New to me CNC

[ddmckee54]

OK, time to Fess up, I make-a-da-nuther-boo-boo. For some reason I designed the mounting bolts for the Z axis NEMA17 stepper motor to use heat set M3 inserts. Normally that shouldn't be a problem. HOWEVER, the NEMA17 motor mounting locations are M3 threaded blind holes. Something tells me that four M3 threaded blind holes facing four M3 threaded blind holes just ain't gonna work to hold the motor in place.

The Z carriage was printed with 80% infill so you would think that if I could just drill the blind holes through with no problem. That actually would work for the two holes closest to the rails. The other two holes however would still be buried in the upright section of the carriage. That's probably what caused the brain-fart of thinking I could get away with using the M3 threaded inserts in a blind hole. Nope, I need to redesign the Z carriage. It's nothing serious, I just need to move the rails, leadscrew, and everything associated with them about 10-12mm farther away from the upright section.

The X axis leadnut block is printing now, by the time it gets done I SHOULD have the changes ready to go. The plan is to get the carriage reprinting by the time I go to bed.

[Zabco]

Step by step, closer and closer.

I learned a long time ago to not trust bolt bin labels. People grab stuff to look at and then just toss it back in any ole bin they want. If I'm looking for s specific size, type of bolt or nut I take another with me for comparison or my small in/metric ruler.

Used to use magic markers also till I got tired of cleaning it off my hands. I find the cost of a small bottle of dykem now to be money well spent. Once dry, it stays on the metal so no having to replace lines that got rubbed off.

[ddmckee54]

Zabco, I just don't understand how I can get purple stains on my hands from a black magic marker. Guess that's what makes them magic?

I got the X axis leadnut block printed along with the new Z carriage, and the heatset inserts have been installed. I thought that I had assembled the Z carriage for the final time, but I was mistaken. I haven't greased the linear bearings yet, so I'll have to partially take it apart to grease it. One of the things I did during the design for my upgrades, was to make sure Future Don wasn't going to curse my name when it's time to service this thing. I'll need to remove the rails to grease the bearings, but it's possible to do that and not lose the alignment. By removing the stepper motor and the two screws retaining the upper end of the rails, it's possible to pull the rails out the top of the carriage. The spindle, spindle clamp, and the bearing block can then be removed as one unit. Since none of the bolts holding the critical alignments in place need to be loosened, the alignment shouldn't change.

I've got the carriage roughly aligned to the bed, meaning that it's as square to the bed as my square and my Mk1 eyeballs can make it. The final alignment won't happen until I've got this thing moving under it's own power. Then I can use a DTI and a 123 block to really dial things in. This is the current condition of the Z carriage.


The X axis leadnut is currently bolted to the bottom of the bed, I kind of got ahead of myself when I did that. I guess it's a good thing that I made it easy to remove the bed to work on the bottom of it. Just remove the four bolts holding the endplate on and the bed can be slid off the rails - bed alignment is not affected.

I need to get a measurement of the distance between the top of the leadnut block and the bottom of the bed, with the leadnut block assembled on the leadscrew. If I did the "Plottin-N-Conivin" right, that distance should measure around 3mm. BUT,... I can't measure the distance until the leadnut block is assembled on the leadscrew. That can't happen until the anti-backlash nut is assembled and adjusted. And THAT can't happen until the leadnut plate is fabricated. And since the X axis and Z axis leadnut plates are very similar, I might as well do them at the same time. That'll be happening next.

[Zabco]

Quick question Don, did you freehand the heat-sets or have you got some sort of guide to keep them square to the surface you are putting them into?

[ddmckee54]

A little of both. I've got a dedicated soldering iron with digital temp control that I use just for setting inserts. I got a set of installation tools, M2 thru M5, that fit the iron. Got both of them off Ebay for less than $30 total. I set the iron's temp to about 250 degrees C for both PLA and PETG.

I'll freehand the installation until the inserts are slightly proud of the surface. Then I'll hold the heat on them for a few seconds. After that I'll do one of two things...
1 - If the inserts are not being set into a recessed pocket, I'll just flip the part over and press it onto the benchtop. That does several things, first it sets the insert flush to the surface. Second, it smushes that ring of molten plastic you usually get around the insert back down around the barbs of the insert. And, it helps suck the heat out of the molten plastic and the insert. (No more burning your tender piddies.)
2 - If the insert is being installed in a recessed area, like for anchor points inside a box, I'll find a scrap of bar or flat stock that'll fit in the recess and use it as a substitute for the benchtop.
No Dilly-dallying around when you're doing this is allowed, otherwise the plastic will cool and you'll need to add more heat.

