New to me CNC

[ddmckee54]

I recently purchased a small CNC router, fully intending to heavily modify it and turn it into a more respectable machine. This machine started out life as a Vevor 3018, the previous owner had upgraded it to a 4030 and upgraded the spindle to the high speed spindle motor. The numbers tell you the size of the work surface in centimeters, so a 3018 has a 30cm x 18cm working surface. As built, these machines are real lightweights, the frame is made of 2020 and 2040 aluminum extrusions. But, Awesome CNC Freak has shown that with some TLC these little guys can be used to do useful work. He's machined a lot of the parts for his DIY 5 axis CNC using his modified 3018.

These are some of the cons that I see and what I plan to do about them:
1) It's a lightweight, it has no mass to it, and no base. I plan on adding a substantial base to this little guy. The first plant I worked in made laminated plastic sheets, I saw them make sheets that were anywhere from about 20 thou thick, up to 11 inches thick. In the years that I worked there, I accumulated several of their rejects. I'm going to use a 400mm x 600mm part of one of those 30mm thick sheets to make the base that every thing else will be bolted to. That 400 x 600 x 30 mm piece weighs over 20 pounds, and I can bolt that solidly to the bench if needed.
2) They only used 10mm guide rails, those things will flex like crazy. I'm going to up-size the 10mm unsupported rails, to 12mm fully supported rails. Just going from 10mm to 12mm rails would be an improvement in rigidity, but using the fully supported rails should make that an orders of magnitude improvement. The X axis rails will be bolted to the base, further increasing their rigidity. The new 12mm Y axis rails will also be fully supported, and bolted to new 2040 extrusions - instead of being just a 10mm rail hanging in space. I also plan on bolting those new 2040 extrusions together, which should also help to stiffen up the gantry. If I have to, I can use this guy to mill out new gantry side-plates out of some more of that 30mm stock.
3) The Vevor control board leaves much to be desired, it's being replaced with an ESP32 control board with MUCH better stepper drivers.
4) Vevor used about the cheapest, lowest torque Nema 17 steppers possible. There's no ID on them at all, but they're about the right size to be the 40-ish oz.in Nema 17 version. I already have MKS42 closed loop stepper controllers for these guys, If I need to upsize the steppers, I can go to 84 oz.in or 92 oz.in steppers in Nema 17, and still drive them with the MKS42's.
5) The stock Z axis just plain sucks, it's made out of injection molded plastic and it's only got 40mm of travel. It also has 10mm rails, but they're a LOT shorter that the X or Y axis rails so that alone makes them much stiffer. I can 3D print a temporary replacement that will give me more travel while working on a permanent solution.
6) The spindle, where to start, it's a GS-775M , 20K rpm, 75W motor. But at least it's got an ER-11 collet adapter on it. I can't complain too much I guess, my Unimat's motor is 100W, my Sherline's is about 125W, and my first CNC - back in the late 90's - had a whopping 60W spindle motor. Awesome CNC Freak used a 200W motor with a speed reducer in his 3018, might do something like that. And then there's always that 1KW water cooled spindle and VFD that's been sitting in a box waiting for me to finish its' project. (That spindle came with a set of metric ER-11 collets.) Or, I've got that 350W Chinesium industrial sewing machine servo motor and servo drive that I got for future repowering of the Sherline or Unimat. I really like the 750W version that I re-powered my drill press with - 300-5000 rpm with the turn of a knob.
7) This thing is drip-fed g-code through a G-code sender, I've got a used Tiny PC coming that will do just that. I've accumulated a DDCS stand alone controller and stepper drives over the years, which are also a possibility.

I got the 400 x 600 x 30mm base cut to size, and all the sharp edges taken off. There's a lot stuff that needs to be bolted to the base, I'm thinking drilling & tapping will be best. I'll just use longer screws for more thread engagement in the plastic. It's HARD plastic, but it IS still just plastic. I knew there was a good reason that I bought that push-pull power tapping attachment.

My 12mm rails arrived a couple days ago. I first ordered the rails about 3 weeks ago, when they showed up I lifted the box I thought "My God, this is an awful heavy box for a pair of 12mm rails." Turned out they were 20mm rails, I checked my order and sure enough 20mm is exactly what I ordered. When I contacted the seller about returning the rails, he made a counter offer. He offered a 40% refund and I just keep the rails, saves both of us the hassle of returning them. So now I have a pair of 20mm diameter, fully supported linear rails that are 1m long for some future project - with 2 sets of bearings.

