... but I suppose a couple slots & bolt holes won't do much to keep it from being recycled into other projects.


-Bats
( afraid to caffeinate, lest my suddenly functional brain realize exactly how wrong I was about absolutely everything in this post )

 

Ok, lemme run through a quick(ish) overview (for you, for anyone else reading the thread, but mostly as an excuse for me to nail down some things my brain's had trouble visualizing):

A axis rotates around the X axis, the B axis rotates around the Y axis, and the C axis is what the endmill does really really fast:


The tricky bit is that the effects of rotating on the B axis will vary depending on where you rotate it (this is true with the A axis too, but the adjustment points are different, and it's a little easier to explain using B). This could probably be more precisely described by adding the U, V, and W axes, but keeping track of six is enough to turn my brain into a pretzel, and another three would turn it into a fourth-dimensional hyperpretzel, and I don't know where I'd find any hypermustard for it.

So... looking at it with a measly six axes and a complete lack of tree puns, this is what happens:

Using a deliberately exaggerated angle for visibility, if you angle the spindle 10° in the B axis and then do a few passes along the Y axis you'll get a surface that looks like this:

(when you go to cut out a piece, you'll also end up with similar ridges at each depth pass on one side, and 10° slope on the other, which can turn the often aesthetic problem of a poor surface into a more commonly practical problem of parts not fitting together)

If instead you angle the whole gantry (shimming up one end of the C-beam on an upright, for instance) by those same 10° in B, you'll end up with this:


While that initially looks bad too, if you first surface the spoilboard and run those same passes again, you'll get this:

...or something that's precisely the same as you would've gotten with a straight gantry, just lying at an angle.

We can see that the big problem here isn't when the gantry is misaligned in B from the rest of the machine, but when the Z axis is misaligned from the gantry and/or when the spindle is misaligned from the Z axis. [[ tangent: The latter two cases will generally have similar effects except when plunging or drilling, and technically the ridges/scallops could be caused by either (it's even possible for the spindle & Z to be misaligned from each other but average out straight relative to the gantry, at which point problems will only appear when plunging & drilling), but at the moment I'm focusing on the mount. ]] This also means that adjusting the gantry in B can't be used to compensate for B misalignment in the spindle.

The "there should be" at the beginning makes this bit sound suspiciously speculative but, yes, it's possible to take advantage of the slots in the angles to shim or wedge one or the other mount to correct A axis misalignment (although having to pull apart & reassemble the whole works each time a shim is added or removed is going to cause its own unpredictabilities). It should (also speculatively) be possible to accomplish a similar adjustment by shimming between the spindle and mount. But the B axis is the sticking point.

I'm not worried about cutting new mounts with the current inaccuracy - it's close enough for that. What I'm worried about is that, once the new mounts are on, I'm going to have exactly the same problem adjusting them. If the new mounts have an ugly surface on top, it doesn't matter (especially because I'm not actually planning to surface them at all), and if the inside surface that mates with the spindle is angled, yes, that's worse, but it's largely mitigated by the two separate mounts being spaced out. The problem is I'll now have a nice, shiny, new aluminum mount... that may or may not mount straight, and that I also won't be able to reliably correct.

It would likely be perfectly acceptable for a platecutter that only has to do 2D work on thin enough materials that the sorta-mostly-almost-square edges don't matter, and with large enough (1/8"+) tools and/or soft enough materials that plunging crookedly won't break anything. Trying to make parts that join on the edges, or drill precise (or even just round) holes, or something like a V-carve inlay with a complex design - where lots of intricate edges have to mate perfectly - with a crooked tool is a recipe for frustration, though. And trust me, I know a thing or two about crooked tools.

Err... and misaligned spindles, too.

And I assume that's an issue even when you mask off the rest of the table and use a shroud... skirt... rubber thingy... err... yeah, I clearly don't know enough about it to even ask a coherent question here.

Also: in trying to track down the right term, instead I found a Norwegian SEO/spam blog full of snippets about bedbug prevention, but pictures of latex fetishist vacuum beds.

I'll give it a look & maybe jump in to pester you over there once I get to that point - I've currently got a pair of Shopvacs and a cannibalized motor from a third that I've been hoping I could put to some use. Right now, though, I've obviously got some more fundamental issues to sort out... And then I've still got a mill that needs to be assembled so I stop injuring myself on the scattered pieces of it.

(and, well, so that I have an assembled mill)

I think it's just a combination of the insulation (which looks all too similar to a spool of Cat5 I had kicking around for years) and the missing strain relief making the cable look a whole lot tinier. Of course, living on the big rock candy mountain with your fancy schmancy 220V, maybe you could run a router off Cat5.


-Bats
( 220V on tap, a rational system of weights and measures, and a landscape littered with castles, princes, and princesses? yeah, suuuure it's a real place )

 

Excellent! Then that should mean that in a quarter of the time it took me to write it, you can explain how to fix it!

I actually meant to try cutting some aluminum limit switch mounts this afternoon, but then got wrapped up pondering the intricacies of Fusion toolpaths, and by the time I checked the forums I was in desperate need of a break. Ahh, productivity!

-Bats
( because it's totally worth spending eight hours to optimize a two minute toolpath that'll be run a half dozen times )

 

I've got email alerts set for some CNC-related search terms (and a few too many others) in the almost-vaguely-not-quite-local area on Craigslist, and woke up today with the solution to all your problems sitting in my inbox...

A brand new CNC vacuum table pump!
(although it actually looks more like a blower than a pump)



A full team of ten 3-phase horses champing at the bit to suck the chrome off trailer hitches and/or the skin off any fingers that get too close!