That works for most applications, it'd be a problem on a circular object though. Someday I might use Chris Borge's ideas and build a dedicated station just for inserts, but that's a problem for Future Don to deal with.

[Zabco]

OK, thanks for info. Seems pretty simple. I was thinking of taking the heating element end of a soldering iron and fabing up some kind of holder that would fit in my drill press. Seems like it would be wasted effort now.

[ddmckee54]

Zabco, I got the idea of using the bench top from Clough42.

The weather was nice for the last couple of days, so I've been harvesting my first crop of dandelions of the season. I hope it's the last one too, but I'm not gonna hold my breath. Anywho, I managed to get a little more work done on the CNC.

These will be the leadnut plates for the X and Z axis when completed. The lower plate, the X axis leadnut plate, is 38x38mm. The upper plate is the Z axis leadnut plate and it's 24x27mm. Why the different sizes? Originally, all three leadnut plates were SUPPOSED to be identical to the X axis plate. The Machine Gods laughed at my plan and sent their minion Murphy to curse my design choices. That's my story and I'm sticking with it.

Despite their different sizes, the plates are very similar. They each get nine holes. The central hole needs to be in the 10.5-11mm range. Ain't got no stinkin' metric drills, I got fractional drills and number drills. A 27/64" drill is just under 10.72mm, that's close enough for this Gubmint contract. There are four holes on a 16mm bolt circle that will be tapped M3. That requires either a 2.5mm drill - which I ain't got, or a #39 drill - which I've got. The last four holes are M3 clearance holes. A 9/64" bit will give me a fit that falls between a normal fit and a loose fit - it works for me. A little extra clearance never hurt Clarence.

[ddmckee54]

Sometimes I'm just not as smart as I think I am...

I got the Z axis leadnut plate drilled and tapped in the appropriate places, I also managed to snap off my M3 spiral tap in the process. While running the tap in far enough to be sure all the chips were cleared out of the threads, I ran the spiral tap through the plate. While trying to start the tap back into the hole I managed to get it started crooked, and snapped it off. Fortunately there was plenty of the broken tap sticking out of the back of the plate that I could grab onto and thread it out. I had one other M3 tap, a 4 flute tap, and wanted to chase the threads - but I didn't want a repeat of the previous disaster. So I drilled a clearance hole in a piece scrap plastic and made a simple M3 tap guide. I used that to chase the threads, and also to tap the one remaining M3 hole on the Z axis leadnut plate.

I then set about assembling the anti-backlash leadnut, and getting it adjusted. The process I used to assemble/adjust the Y axis leadnut is identical for all three leadnuts; the only thing that varies is the shape of the leadnut plate. So... Onto installing the leadnut into the spindle slide.

Anddddd... it doesn't fit. Oh, it fits into the pocket alright, it's just that ALL of the leadnut doesn't fit into the pocket. The top of the leadnut plate is still 1-2mm proud of the surface and it should be flush.

The cause of this evil deed? When assembling the Y axis leadnut I discovered that when using the M3x35mm bolts as originally designed, if the two halves of the leadnut weren't clocked properly, I either couldn't assemble the leadnut halves or the nylock adjusting nuts wouldn't lock. My leadscrews are T8 2 start screws, with a 4mm pitch. With the Y axis leadnut, the only way the M3x35mm screws would work was if the 2 halves of the leadnut were threaded so close together that I couldn't remove the backlash in the threads. Clocking the 2nd half of the leadnut to the other start moves that half by 2mm, which allowed me to adjust out the backlash. Unfortunately, that also moved the adjusting nut by 2mm, far enough that the nylon locking ring wasn't doing its' job. I had M3x40mm screws, which solved that problem. What it didn't solve was that the pocket the leadnut fits into on the spindle slide had 2mm of clearance - when using an M3x35mm screw.

Sometimes I'm just not as smart as I think I am.