I got the X axis 12mm rails cut to length yesterday. I needed 450mm of rail for an exact fit, I cut them to 430mm so I could move them around a bit if needed. The rails are hardened so I had to use the spinning wheel of death in an angle grinder to deal with them - I don't want to have to cut them more than once. When I started mocking things up I discovered that by some happy coincidence the bottom of the bed is exactly 1/4' above the top of the bearings - talk about dumb luck! And I just happen to have a couple of short chunks of 1/4" x 2" aluminum flat stock laying around. The bed will be in the original location, so no mucking about with the X axis leadscrew.

I need 370mm for the Y axis rails and I originally planned on cutting them at 350mm. I stared at it some more tonight and I realized that I need most of that 370mm length. I'll probably cut them at 365mm. I think I can keep the Y axis leadscrew in the same spot, but when I print the replacement Y axis carriage I'll most likely need to move the lead nut location. The new 2040 extrusions for the Y axis rails should be here in the next day or so, then I'll have a better idea what things could/will look like on the gantry.

So far MOST of the work on this thing has been me plottin'-n-coniviin' how to make this thing better, but there are a couple of things to see. Tomorrow I'm going to HAVE to remember to take the camera down to the shop with me to take some pictures.

Don

[ddmckee54]

It's picture time. This is the top of the old cnc, or what's left of it.

That's a 12" scale in the upper LH corner for size reference.

Here's the belly of the beast.

Both the horseshoe shaped top and the base are 1 piece metal castings. I took them apart to make getting this off my workbench a little less clumsy. I'm pretty sure the base is aluminum, but as heavy as the top section is it could be Zamak. Then again, there IS a lot of steel bolted to the top. That orangish blob in the center is the 2 piece carriage for the Bosch 1Hp router. It was machined using the original convoluted belt drive system that could only handle a DOC of about 0.010" at MAYBE a 10"/minute feedrate. I remember it seemed like it took about a thousand passes.

OK, this is the new toy, it's sitting on its' base but nothing is bolted down yet.

The Sherline is visible sitting in the corner, that corner is where the old cnc sat for at least 15 years.

This next shot shows dumb luck in action.

In the background you see one of the new X axis 12mm rails with its' bearing blocks, just in front of it is the existing 10mm rail that's 450mm long and only supported by an M5 bolt at each end. The new 12mm rails are bolted to a solid aluminum extrusion that will be bolted to the base by a pair of M5 bolts every 100mm. The rails will be shimmed as required to make sure they stay flat. In the foreground is the 1/4" x 2" aluminum bar that the bearings will be bolted to. As you can see, that bar JUST fits under the work table. Like I said, this is dumb luck in action - not prior planning. Right in front of that is one of the 2040 extrusions that are the major support of the machine, and the just hang off 2 M5 bolts at each end. There's about a 4.5mm gap between the extrusion and the surface. It's no wonder that people complain about the lack of rigidity in these things, there's just so many places built into them where things can flex. I intend to make spacers and bolt through the 2040 extrusion and the spacer into my 30mm base.

This is the spindle, in all its' [s]glory[/s] whatever.

This assembly is 60mm at it's widest, and it uses every mm of the existing rails to get its' 300mm of spindle travel. The problem is that the new bearing blocks are 40mm long, and there's 2 per rail for stability. That's 80mm, and if you figure in a generous clearance Clarence - you're up to 85mm. So any way you slice it, with the existing gantry set-up I'm going to lose 25mm of work area. For now, I can live with a 4027 instead of a 4030. Especially when you consider that my old cnc was a 3020. You can also see that they didn't use any more plastic in those moldings than they absolutely had to, it's not just the rails that flex.

This shows where the new Y axis rails will sit in relation to the existing rails. The camera really messes with things, the old 10mm rails look bigger than the new 12mm rails, but it just ain't so - I checked to be sure.