And just look at those big, sad eyes - like a big, sad, industrial, and vaguely militaristic puppy dog left waiting outside for a new owner to take it home and love it:


Already palletized and easy to move! It might even weigh less than my mill!

(but probably not)


-Bats
( I'll accept my generous finder's fee in custom adjustable spindle mounts and large quantities of aluminum plate )

 

Exactly! I usually find A, B, and C to be a little easier in CNC terms because the order sort of inherently associates them with the X, Y, and Z that they respectively revolve around. In this case, though, pitch, roll and yaw might've made things a little easier to visualize - especially given the difficulties agreeing on exactly which X is X.

-Bats
( I bet Ayn Rand never had that problem )

 

Yeah, but mine's set up sideways (long axis running left to right, short gantry running front to back), and trying to deal with the horizontal axis as Y and the vertical as X was giving me constant headaches, so my gantry became Y. Thus did much confusion ensue, along with the (my)X and (your)X notation.

Several times I've considered changing it, just to bring it into agreement with the rest of the world, but I don't agree with the rest of the world on much of anything else, so I'm not sure why this should be any different.


-Bats
( I've also considered changing it several times, just for variety )

 

Ah, retrospect

Mostly.

Especially.

Ok, I think I see what you're getting at here, but my brain's refusing to wake up today (actually, I'm not sure it ever woke up yesterday, either), so I'm probably going to have to play with some models later to force the concept through.

I think that latter is where I saw the problem - although it was likely colored by old fears, stemming from a history with stock that may not have two square or parallel sides and a machine that couldn't reliably create them (A & B axis alignment being prone to shifting dramatically after each crash and subtly each too-aggressive cut), making precisely-aligned two-sided pieces one of the most difficult and dreaded projects. In thinking about it since, yes, it should be relatively simple on the Lead, as long as I get an end mill long enough to square the full thickness along one side (I might already have one) for alignment. Or I could wait & square the whole block on the mill for practice. Maybe I'll see how frustrated I am with the aluminum v1 and just how much of a hurry I'm in to get rid of it.

Hey, nobody calls this Bat a square!

Somehow I keep picturing the long sleeve transferring out-and-downward pulling stresses to the head of the screw, making the longer screw length more prone to bending, but I suspect that's just a hallucination brought on by insufficient caffeination and/or engineering background.

I probably would just turn the whole batch in the 3-jaw, then stick the 4-jaw on it (have I ever mentioned that 4-jaw doesn't have a backplate?), mark two of the jaws to leave in position between pieces and loosen the others just enough to stick in the next piece for drilling - figuring that in a non-production situation like this, it really doesn't much matter if they're identically off-center, since they'll be turned until an indicator is happy, not turned by x° with the expectation of a given offset.

I'm interested, though - how do you make your soft jaws? Do you have a chuck with two-piece jaws, or make something to bolt onto/fit over the fixed jaws? I've considered the latter on occasion, but never had big enough chunks of stock to spare when it would've helped.

Ok, this bit I'm not so clear on... You're suggesting the inside surface of the corners isn't flat enough already? That filing the screw slots wider would somehow disrupt the surface? Or that this is the solution to some other problem that's so obvious I couldn't possibly have overlooked it (and therefore obviously overlooked)?

...



That...

...never even occurred to me.

(although actually there are eight of them)

Those did come out pretty nice. I may have to give that a little thought... although in the time it takes to fiddle with the toolpaths & order the stock, I could probably have filed all the slots by hand. I also don't really want to get into milling any more aluminum than absolutely necessary while I'm using the MDF mounts, so it would probably mean cutting & remounting the spindle on the new ones, just to cut the new corners and take it all apart again.

One of these days, I'm gonna learn to weld.

Oooo... I could use 3/8" endmills in the ER16. That's rather exciting. And yeah, using two bars per mount with two screws each would eat up a lot more Al, but would probably make adjustment easier. Although even if I exactly duplicate the current MDF mounts in Al without slimming them down, it looks like the spindle would still be too close to the rail to work without cutting a channel into the corner bars too. Hardly a showstopper, though.


Also, I should probably mention that I have finally gotten around to making some test runs in Aluminum over the past couple days, trying to iron out toolpath types, feeds & speeds, and how to most efficiently weld the greatest amount of aluminum to the flutes of the mill. The results have been mixed - it seems like I need much higher spindle speeds and/or much lower feeds than the surface speed/chipload recommendations for Al would suggest or the machine gets unhappy (although when I push it too hard it looks like the whole gantry bucks on the (your) Y rails, more than any flex in the C-beam or the mounts), and the slower feeds mean I had to program in frequent retracts and constantly chase the tool around with alcohol to keep it from welding (which, oddly, seems far more effective than using constant compressed air to clear the chips).

The issues are also compounded by using a 4-flute bit (because they were more expendable for experimentation than the two 2-flutes I have left) and, almost certainly, from cutting hardware store mystery metal extrusion (some 1/8" thick L-profile I had kicking around) rather than 6061.

This is last night's - the surface finish shows a lot of chatter (possibly due to too little tool engagement?), but it's awfully decorative.



In the end, it turned out reasonably well - those actually aren't huge gouges on the corners - just the patterning where the Fusion's adaptive toolpath changed from the nice pretty spiral to fill in the corners with some rather ugly smears.

Of course, I also had my alignment skewed by at least 1/8", making the whole pattern fall off the edge of the stock and turning the slot on the lower left into a notch, making it utterly useless.

But still pretty.


-Bats
( maybe I could add a chain and sell it on Etsy as a "modern primitive industrial talisman" necklace )

 

Straight lines


-Bats
( who sez I can't write short posts? )