[ddmckee54]

OKAY.... The reprinted spindle slide is finally done, and this time it worked. I modified the depth of the pocket for the leadnut assembly. I had forgotten about the screws to hold the bearings in place on the first iteration and had manually drilled the screw holes. I modeled those in, and I reduced the bore of the holes for the linear bearings from 15mm to 14.9mm. It didn't work the first time I reprinted the spindle slide though, but that was operator error. The first time I had started the print before I went to bed, when I got up the next l morning I ASSUMED the print was complete and popped the print off the build plate. When I started examining the print I realized it was missing something, like the top 3mm of the print. It was about this time that I realized the print wasn't DONE, it had run out of filament and paused itself - waiting for me to add more filament. Whoopsie, would have been nice if I had remembered the printer could do that BEFORE I ripped the print off the build plate.

OKEE-DOKEE, I aborted the paused print, added a fresh roll of filament, and started a new print. I also ordered 2 more rolls of grey PETG filament, 'cause I'm really liking this stuff and I gonna reprint the RT7R in PETG.

[ddmckee54]

I got my roll of Mango Yellow PETG today, so I can start reprinting the RT7R's yellow parts anytime. It's a little darker than the Gold PLA I was using, and the Bruder Yellow - but I'll live with it.

On the CNC front, I got the X axis leadnut plate drilled and tapped yesterday, today I got the X axis leadnut assembly assembled and adjusted. I also got the Z axis put back together - mostly. I still have to cut the spare leadscrew to length and get it installed. If I take the lower leadscrew bearing out, I think I'll have enough room to be able to install the leadscrew that way. If not, I'll be taking the spindle slide and rails out one more time. Yesterday I also got the drag chain I'm going to use for the X axis. My choices were: 10mmx15mm, 10mmx20mm, 15mmx30mm, or larger. My cables are 7mm in diameter, I need 22AWG - 6 conductor shielded cable for the steppers. I actually only need 4 conductors for the stepper - but I'll need 6 conductors to install the MKS42 stepper/servo conversion kit. (I am NOT using that unshielded 28AWG ribbon cable!) I've got 16AWG - 2 conductor shielded cable for the spindle motor. I'll need a 3rd cable if I ever install homing and/or min/max travel limit switches. The 10x15 drag chain would handle 1 cable with no problem, 2 would fit but it'd be tight, MAYBE 3 if you zig-zag stacked them, but it wouldn't be pretty. The 15x30 chain is what I ordered.

[ddmckee54]

Mechanically, this is starting to come together. I got the Z leadscrew cut to length, I installed the Z leadscrew, I disassembled the bed enough to remove the X leadnut block, I installed the X leadnut assembly in the leadnut block, and I reassembled the machine enough to measure the gap between the bed and the top of the leadnut block. When I designed the leadnut block I wanted to be sure that my block wasn't too high, so I subtracted 3mm from what I had sketched out and printed the block. I must have already subtracted that 3mm when I drew the sketch, because when I measured the gap it was 6.17mm. It's no big deal, I'll just print a 6+ mm shim instead of a 3+ mm shim. Here's a view of the gap from the motor end of the leadscrew.


This is a view from the other end of the leadscrew.


One thing I discovered when assembling the Z leadscrew is that the 84 oz-in stepper motor shafts are about 10-15mm longer than the original motor shafts were. That gap you see between the blue coupler and the Z axis motor shouldn't be there. I'm going to lose about 10-15mm of travel on all three axis when I install the larger motors.

[Zabco]

Stepper motor shafts can't be trimmed back?

[ddmckee54]

I was assuming that they had been hardened. However, the hacksaw made fairly quick work of whacking 10mm off the end - so I guess I was wrong about the hardness. I found that the Z carriage will flex. If I can make it move by pushing on it - it'll move under load.

I'm in the process of redesigning both the slide and the carriage. I'm going to bolt 1/8"x1-1/2" HRS on both sides of the carriage to keep it from flexing. Since my carriage mounting plate is 84-ish mm wide, the spindle slide is 90mm wide, the carriage is 60mm wide, and I've only got 24mm from the carriage mounting plate to the back of the spindle slide when I need 40mm... I need to play around with the numbers, get creative, and see how things look in the 3D model.

[ddmckee54]

I got the spindle slide and the Z carriage reprinted, I even designed and printed the X axis leadnut block, That should be the last of the mechanical parts that need to be printed - I think!