I just got the 2040 extrusions to replace the existing 2020's. If I did the arithmetic right, I should have about a 15-16mm between the new extrusions when they're installed. I intend to make solid spacer blocks to fit between the 2040 extrusions and effectively turn them into a truss. At that point, the weak link in the gantry will probably be the 15mm phenolic side plates. If that's the case, I can try bolting on a stiffening rib, or just making some new side plates out of my 30mm stock.

The major renson I went with an ESP32 based controller is that the MKS DLC32 has the horsepower, and the programming, to function as a stand-alone controller if desired - no drip feed from GRBL required. Just load your g-code onto a thumbdrive, plug that into the controller, and run the file.

That's enough yapping for today, I have to go make myself some supper.

Don

[ddmckee54]

I got a little more done today, but nothing worthy of any pictures. I finally quit waffling about the Y axis rail length, I needed 370mm so I marked them at 370mm. When I cut the rails, I cut on the"good" side of the line rather than the waste side. The kerf from the spinning wheel of death, and its' clean-up, gave me about 3mm of clearance. The 2040 rail supports I cut at 370mm on the table saw with a carbide blade, I took it slow, wore ear protection, and it worked like a charm - or so I thought. Except... They weren't the right length, and they weren't even the SAME length - despite the fact that the fence setting had never been changed. After doing a root-cause analysis of the problem, it was determined that some NUMBSKULL had forgotten to lock the fence down on the saw. Fortunately they had grown in length rather than shrinking, so they were saveable. I set the fence back to 370mm, locked it down this time, and trimmed the pieces to length. I tapped the ends of the extrusion M5, and replaced the existing 2020 extrusions. I was a little off on my estimate of the gap between the new extrusions, it's actually 16.5mm.

I figured out why this particular 30mm sheet was scrapped, the rail in the foreground in the above pictures rocks back and forth. I can hold one end down and measure about a 0.015" gap under the other end, so there's probably about a 0.008" lump in the middle. Looks like I've got some shimming in my future. The background rail sits flat now, but I'll probably have to shim it to level it to the front rail.

[ddmckee54]

I've been working on figuring out just exactly how I'm going to attach the new pieces to the existing hardware, so I started 3D modeling the relevant bits. The hardest part of that was determining the actual location of the leadscrew in relation to the new linear rails. I could determine the position of the existing rails in relation to the mounting locations for the existing 2020 extrusions and I'm reusing those same mounting holes for my new 2040 extrusions. So I had a fixed starting point. As near as I can tell, the center of the leadscrew is on the vertical centerline of the existing 10mm rails. However, it is not centered BETWEEN those rails. Oh no, couldn't do that, that'd be too easy. The leadscrew's centerline is 1mm BELOW that center - and I am NOT moving that leadscrew.(Yet) After a lot of head scratching, and double-checking/triple-checking/quadruple-checking of measurements, I started modeling the important bits of the Y & Z axis. This is where I'm at now:

The orange colored bit is the Y axis leadscrew, the cyan bit is the mounting plate for the bearing blocks/lead nut holder/Z axis. I ordered enough anti-backlash lead nuts to replace all of what they used as lead nuts. I don't think any of them were actually bolted to anything, so far they've just been a push fit in the moldings. Before I ordered them though I figured it just MIGHT behoove me to determine what flavor of T8 trapezoidal screw they were. It turns out they are T8 screws with a 2mm pitch, 2 starts, and a 4mm lead, so that's the flavor that I ordered. Things will be a little "tight" where the Y axis lead nut will live - there's 19mm between the bearing blocks, and the lead nut will be occupying 14.5mm of that. I'm going to 3D print the lead nut holder and there's plenty of room above and below the lead screw to put plenty of meat for the lead nut to pull/push on. The Z axis is still just a figment of my imagination, once I can get it out of my head and into the computer I'll share it. I do know that I want to shoot for 75-80mm of Z travel, that'll let me fasten a replaceable spoil board to the bed and still give me a decent work envelope.

Don

[ddmckee54]

One thing that I just figured out today is that I don't need to bolt the X axis rails to the base, then square and level everything else up to them. The side frames of the CNC are 2040 extrusions, so I can bolt the rails to the side frames directly to them. Saving much tearing of hair and gnashing of teeth. I'm going to use the "Easy" button. I also discovered that the M5 x 10 SHCS that I ordered were JUST long enough that they bottomed out in the slot of the extrusion before the rail was completely tight. I was not looking forward to having to trim that many M5 x 10 SHCS - no matter how I would have done it. Then I remembered that I had ordered a bunch of M5 washers that were 0.5mm thick, for my RT7R project, and hadn't used them yet. "Easy" button time again, but I will have to order more washers - soon.

The only down-side I can see to bolting the X rails to the side frames is that the distance the bed has to span between supports will be 250mm instead of the 200mm it is now. If that turns out to be a problem then I can bolt some support ribs to the bottom of the bed.

[ddmckee54]

Been a while since I updated this so I'll bring you up to speed. I got spindle mount and clamp designed. I got the anti-backlash nut a few days ago, so I was able to get that part of the spindle slide design corrected/finalized. I sectioned the spindle clamp so you could see how I'm bolting the back half of the spindle mount to the slide.

The mounting holes bolt circle for the nut IS 16mm in diameter, and the major diameter of the part of the nut inside the slide IS 14mm. At least 0.5mm of the 3mm diameter of each M3 screw would protrude into the bore of the spindle slide. There's no way I can use a heat-set insert on these, and I don't trust just threading an M3 screw into plastic - especially when part of those threads don't even exist.

But fear not M'Lords, I have a clever plan. I'm going to change the diameter of the mounting bolt circle to 18mm by slotting the existing holes. Unfortunately I still can't use heat-set inserts though. The only part of the nut inside the slide that's 14mm is the rear flange of the spring-loaded part. And I don't why it's that big, the OD of the spring is 12mm, so you'd think that 13mm would be good enough. Maybe they started with 14mm stock? I'm not going to use M3 machine screws to mount the nut to the slide, I'm going to use long-ish M3 sheet metal screws.

Now I've got a question that I need a little feedback on. Right now I've got the leadscrew nut on the top of the slide, do I need to put it on the bottom? I want the tool forces to be transmitted to the leadscrew by the slide pushing on the flange of the leadscrew nut, not by the slide pulling on the M3 mounting screws.

One thing that I figured out is that I don't need to bolt the X axis rails to the base, then square and level everything else up to them. The side frames of the CNC are 2040 extrusions, so I can bolt the rails to the side frames and save much tearing of hair and gnashing of teeth. I'm going to use the "Easy" button. I also discovered that the M5 x 10 SHCS that I ordered were JUST long enough that they bottomed out in the slot of the extrusion before the rail was completely tight. I was not looking forward to having to trim that many M5 x 10 SHCS - no matter how I would have done it. Then I remembered that I had ordered a bunch of M5 washers, 0.5mm thick, for my RT7R project - and hadn't used them yet. "Easy" button time again, but I will have to order more - soon.

Well, ain't that just a kick in the teeth. All the various bits and pieces have arrived, sooo... I started assembling the Y rails, and guess what? They DON'T fit! I pre-assembled the tee-nuts onto the rails. Since that would be easier than trying to pre-position the nuts in the extrusions - they would probably move around in the slots. But I could not get the rails to slide into the slots. The tee-nuts fit in the slot just fine, so i started looking for other causes. When installed in the extrusions, the tee-nuts were close enough to being on 20mm centers for using a digital-guesstimator. The holes in the rails on the other hand were on 21mm centers, I know these were cheap rails, but still... Where was quality control, aren't they supposed to check that kind of stuff? Guess these rails must have been made on a Friday afternoon, or a Monday morning. I've got a 5mm end mill, I'll probably set up a jig and just move all the holes, on all the rails, in one set-up.

Don

[ddmckee54]

I did set up the jig, it's sketchy at best - but it did work.

Yeah it looks sketchy, yes it's made out of scraps, yup that's a 5mm end mill chucked in a drill press, and if you looked at it wrong bad things would probably happen. But it didn't need to survive for long, it just needed to be able to take a crescent shaped slice, about 0.75mm at its' widest, through 4mm of aluminum - 32 times. And it passed that test with flying colors, here's a completed rail still in the jig.

You don't get many chips taking that small of a bite.