I took the bed back apart, installed the leadnut block shim, and put it back together. There's a little binding as the leadnut approaches the motor end, it's not as noticeable at the other end. I just centered the leadnut block between the bearings, and I suspect that it's not quite lined up correctly side to side. The T8 leadscrew WILL flex, that's why I don't notice the drag when the bed is in the center of its' travel. When the bed reaches the end of it's travel to the motor end, the non-adjustable end of the leadnut is only a few mm away from the motor coupling. When the bed reaches the end of its' travel in the other direction, there's still about 80-100mm of leadscrew between the leadscrew support bearing and the non-adjustable end of the leadnut. That 80-100mm of leadscrew would explain why I notice the drag at the motor end, and not so much at the other end.

My current plan is to remove the bed and loosen the leadnut block enough that it can move, but not easily. I'll then put the bed back together and run it back and forth a few times, that should let the leadnut block find its' own center. Then, it'll just be a matter of carefully removing the bed, tightening the leadnut block mounting bolts, reassembling the bed, and trying it again. If it still binds after that, at least I'll know that I've got a vertical misalignment problem and not a side to side problem.

[Zabco]

Don't know how long your existing coupling is but would something like one of these work?

https://www.mcmaster.com/products/co...-couplings-2~/

[ddmckee54]

Zabco:

My existing couplers are solid, have 5mm x 8mm bore, with a 16mm OD and are 25mm long. The couplers fit into the 22mm bores for the motor alignment rings, so that only about half of the coupler is exposed. Once the motor is installed, there's no way to tighten the set screw on the motor shaft. The couplers have to be installed and tightened onto the motor shaft before the motor is installed, so the coupler needs to fit thru that 22mm bore. Most of the couplers designed to handle slight misalignment will have a 25mm OD, or larger.

[ddmckee54]

Progress has been made, tonight I put the Z carriage back in place. It feels stiffer, before when I pushed on the top of the carriage I could feel it flex - that's not happening now. I even added 15mm to the height of the carriage to compensate for the travel loss caused by the coupler. Here's what it looks like with the new Z carriage and the stiffening plates.

Adding that 15mm in height means that the leadscrew isn't long enough to reach reach the lower bearing anymore. I've got a replacement on order. but it's not due for a couple weeks yet. If by some miracle I get this thing running before then, the lower end can just run wild.

I also took a hard look at the alignment of the X axis leadscrew, both horizontal and vertical. Side to side it looks pretty good, it is DEFINITELY vertically challenged though. From what I can see, it looks like the leadscrew is about 2-3mm too low. With the leadnut block firmly bolted to the bed, I was able to get decent measurements from the top of the bed to the top of the leadscrew, from the top of the bed to the top of the coupler, the leadscrew diameter, and the coupler diameter. After running the numbers, I determined that my 6.17mm thick shim SHOULD have been 4.06mm thick. I'll have to add a stack of washers under the heads of the mounting bolts if they bottom out in the slot before they are able to clamp down. I don't think I've got the extra 2mm of clearance under the clamp that would be required by the thinner shim.

[ddmckee54]

I reprinted the shim for the X axis leadnut block. I had calculated that I needed about a 4.1mm thick shim. So I printed a 4mm shim - reasoning that it's a LOT easier to add to the thickness of a solid block than it is to subtract from it. When I put things back together, sure enough the leadscrew WOULDN'T slip into the coupler. This time it was hitting on the top of the coupler. It was close enough that I could force it into the coupler, but then the leadscrew was jammed and it wouldn't turn. I started looking around for something I could use as a shim. Since I some old business cards laying around from an earlier attempt at leveling the base, I decided to give one of them a shot. Dumb-luck strikes again, it was like baby bear's porridge - just right. The leadscrew slips right into the coupler. And, when turning the leadscrew by hand, I can't feel any difference in drag between when the leadscrew is in the coupler and when it's not.

I'm ninety-nine and forty-four one hundredths percent sure that brings me to a project milestone - the point where I'm done with the mechanical modifications and start aligning the bed to each of the axis. (If you know where the 99-44/100% came from, you're probably an old fart like me.)

[Zabco]

Amost pure. I'll take dumb-luck, or any kind of luck, any day.

[ddmckee54]

Zabco, I remember it from the old Ivory Snow commercials - "it's 99-44/100% pure."

As the World Turns was my mom's soap opera of choice, and Ivory Snow was a big sponsor of that show. Even as a farm mom, not even baling hay came before that soap opera.