I then started putting things together and ran into more problems. Since I'm using 2040 extrusions instead of the original 2020's, I needed to drill holes for 4 more M5 bolts - that hadn't happened yet. I don't know how much I'm paying the guy that drilled the holes, but it's TOO much. The exit point for one of the holes had about a 2mm offset from the entry, a LOT of file work later and that was corrected. You remember when I said that the M3 mounting bolts for the Y axis stepper would JUST clear the new 2040 extrusions? Well they do, they DON'T however clear the rail flanges. Take the rails/extrusions out, clip the corners off the flanges, and reinstall the rails/extrusions. Now, how much clearance do I have between the bearing blocks? WHERE'S THE FLIPPIN' BEARING BLOCKS? Take the rails/extrusions out, install the bearing blocks, and reinstall the rails/extrusions. NOW how much clearance do we have Clarence? About a mm, OK, a miss is as good as a mile. WADAMINUT, where's the grease ports? I'd installed the blocks so that the grease ports were pointing toward each other instead of away from each other. Take the rails/extrusions out, flip the bearing blocks around, and reinstall the rails/extrusions - for about the leventy-leventh time.

OK, now it was time to get serious and start getting this thing squared up. I made sure that both of the 2040 extrusions were in plane and perpendicular to the main side frame extrusions. I made sure that both the side plates were the same distance from the ends of the main frame rails, so the Y axis had a good chance of being perpendicular to the X axis. Then I went around and tightened the bolts, one last time. Annnddd...

Ya know that feeling, when the wrench suddenly loses all resistance and just spins round-n-round-n-round? Yup, I stripped the threads, and I THOUGHT I was being careful. And that's where I left it today.

I know that I ran the M5 threads at least 20-25mm deep in the ends of the extrusions, and I know that after going through the 15mm side frames the M5x20 bolts only had about 4-4.5mm of thread engagement in the extrusions. So there SHOULD be 10-15mm of good threads in the extrusion yet. My current plan is to get M5x30 bolts, that extra length of thread engagement should take care of the problem. (As long as I'm REALLY careful this time.)

[Zabco]

Sorry about the issues you are having but it's all an educational moment, right?

I used my drill press as a mill for a number of years. Mostly on aluminum and plastic but on some steel as well. Never hard cutting or for very long at a stretch. I even have a cheap chinese XY table I bought to use on it. Still have the drill press and it still works fine with no slop in the bearings. A big heavy Delta bench top model they quit making decades ago.

[ddmckee54]

My drill press is a Shopfox bench model. I repowered it a year or so ago with one of those Chinese industrial sewing machine servo motors. I went from a 3/4Hp motor to a 1Hp motor and variable speed from 300rpm to 4500rpm by turning a knob.


Educational moment, yeah that's the POLITE way to put it. Still waiting on the M5x30 bolts, so I've been working of how to fit the mounting bolts for the Y axis leadnut into the available space - 19mm max. M3 bolts on a 16mm bolt circle doesn't leave a whole lot of room to spare - like absolutely none. That being said, the 3D printed leadnut block was deleted from the design. In the process of doing that I discovered that I had never anchored the Y leadscrew into position, because I was never sure where it would actually be located relative to the new rails. That led to much head-scratching as to how I could do that with the tools that I had - an 8" digital guesstimator. (Even though it's a good one.) After much careful measuring, tweaking of the 3D model, more measuring, and more tweaking, I finally got the real world and the 3D model to agree with each other - AND anchored the Y Axis leadscrew in position.

The Z axis quickly showed me that there was NO way I could directly mount the leadnut to the Z axis leadnut to the bearing carrier. Eventually I settled on mounting the leadnut to a 1/8" plate and mount that plate to the bearing carrier/slide. 1/8x1-1/2 HRS flat stock is fairly easy to get, so that's what I'll use as a starting point. I had originally hoped that I would be able to design one leadnut mounting plate and use it for all 3 axis, the Y axis quickly educated me in the folly of my ways. The spacing between the Y axis rails is fixed, as are the position of the Y axis leadscrew, and the positions of the Y axis bearing blocks. The Z axis leadnut plate would NOT work - not even with modifications. So I basically started over, the only things I kept from the Z axis mounting plate were the tapped M3 mounting bolt holes, the clearance hole for the anti-backlash spring, and a maximum width of 36mm - so I could still use 1/8x1-1/2 HRS flat stock. I found that I needed to knock the corners off the mounting plate to clear the X axis rails/extrusions, but that's no big deal. I'm still scratching my head about the bolt locations for mounting the leadnut plate to the X axis bearing blocks, there's some fairly important stuff that I need the holes to miss. When I get the bolt locations nailed down I'll try to remember to get a screenshot so you know what I'm talking about.

[ddmckee54]

It's taken longer than I'd hoped, but I think I've got a solution to my leadnut problem. I'd purchased 3 anti-backlash leadnuts that were designed for 3D printers. I got to playing around with one of them and realized that the way they worked wasn't going to cut the mustard for this application. They are basically 2 leadnuts installed back to back with a spring between them. The 2 halves are clocked together by a tab and slot arrangement. Only one of the leadnuts is fixed, the other just floats on the leadscrew. Even with all the compression I could get out of the spring, it would still allow the leadnut to move on the leadscrew. The only pre-load you've got on the leadscrew is that spring, and it just ain't enough. This is what I'm going to try.

It's still just 2 leadnuts back to back, but now I can adjust the amount of pre-load on the screw. This is actually parts from the anti-backlash nut along with a different style of leadnut. The part on the right, with the slots in it, is from the anti-backlash nut. It has a 22mm OD flange with 4 mounting holes. The part on the left is also 22mm in diameter, but only has 2 mounting holes. The sides have been milled off, leaving a 10.5mm wide flange. I'm not showing the original spring, which I will also reuse. I cobbled together a test rig for this set-up and it seems to work. I can tighten things down to the point where I can lock up the leadscrew. I got some Belleville washers, and the current plan is to stack them with a flat washer between each pair so they can't just slip together - losing the leadscrew pre-load. The stack-up shown is a Belleville-Flat-Belleville stack. It's going to take some playing around with things to find the sweet-spot, where's there's minimal backlash and no lost steps. I also realized that the leadnuts will need to be assembled after mounting to the leadnut plate. The leadnut plates will be 1/8" HRS, tapped for M3, that should give me 5-6 complete threads in each hole.

This is what the 3D model looks like now.

The orange bit is the Y axis leadscrew, which I realized a couple hours ago just ain't right. The large lump on the left end should be on the right. That's not that big of a deal, but it will break the constraints in this assembly when I fix it. The yellow parts are the leadnut assemblies for the Y and Z axis. The dark blue parts are the Y and Z leadnut plates. The cyan part is the mounting plate for both the Y axis linear bearings and the Z carriage assembly. I don't show it, but all the linear bearing mounting holes will be countersunk.

Screw it, I'm calling it a day.

[Zabco]

I like your solution, simple and looks like it should work fine. Since the end with the nuts/washers appears to be on the inside of their respective carriages I'm assuming (I know) that you will adjust the nuts till you get the fit you want and then slide the carriage over and bolt the larger lead nut in place? Lubrication?

[ddmckee54]

Zabco:

The initial assembly of the lead nut/lead-nut plate will be complicated, and it will NOT be done while installed in the carriage. I've got a short length of T8 lead-screw that will be used as an assembly jig. The fixed part of the lead-nut will be anchored to the lead-nut plate by four M3 screws, two short screws and two long screws. I only show the long screws in my 3D model because they are also used to apply pre-load to the lead-screw. During the initial assembly the long M3 screws will only be partially threaded in, 10-20mm at most. Then the original anti-backlash spring, and the floating lead-nut will be installed on the lead-screw. The floating lead-nut will then be tightened down until I have a small gap between the fixed leadnut and the floating one, I'm shooting for between 0.5-2mm when the nuts are clocked together properly. At this point the spring washers and pre-load adjusting nuts can be loosely installed. Once the adjusting nuts are in place the lead-nut assembly can be removed from the assembly jig without fear of the spring causing it to explode. Then it's just a matter of rinse, lather, rinse, repeat until all the lead-nuts/lead-nut plate assemblies have been assembled. The X & Y axis I MIGHT be able to adjust in place, I've got a 5.5mm Wiha nut-driver that could be up to the task, time will tell. The Z axis on the other hand is going to be a royal P.I.T.A. But it is what it is.

Lubrication of the lead-screws is still up for debate - it'll either be a periodic application of grease or oil. I've got a set of grease zerks, including the 6mm zerks I'll need on the way. That will allow me to periodically grease the linear bearings. I've just got to be sure that the bearings are oriented so that I can get to the zerks. The Y axis bearings are going to be relatively easy since they're fairly accessible.

The Z axis slide will need to be pulled off the rails, the bearings packed by hand, and then reinstalled on the rails.

The X axis bearings are installed under the bed, they'll need to be disconnected from the bed, slid out from under the bed, greased, then reinstalled. Which really sounds like a lot of work. It might be easier just to poke a couple of access holes through the base, big enough to get the grease gun through. Then when it's time to grease things, I can flip this thing on its' side, move the bearings over the access holes, grease'm, and move along.

Yup, Plan B it is. I can even 3D print a couple of covers for the holes to keep chips and other nastiness out of them. I'm not looking forward to punching the holes through the base though, that's some tough stuff - and it's over 1" thick,

[ddmckee54]

I've been picking away at this thing all week, and it's starting to drive me up the wall. I flipped the Y lead-screw around, and it didn't break as much as I thought it would. But, I have a small issue with Alibre that's REALLY irritating. This is the latest assembly drawing of my new CNC's 3D model.

You see that yellow object in the middle? That's not where it's supposed to be! The lower surface of the flange should be coincident to the upper surface of the dark blue lead-nut plate. The Z carriage, basically everything in front of the cyan colored plate, is one sub-assembly. In THAT sub-assembly, everything behaves like it should, including the lead-nut. However, when the Z carriage assembly is added to the main assembly, the Z axis lead-nut turns into the misbehaving red-headed step-child that you see above,

I thought this problem felt kinda familiar. About a year ago I was working on designs for 1/16 scale RC truck differentials, based on a modified cheap Chinesium 1/10 scale RC car differential. I started out wanting just the front and rear axles for a tandem dual drive set-up. Later, after seeing how a fellow builder had modified the front axles from a similar 1/10 scale RC crawler into powered steer axles for his 1/14 scale RC telehandler, my designs morphed into adding a powered steer axle for a 6x6 Bruder truck conversion. I had designed a powered steer axle, and tested it as an assembly, where the steering worked fine. When I added that sub-assembly to the main truck, it would no longer steer. The same thing happened with the rear axles assembly. As seperate sub-assembly it would articulate, when added to the main assembly it would not. I had a buildlog on another site detailing the designs of the differentials.

I checked back through that Frankendiff build log and found I had run into a similar road-block there. I have a perpetual off-line license for Alibre Design Pro V.22, I am NOT going to pay any more to upgrade it - and maybe not have it work any better. I've checked, seems like sometimes it works, sometimes it don't. AND, then I would have to upgrade to a version of WINDOZE that I like even less than the WIN7 Pro I've got now.

[Zabco]

Whoa, that's odd. I don't think I've ever seen that happen with any of the assemblies/sub-assemblies I've created in Alibre. I'm using the Atom version not the Design Pro though. Like the constraint setting between the two parts is getting changed from coincident to off-set somehow. May have to discuss with the support staff at Alibre.

[ddmckee54]

In searching the Alibre forums, it seems to be hit or miss. Sometimes it works, sometimes it doesn't. What I need to REMEMBER to do as a work around, is that I've got to check for interferences in the sub-assembly - not wait until the main assembly. I haven't tried digging into this yet, but is there a way to get Alibre to tell you if you have interferences between parts in an assembly? When I was working on the RT7R's lift assembly I had an interference between two parts that I didn't catch until I'd printed the inner and outer lift arms, and they wouldn't fold up completely.

Before I completely tear this thing apart again here's a couple shots of what it looks like with the new rails installed.

I installed the mocked-up lead-nut assembly just as a sanity check - it fits so I guess I'm still sane.

Installing the X axis rails on the side frames is causing some issues.

That change, while it made the alignment of the machine MUCH easier also threw a monkey wrench into some of the other stuff. There is no longer 1/4" between the bottom of the bed and the bearing blocks, it's more like 3-ish mm. I've got some 1/4"x1-1/2" aluminum angle that I will modify to make the bed/bearing mounting brackets. I'll lose another 3mm of Z work height, bringing the max working Z height down to about 60mm, but that will be fixed after I get this thing running again. It can make itself new extended Z height side plates. The X axis lead-nut mounting block will also need to change. The current plan is to add 3mm to the dimensions of the existing mount, and print that. Then I install that lead-nut, measure how thick of a shim I need between the lead-nut and the bottom of the bed, print the shim, and install it - Eazzee-Peasee.

[Zabco]

I find Alibre's error messages to be very unhelpful. They tell you there is a problem but don't tell you what the problem is in clear english. I finally figured out that when I try to create a constraint and it tells me the part is over-constrained when I have less than three constraints I know that there is a dimensional error between the two parts. Probably most common when trying to tie two parts together by matching up a pairs of holes. I could swear I made the spacing between the holes exactly the same on both pieces when I go back and check, sure enough they aren't. Sometimes only 0.00001mm difference. I find that relying on snaps is the biggest cause of this. Looks like I've snapped a circle center to the exact intersection of two lines but zooming way in will show the circle center is just a bit off. Need to set more actual dimensions to know references.

[ddmckee54]

Error messages... Been there - done that. I kept getting the over constrained message when attempting to constrain the top of the Y axis lead-nut plate coincident to the top of the Y axis bearing block mounting plate. (While the hole in that plate was coaxial to the lead-screw - which was anchored. And the bearing blocks were coaxial to the rails - which were also anchored) Finally I gave up on trying to constrain them coincident and constrained the angle between the surfaces to 0 degrees. Just for shits and giggles, I decided to measure the distance between the surfaces. It turned out to be 0.00075mm, or some ridiculously small number like that, when it should have been exactly 0.

Don't know if setting actual dimensions will help or not. I've measured objects that have known dimensions, and gotten values that would round off to the correct amount - but weren't displayed as that value. I suspect that somewhere in Alibre's settings, there's one setting where we can tell it how close is actually close enough. Round off error can be a royal P.I.T.A. at times. Using snaps can also have its' issues. I've had times when two nodes are close enough that they appear to be one point and Alibre grabs whichever one it wants to - not always the one you wanted.

[ddmckee54]

I managed to get a few things crossed off the ToDo list, AND I've figured out who the culprit is for the lead-nut assembly misbehaving. It's the Nut-Bolt-Washer assembly, and in particular it's the wave washers. When I try to constrain the surface of the wave washer to the face of the bolt, I got NO options for the constraint. Sooo... What I originally did was to anchor every thing in place. I have no idea why it worked in the Z carriage assembly and not in the main assembly. I deleted the wave washers from the NBW assembly, constrained the flat washer to where the surface of the wave washer would normally be, and the little toad started behaving properly. Onwards and upwards I guess.

[Zabco]

Interesting. Never tried to create a wave washer before, or anything like it. Problem may stem from there being no flat surface to constrain to. There would, at most, only be a single line right at the apex of the curve and would be very difficult to precisely select. and if it weren't exactly at zero degrees to the surface it was to be linked with it wouldn't work. I think your work around, replacing the wave washer in the drawing with a 'conventional' flat washer is the way to go. Label it as a wave washer so you remember what it is supposed to be.

[ddmckee54]

The original Nut-Bolt-Washer assembly consisted of an M3x35 socket head cap screw, a wave washer, a flat washer, another wave washer, and an M3 nylock nut - in that order. I simply deleted the 2 wave washers from the assembly, and used an offset constraint between the flat washer and the appropriate face of the bolt. I moved it 1mm closer to the head of the bolt, since that's the un-compressed dimension of the wave washer.

Making the wave washer, or at least approximating one, was fairly easy. I just made a cylinder of the appropriate dimensions, created a reference plane on the axis of the cylinder, projected the cylinder on that plane, drew 2 arcs of the correct size and location on that projection, then trimmed the 2 short line segments between the arcs so that I had 2 separate objects in the sketch. Do a cut extrude through everything and you're golden. One thing that I do is offset all sides of the original projection to the outside. This does 2 things,one - it ensures that when you do the cut extrude you get everything and don't wind up with any left over surfaces, and two - it keeps you from having a line intersecting an arc. Alibre pukes all over you for committing that sin.